Forming semiconductor cells with regions of varying conductivity

Abstract

A semiconductor memory cell and arrays of memory cells are provided In at least one embodiment, a memory cell includes a substrate having a top surface, the substrate having a first conductivity type selected from a p-type conductivity type and an n-type conductivity type; a first region having a second conductivity type selected from the p-type and n-type conductivity types, the second conductivity type being different from the first conductivity type, the first region being formed in the substrate and exposed at the top surface; a second region having the second conductivity type, the second region being formed in the substrate, spaced apart from the first region and exposed at the top surface; a buried layer in the substrate below the first and second regions, spaced apart from the first and second regions and having the second conductivity type; a body region formed between the first and second regions and the buried layer, the body region and having the first conductivity type; and a gate positioned between the first and second regions and above the top surface; wherein a state of the body region is maintained by applying a voltage to the substrate and a nonvolatile memory configured to store data upon transfer from the body region.

Description

CROSS-REFERENCE

in In one particular non-limiting embodiment, terminals 72 and 74 are allowed to float, about +18 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. For example, voltage applied to terminal 70 may be in the range of about +12.0 volts to about +20.0 volts, and voltage applied to terminal 76 may be in the range of about 0.0 volts to about 1.0 volts.

When power is restored to cell 50, the state of the cell 50 as stored on floating gate/trapping layer 60 is restored into floating body region 24. The restore operation (data restoration from non-volatile memory to volatile memory) is described with reference to FIGS. 8A and 8B. Prior to the restore operation/process, the floating body 24 is set to a positive charge, i.e., a “1” state is written to floating body 24. In one embodiment, to perform the restore operation, both SL terminal 72 and BL terminal 74 are left floating. A large negative voltage is applied to WL terminal 70 and a low positive voltage is applied to BW terminal 76, while substrate terminal 78 is grounded. If the floating gate/trapping layer 60 is not negatively charged, no electrons will tunnel from floating gate/trapping layer 60 to floating body 24, and cell 50 will therefore be in a state “1”. Conversely, if floating gate/trapping layer 60 is negatively charged, electrons tunnel from floating gate/trapping layer 60 into floating body 24, thereby placing cell 50 in a state “0”. In one particular non-limiting embodiment, about −18.0 volts is applied to terminal 70, and about +0.6 volts is applied to terminal 76. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. For example, voltage applied to terminal 70 may be in the range of about −12.0 volts to about −20.0 volts, and voltage applied to terminal 76 may be in the range of about 0.0 volts to about +10 volts, while about 0.0 volts is applied to terminal 78.

Note that this process occurs non-algorithmically, as the state of the floating gate/trapping layer 60 does not have to be read, interpreted, or otherwise measured to determine what state to restore the floating body 24 to. Rather, the restoration process occurs automatically, driven by electrical potential differences. Accordingly, this process is orders of magnitude faster than one that requires algorithmic intervention. Similarly, it is noted that the shadowing process also is performed as a non-algorithmic process. From these operations, it has been shown that cell 50 provides a memory cell having the advantages of a DRAM cell, but where non-volatility is also achieved.

FIGS. 9A-9D illustrate another embodiment of operation of cell 50 to perform a volatile to non-volatile shadowing process, which operates by a hot electron injection process, in contrast to the tunneling process (e.g. Fowler-Nordheim tunneling process) described above with regard to FIGS. 7A-7B. FIG. 9E illustrates the operation of an NPN bipolar device 90, as it relates to the operation of cell 50. Floating body 24 is represented by the terminal to which voltage V_FB is applied in FIG. 9E, and the terminals 72 and 74 are represented by terminals to which voltages V_SL and V_BL are applied, respectively. When V_FB is a positive voltage, this turns on the bipolar device 90, and when V_FB is a negative or neutral voltage, the device 90 is turned off. Likewise, when floating body 24 has a positive voltage, this turns on the cell 50 so that current flows through the NPN junction formed by 16, 24 and 18 in the direction indicated by the arrow in floating body 24 in FIG. 9A, and when floating body 24 has a negative or neutral voltage, cell is turned off, so that there is no current flow through the NPN junction.

To perform a shadowing process according to the embodiment described with regard to FIGS. 9A-9D, a high positive voltage is applied to terminal 72 and a substantially neutral voltage is applied to terminal 74. Alternatively, a high positive voltage can be applied to terminal 74 and a substantially neutral voltage can be applied to terminal 72. A positive voltage less than the positive voltage applied to terminal 72 or 74 is applied to terminal 70 and a low positive voltage less than the positive voltage applied to terminal 72 or 74 is applied to terminal 76. A high voltage in this case is a voltage greater than or equal to about +3 volts. In one example, a voltage in the range of about +3 to about +6 volts is applied, although it is possible to apply a higher voltage. The floating gate/trapping layer 60 will have been previously initialized or reset to have a positive charge prior to the operation of the cell 50 to store data in non-volatile memory via floating body 24. When floating body 24 has a positive charge/voltage, the NPN junction is on, as noted above, and electrons flow in the direction of the arrow shown in the floating body 24 in FIG. 9A. The application of the high voltage to terminal 72 at 16 energizes/accelerates electrons traveling through the floating body 24 to a sufficient extent that they can “jump over” the oxide barrier between floating body 24 and floating gate/trapping layer 60, so that electrons enter floating gate/trapping layer 60 as indicated by the arrow into floating gate/trapping layer 60 in FIG. 9A. Accordingly, floating gate/trapping layer 60 becomes negatively charged by the shadowing process, when the volatile memory of cell 50 is in state “1” (i.e., floating body 24 is positively charged), as shown in FIG. 9B.

When volatile memory of cell 50 is in state “0”, i.e., floating body 24 has a negative or neutral charge/voltage, the NPN junction is off, as noted above, and electrons do not flow in the floating body 24, as illustrated in FIG. 9C. Accordingly, when voltages are applied to the terminals as described above, in order to perform the shadowing process, the high positive voltage applied to terminal 72 does not cause an acceleration of electrons in order to cause hot electron injection into floating gate/trapping layer 60, since the electrons are not flowing. Accordingly, floating gate/trapping layer 60 retains its positive charge at the end of the shadowing process, when the volatile memory of cell 50 is in state “0” (i.e., floating body 24 is neutral or negatively charged), as shown in FIG. 9D. Note that the charge state of the floating gate/trapping layer 60 is complementary to the charge state of the floating body 24 after completion of the shadowing process. Thus, if the floating body 24 of the memory cell 50 has a positive charge in volatile memory, the floating gate/trapping layer 60 will become negatively charged by the shadowing process, whereas if the floating body of the memory cell 50 has a negative or neutral charge in volatile memory, the floating gate/trapping layer 60 will be positively charged at the end of the shadowing operation. The charges/states of the floating gates/trapping layers 60 are determined non-algorithmically by the states of the floating bodies, and shadowing of multiple cells occurs in parallel, therefore the shadowing process is very fast.

In one particular non-limiting example of the shadowing process according to this embodiment, about +3 volts are applied to terminal 72, about 0 volts are applied to terminal 74, about +1.2 volts are applied to terminal 70, about +0.6 volts are applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. For example, voltage applied to terminal 72 may be in the range of about +3 volts to about +6 volts, the voltage applied to terminal 74 may be in the range of about 0.0 volts to about +0.4 volts, the voltage applied to terminal 70 may be in the range of about 0.0 volts to about +1.6 volts, and voltage applied to terminal 76 may be in the range of about 0.0 volts to about +1.0 volts, while about 0.0 volts is applied to terminal 78.

Turning now to FIGS. 10A-10B, another embodiment of operation of cell 50 to perform a restore process from non-volatile to volatile memory is schematically illustrated, in which the restore process operates by a band-to-band tunneling hot hole injection process (modulated by the floating gate/trapping layer 60 charge), in contrast to the electron tunneling process described above with regard to FIGS. 8A-8B. In the embodiment illustrated in FIGS. 10A-10B, the floating body 24 is set to a neutral or negative charge prior to performing the restore operation/process, i.e., a “0” state is written to floating body 24. In the embodiment of FIGS. 10A-10B, to perform the restore operation, terminal 72 is set to a substantially neutral voltage, a positive voltage is applied to terminal 74, a negative voltage is applied to terminal 70, a positive voltage that is less positive than the positive voltage applied to terminal 74 is applied to terminal 76, and a substantially neutral voltage is applied to terminal 78. If the floating gate/trapping layer 60 is negatively charged, as illustrated in FIG. 10A, this negative charge enhances the driving force for the band-to-band hot hole injection process, whereby holes are injected from the n-region 18 into floating body 24, thereby restoring the “1” state that the volatile memory cell 50 had held prior to the performance of the shadowing operation. If the floating gate/trapping layer 60 is not negatively charged, such as when the floating gate/trapping layer 60 is positively charged as shown in FIG. 10B or is neutral, the hot band-to-band hole injection process will not occur, as illustrated in FIG. 10B, resulting in memory cell 50 having a “0” state, just as it did prior to performance of the shadowing process. Accordingly, if floating gate/trapping layer 60 has a positive charge after shadowing is performed, the volatile memory of floating body 24 will be restored to have a negative charge (“0” state), but if the floating gate/trapping layer 60 has a negative or neutral charge, the volatile memory of floating body 24 will be restored to have a positive charge (“1” state).

In one particular non-limiting example of this embodiment, about 0 volts is applied to terminal 72, about +2 volts is applied to terminal 74, about −1.2 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. For example, voltage applied to terminal 72 may be in the range of about +1.5 volts to about +3.0 volts, voltage applied to terminal 74 may be in the range of about 0.0 volts to about +0.6 volts, voltage applied to terminal 70 may be in the range of about 0.0 volts to about −3.0 volts, voltage applied to terminal 76 may be in the range of about 0.0 volts to about +1.0 volts, and about 0.0 volts is applied to terminal 78.

Note that this process occurs non-algorithmically, as the state of the floating gate/trapping layer 60 does not have to be read, interpreted, or otherwise measured to determine what state to restore the floating body 24 to. Rather, the restoration process occurs automatically, driven by electrical potential differences. Accordingly, this process is orders of magnitude faster than one that requires algorithmic intervention. From these operations, it has been shown that cell 50 provides a memory cell having the advantages of a DRAM cell, but where non-volatility is also achieved.

After restoring the memory cell(s) 50, the floating gate(s)/trapping layer(s) 60 is/are reset to a predetermined state, e.g., a positive state, so that each floating gate/trapping layer 60 has a known state prior to performing another shadowing operation. The reset process operates by the mechanism of electron tunneling from the floating gate/trapping layer 60 to the source region 16, as illustrated in FIG. 11.

To perform a reset operation according to the embodiment of FIG. 11, a highly negative voltage is applied to terminal 70, a substantially neutral voltage is applied to SL terminal 72, BL terminal 74 is allowed to float or is grounded, a positive voltage is applied to terminal 76, while substrate terminal 78 is grounded. By applying a neutral voltage to terminal 72 and maintaining the voltage of region 16 to be substantially neutral, this causes region 16 to function as a sink for the electrons from floating gate/trapping layer 60 to travel to by electron tunneling. A large negative voltage is applied to WL terminal 70 and a low positive voltage is applied to BW terminal 76. If the floating gate/trapping layer 60 is negatively charged, electrons will tunnel from floating gate/trapping layer 60 to region 16, and floating gate/trapping layer 60 will therefore become positively charged. As a result of the reset operation, all of the floating gate/trapping layers will become positively charged. In one particular non-limiting embodiment, about −18.0 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. For example, voltage applied to terminal 70 may be in the range of about −12.0 volts to about −20.0 volts, the voltage applied to terminal 76 may be in the range of about 0.0 volts to about 1.0 volts, and about 0.0 volts is applied to terminal 78.

Having described the various operations of cell 50 above, reference is again made to FIG. 1 to describe operation of a memory device having a plurality of memory cells 50. The number of memory cells can vary widely, for example ranging from less than 00 Mb to several Gb, or more. It is noted that, except for the DRAM operations of writing and reading (event 104), which by necessity must be capable of individual, controlled operations, the remaining operations shown in FIG. 1 can all be carried out as parallel, non-algorithmic operations, which results in a very fast operating memory device.

At event 102, the memory device is initialized by first setting all of the floating gates/trapping layers to a positive state, in a manner as described above with reference to FIG. 11, for example. For example, a control line can be used to input a highly negative voltage to each of terminals 70, in parallel, with voltage settings at the other terminals as described above with reference to FIG. 11. Individual bits (or multiple bits, as described below) of data can be read from or written to floating bodies 24 of the respective cells at event 104.

The shadowing operation at event 106 is conducted in a mass parallel, non-algorithmic process, in any of the same manners described above, with each of the cells 50 performing the shadowing operation simultaneously, in a parallel operation. Because no algorithmic interpretation or measurement is required to transfer the data from non-volatile to volatile memory (24 to 60), the shadowing operation is very fast and efficient.

To restore the data into the volatile portion of the memory cells 50 of the memory device (i.e., restore charges in floating bodies 24), a state “0” is first written into each of the floating bodies 24, by a parallel process, and then each of the floating bodies is restored in any of the same manners described above with regard to a restoration process of a single floating body 24. This process is also a mass, parallel non-algorithmic process, so that no algorithmic processing or measurement of the states of the floating gates/trapping layers 60 is required prior to transferring the data stored by the floating gates/trapping layers 60 to the floating bodies 24. Thus, the floating bodies are restored simultaneously, in parallel, in a very fast and efficient process.

Upon restoring the volatile memory at event 108, the floating gates/trapping layers 60 are then reset at event 110, to establish a positive charge in each of the floating gates/trapping layers, in the same manner as described above with regard to initializing at event 110.

FIG. 12 shows another embodiment of a memory cell 50 according to the present invention. The cell 50 includes a substrate 12 of a first conductivity type, such as a p-type conductivity type, for example. Substrate 12 is typically made of silicon, but may comprise germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials known in the art. The substrate 12 has a surface 14. A first region 16 having a second conductivity type, such as n-type, for example, is provided in substrate 12 and which is exposed at surface 14. A second region 18 having the second conductivity type is also provided in substrate 12, which is exposed at surface 14 and which is spaced apart from the first region 16. First and second regions 16 and 18 are formed by an implantation process formed on the material making up substrate 12, according to any of implantation processes known and typically used in the art.

A buried layer 22 of the second conductivity type is also provided in the substrate 12, buried in the substrate 12, as shown. Region 22 is also formed by an ion implantation process on the material of substrate 12. A body region 24 of the substrate 12 is bounded by surface 14, first and second regions 16,18 and insulating layers 26 (e.g. shallow trench isolation (STI, which may be made of silicon oxide, for example). Insulating layers 26 insulate cell 50 from neighboring cells 50 when multiple cells 50 are joined to make a memory device. A gate 60 is positioned in between the regions 16 and 18, and above the surface 14. The gate 60 is insulated from surface 14 by an insulating layer 62. Insulating layer 62 may be made of silicon oxide and/or other dielectric materials, including high-K dielectric materials, such as, but not limited to, tantalum peroxide, titanium oxide, zirconium oxide, hafnium oxide, and/or aluminum oxide. The gate 60 may be made of polysilicon material or metal gate electrode, such as tungsten, tantalum, titanium and their nitrides.

A resistance change memory element 40 is positioned above one of the regions 16, 18 (18 in FIG. 12) having second conductivity type and connected to one of the terminals 72, 74 (74 in FIG. 12). The resistance change memory element 40 is shown as a variable resistor, and may be formed from phase change memory material such as a chalcogenide or conductive bridging memory or metal oxide memory, and may take the form of metal-insulator-metal structure, in which transition metal oxide or perovskite metal oxide is used in conjunction with any reasonably good conductors.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, bit line (BL) terminal 74, buried well (BW) terminal 76 and substrate terminal 78. Terminal 70 is connected to the gate 60. Terminal 74 is connected to first region 16 and terminal 72 is connected to resistance change memory element 40 which is, in turn, connected to second region 18. Alternatively, terminal 72 can be connected to resistance change memory element 40 and terminal 74 can be connected to first region 16. Terminal 76 is connected to buried layer 22 and terminal 78 is connected to substrate 12.

A non-limiting embodiment of the memory cell 50 is shown in FIG. 13. The second conductivity region 16 is connected to an address line terminal 74 through a conductive element 38. The resistance change memory element 40 in this embodiment includes a bottom electrode 44, a resistance change material 46 and a top electrode 48. Resistance change memory element 40 is connected to the second conductivity region 18 on the substrate 12 through a conductive element 42. The resistance change material 46 may be connected to an address line (such as terminal 72 in FIG. 13) through electrode 48 formed from a conductive material. The conductive element 42 may comprise tungsten or silicided silicon materials. Electrodes 44, 48 may be formed from one or more conductive materials, including, but not limited to titanium nitride, titanium aluminum nitride, or titanium silicon nitride. Resistance change material 46 is a material in which properties, such as electrical resistance, can be modified using electrical signals. For the case of phase change memory elements, the resistivity depends on the crystalline phase of the material, while for the metal oxide materials, the resistivity typically depends on the presence or absence of conductive filaments. A crystalline phase of a phase change type resistive change material exhibits a low resistivity (e.g., ˜1 kΩ) state and an amorphous phase of that material exhibits a high resistivity state (e.g., >100 kΩ). Examples of phase change material include alloys containing elements from Column VI of the periodic table, such as GeSbTe alloys. Examples of metal-insulator-metal resistance change materials include a variety of oxides such as Nb₂O₅, Al₂O₃, Ta₂ O₅, TiO₂, and NiO and perovskite metal oxides, such as SrZrO₃, (Pr,Ca)MnO₃ and SrTiO₃:Cr.

When power is applied to cell 50, cell 50 operates like a capacitorless DRAM cell. In a capacitorless DRAM device, the memory information (i.e., data that is stored in memory) is stored as charge in the floating body of the transistor, i.e., in the bodies 24 of the cells 50 of a memory device. The presence of the electrical charge in the floating body 24 modulates the threshold voltage of the cell 50, which determines the state of the cell 50. In one embodiment, the non-volatile memory 40 is initialized to have a low resistance state.

A read operation can be performed on memory cell 50 through the following bias condition. A neutral voltage is applied to the substrate terminal 78, a neutral or positive voltage is applied to the BW terminal 76, a substantially neutral voltage is applied to SL terminal 72, a positive voltage is applied to BL terminal 74, and a positive voltage more positive than the voltage applied to BL terminal 74 is applied to WL terminal 70. If cell 50 is in a state “1” having holes in the body region 24, then a lower threshold voltage (gate voltage where the transistor is turned on) is observed compared to the threshold voltage observed when cell 50 is in a state “0” having no holes in body region 24. In one particular non-limiting embodiment, about 0.0 volts is applied to terminal 72, about +0.4 volts is applied to terminal 74, about +1.2 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a substantially neutral voltage is applied to the substrate terminal 78, a neutral or positive voltage is applied to the BW terminal 76, a substantially neutral voltage is applied to SL terminal 72, a positive voltage is applied to BL terminal 74, and a positive voltage is applied to WL terminal 70, with the voltage applied to BL terminal 74 being more positive than the voltage applied to terminal 70. If cell 50 is in a state “1” having holes in the body region 24, then the parasitic bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned on and a higher cell current is observed compared to when cell 50 is in a state “0” having no holes in body region 24. In one particular non-limiting embodiment, about 0.0 volts is applied to terminal 72, about +3.0 volts is applied to terminal 74, about +0.5 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a positive voltage is applied to the substrate terminal 78, a substantially neutral voltage is applied to BL terminal 74, and a positive voltage is applied to WL terminal 70. Cell 50 provides a P1-N2-P3-N4 silicon controlled rectifier device, with substrate 78 functioning as the P1 region, buried layer 22 functioning as the N2 region, body region 24 functioning as the P3 region and region 16 or 18 functioning as the N4 region. The functioning of the silicon controller rectifier device is described in further detail in application Ser. No. 12/533,661 filed July 31, 2009 and titled “Methods of Operating Semiconductor Memory Device with Floating Body Transistor Using Silicon Controlled Rectifier Principle”. In this example, the substrate terminal 78 functions as the anode and terminal 72 or terminal 74 functions as the cathode, while body region 24 functions as a p-base to turn on the SCR device. If cell 50 is in a state “1” having holes in the body region 24, the silicon controlled rectifier (SCR) device formed by the substrate, buried well, floating body, and the BL junction will be turned on and a higher cell current is observed compared to when cell 50 is in a state “0” having no holes in body region 24. A positive voltage is applied to WL terminal 70 to select a row in the memory cell array 80 (e.g., see FIGS. 23A-B), while negative voltage is applied to WL terminal 70 for any unselected rows. The negative voltage applied reduces the potential of floating body 24 through capacitive coupling in the unselected rows and turns off the SCR device of each cell 50 in each unselected row. In one particular non-limiting embodiment, about +0.8 volts is applied to terminal 78, about +0.5 volts is applied to terminal 70 (for the selected row), and about 0.0 volts is applied to terminal 74. However, these voltage levels may vary.

FIG. 14 illustrates write state “1” operations that can be carried out on cell 50, by performing band-to-band tunneling hot hole injection or impact ionization hot hole injection. To write state “1” using band-to-band tunneling mechanism, the following voltages are applied to the terminals: a positive voltage is applied to BL terminal 74, a substantially neutral voltage is applied to SL terminal 72, a negative voltage is applied to WL terminal 70, a positive voltage less than the positive voltage applied to terminal 74 is applied to BW terminal 76, and a substantially neutral voltage is applied to the substrate terminal 78. Under these conditions, holes are injected from BL terminal 74 into the floating body region 24, leaving the body region 24 positively charged. In one particular non-limiting embodiment, a charge of about 0.0 volts is applied to terminal 72, a charge of about +2.0 volts is applied to terminal 74, a charge of about −1.2 volts is applied to terminal 70, a charge of about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied; as described above.

Alternatively, to write state “1” using an impact ionization mechanism, the following voltages can be applied to the terminals: a positive voltage is applied to BL terminal 74, a substantially neutral voltage is applied to SL terminal 72, a positive voltage less than the positive voltage applied to terminal 74 is applied to WL terminal 70, a positive voltage less positive than the positive voltage applied to BL terminal 74 is applied to BW terminal 76, and a substantially neutral voltage is applied to the substrate terminal 78. Under these conditions, holes are injected from BL terminal 74 into the floating body region 24, leaving the body region 24 positively charged. In one particular non-limiting embodiment, +0.0 volts is applied to terminal 72, a charge of about +2.0 volts is applied to terminal 74, a charge of about +0.5 volts is applied to terminal 70, a charge of about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

In an alternate write state “1” using impact ionization mechanism, a positive bias can be applied to substrate terminal 78. The parasitic silicon controlled rectifier device of the selected cell is now turned off due to the negative potential between the substrate terminal 78 and the BL terminal 74. The functioning of the silicon controller rectifier device is described in further detail in application Ser. No. 12/533,661 filed Jul. 31, 2009 and titled “Methods of Operating Semiconductor Memory Device with Floating Body Transistor Using Silicon Controlled Rectifier Principle”. Under these conditions, electrons will flow near the surface of the transistor, and generate holes through impact ionization mechanism. The holes are subsequently injected into the floating body region 24. In one particular non-limiting embodiment, +0.0 volts is applied to terminal 72, a charge of about +2.0 volts is applied to terminal 74, a charge of about +0.5 volts is applied to terminal 70, and about +0.8 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, the silicon controlled rectifier device of cell 50 can be put into a state “1” (i.e., by performing a write “1” operation) by applying the following bias: a neutral voltage is applied to BL terminal 74, a positive voltage is applied to WL terminal 70, and a positive voltage is applied to the substrate terminal 78, while SL terminal 72 and BW terminal 76 are left floating. The positive voltage applied to the WL terminal 70 will increase the potential of the floating body 24 through capacitive coupling and create a feedback process that turns the SCR device on. Once the SCR device of cell 50 is in conducting mode (i.e. has been “turned on”) the SCR becomes “latched on” and the voltage applied to WL terminal 70 can be removed without affecting the “on” state of the SCR device. In one particular non-limiting embodiment, a voltage of about 0.0 volts is applied to terminal 74, a voltage of about +0.5 volts is applied to terminal 70, and about +3.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above, e.g., the voltage applied to terminal 78 remains greater than the voltage applied to terminal 74.

A write “0” operation of the cell 50 is now described with reference to FIG. 15. To write “0” to cell 50, a negative bias is applied to SL terminal 72 and/or BL terminal 74, a neutral or negative voltage is applied to WL terminal 70, and a substantially neutral voltage is applied to substrate terminal 78. Under these conditions, the p-n junction (junction between 24 and 16 and between 24 and 18) is forward-biased, evacuating any holes from the floating body 24. In one particular non-limiting embodiment, about −1.0 volts is applied to terminal 72, about −1.0 volts is applied to terminal 70, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a write “0” operation can be performed to cell 50 by applying a positive bias to WL terminal 70, and substantially neutral voltages to SL terminal 72, BL terminal 74, and substrate terminal 78. Under these conditions, the holes will be evacuated from the floating body 24. In one particular non-limiting embodiment, about 1.0 volts is applied to terminal 70, about 0.0 volts are applied to terminals 72 and 74, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a write “0” operation can be performed by putting the silicon controlled rectifier device into the blocking mode. This can be performed by applying the following bias: a positive voltage is applied to BL terminal 74, a positive voltage is applied to WL terminal 70, and a positive voltage is applied to the substrate terminal 78, while leaving SL terminal 72 and BW terminal 76 floating. Under these conditions the voltage difference between anode and cathode, defined by the voltages at substrate terminal 78 and BL terminal 74, will become too small to maintain the SCR device in conducting mode. As a result, the SCR device of cell 50 will be turned off. In one particular non-limiting embodiment, a voltage of about +0.8 volts is applied to terminal 74, a voltage of about +0.5 volts is applied to terminal 70, and about +0.8 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

A holding or standby operation is implemented to enhance the data retention characteristics of the memory cells 50. The holding operation can be performed by applying the following bias: a substantially neutral voltage is applied to BL terminal 74, a neutral or negative voltage is applied to WL terminal 70, and a positive voltage is applied to the substrate terminal 78, while leaving SL terminal 72 and BW terminal 76 floating. Under these conditions, if memory cell 50 is in memory/data state “1” with positive voltage in floating body 24, the SCR device of memory cell 50 is turned on, thereby maintaining the state “1” data. Memory cells in state “0” will remain in blocking mode, since the voltage in floating body 24 is not substantially positive and therefore floating body 24 does not turn on the SCR device. Accordingly, current does not flow through the SCR device and these cells maintain the state “0” data. In this way, an array of memory cells 50 can be refreshed by periodically applying a positive voltage pulse through substrate terminal 78. Those memory cells 50 that are commonly connected to substrate terminal 78 and which have a positive voltage in body region 24 will be refreshed with a “1” data state, while those memory cells 50 that are commonly connected to the substrate terminal 78 and which do not have a positive voltage in body region 24 will remain in blocking mode, since their SCR device will not be turned on, and therefore memory state “0” will be maintained in those cells. In this way, all memory cells 50 commonly connected to the substrate terminal will be maintained/refreshed to accurately hold their data states. This process occurs automatically, upon application of voltage to the substrate terminal 78, in a parallel, non-algorithmic, efficient process. In one particular non-limiting embodiment, a voltage of about 0.0 volts is applied to terminal 74, a voltage of about −1.0 volts is applied to terminal 70, and about +0.8 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships therebetween.

When power down is detected, e.g., when a user turns off the power to cell 50, or the power is inadvertently interrupted, or for any other reason, power is at least temporarily discontinued to cell 50, data stored in the floating body region 24 is transferred to the resistance change memory 40. This operation is referred to as “shadowing” and is described with reference to FIGS. 16A-16B.

To perform a shadowing process, a positive voltage is applied to terminal 72 and a substantially neutral voltage is applied to terminal 74. A neutral voltage or slightly positive voltage is applied terminal 70, a low positive voltage is applied to terminal 76, and a substantially neutral voltage is applied to terminal 78. These voltage levels can be driven by the appropriate circuitry controlling the memory cell array when the power shutdown is expected (such as during standby operation or when entering power savings mode) or from external capacitors in the event of abrupt and sudden power interruption.

When the floating body has a positive potential, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned on (FIG. 16A). The positive voltage applied to terminal 72 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the state of the materials from a low resistivity state to a high resistivity state. In the case of phase change materials, this involves the change of the crystallinity of the chalcogenide materials from crystalline state to amorphous state, while in metal oxide materials, this typically involves the annihilation of conductive filaments. Accordingly, the non-volatile resistance change material will be in a high resistivity state when the volatile memory of cell 50 is in state “1” (i.e. floating body 24 is positively charged).

When the floating body is neutral or negatively charged, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned off (FIG. 16B). Therefore, when voltages are applied as described above, no electrical current will flow through the resistance change memory 40 and it will retain its low resistivity state. Accordingly, the non-volatile resistance change material will be in a low resistivity state when the volatile memory of cell 50 is in state “0” (i.e. floating body is neutral or negatively charged).

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 72, a constant current of about 700 μA is applied to terminal 74, about +1.0 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage and current levels may vary, while maintaining the relative relationships between the charges applied, as described above. To change the non-volatile phase change memory from low resistivity state to high resistivity state, a current level between 600 μA and 1 mA can be used. Lower current will be needed as the phase change material is scaled to smaller geometry. The current levels employed in metal oxide systems vary greatly depending on the materials used, ranging from tens of microamperes to tens of milliamperes.

Note that this process occurs non-algorithmically, as the state of the floating body 24 does not have to be read, interpreted, or otherwise measured to determine what state to write the non-volatile resistance change memory 40 to. Rather, the shadowing process occurs automatically, driven by electrical potential differences. Accordingly, this process is orders of magnitude faster than one that requires algorithmic intervention.

When power is restored to cell 50, the state of the cell 50 as stored on the non-volatile resistance change memory 40 is restored into floating body region 24. The restore operation (data restoration from non-volatile memory to volatile memory) is described with reference to FIGS. 17A-17B. In one embodiment, to perform the restore operation, a negative voltage is applied to terminal 70, a positive voltage is applied to terminal 74, a negative voltage is applied to terminal 72, a low positive voltage is applied to terminal 76, and a substantially neutral voltage is applied to terminal 78.

This condition will result in result in band-to-band tunneling hole injection into the floating body 24 (see FIG. 17A). However, if the resistance change memory is in low resistivity state, the negative voltage applied to terminal 72 will evacuate holes in the floating body 24 (see FIG. 17B) because the p-n junction formed by the floating body 24 and the region 18 is forward-biased. Consequently, the volatile memory state of memory cell 50 will be restored to state “0” upon completion of the restore operation, restoring the state that the memory cell 50 held prior to the shadowing operation.

If the resistance change memory 40 is in high resistivity state, no current flows through the resistance change memory 40, hence the holes accumulated in the floating body 24 will not be evacuated (FIG. 17A). As a result, the memory state “1” that the memory cell 50 held prior to the shadowing operation will be restored.

In one particular non-limiting example of this embodiment, about −1.0 volts is applied to terminal 72, about +2.0 volts is applied to terminal 74, about −1.2 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and a neutral voltage is applied to the substrate terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

Note that this process occurs non-algorithmically, as the state of the non-volatile resistance change memory 40 does not have to be read, interpreted, or otherwise measured to determine what state to restore the floating body 24 to. Rather, the restoration process occurs automatically, driven by resistivity state differences. Accordingly, this process is orders of magnitude faster than one that requires algorithmic intervention.

After restoring the memory cell(s) 50, the resistance change memory(ies) 40 is/are reset to a predetermined state, e.g., a low resistivity state as illustrated in FIG. 18, so that each resistance change memory 40 has a known state prior to performing another shadowing operation.

To perform a reset operation according to the embodiment of FIG. 18, a neutral or slightly positive voltage is applied to terminal 70, a substantially neutral voltage is applied to BL terminal 74, a positive voltage is applied to SL terminal 72, a positive voltage is applied to terminal 76, and a neutral voltage is applied to substrate terminal 78.

When the floating body has a positive potential, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned on. The positive voltage applied to terminal 72 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the resistance change materials from a high resistivity state to a low resistivity state. The voltage applied to terminal 72 initially has to exceed a threshold value (sometimes referred to as ‘dynamic threshold voltage’) to ensure that all resistance change memory materials (including ones in high resistivity state) are conducting. Accordingly, all the non-volatile resistance change memory 40 will be in a low resistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, a constant current of about 400 μA is applied to terminal 72, about +1.0 volts is applied to terminal 70, and about +0.6 volts is applied to terminal 76. However, these voltage levels may: vary, while maintaining the relative relationships between the charges applied, as described above. The dynamic threshold voltage of a phase change non-volatile memory is typically greater than 1.0 volts, upon which the high resistivity phase change materials will become conducting. The current level required to change phase change memory materials to low resistivity state typically range between 100 μA to 600 μA. For the case of metal oxide systems, the threshold voltage and the current level vary depending on the materials.

In another embodiment, the resistance change memory 40 is initialized to have a high resistivity state. When power is applied to cell 50, cell 50 operates like a capacitorless DRAM cell. In a capacitorless DRAM device, the memory information (i.e., data that is stored in memory) is stored as charge in the floating body of the transistor, i.e., in the body 24 of cell 50. The presence of the electrical charge in the floating body 24 modulates the threshold voltage of the cell 50, which determines the state of the cell 50.

A read operation can be performed on memory cell 50 through the following exemplary bias condition. A neutral voltage is applied to the substrate terminal 78, a neutral or positive voltage is applied to the BW terminal 76, a substantially neutral voltage is applied to SL terminal 72, a positive voltage is applied to BL terminal 74, and a positive voltage more positive than the voltage applied to BL terminal 74 is applied to WL terminal 70. If cell 50 is in a state “1” having holes in the body region 24, then a lower threshold voltage (gate voltage where the transistor is turned on) is observed compared to the threshold voltage observed when cell 50 is in a state “0” having no holes in body region 24. In one particular non-limiting embodiment, about 0.0 volts is applied to terminal 72, about +0.4 volts is applied to terminal 74, about +1.2 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a neutral voltage is applied to the substrate terminal 78, a neutral or positive voltage is applied to the BW terminal 76, a positive voltage is applied to BL terminal 74, and SL terminal 72 is left floating or grounded, and a neutral or positive voltage less positive than the positive voltage applied to BL terminal 74 is applied to WL terminal 70. If cell 50 is in a state “1” having holes in the body region 24, then the bipolar transistor formed by BL junction 16, floating body 24, and buried layer 22 is turned on. As a result, a higher cell current is observed compared to when cell 50 is in a state “0” having no holes in body region 24. In one particular non-limiting embodiment, terminal 72 is left floating, about +3.0 volts is applied to terminal 74, about +0.5 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

In another embodiment of the read operation that can be performed on memory cell 50, a positive voltage is applied to the substrate terminal 78, a neutral voltage is applied to BL terminal 74, SL terminal 72 is left floating or grounded, a neutral or positive voltage is applied to WL terminal 70, while BW terminal 76 is left floating. If cell 50 is in state “1” with the body region 24 positively charged, the silicon controlled rectifier (SCR) device formed by the substrate 12, buried well 22, floating body 24, and the BL junction 74 will be turned on and a higher cell current is observed compared to when cell 50 is in a state “0” with the body region 24 in neutral state or negatively charged. In one particular non-limiting embodiment, about +0.8 volts is applied to terminal 78, about +0.5 volts is applied to terminal 70, and about 0.0 volts is applied to terminal 74, while terminals 72 and 76 are left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

The following conditions describe a write state “1” operation that can be performed on memory cell 50, where the resistance change memory 40 is in a high resistivity state. To write state “1” using a band-to-band tunneling mechanism, the following voltages are applied to the terminals: a positive voltage is applied to BL terminal 74, SL terminal 72 is left floating or grounded, a negative voltage is applied to WL terminal 70, a neutral or positive voltage is applied to the BW terminal 76, and a neutral voltage is applied to the substrate terminal 78. Under these conditions, holes are injected from BL junction 16 into the floating body region 24, leaving the body region 24 positively charged. In one particular non-limiting embodiment, about +2.0 volts is applied to terminal 74, about −1.2 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, about 0.0 volts is applied to terminal 78, and terminal 72 is left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, to write state “1” using an impact ionization mechanism, the following voltages are applied to the terminals: a positive voltage is applied to BL terminal 74, SL terminal 72 is left floating or grounded, a positive voltage is applied to WL terminal 70, a neutral or positive voltage is applied to BW terminal 76, and a substantially neutral voltage is applied to the substrate terminal 78. Under these conditions, holes are injected from BL junction 16 into the floating body region 24, leaving the body region 24 positively charged. In one particular non-limiting embodiment, a potential of about +2.0 volts is applied to terminal 74, a potential of about +0.5 volts is applied to terminal 70, a potential of about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78, while terminal 72 is left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, the silicon controlled rectifier device can be operated to put cell 50 into a state “1” by applying the following bias: a substantially neutral voltage is applied to BL terminal 74, a positive voltage is applied to WL terminal 70, and a positive voltage is applied to the substrate terminal 78, while SL terminal 72 and BW terminal 76 are left floating. The positive voltage applied to the WL terminal 70 will increase the potential of the floating body 24 through capacitive coupling and create a feedback process that turns the device on. In one particular non-limiting embodiment, a charge of about 0.0 volts is applied to terminal 74, a charge of about +0.5 volts is applied to terminal 70, and about +3.0 volts is applied to terminal 78. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

A write “0” operation of the cell 50 is now described. To write “0” to cell 50, a negative bias is applied to BL terminal 74, SL terminal 72 is grounded or left floating, a neutral or negative voltage is applied to WL terminal 70, a neutral or positive voltage is applied to BW terminal 76, and a substantially neutral voltage is applied to substrate terminal 78. Under these conditions, the p-n junction (junction between 24 and 18) is forward-biased, evacuating any holes from the floating body 24. In one particular non-limiting embodiment, about −2.0 volts is applied to terminal 74, about −1.2 volts is applied to terminal 70, about 0.0 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78, while terminal 72 is grounded or left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

In an alternate write “0” operation, a neutral voltage is applied to BL terminal 74, a positive voltage is applied to WL terminal 70, a neutral or positive voltage is applied to BW terminal 76, a substantially neutral voltage is applied to substrate terminal 78, while terminal 72 is grounded or left floating. Under these conditions, holes from the floating body 24 are evacuated. In one particular non-limiting embodiment, about +1.5 volts is applied to terminal 70, about 0.0 volts is applied to terminal 74, about 0.0 volts is applied to terminal 76, about 0.0 volts is applied to terminal 78, while terminal 72 is grounded or left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a write “0” operation can be performed by putting the silicon controlled rectifier device of cell 50 into the blocking mode. This can be performed by applying the following bias: a positive voltage is applied to BL terminal 74, a positive voltage is applied to WL terminal 70, and a positive voltage is applied to the substrate terminal 78, while leaving SL terminal 72 and BW terminal 76 floating. In one particular non-limiting embodiment, a charge of about +0.8 volts is applied to terminal 74, a charge of about +0.5 volts is applied to terminal 70, and about +0.8 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

A holding or standby operation is implemented to enhance the data retention characteristics of the memory cells 50. The holding operation can be performed by applying the following bias: a substantially neutral voltage is applied to BL terminal 74, a neutral or negative voltage is applied to WL terminal 70, and a positive voltage is applied to the substrate terminal 78, while leaving SL terminal 72 and BW terminal 76 floating. Under these conditions, if memory cell 50 is in memory/data state “1” with positive voltage in floating body 24, the SCR device of memory cell 50 is turned on, thereby maintaining the state “1” data. Memory cells in state “0” will remain in blocking mode, since the voltage in floating body 24 is not substantially positive and therefore floating body 24 does not turn on the SCR device. Accordingly, current does not flow through the SCR device and these cells maintain the state “0” data. In this way, an array of memory cells 50 can be refreshed by periodically applying a positive voltage pulse through substrate terminal 78. Those memory cells 50 that are commonly connected to substrate terminal 78 and which have a positive voltage in body region 24 will be refreshed with a “1” data state, while those memory cells 50 that are commonly connected to the substrate terminal 78 and which do not have a positive voltage in body region 24 will remain in blocking mode, since their SCR device will not be turned on, and therefore memory state “0” will be maintained in those cells. In this way, all memory cells 50 commonly connected to the substrate terminal will be maintained/refreshed to accurately hold their data states. This process occurs automatically, upon application of voltage to the substrate terminal 78, in a parallel, non-algorithmic, efficient process. In one particular non-limiting embodiment, a voltage of about 0.0 volts is applied to terminal 74, a voltage of about −1.0 volts is applied to terminal 70, and about +0.8 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships therebetween.

To perform a shadowing process on memory cell 50, a positive voltage is applied to terminal 72 and a substantially neutral voltage is applied to terminal 74. A neutral voltage or positive voltage is applied terminal 70 and a low positive voltage is applied to terminal 76, while the substrate terminal 78 is grounded.

When the floating body has a positive potential, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 and/or BW terminal 76 will be turned on. The positive voltage applied to terminal 72 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the materials from a high resistivity state to a low resistivity state. The voltage applied to terminal 72 initially has to exceed the dynamic threshold voltage (typically larger than 1.0 volts) to ensure that the resistance change memory 40 (even if it is in high resistivity state) will be conducting. Accordingly, the non-volatile resistance change material will be in a low resistivity state when the volatile memory of cell 50 is in state “1” (i.e. floating body 24 is positively charged).

When the floating body is neutral or negatively charged, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 and/or BW terminal 76 will be turned off. Therefore, when voltages are applied as described above, no electrical current will flow through the resistance change memory 40 and it will retain its high resistivity state. Accordingly, the non-volatile resistance change material will be in a high resistivity state when the volatile memory of cell 50 is in state “0” (i.e. floating body is neutral or negatively charged).

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, a constant current of about 400 μA is applied to terminal 72, about +1.0 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage and current levels may vary, while maintaining the relative relationships between the charges applied, as described above. The current level required to change phase change memory materials to low resistivity state typically range between 100 μA to 600 μA, while that of metal oxide systems vary depending on the materials. The current level is expected to decrease as the resistance change material is scaled to smaller geometry.

In another embodiment, the following bias can be applied: a neutral voltage is applied to terminal 72, a neutral voltage or positive voltage is applied to terminal 70, a positive voltage is applied to terminal 78, while terminals 74 and 76 are left floating. When the floating body 24 has a positive potential, the silicon controlled rectifier device formed by the SL 72 junction, floating body 24, buried layer 22, and substrate 12 will be turned on. The positive voltage applied to terminal 78 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the materials from a high resistivity state to a low resistivity state. For phase change materials, the crystalline state changes from amorphous phase to crystalline phase, while in metal oxide systems, this typically involves the formation of conductive filaments. Accordingly, the non-volatile resistance change material will be in a low resistivity state when the volatile memory of cell 50 is in state “1” (i.e. floating body 24 is positively charged).

When the floating body 24 is neutral or negatively charged, the silicon controlled rectifier device will be turned off. Therefore, no electrical current flows through the resistance change memory 40 and it will retain its high resistivity state. Accordingly, the non-volatile resistance change material will be in a high resistivity state when the volatile memory of cell 50 is in state ‘0” (i.e. floating body 24 is neutral or negatively charged).

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 72, a constant current of about 400 μA is applied to terminal 78, about +1.0 volts is applied to terminal 70, while terminals 74 and 76 are left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above. The current level required to change phase change memory materials to low resistivity state typically range between 100 μA to 600 μA and is expected to decrease as the phase change memory is being scaled to smaller dimension. In metal oxide systems, it varies depending on the materials used.

The restore operation (data restoration from non-volatile memory to volatile memory) is now described. In one embodiment, to perform the restore operation, a negative voltage is applied to terminal 70, a positive voltage is applied to terminal 72, a neutral voltage is applied to terminal 74, a neutral or low positive voltage is applied to terminal 76, and a substantially neutral voltage is applied to terminal 78.

If the resistance change memory 40 is in low resistivity state, this condition will result in holes being injected into the floating body 24, generated through the band-to-band tunneling mechanism, thereby restoring the state “1” that the memory cell 50 held prior to the shadowing operation. If the resistance change memory 40 is in high resistivity state, no holes will be generated; consequently, the volatile memory state of memory cell 50 will be restored to state “0”. Upon completion of the restore operation, the volatile memory of cell 50 is restored to the state that the volatile memory of memory cell 50 held prior to the shadowing operation.

In one particular non-limiting example of this embodiment, about +2.0 volts is applied to terminal 72, about +0.0 volts is applied to terminal 74, about −1.2 volts is applied to terminal 70, about 0.0 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

In another embodiment of the restore operation, the following bias can be applied: a neutral voltage is applied to terminal 72, a positive voltage is applied to terminal 70, a positive voltage is applied to terminal 78, while terminals 74 and 76 are left floating. The positive voltage applied to the WL terminal 70 will increase the potential of the floating body 24 through capacitive coupling. If the resistance change memory 40 is in a low resistivity state, this will create a feedback process that latches the device on and the volatile state of the memory cell 50 will be in state “1”. If the resistance change memory 40 is in a high resistivity state, the volatile state of the memory cell 50 will remain in state “0”. In one particular non-limiting embodiment, a charge of about 0.0 volts is applied to terminal 72, a charge of about +0.5 volts is applied to terminal 70, about +0.8 volts is applied to terminal 78, while terminals 74 and 76 are left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

After restoring the memory cell(s) 50, the resistance change memory 40 is/are reset to a high resistivity state, so that each resistance change memory 40 has a known state prior to performing another shadowing operation.

To perform a reset operation according to one embodiment, a neutral voltage or positive voltage is applied to terminal 70, a substantially neutral voltage is applied to BL terminal 74, a positive voltage is applied to SL terminal 72, a neutral or positive voltage is applied to terminal 76, and a substantially neutral voltage is applied to terminal 78.

When the floating body 24 has a positive potential, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 and/or BW terminal 76 will be turned on. The positive voltage applied to terminal 72 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the materials from a low resistivity state to a high resistivity state. Accordingly, all the non-volatile resistance change memory 40 will be in a high resistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, a constant current of about 700 μA is applied to terminal 72, about +1.0 volts is applied to terminal 70, about +0.6 volts is applied to terminal 76, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. To change the non-volatile phase change memory from low resistivity state to high resistivity state, a current level between 600 μA and 1 mA can be used. Lower current will be needed as the phase change material is scaled to smaller geometry.

In an alternative embodiment of the reset operation, the following bias can be applied: a neutral voltage is applied to terminal 72, a neutral voltage or positive voltage is applied to terminal 70, a positive voltage is applied to terminal 78, while terminals 74 and 76 are left floating.

When the floating body 24 has a positive potential, the silicon controlled rectifier device formed by the SL 72 junction, floating body 24, buried layer 22, and substrate 12 will be turned on. The positive voltage applied to terminal 78 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the materials from a low resistivity state to a high resistivity state. Accordingly, the non-volatile resistance change material will be in a high resistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 72, a constant current of about 700 μA is applied to terminal 78, about +1.0 volts is applied to terminal 70, while terminals 74 and 76 are left floating. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above. To change the non-volatile phase change memory from low resistivity state to high resistivity state, a current level between 600 μA and 1 mA can be used. Lower current will be needed as the phase change material is scaled to smaller geometry.

In this embodiment of the memory cell operations, the volatile memory operations can be performed in the same manner regardless of the state of the resistance change memory, i.e. there is no interference from the non-volatile memory state to the volatile memory operations. An alternative embodiment of the memory cell operations is described in flowchart 200 in FIG. 24. At event 202, when power is applied to the memory device, the memory device can be operated without the non-volatile memory of the device being set to a predetermined known state. The memory device may operate in the same manner as a volatile memory cell upon restore operation 208. As a result, the memory cell 50 can operate into the volatile operation mode faster, without first resetting the non-volatile memory state. The reset operation 204 can be performed just prior to writing new data into the non-volatile memory cell during the shadowing operation 206. In an alternative embodiment, the volatile and non-volatile memory can be configured to store different data, for example when the non-volatile memory is being used to store “permanent data”, which does not change in value during routine use. For example, this includes operating system image, applications, multimedia files, etc. The volatile memory can be used to store state variable. In this embodiment, the reset operation 204 can be bypassed.

FIGS. 19A-19B show another embodiment (perspective, cross-sectional view and top view, respectively) of the memory cell 50 described in this invention. In this embodiment, cell 50 has a fin structure 52 fabricated on substrate 12, so as to extend from the surface of the substrate to form a three-dimensional structure, with fin 52 extending substantially perpendicularly to, and above the top surface of the substrate 12. Fin structure 52 is conductive and is built on buried well layer 22. Buried well layer 22 is also formed by an ion implantation process on the material of substrate 12. Buried well layer 22 insulates the floating substrate region 24, which has a first conductivity type, from the bulk substrate 12. Fin structure 52 includes first and second regions 16, 18 having a second conductivity type. Thus, the floating body region 24 is bounded by the top surface of the fin 52, the first and second regions 16, 18 the buried well layer 22, and insulating layers 26. Insulating layers 26 insulate cell 50 from neighboring cells 50 when multiple cells 50 are joined to make a memory device. Fin 52 is typically made of silicon, but may comprise germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials known in the art.

Device 50 further includes gates 60 on three sides of the floating substrate region 24 as shown in FIG. 19A. Alternatively, gates 60 can enclose two opposite sides of the floating substrate region 24. Gates 60 are insulated from floating body 24 by insulating layers 62. Gates 60 are positioned between the first and second regions 16, 18, adjacent to the floating body 24.

A resistance change memory element 40 is positioned above the region having second conductivity type. The resistance change memory element 40 is shown as a variable resistor, and may be formed from resistance change memory element known in the art. In one embodiment, the non-volatile memory is initialized to have a low resistance state. In another alternate embodiment, the non-volatile memory is initialized to have a high resistance state.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, bit line (BL) terminal 74, buried well (BW) terminal 76 and substrate terminal 78. Terminal 70 is connected to the gate 60. Terminal 74 is connected to first region 16 and terminal 72 is connected to resistance change memory element 40, which is, in turn, connected to second region 18. Alternatively, terminal 74 can be connected to resistance change memory element 40 and terminal 72 can be connected to first region 16. Terminal 76 is connected to buried layer 22 and terminal 78 is connected to substrate 12.

The operations of the embodiment of memory cell 50 shown in FIGS. 19A-19B are the same as those described above with regard to the embodiment of memory cell 50 of FIG. 12. Equivalent terminals have been assigned with the same numbering labels in both figures.

FIG. 20 illustrates another embodiment of the memory cell 50 fabricated on a silicon-on-insulator (SOI) substrate. The cell 50 includes a substrate 12 of a first conductivity type, such as a p-type conductivity type, for example. Substrate 12 is typically made of silicon, but may comprise germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials known in the art. The substrate 12 has a surface 14. A first region 16 having a second conductivity type, such as n-type, for example, is provided in substrate 12 and which is exposed at surface 14. A second region 18 having the second conductivity type is also provided in substrate 12, which is exposed at surface 14 and which is spaced apart from the first region 16. First and second regions 16 and 18 are formed by an implantation process formed on the material making up substrate 12, according to any of implantation processes known and typically used in the art. A buried insulator layer 22 insulates the body region 24 from the substrate 12. The body region 24 is bounded by surface 14, first and second regions 16 and 18, and the buried insulator layer 22. The buried insulator layer 22 may be buried oxide (BOX).

A gate 60 is positioned in between the regions 16 and 18, and above the surface 14. The gate 60 is insulated from surface 14 by an insulating layer 62. Insulating layer 62 may be made of silicon oxide and/or other dielectric materials, including high-K dielectric materials, such as, but not limited to, tantalum peroxide, titanium oxide, zirconium oxide, hafnium oxide, and/or aluminum oxide. The gate 60 may be made of polysilicon material or metal gate electrode, such as tungsten, tantalum, titanium and their nitrides.

A resistance change memory element 40 is positioned above the region having second conductivity type 16. The resistance change memory element 40 is shown as a variable resistor, and may be formed from phase change material or metal-insulator-metal systems as described in previous embodiments above.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, bit line (BL) terminal 74, and substrate terminal 78. Terminal 70 is connected to the gate 60. Terminal 74 is connected to first region 16 and terminal 72 is connected to resistance change memory element 40 which is connected to second region 18. Alternatively, terminal 74 can be connected to resistance change memory element 40 and terminal 72 can be connected to first region 16. Terminal 78 is connected to substrate 12.

When power is applied to cell 50, cell 50 operates like a capacitorless DRAM cell. In a capacitorless DRAM device, the memory information (i.e., data that is stored in memory of the cells) is stored as charge in the floating bodies 24 of the transistors, i.e., in the bodies 24 of cells 50. The presence of the electrical charge in the floating body 24 modulates the threshold voltage of the cell 50, which determines the state of the cell 50. In one embodiment, the non-volatile memory is initialized to have a low resistance state.

To perform a read operation on memory cell 50 according to one embodiment of the present invention, a neutral or negative voltage is applied to the substrate terminal 78, a substantially neutral voltage is applied to SL terminal 72, a positive voltage is applied to BL terminal 74, and a positive voltage more positive than the positive voltage applied to BL terminal 74 is applied to WL terminal 70. If cell 50 is in a state “1” having holes in the body region 24, then a lower threshold voltage (gate voltage where the transistor is turned on) is observed compared to the threshold voltage observed when cell 50 is in a state “0” having substantially no holes in body region 24. In one particular non-limiting embodiment, about 0.0 volts is applied to terminal 72, about +0.4 volts is applied to terminal 74, about +1.2 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a neutral or negative voltage is applied to the substrate terminal 78, a substantially neutral voltage is applied to SL terminal 72, a positive voltage is applied to BL terminal 74, and a positive voltage less positive than the positive voltage applied to BL terminal 74 is applied to WL terminal 70. If cell 50 is in a state “1” having holes in the body region 24, then the parasitic bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned on and a higher cell current is observed compared to when cell 50 is in a state “0” having no holes in body region 24. In one particular non-limiting embodiment, about 0.0 volts is applied to terminal 72, about +3.0 volts is applied to terminal 74, about +0.5 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

A write state “1” operation can be carried out on cell 50 by performing band-to-band tunneling hot hole injection or impact ionization hot hole injection. To write state “1” using band-to-band tunneling mechanism, the following voltages are applied to the terminals: a positive voltage is applied to BL terminal 74, a substantially neutral voltage is applied to SL terminal 72, a negative voltage is applied to WL terminal 70, a neutral or negative voltage is applied to the substrate terminal 78. Under these conditions, holes are injected from BL terminal 74 into the floating body region 24, leaving the body region 24 positively charged. In one particular non-limiting embodiment, a charge of about 0.0 volts is applied to terminal 72, a potential of about +2.0 volts is applied to terminal 74, a potential of about −1.2 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, to write state “1” using an impact ionization mechanism, the following voltages are applied to the terminals: a positive voltage is applied to BL terminal 74, a substantially neutral voltage is applied to SL terminal 72, a positive voltage is applied to WL terminal 70, and a neutral or negative voltage is applied to the substrate terminal 78. Under these conditions, holes are injected from the region 16 into the floating body region 24, leaving the body region 24 positively charged. In one particular non-limiting embodiment, +0.0 volts is applied to terminal 72, a potential of about +2.0 volts is applied to terminal 74, a potential of about +0.5 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary while maintaining the relative relationships between the voltages applied, as described above.

A write “0” operation of the cell 50 is now described. To write “0” to cell 50, a negative bias is applied to SL terminal 72 and/or BL terminal 74, a neutral or negative voltage is applied to WL terminal 70, and a neutral or negative voltage is applied to substrate terminal 78. Under these conditions, the p-n junction (junction between 24 and 16 and between 24 and 18) is forward-biased, evacuating any holes from the floating body 24. In one particular non-limiting embodiment, about −1.0 volts is applied to terminal 72, about −1.0 volts is applied to terminal 70, and about 0.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the voltages applied, as described above.

Alternatively, a write “0” operation can be performed to cell 50 by applying a positive bias to WL terminal 70, and substantially neutral voltages to SL terminal 72 and BL terminal 74, and a neutral or negative voltage to substrate terminal 78. Under these conditions, the holes will be removed from the floating body 24 through charge recombination. In one particular non-limiting embodiment, about 1.0 volts is applied to terminal 70, about 0.0 volts are applied to terminals 72 and 74, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

To perform a shadowing process, a positive voltage is applied to terminal 72 and a substantially neutral voltage is applied to terminal 74. A neutral voltage or positive voltage is applied terminal 70 and a neutral or negative voltage is applied to terminal 78.

When the floating body has a positive potential, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned on. The positive voltage applied to terminal 72 is controlled (e.g., varied to maintain a constant current) such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the materials from a low resistivity state to a high resistivity state. Accordingly, the non-volatile resistance change material will be in a high resistivity state when the volatile memory of cell 50 is in state “1” (i.e. floating body 24 is positively charged).

When the floating body is neutral or negatively charged, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned off. Therefore, when voltages are applied as described above, no electrical current will flow through the resistance change memory 40 and it will retain its low resistivity state. Accordingly, the non-volatile resistance change material will be in a low resistivity state when the volatile memory of cell 50 is in state ‘0” (i.e. floating body is neutral or negatively charged).

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, about 700 μA is applied to terminal 72, about +1.0 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. To change the non-volatile phase change memory from low resistivity state to high resistivity state, a current level between 600 μA and 1 mA can be used. The current level is expected to decrease as the phase change material is scaled to smaller geometry.

Note that this process occurs non-algorithmically, as the state of the floating body 24 does not have to be read, interpreted, or otherwise measured to determine what state to write the non-volatile resistance change memory 40 to. Rather, the shadowing process occurs automatically, driven by electrical potential differences. Accordingly, this process is orders of magnitude faster than one that requires algorithmic intervention.

When power is restored to cell 50, the state of the cell 50 as stored on the non-volatile resistance change memory 40 is restored into floating body region 24. In one embodiment, to perform the restore operation, a negative voltage is applied to terminal 70, a positive voltage is applied to terminal 74, a negative voltage is applied to terminal 72, and a neutral or negative voltage is applied to terminal 78.

If the resistance change memory 40 is in high resistivity state, this condition will result in holes injection into the floating body 24, generated through the band-to-band tunneling mechanism, thereby restoring the state “1” that the memory cell 50 held prior to the shadowing operation.

If the resistance change memory 40 is in low resistivity state, the negative voltage applied to terminal 72 will evacuate holes injected into the floating body 24 because the p-n junction formed by the floating body 24 and the region 16 is forward-biased. Consequently, the volatile memory state of memory cell 50 will be restored to state “0” upon completion of the restore operation, restoring the state that the memory cell 50 held prior to the shadowing operation.

In one particular non-limiting example of this embodiment, about −1.0 volts is applied to terminal 72, about +2.0 volts is applied to terminal 74, about −1.2 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

Note that this process occurs non-algorithmically, as the state of the non-volatile resistance change memory 40 does not have to be read, interpreted, or otherwise measured to determine what state to restore the floating body 24 to. Rather, the restoration process occurs automatically, driven by resistivity state differences. Accordingly, this process is orders of magnitude faster than one that requires algorithmic intervention.

After restoring the memory cell(s) 50, the resistance change memory 40 is/are reset to a predetermined state, e.g., a low resistivity state, so that each resistance change memory 40 has a known state prior to performing another shadowing operation.

To perform a reset operation according to the present embodiment, a neutral voltage or positive voltage is applied to terminal 70, a substantially neutral voltage is applied to BL terminal 74, a positive voltage is applied to SL terminal 72, and a neutral or negative voltage is applied to terminal 78.

When the floating body has a positive potential, the bipolar transistor formed by the SL terminal 72, floating body 24, and BL terminal 74 will be turned on. The positive voltage applied to terminal 72 is optimized such that the electrical current flowing through the resistance change memory 40 is sufficient to change the resistivity of the materials from a high resistivity state to a low resistivity state. Accordingly, all the non-volatile resistance change memory 40 will be in a low resistivity state upon completion of the reset operation.

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, about 400 μA is applied to terminal 72, about −1.0 volts is applied to terminal 70, and about −2.0 volts is applied to terminal 78. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above. The current level required to change phase change memory materials to low resistivity state typically range between 100 μA to 600 μA. The current level requirement is expected to decrease as the phase change memory dimension is reduced.

FIG. 21 illustrates an alternative embodiment of a memory cell 50 according to the present invention. In this embodiment, cell 50 has a fin structure 52 fabricated on a silicon-on-insulator (SOI) substrate 12, so as to extend from the surface of the substrate to form a three-dimensional structure, with fin 52 extending substantially perpendicularly to, and above the top surface of the substrate 12. Fin structure 52 is conductive and is built on buried insulator layer 22, which may be buried oxide (BOX). Insulator layer 22 insulates the floating substrate region 24, which has a first conductivity type, from the bulk substrate 12. Fin structure 52 includes first and second regions 16, 18 having a second conductivity type. Thus, the floating body region 24 is bounded by the top surface of the fin 52, the first and second regions 16, 18 and the buried insulator layer 22. Fin 52 is typically made of silicon, but may comprise germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials known in the art.

Device 50 further includes gates 60 on three sides of the floating substrate region 24, as shown in FIG. 21. Alternatively, gates 60 can enclose two opposite sides of the floating substrate region 24. Gates 60 are insulated from floating body 24 by insulating layers 62. Gates 60 are positioned between the first and second regions 16, 18, adjacent to the floating body 24.

A resistance change memory element 40 is positioned above the region having second conductivity type. The resistance change memory element 40 is shown as a variable resistor, and may be formed from phase change material or metal-insulator-metal systems, for example. In one embodiment, the non-volatile memory is initialized to have a low resistance state. In another alternate embodiment, the non-volatile memory is initialized to have a high resistance state.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, bit line (BL) terminal 74, and substrate terminal 78. Terminal 70 is connected to the gate 60. Terminal 74 is connected to first region 16 and terminal 72 is connected to resistance change memory element 40 which is connected to second region 18. Alternatively, terminal 74 can be connected to resistance change memory element 40 and terminal 72 can be connected to first region 16. The bulk substrate 12 is connected to terminal 78.

Cell 50 includes four terminals: word line (WL) terminal 70, source line (SL) terminal 72, bit line (BL) terminal 74 and substrate terminal 78. Gate 60 is connected to terminal 70, first and second regions 16, 18 are connected to terminals 74 and 72, respectively, or vice versa, and the bulk substrate 12 is connected to terminal 78.

The operations of the embodiment of memory cell 50 shown in FIG. 21 are the same as for memory cell 50 described in FIG. 20. Equivalent terminals have been assigned with the same numbering labels in both figures.

Up until this point, the description of cells 50 have been in regard to binary cells, in which the data memories, both volatile and non-volatile, are binary, meaning that they either store state “1” or state “0”. However, in an alternative embodiment, any of the memory cell embodiments described herein can be configured to function as multi-level cells, so that more than one bit of data can be stored in each cell 50. FIG. 22 illustrates an example of voltage states of a multi-level cell wherein two bits of data can be stored in each cell 50. In this case, a voltage less than or equal to a first predetermined voltage and greater than a second predetermined voltage that is less than the first predetermined voltage in floating body or base region 24 volts is interpreted as state “01”, a voltage less than or equal to the second predetermined voltage is interpreted as state “00”, a voltage greater than the first predetermined voltage and less than or equal to a third predetermined voltage that is greater than the first predetermined voltage is interpreted to be state “10” and a voltage greater than the third predetermined voltage is interpreted as state “11”.

During the shadowing operation, the potential of the floating body or base region 24 in turn determines the amount of current flowing through the resistance change memory 40 or the floating gate 60, which will in turn determine the state of the non-volatile memory. The resistivity state of the resistance change memory 40 or the charge stored on the floating gate 60 can then be configured to store multi-level bits.

During restore operation, the resistivity state of the resistance change memory 40 or the charge of the floating gate 60 will subsequently determine the voltage state of the floating body or base region 24.

FIG. 23A shows an example of array architecture 80 of a plurality of memory cells 50 arranged in a plurality of rows and columns according to an embodiment of the present invention. The memory cells 50 are connected such that within each row, all of the gates 60 are connected by a common word line terminal 70. The first regions 18 are connected to resistance change materials 40. Within the same row, they are then connected by a common source line 72. Within each column, the second regions 16 are connected to a common bit line terminal 74. Within each row, all of the buried layers 22 are connected by a common buried well terminal 76. Likewise, within each row, all of the substrates 12 are connected by a common substrate terminal 78.

FIG. 23B shows an example of array architecture 80 of a plurality of memory cells 50 fabricated on a silicon-on-insulator (SOI) substrate, arranged in a plurality of rows and columns according to an embodiment of the present invention. The memory cells 50 are connected such that within each row, all of the gates 60 are connected by a common word line terminal 70. The first regions 18 are connected to resistance change materials 40. Within the same row, they are then connected by a common source line 72. Within each column, the second regions 16 are connected to a common bit line terminal 74. Likewise, within each row, all of the substrates 12 are connected by a common substrate terminal 78.

FIG. 25 is a schematic of an equivalent circuit model of a memory cell 50 using a resistance change element 40 with a thin capacitively coupled thyristor (TCCT) access device 130 according to an embodiment of the present invention. TCCT device 130 includes four regions with alternating n-type and p-type conductivity, along with a gate capacitively coupled to the p-region near the cathode terminal. In FIG. 25, the TCCT device 130 is shown as a back-to-back diode 134 with a gate terminal 132. A resistive change memory 40 is used to store non-volatile data, as it is able to retain its state in the absence of power. Examples of resistive change memory include phase change memory, conductive bridging memory, and metal oxide memory.

A plurality of memory cells 50 according to a non-limiting embodiment of the present invention is shown in FIG. 26, where a phase change element is used to illustrate the resistive change memory. Memory cells 50 are formed vertically and are insulated from one another by insulator layers 172. The vertical arrangement results in a compact cell size. The p-n-p-n regions 168, 166, 164, and 162 forming the thyristor device 130 are formed using semiconductor materials, such as silicon or polysilicon. A gate 170 is capacitively coupled to the p-region 164. The TCCT device 130 is formed on top of a conductor layer 160. The conductor layer 160 can be made of semiconductor materials such as silicon, germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials, or conductor materials such as tungsten (W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory 40 on top of the thyristor device 130 is formed by a bottom electrode 180, a chalcogenide material 182, and a top electrode 184. The bottom electrode 180 can be made from titanium nitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titanium aluminum nitride (TiAlN) layer, or other electrode layer. Phase change material 182 is a material having properties, such as electrical resistance, that depend on the crystalline phase of the material. Crystalline phase will exhibit a low resistivity state and amorphous phase will exhibit a high resistivity state. Examples of phase change material include alloys containing elements from Column VI of the periodic table, such as GeSbTe alloys. The top electrode layer 184 can be formed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 is connected to the gate 170. Terminal 72 is connected to the phase change memory top electrode 184 and terminal 74 is connected to the conductor layer 160.

The TCCT device 130 can operate in two modes: a low impedance conducting mode and a high impedance blocking mode. Gate 170 is used to assist the switching between the two states by modifying the potential of the base region 164 through capacitive coupling. To select a resistive change memory element 40, the TCCT device 130 operates in a conducting mode.

The read operation of the memory cell 50 can be performed as follows. A positive voltage is applied to the SL terminal 72, a substantially neutral voltage is applied to the BL terminal 74, and a positive voltage is applied to WL terminal 70. The positive voltage applied to the SL terminal 72 needs to be lower than the switching voltage of the resistive change element 40 to avoid unintentional writing of the resistive change element 40. If the resistive change element 40 is in high resistance state, no current will flow through the memory cell 50. If the resistive change element 40 is in low resistance state, a higher current will be observed flowing through the memory cell 50. In one particular non-limiting embodiment, about +0.5 volts is applied to terminal 72, about 0.0 volts is applied to terminal 74, and about +0.5 volts is applied to terminal 70. However, these voltage levels may vary while maintaining the relative relationships between the charges applied, as described above.

To write the phase change memory element 40 into a low resistance state, which is often referred to as “SET” state, the following bias is applied. A positive voltage is applied to SL terminal 72, a substantially neutral voltage is applied to the BL terminal 74, and a positive voltage is applied to WL terminal 70. The positive voltage applied to terminal 72 is controlled so that the electrical current flowing through the phase change memory 40 is substantially constant and is sufficient to change the phase of the materials to a low resistivity state.

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, about 400 μA is applied to terminal 72, and about +0.5 volts is applied to terminal 70. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

To write the phase change memory element 40 into a high resistance state, which is often referred to as “RESET” state, the following bias is applied. A positive voltage is applied to SL terminal 72, a substantially neutral voltage is applied to the BL terminal 74, and a positive voltage is applied to WL terminal 70. The positive voltage applied to terminal 72 is controlled so that the electrical current flowing through the phase change memory 40 is substantially constant and is sufficient to change the phase of the material to a low resistivity state.

In one particular non-limiting example of this embodiment, about 0.0 volts is applied to terminal 74, about 700 μA is applied to terminal 72, and about +0.5 volts is applied to terminal 70. However, these voltage levels may vary, while maintaining the relative relationships between the charges applied, as described above.

To increase the memory density, the memory cell 50 can be stacked in the vertical direction to form a three-dimensional memory array. FIG. 27 shows an example of a three-dimensional memory array 150 according to an embodiment of the present invention, in which memory array 80, comprising a two-dimensional array of memory cells 50 (i.e., rows and columns of interconnected memory cells 50 (although only one plane corresponding to one row or one column is shown in FIG. 26, and only one plane is likewise shown in FIG. 27) is stacked in the vertical direction, insulated by an insulator layer 190. The insulation layer 190 is typically made of silicon oxide, although other insulating materials can be used.

FIG. 28 illustrates an example of memory array architecture of the memory array 150, where two vertical stacks of memory array 80 are shown. At each stack, the memory cells 50 are connected such that within each row, all of the gates 170 are connected in common word line terminals 70 and the conductor layer 160 is connected to the common bit line terminals 74. Within each column, the top electrodes 184 are connected to common source line terminals 72. In another embodiment of the memory array architecture, the source line terminals 72 can be shared between the memory cells 50 in the first and second level of the stacks. In another embodiment, the gates 170 and WL terminals 70 can control regions 164 of two adjacent vertical stacks in two adjacent columns. This will further reduce the size of memory array 150.

FIGS. 29-35 illustrate an embodiment of a sequence of fabrication steps of the memory array 150. As shown in FIG. 29, a conductor layer 160 is deposited on an insulator layer 190, followed by a polysilicon layer 162. The polysilicon is doped to form n-type region, either through ion implantation process or through in-situ deposition process. The conductor layer 160 and the polysilicon layer 162 are then patterned and etched to form column lines of the memory array.

Subsequently, insulator layer 172 is deposited on the polysilicon layer 162. Holes are then patterned and etched through the insulator layer 172. Polysilicon films are then deposited to fill the holes, followed by a planarization step. An ion implantation process can then be performed to form the p-n-p regions 168, 166, and 164 shown in FIG. 30.

Following the formation of the p-n-p regions 168, 166 an 164, the insulator layer 172 is patterned to form the row lines of the memory array and etched as shown in FIG. 31. A thin layer of insulating layer 174 is then deposited as shown in FIG. 32. The insulator layer 174 is typically silicon oxide, but other insulating materials particularly with high dielectric constants may be used. As shown in FIG. 33, this is then followed by a polysilicon deposition step to form the gates 170. An insulating layer 176 is subsequently deposited following the polysilicon 170 deposition. A chemical mechanical polish (CMP) or a dry etch process can then be performed to planarize the resulting films.

As shown in FIG. 34, a bottom electrode 180, a phase change material 182, and a top electrode 184 are subsequently deposited. These films are then patterned and etched to form the row lines of the memory array. An insulating layer 290 is then deposited to cap the resulting layers, as depicted in FIG. 35.

Another embodiment of an array 80 of memory cells 50 is shown in FIG. 36. Memory cells 50 are formed vertically and are insulated from one another by an insulator layer 172. The vertical arrangement results in a compact cell size. The p-n-p-n regions 168, 166, 164, and 162 forming the thyristor device is formed using semiconductor materials, such as silicon or polysilicon. A gate 170 is capacitively coupled to and encloses the p-region 64. The TCCT device 130 is formed on top of a conductor layer 160. The conductor layer 160 can be made of semiconductor materials such as silicon, germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials, or conductor materials such as tungsten (W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory 40 on top of the thyristor device 130 is formed by a bottom electrode 180, a chalcogenide material 182, and a top electrode 184. The bottom electrode 180 can be made from titanium nitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titanium aluminum nitride (TiAlN) layer, or other electrode layer. Phase change material 182 is a material having properties, such as electrical resistance, that depend on the crystalline phase of the material. Crystalline phase will exhibit a low resistivity state and amorphous phase will exhibit a high resistivity state. Examples of phase change material include alloys containing elements from Column VI of the periodic table, such as GeSbTe alloys. The top electrode layer 84 can be formed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 is connected to the gate 170. Terminal 72 is connected to the phase change memory top electrode 184 and terminal 74 is connected to the conductor layer 160.

To increase the memory density, the arrays 80 of memory cells 50 can be stacked in the vertical direction to form a three-dimensional memory array 150. In another embodiment, the gates 170 and WL terminals 70 can control regions 164 of two adjacent vertical stacks in two adjacent columns. This will further reduce the memory array size.

Another embodiment of an array 80 of memory cells 50 is shown in FIG. 37. Memory cells 50 are formed vertically and are insulated from one another by an insulator layer 172. The vertical arrangement results in a compact cell size. The p-n-p-n regions 168, 166, 164, and 162 forming the thyristor device 130 is formed using semiconductor materials, such as silicon or polysilicon. A gate 170 is capacitively coupled to the p-region 164. The TCCT device 130 is formed on top of a conductor layer 160. The conductor layer 160 can be made of semiconductor materials such as silicon, germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials, or conductor materials such as tungsten (W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory 40 on top of the thyristor device 130 is formed by a bottom electrode 180, a chalcogenide material 182, and a top electrode 184. The bottom electrode 180 can be made from titanium nitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titanium aluminum nitride (TiAlN) layer, or other electrode layer. Phase change material 182 is a material having properties, such as electrical resistance, that depend on the crystalline phase of the material. Crystalline phase will exhibit a low resistivity state and amorphous phase will exhibit a high resistivity state. Examples of phase change material include alloys containing elements from Column VI of the periodic table, such as GeSbTe alloys. The top electrode layer 184 can be formed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 is connected to the gate 170. Terminal 72 is connected to the phase change memory top electrode 184 and terminal 74 is connected to the conductor layer 160.

To increase the memory density, the arrays 80 of memory cells 50 can be stacked in the vertical direction to form a three-dimensional memory array 150. In another embodiment, the gates 170 and WL terminals 70 can control regions 164 of two adjacent vertical stacks in two adjacent columns. This will further reduce the memory array size.

Another embodiment of memory cells 50 is shown in FIG. 38. Memory cell 50 is formed vertically and is insulated from one another by an insulator layer 172. The vertical arrangement results in a compact cell size. The p-n-p-n regions 168, 166, 164, and 162 forming the thyristor device 130 is formed using semiconductor materials, such as silicon or polysilicon. A gate 170 is capacitively coupled to and encloses the p-region 164. The TCCT device is formed on top of a conductor layer 160. The conductor layer 160 can be made of semiconductor materials such as silicon, germanium, silicon germanium, gallium arsenide, carbon nanotubes, or other semiconductor materials, or conductor materials such as tungsten (W), aluminum (Al), titanium (Ti), or copper (Cu).

The phase change memory on top of the thyristor device is formed by a bottom electrode 180, a chalcogenide material 182, and a top electrode 184. The bottom electrode 180 can be made from titanium nitride (TiN) layer, titanium silicon nitride (TiSiN) layer, titanium aluminum nitride (TiAlN) layer, or other electrode layer. Phase change material 182 is a material having properties, such as electrical resistance, that depend on the crystalline phase of the material. Crystalline phase will exhibit a low resistivity state and amorphous phase will exhibit a high resistivity state. Examples of phase change materials that can be used include alloys containing elements from Column VI of the periodic table, such as GeSbTe alloys. The top electrode layer 184 can be formed from aluminum (Al), titanium (Ti), or copper (Cu) layer.

Cell 50 includes several terminals: word line (WL) terminal 70, source line (SL) terminal 72, and bit line (BL) terminal 74. Terminal 70 is connected to the gate 170. Terminal 72 is connected to the phase change memory top electrode 184 and terminal 74 is connected to the conductor layer 160.

To increase the memory density, the arrays 80 of memory cells 50 can be stacked in the vertical direction to form a three-dimensional memory array 150. In another embodiment, the gates 170 and WL terminals 70 can control regions 14 of two adjacent vertical stacks in two adjacent columns. This will further reduce the memory array size.

While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.

Claims

1. A semiconductor memory cell comprising:

a substrate having a top surface, said substrate having a first conductivity type selected from a p-type conductivity type and an n-type conductivity type;

a first region having a second conductivity type selected from said p-type and n-type conductivity types, said second conductivity type being different from said first conductivity type, said first region being formed in said substrate and exposed at said top surface;

a second region having said second conductivity type, said second region being formed in said substrate, spaced apart from said first region and exposed at said top surface;

a buried layer in said substrate below said first and second regions, spaced apart from said first and second regions and having said second conductivity type;

a body region formed between said first and second regions and said buried layer, said body region having said first conductivity type;

a gate positioned between said first and second regions and above said top surface; and

a nonvolatile memory configured to store data upon transfer from said body region;

wherein a data state of said body region is maintained by applying a voltage to said substrate.

2. The semiconductor memory cell of claim 1, wherein said nonvolatile memory is further configured to restore data to said body region.

3. The semiconductor memory cell of claim 1, wherein said nonvolatile memory comprises a floating gate or trapping layer positioned in between said first and second regions, above said top surface and below said gate.

4. The semiconductor memory cell of claim 1, wherein said nonvolatile memory comprises a resistance change element connected to one of said first and second regions.

5. The semiconductor memory cell of claim 4, wherein said resistance change element comprises a phase change material.

6. The semiconductor memory cell of claim 4, wherein said resistance change element comprises a metal-oxide-metal system.

7. The semiconductor memory cell of claim 1, wherein nonvolatile memory is configured to store data upon transfer from said body region resulting from an instruction to back up said data stored in said body region.

8. The semiconductor memory cell of claim 1, wherein said transfer from said body region commences upon loss of power to said cell, wherein said cell is configured to perform a shadowing process wherein said data in said body region is loaded into and stored in said nonvolatile memory.

9. The semiconductor memory cell of claim 8, wherein said loss of power to said cell is one of unintentional power loss or intentional power loss, wherein intentional power loss is predetermined to conserve power.

10. The semiconductor memory cell of claim 8, wherein, upon restoration of power to said cell, said data in said non-volatile memory is loaded into said body region and stored therein.

11. The semiconductor memory cell of claim 10, wherein said cell is configured to reset said nonvolatile memory to an initial state after loading said data into said body region upon said restoration of power.

12. The semiconductor memory cell of claim 11, wherein said cell is configured to reset said nonvolatile memory just prior to writing new data into said nonvolatile memory during a shadowing operation.

13. A semiconductor memory array, including:

a plurality of semiconductor memory cells as recited in claim 1 arranged in a matrix of rows and columns.

14. The semiconductor memory array of claim 13, further comprising a plurality of said matrices vertically stacked and electrically connected to form a three-dimensional array.

15. The semiconductor cell of claim 1, further comprising:

a source line terminal electrically connected to one of said first and second regions;

a bit line terminal electrically connected to the other of said first and second regions;

a word line terminal connected to said gate;

a buried well terminal electrically connected to said buried layer, and

a substrate terminal electrically connected to said substrate below said buried layer.

16. The semiconductor memory cell of claim 15, wherein said nonvolatile memory comprises a resistance change element connected to one of said first and second regions, and wherein one of said source line terminal and said bit line terminal is connected to said resistance change element.

17. The semiconductor memory cell of claim 15, wherein a data state of said body region is maintained by said applying voltage to said substrate comprises applying a voltage to said substrate terminal.

18. The semiconductor memory cell of claim 17, wherein said voltage applied to said substrate terminal automatically activates said cell when said floating body has a first data state to refresh said first data state, and wherein when said body region of said cell has a second data state, said cell automatically remains deactivated upon application of said voltage to said substrate terminal so that said body region of said cell remains in said second data state.

19. The semiconductor memory cell of claim 17, wherein said substrate terminal is periodically biased by pulsing said substrate terminal with said voltage, and wherein said data state of said body region of said cell is refreshed upon each said pulse.

20. The semiconductor memory cell of claim 17, wherein said substrate terminal is constantly biased by application of said voltage thereto, and said body region constantly maintains said data state.

21. The semiconductor memory cell of claim 1, wherein said first and second regions are formed in a fin that extends above said buried layer, said gate is provided on opposite sides of said fin, between said first and second regions, and said body region is between said first and second regions and between said gate on opposite sides of said fin.

22. The semiconductor memory cell of claim 21, wherein said gate is additionally provided above a top surface of said body region.

23. A semiconductor memory cell comprising:

an arrangement of layers having alternating conductivity types selected from p-type conductivity type and n-type conductivity type configured to function as a silicon controlled rectifier device to store data in volatile memory; and

a nonvolatile memory configured to store data upon transfer from volatile memory.

24. The semiconductor memory cell of claim 23, wherein said silicon controlled rectifier device is provided as a P1-N2-P3-N4 silicon-rectifier device.

25. The semiconductor memory cell of claim 24, wherein said cell comprises:

a substrate having a top surface, said substrate having a p-type conductivity type;

a first region having an n-type conductivity type said first region being formed in said substrate and exposed at said top surface;

a second region having said n-type conductivity type, said second region being formed in said substrate, spaced apart from said first region and exposed at said top surface;

a buried layer in said substrate below said first and second regions, spaced apart from said first and second regions and having said n-type conductivity type; and

a body region formed between said first and second regions and said buried layer, said body region having said p-type conductivity type;

wherein said substrate functions as the P1 region of said P1-N2-P3-N4 silicon-rectifier device, said buried layer functions as the N2 region of said P1-N2-P3-N4 silicon-rectifier device, said body region functions as the P3 region of said P1-N2-P3-N4 silicon-rectifier device and said first region or said second region functions as the N4 region of said of P1-N2-P3-N4 silicon-rectifier device.

26. The semiconductor memory cell of claim 25, further comprising a gate positioned between said first and second regions and above said top surface.

27. The semiconductor memory cell of claim 26, wherein said nonvolatile memory comprises a floating gate or trapping layer positioned in between said first and second regions, above said top surface and below said gate.

28. The semiconductor memory cell of claim 26, wherein said nonvolatile memory comprises a resistance change element connected to one of said first and second regions.

29. A method of operating a memory cell having a floating body for storing, reading and writing data as volatile memory, and a nonvolatile memory for storing data, the method comprising:

reading and storing data to the floating body while power is applied to the memory cell;

biasing a substrate terminal connected to a substrate of said memory cell to operate said memory cell as a silicon rectifier device in a conducting operation when said floating body has a first data state, but wherein a blocking operation results when said floating body has a second data state; and

transferring the data stored in the floating body to the nonvolatile memory when power to the cell is interrupted.

30. A method of operating a semiconductor storage device comprising a plurality of memory cells each having a floating body for storing, reading and writing data as volatile memory, and a resistance change element for storing data as non-volatile memory, the method comprising:

reading and storing data to the floating bodies as volatile memory while power is applied to the device;

biasing a substrate terminal connected to a substrate of said memory cell to operate said memory cell as a silicon rectifier device in a conducting operation when said floating body has a first data state, but wherein a blocking operation results when said floating body has a second data state;

transferring the data stored in the floating bodies, by a parallel, non-algorithmic process, to the resistance change elements corresponding to the floating bodies, when power to the device is interrupted; and

storing the data in the resistance change elements as non-volatile memory.

31. The method of claim 30, further comprising:

transferring the data stored in the resistance change elements, by a parallel, non-algorithmic, restore process, to the floating bodies corresponding to the resistance change elements, when power is restored to the cell;

and storing the data in the floating bodies as volatile memory.