Magnetic tunnel junction magnetic device, memory and writing and reading methods using said device

Abstract

magnetic tunnel junction magnetic device (16) for writing and reading uses a reference layer (20c) and a storage layer (20a) separated by a semiconductor or insulating layer (20b), which can include an antiferromagnetic layer adjacent the storage layer. The blocking temperature of the magnetisation magnetization of the storage layer is less than that of the reference layer. The storage layer is heated (22, 24) above the blocking temperature of its magnetisation magnetization. A magnetic field (34) or a magnetic torque created by the injection of spin polarized electrons is applied (26) to it orientating its magnetization with respect to that of the reference layer without modifying the orientation of the reference layer.

Description

He this being typically between around 20 Oe and 60 Oe (around 1600 A/m and 4800 A/m), is applied in the direction in which one wishes to orientate the magnetisation of the storage layer F1.

The magnetisation of said storage layer F1 than orientates itself in the direction of the applied field He whereas that of the reference layer F2, also called “pinned layer”, always remains orientated in the same direction.

The heating of the junction may be controlled by sending a short current impulse (around 10⁵ A/cm² to 10⁶ A/cm² for a few nanoseconds) through the junction.

The magnetic field He is created by sending current impulses in the conductive lines situated in the planes lying above and/or below the magnetic tunnel junctions.

A second possibility of provoking the switching of the magnetisation of the storage layer during its cooling may consist in injecting in said layer a current of electrons in which the spin is polarised, according to one of the techniques detailed hereafter.

The present invention consists in this case in combining the heating of the material of the storage layer, in order to reduce the reversal field of the magnetisation of said layer, with the application of a magnetic torque to this magnetisation, during the cooling of the storage layer, by flowing a current of electrons in which the spin is polarised through the storage layer.

It is also possible to combine the switching, through application of a local field generated by sending a current in an upper or lower conductive line, with the injection of a current of electrons with polarised spin in the storage layer of the junction.

Four major advantages of the present invention may be highlighted:

1) Flawless Selection of Storage Elements:

The present invention enables much better selection of storage elements than known technologies. Indeed, let us assume that the storage elements are organised into a square array as seen in FIG. 2, which represents the architecture of a known MRAM.

In said known memory, one distinguishes three levels of lines:

upper conductive lines 10 that serve to generate the magnetic field Hx to apply to the magnetic tunnel junctions 2 during the writing and that also serve as electrical contacts for said junctions during the reading,

lower conductive lines 12 that only serve to generate the magnetic field Hy at the moment of the writing, and

control lines 14 that act on the transistor gates 4 to put them into the passing position (saturated) or closed position (blocked).

According to a known writing procedure, the writing is carried out by sending current impulses along the upper and lower conductive lines, which cross at the storage element that one wishes to address. However, if there NiO₃₀₀/Co₆/(Pt₁₈/CO₆)₂/Cu₃₀/(CO₆/Pt₁₈)₂

In the case of FIG. 5, the increase in the coerciveness of one of the multi-layers is obtained by coupling the magnetisation of said multi-layer to an adjacent antiferromagnetic layer (for example, NiO (case of FIG. 5), PtMn, PdPtMn or FeMn).

The same result may be obtained by combining a multi-layer of Co/Pt to an alloy of FePt.

Moreover, each of the abovementioned materials has its own variation of coercive field as a function of the temperature.

FIG. 6 shows, for example, the variations in the Hr reversal field (in Oe) of a multi-layer (Co 0.6 nm/Pt 1.4 nm) as a function of the temperature T (in ° C.) for a “full wafer” wafer, of macroscopic lateral dimension (curve I), and in arrays of pads of submicronic dimensions (curve II).

With the thicknesses of Co and Pt used, the Hr reversal field decreases rapidly with the temperature and virtually cancels itself out at a temperature Tc of around 200° C.

If one increases the thickness of Co at fixed Pt thickness, the reversal field decreases less rapidly, in other words cancels out at a temperature greater than 200° C. Similarly, in the alloy FePt, the reversal field cancels out around 500° C.

Therefore, by forming for example a magnetic tunnel junction that combines a multi-layer, formed of alternating layers of Co and layers of Pt, with a FePt alloy electrode, one forms a structure according to the invention. By sending a current impulse through the junction, one raises the temperature of said junction up to around 200° C.

One then cuts the current that is flowing through the junction and, during the cooling of said junction, one applies a weak magnetic field by means of lower or upper conductive lines
where θ_s and θ_p respectively represent the angles marking respectively the magnetisations of the storage layer and the pinned layer, or reference layer, in the plane of the junction.

ΔR/R_par=(R_ant−R_par)/R_par is the total magnetoresistance amplitude.

The reading of the level of intermediate resistance between the parallel resistance R_par and the antiparallel resistance R_ant therefore makes it possible to determine the direction of the magnetisation of the storage layer.

In the structures described previously, it is possible to insert thin layers of another material at the interface between the magnetic layer and the tunnel barrier layer.

Said thin layers may be magnetic layers, intended to reinforce the polarisation of the electrons in the neighbourhood of the interface with the tunnel barrier layer, or non magnetic layers making it possible to form quantum wells depending on the spin in the neighbourhood of the tunnel barrier layer or to increase the magnetic decoupling of two magnetic layers on either side of the tunnel junction.

Claims

1. magnetic A magnetic device comprising a magnetic tunnel junction that comprises:

a first magnetic layer forming defining a reference layer and having a magnetisation magnetization of fixed direction,

a second magnetic layer forming defining a storage layer and having a magnetisation magnetization of variable direction, and

a third layer defining a tunnel barrier that is semiconductive or electrically insulating and which separate's the first layer from the second layer,

wherein the first and second magnetic layers have respective blocking temperatures and wherein the blocking temperature of the magnetisation of the storage layer is lower than the blocking temperature of the magnetisation of the reference layer and in that, wherein the device further comprises:

means for heating the storage layer to a temperature higher than the blocking temperature of the magnetisation of said storage layer, said means for heating the storage layer being means provided to make generating an electric current flow through the magnetic tunnel junction, wherein the storage layer is heated to a temperature higher than the blocking temperature of the storage layer, and

means for applying, to said the storage layer, a magnetic field capable of orientating the magnetisation magnetization of said the storage layer with respect to the magnetisation magnetization of the reference layer, without modifying the orientation of said the magnetization of the reference layer.

2. device The device according to claim 1, in which wherein the blocking temperatures of the storage and reference layers have values greater than the value of the operating temperature of the device outside of heating of the tunnel junction.

3. device The device according to claim 1, in which wherein the magnetisation magnetization of each of the storage and reference layers is substantially perpendicular to the plane of said the storage and reference layers.

4. device The device according to claim 3, in which wherein the storage layer is comprises a Co—Pt or Co—Pd alloy mono-layer or a multi-layer formed by a stack of layers of Co alternating with layers of Pt or Pd in, such a way that the resulting coercive field of the storage layer rapidly decreases when with increasing the temperature increases.

5. device The device according to claim 3, in which wherein the storage layer is comprises a mono-layer in of a cobalt rich alloy with iron or nickel or chromium and platinum or palladium, or a multi-layer formed by a stack of cobalt rich layers with iron or nickel or chromium, alternating with layers of Pt or Pd in such a way that, such that the resulting coercive field of the storage layer rapidly decreases when the with increasing temperature increases.

6. device The device according to claim 1, in which wherein the magnetisation magnetization of each of the storage and reference layers is substantially parallel to the plane of said the storage and reference layers.

7. device The device according to claim 1, further comprising a first an antiferromagnetic layer combined magnetically coupled with the reference layer, wherein the antiferromagnetic layer comprises PtMn alloy or a PtPdMn alloy.

8. device The device according to claim 7, in which wherein the blocking temperature of the magnetisation of said first the antiferromagnetic layer is higher than the blocking temperature of the storage layer.

9. device The device according to claim 1, in which wherein the reference layer is a multi-layer comprising two magnetic layers and an intermediate layer in of Ru or Re or Ir or Rh, wherein the two magnetic layers being are separated by the intermediate layer and coupled in an antiparallel maimer manner by interaction through said the intermediate layer.

10. device The device according to claim 1, further comprising a second anti ferromagnetic an antiferromagnetic layer coupled to the storage layer by exchange anisotropy.

11. device The device according to claim 10, in which wherein the blocking temperature of the magnetisation of said second antiferromagnetic layer is lower than the blocking temperature of the reference layer.

12. device The device according to claim 1, in which wherein the means for applying a magnetic field to the storage layer comprise means of injecting, in said storage layer, a current of electrons in which the spin is polarised polarized.

13. memory A memory comprising a matrix of storage elements that are addressable by addressing lines and columns, wherein each storage element comprises: a magnetic device according to claim 1, and wherein the means for generating an electric current comprises a means of current switching placed circuit in series with said each magnetic device, wherein each magnetic device being is linked to an addressing line and each means of current switching being circuit is linked to an addressing column.

14. Method A method for writing information in a magnetic device according to claim 1, in which: one heats comprising heating the storage layer to a temperature higher than the blocking temperature of the magnetisation of said the storage layer, and during the cooling of the storage layer, one applies applying to said the storage layer a magnetic field capable of orientating the magnetisation magnetization of said the storage layer with respect to the magnetisation magnetization of the reference layer, without modifying the orientation of said the magnetization of the reference layer.

15. Method The method according to claim 14, in which wherein the value, seen by magnetic field strength applied at the reference layer, of the magnetic field applied during the storage, writing is less than the value that the magnetic field strength necessary for reversing the magnetisation magnetization of the reference layer takes at the maximum temperature attained by said the reference layer during the heating of the junction.

16. Method The method according to claim 14, in which wherein the storage layer is coupled to an antiferromagnetic layer by exchange anisotropy and one heats the storage layer and said the antiferromagnetic layer are heated to a temperature higher than the blocking temperatures of the magnetisation of said the storage and antiferromagnetic layers and, during the cooling of the antiferromagnetic layer, one orientates the magnetisation magnetization of the storage layer is oriented in any direction whatsoever predefined by the direction of magnetisation of the magnetic field applied during the cooling.

17. Method A method for reading information memorised memorized in the magnetic device according to claim 1, in which one determines wherein the resistance value of the magnetic tunnel junction is determined, and one deduces the orientation of the magnetisation of the storage layer is ascertained from said the resistance value.

18. The device according to claim 1, wherein the storage layer comprises a single layer or multilayer structure and wherein the reference layer is in contact with an antiferromagnetic layer.

19. The device according to claim 1, wherein the reference layer comprises a single layer or a multilayer structure, and wherein the storage layer is in contact with an antiferromagnetic layer.

20. The device according to claim 3, wherein the storage layer comprises a Co/Ni or a Cu/Ni or a multilayer comprising a stack of cobalt or copper layers alternating with layers of nickel, such that a resulting coercive field of the storage layer rapidly decreases with increasing temperature, and wherein the reference layer comprises a layer of FePt or FePd alloy.

21. The method according to claim 15 further comprising injecting spin-polarized electrons into the storage layer during writing that apply a magnetic torque to the magnetization of the storage layer, wherein the magnetic torque applied at the reference layer is less than the magnetic torque for reversing the magnetization of the reference layer at the maximum temperature attained by the reference layer during the heating of the junction.

22. A magnetic device comprising:

a magnetic tunnel junction including a first magnetic layer defining a reference layer having a blocking temperature and a magnetization in a fixed direction, a second magnetic layer defining a storage layer having a blocking temperature and having a magnetization of variable direction, and a third layer defining a tunnel barrier layer intermediate to the first layer and the second layer, wherein the blocking temperature of the storage layer is lower than the blocking temperature of the reference layer; and

circuitry configured to inject a current of spin polarized electrons into the storage layer, such that the tunnel junction is heated and a magnetic torque is applied to the storage layer which orients the magnetization of the storage layer with respect to the magnetization of the reference layer, without modifying the orientation of the magnetization of the reference layer.

23. The device according to claim 22, wherein the storage layer, the reference layer, and a layer portion of the circuitry comprise layers having out-of-the-plane magnetization or in-the-plane magnetization.

24. The device according to claim 22, wherein the device comprises a storage element of a memory comprising a matrix of storage elements that are addressable by addressing lines and columns, wherein each storage element comprises a current switching circuit placed in series with each device, wherein each device is linked to one of an addressing line or addressing column, and each current switching circuit is linked to the other of the addressing line or addressing column.

25. The device according to claim 22 further comprising: a spin-polarizing layer on an opposite side of the storage layer from the reference layer; and a non-magnetic metallic layer intermediate to the spin polarizing layer and the storage layer, wherein the reference layer and the spin polarizing layer comprise oppositely magnetized layers.

26. The device according to claim 22 further comprising a conductive line above or below the magnetic tunnel junction and configured to, generate a magnetic field at the storage layer that orients the magnetization of the storage layer with respect to the magnetization of the reference layer, without modifying the magnetization of the reference layer.

27. The device according to claim 26, wherein the magnetic field, generated by the conductive line is substantially perpendicular to the direction of polarization of the spin polarized electrons injected in the storage layer.

28. A method for writing information in a magnetic device according to claim 22, comprising injecting a current impulse of spin polarized electrons through the magnetic tunnel junction during a heating phase, and in a cooling phase, applying a magnetic torque to the magnetization of the storage layer that is capable of orientating the magnetization of the storage layer with respect to the magnetization of the reference layer, without modifying the orientation of the reference layer.

29. The method according to claim 28, in which the magnetic torque applied to the magnetization of the reference layer during writing is less than the magnetic torque necessary for reversing the magnetization of the reference layer at the maximum temperature attained by the reference layer during the heating phase.

30. The method according to claim 28, in which the storage layer is coupled to an antiferromagnetic layer by exchange anisotropy and the storage layer and the antiferromagnetic layer are heated to a temperature higher than blocking temperatures of the storage and antiferromagnetic layers and, during the cooling phase, the magnetization of the storage layer is oriented in a direction corresponding to the direction of magnetization induced by the magnetic torque.

31. The method of claim 28 further comprising applying a magnetic field to the storage layer during the cooling phase to orient the magnetization of the storage layer with respect to the magnetization of the reference layer.

32. A memory cell comprising:

a tunnel junction that includes a storage layer adjacent and in contact with an antiferromagnetic layer; and

a reference layer separated from the storage layer by a tunnel barrier layer.

33. The memory cell of claim 32 further comprising circuitry configured to inject a current of spin-polarized electrons into the storage layer, wherein the spin-polarized electrons heats the storage layer and the antiferromagnetic layer to a temperature higher than blocking temperatures of the storage and antiferromagnetic layers and apply a magnetic torque to set a magnetic orientation of the storage layer with respect to a magnetic orientation of the reference layer, without modifying the magnetic orientation of the reference layer.

34. The memory cell of claim 32 further comprising circuitry configured to generate a magnetic field at the storage layer that orients the magnetization of the storage layer with respect to the magnetization of the reference layer, without modifying the magnetization of the reference layer.

35. A method for writing to a magnetic device comprising:

providing a magnetic tunnel junction including a first magnetic layer forming a reference layer and having a magnetization of set direction, a second magnetic layer forming a storage layer and having a magnetization of variable direction, and a third layer defining a tunnel barrier that separates the first and second layers, wherein the storage layer and reference layer have respective blocking temperatures, and the blocking temperature of the storage layer is lower than the blocking temperature of the reference layer;

flowing electric current through the magnetic tunnel junction and heating the storage layer to a temperature higher than the blocking temperature of the storage layer; and

applying a magnetic field to the storage layer to orient the magnetization of the storage layer with respect to the magnetization of the reference layer, without modifying the orientation of the reference layer.

36. The method of claim 35 further comprising reading information stored in the storage layer by determining a resistance value of the magnetic tunnel junction, and ascertaining the orientation of the magnetization of the storage layer from the resistance value.

37. The method of claim 35, wherein flowing electric current comprises injection a current impulse of spin polarized electrons through the magnetic tunnel junction to apply a magnetic torque to the magnetization of the storage layer capable of orientating the magnetization of the storage layer with respect to the magnetization of the reference layer without modifying the magnetization of the reference layer.

38. A method for writing to a magnetic device comprising:

providing a magnetic tunnel junction including a first magnetic layer defining a reference layer having a blocking temperature and having a magnetization of set direction, a second magnetic layer defining a storage layer having a blocking temperature and having a magnetization of variable direction, and a third layer defining a tunnel barrier intermediate to the first layer and the second layer, wherein the storage layer and the reference layer have respective blocking temperatures, and the blocking temperature of the storage layer is lower than the blocking temperature of the reference layer;

injecting a current impulse of spin polarized electrons through the magnetic tunnel junction during a first phase to heat the storage layer above the blocking temperature of the storage layer, and in a second phase, reducing the current through the tunnel junction to allow the storage layer to cool below the blocking temperature of the storage layer, wherein a magnetic torque of the spin polarized electrons is applied to the storage layer that orients the magnetization of the storage layer with respect to the magnetization of the reference layer, without modifying the orientation of the reference layer.

39. The method of claim 38, wherein the storage layer is coupled to an antiferromagnetic layer by exchange anisotropy and the storage layer and the antiferromagnetic layer are heated to a temperature higher than blocking temperatures of the storage and antiferromagnetic layers and, during the cooling of the antiferromagnetic layer, the magnetization of the storage layer is oriented in a direction corresponding to the direction of magnetization induced by the magnetic torque.

40. The method according to claim 38, further comprising applying a magnetic field to the storage layer, such that the magnetization of the storage layer is oriented with respect to the magnetization of the reference layer, without modifying the orientation of the reference layer.