A microstructure design for high IR sensitivity having a two level infrared bolometer microstructure, the lower level having a reflective metal film surface such as Pt, Au, or Al to reflect IR penetrating to that level, the upper level being separated from the lower level by an air gap of about 1-2 microns which allows the reflected IR to interfere with the incident IR and increase the sensitivity to a higher level.
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1. A two-level microbridge infrared bolometer structure comprising:
a bolometer structure on a semiconductor substrate, said structure having a lower section on the surface of the substrate and a microbridge upper detector plane structure spaced from and immediately above the lower section; an infrared-reflective thin film metal coating on the surface of said lower section; said upper microbridge detector plane structure comprising a planar sandwich structure including a first supporting dielectric thin film layer, and a thin film temperature responsive resistive element having first and second terminals; downwardly extending dielectric leg portion means which are a downwardly extending continuation of said upper structure first dielectric layer supporting said upper microbridge detector plane structure above said lower section so that a thermal isolation gap exists between said upper and detector plane structure and said lower sections section; and, electrically conductive paths included in said downwardly extending leg portion means connecting said first and second terminals to said lower section.
2. The microbridge structure according to
4. The microbridge structure according to
5. The microbridge structure according to
6. The microbridge structure according to
8. The microbridge structure according to
9. The microbridge structure according to claim 3 8 wherein the first supporting dielectric thin film layer in is on the order of 100 nm in thickness and the second dielectric thin film layer is on the order of 250 nm in thickness.
10. The microbridge structure according to
11. The microbridge structure according to
12. A two-level microbridge infrared bolometer structure comprising:
a bolometer microstructure on a semiconductor substrate, said structure having a lower section on the surface of the substrate and a microbridge upper detector plane structure spaced from and immediately above the lower section; an infrared reflective thin film metal coating on the surface of said lower section, said metal being selected from the group consisting of Au, Pt, and Al; said upper microbridge detector plane structure comprising a planar sandwich structure including a first bridging dielectric thin film layer, a thin film temperature responsive resistive element selected from the group consisting of vanadium oxide and titanium oxide, said resistive element having first and second terminals, a second dielectric thin film layer over said first dielectric layer and resistive layer, and a thin film absorber layer; downwardly extending dielectric leg portion means which are a downwardly extending continuation of said upper structure first dielectric layer supporting said upper microbridge detector plane structure above said lower section so that an air gap on the order of 1-2 microns exists between said upper and detector plane structure and said lower sections section; and, electrically conductive paths included in said downwardly extending leg portion means connecting said first and second terminals to said lower section. 13. A two-level microbridge uncooled infrared thermal detector means comprising: a pixel on a semiconductor substrate, said pixel having a lower section on the surface of said substrate and a microbridge upper detector section spaced from and immediately above the lower section; said lower section including integrated circuit means and infrared-reflective means coating said integrated circuit means; said microbridge upper detector section comprising a bridging dielectric layer having mounted thereon temperature responsive means having first and second terminals, said microbridge upper detector section being supported above said lower section by dielectric leg portions which are downward extending continuations of the bridging dielectric layer to thereby support said upper section and so that a thermal isolation gap is defined between said upper and lower sections; and said first and second terminals being continued down said leg portions to said integrated circuit means; and said two-level microbridge uncooled infrared thermal detector means being further characterized by the size of said gap, i.e., the distance between said upper and lower sections, being selected so that infrared radiation which initially passes through said upper section to said infrared-reflective means is then reflected toward and is intensified at said upper section to optimize infrared absorption over a preselected band
of infrared wavelengths. 14. The thermal detector means of said temperature responsive means is a thin film resistive element; said upper detector section includes absorber means covering said resistive element; and said gap is selected so that infrared radiation reflected from said infrared-reflective means is intensified at said absorber means, to thereby optimize the absorption of infrared radiation in said upper detector section. 18. The thermal detector means according to claim 17 wherein the absorber means is a layer on the order of 30 nm in thickness. 19. The thermal detector means of claim 13 wherein said infrared-reflective means is a thin film metal coating. 20. The thermal detector means of claim 13 wherein said infrared-reflective means is a thin film metal coating selected from the group consisting of Au, Pt, and Al. 21. The thermal detector means according to claim 20 wherein the coating about 50 nm in thickness. 22. The thermal detector means of claim 13 wherein said temperature responsive means is a thin film resistive element. 23. The thermal detector means of claim 22 wherein said thin film resistive element is selected from the group consisting of vanadium oxide and titanium oxide. 24. The thermal detector means according to claim 23 wherein said thin film resistive element is on the order of 50-75 nm in thickness. 25. The thermal detector means of claim 22 wherein said thin film resistive element is V2 O3. 26. The thermal detector means of claim 22 wherein said thin film resistive element is V2 O3 operated in its semiconductor phase. 27. The thermal detector means according to claim 13 wherein said gap between said upper and lower sections is in the range of about 1-2 microns. 28. A two-level microbridge infrared bolometer structure comprising: a bolometer structure on a semiconductor substrate, said structure having a lower section on the surface of the substrate and a microbridge upper detector plane structure spaced from and immediately above the lower section by a thermal isolation gap of between about 1-2 microns, the upper microbridge upper detector plane structure including a thin film resistive element having first and second terminals; an infrared-reflective thin film on the surface of said lower section; and electrically conductive paths connecting said first and second terminals to said lower section. |
The field of the invention is in a high sensitivity two-level microstructure infrared bolometer array which can produce absorptance levels of greater than 80% and also achieve high IR sensitivity over a wavelength range from 8-14 microns.
This invention is an improvement on co-pending application Ser. No. 887,495, filed Jul. 16, 1986, entitled "Thermal Sensor", and assigned to the same assignee as the present invention. The teachings of the co-pending application are incorporated herein by reference. In the co-pending application the invention is directed to a pixel size sensor of an array of sensors, for an infrared microbridge construction of high fill factor, made possible by placing the detector microbridge on a second plane above the silicon surface carrying the integrated components and bus lines. The improvement in the present invention is directed to a structure which increases the sensitivity.
FIGS. 1 and 2 are front and top views of a microstructure design according to the invention.
FIG. 3 is a graphical plot of overall absorptance vs. wavelength of the device over a selected wavelength including 8-14 microns.
FIG. 4 shows graphically the transmittance, absorption and reflectance of the resistive layer.
FIG. 5 shows graphically absorption vs. air gap thickness.
FIG. 6 shows absorption of entire structure vs. metal absorber thickness.
FIG. 7 shows measured optical properties of Si3 N4.
A cross section view of the two-level microbridge bolometer pixel 10 is shown in FIG. 1. The device 10 has two levels, an elevated microbridge detector level 11 and a lower level 12. The lower level has a flat surfaced semiconductor substrate 13, such as a single crystal silicon substrate. The surface 14 of the substrate has fabricated thereon conventional components of an integrated circuit 15 such as diodes, bus lines, connections and contact pads (not specifically shown), the fabrication following conventional silicon IC technology. The IC is coated with a protective layer of silicon nitride 16.
The elevated detector level 11 includes a silicon nitride layer 20, a thin film resistive layer 21, preferably a vanadium or titanium oxide (such as V2 O3, TiOx, VOx), and air gap spacing between the reflector and the detector structure.
A layer of phos-glass or other easily soluble material in the range of about 1-2 microns thick is deposited and the slopes 30 and 30' are thoroughly rounded to eliminate slope coverage problems. The upper level silicon nitride base layer 20 is then deposited, the resistive film 21 is deposited, connections down the slope to lower plane contact pads are made, and a silicon nitride passivation layer 22 covers the layers 21 and 20. A thin metal absorber coating 23 (about 15-40A) is deposited on top of the upper level. The slots 35, 36 and 37, earlier mentioned are made and the phos-glass is dissolved from beneath the detector plane. As earlier described, by depositing Pt, Au or other reflecting thin film 18 on the substrate before the stack is formed, it is possible to reflect transmitted radiation reaching the reflecting film back to the absorber coating.
The optical properties of the total structure are achieved by careful selection of optical materials with the proper optical and electrical properties. The top film must reflect little radiation and generally transmit a significant percentage of the non-absorbed radiation through to the reflected light at a nodal position in the film determined by the air gap distance. Stated otherwise, the air gap distance is determined so that the reflected light is at a nodal position in the film. An additional constraint on the absorbing film is that to be compatible with the total structure, the absorbing material must be very thin (and hence have a low mass).
To optimize the absorption in the structure, the thickness of all the absorbing layers and the air gap distance must be controlled. The absorbing films in the present device consist of ABx ABx , SIN SiN, and the thin absorbing metal described above. In practice, the ABx ABx and SIN nitride SiN thicknesses are chosen by electrical and physical requirements. Both have absorption levels ranging from 10-20% in the spectral region of interest (FIGS. 4 and 7). A combination of these materials produces an absorption of no more than about 30% in the 8-14 micron region. This absorption level is very close to ideal, however, for use with a Pt reflective layer and an air gap which intensifies the field in the absorbing film, it is possible to achieve absorptances in excess of 80% (FIG. 5) in this configuration. The use of a thin absorbing metal which in the standard design provides 50% absorption, here is used to fine tune the absorption for maximum effect. FIG. 6 shows the small absorption improvements that can be achieved by using this metal film.
In this two-level structure, the low thermal mass structure 11 is separated from the Pt/substrate Pt substrate layer by an air gap. The interference properties of this reflected radiation are such that significant absorption is achieved by for a wide range of wavelengths and air gap spacing between the Pt reflector and the detector structure.
For this optical interference to occur in the detector, it is necessary to avoid other films in the detector structure which reflect IR. The use of ABx which has both a high TCR and a low IR reflectance (FIG. 4) ideally meets these requirements. Thus the merging of this absorption phenomenon into a detector structure which has a detector material processing both a high TCR and low reflectance permits this interference effect to occur.
There is a substantial degree of variability of detector absorptance with air gap in the structure. Referring to the table below which shows wavelength in nanometers in the left column vs. air gap in microns across the top it can be seen that with an air gap of only 0.5 micron the detector absorptance varies widely with wavelength and it is not very high. With air gaps of 1-2 microns and especially at 1.5 microns the absorptance is relatively high across the desired wavelength spread.
TABLE 1 |
______________________________________ |
DETECTOR ABSORPTANCE |
Air Gap (microns) |
Wavelength (NM) |
.5 .75 1.0 1.5 2.0 |
______________________________________ |
8000 .89 .91 .9 .84 .76 |
9000 .84 .88 .86 .81 |
10000 .76 .82 .84 .84 .82 |
11000 .69 .77 .8 .82 .82 |
12000 .66 .74 .79 .83 .84 |
13000 .64 .78 .85 .93 .94 |
14000 .56 .72 .83 .95 .98 |
15000 .47 .64 .77 .92 .99 |
______________________________________ |
The effect of gap thickness on the absorptance vs. wavelength in the regions of interest are further displayed graphically in FIG. 5. It can be seen in the curve of 1.5 microns gap thickness that at 8 microns the absorptance of the structure is climbing rapidly towards 90% and more, and that it remains relatively high out to about 14 microns. The curve for a gap of 2 microns shows that at IR wavelengths of 14 microns the absorptance is better and well above 90%. In measuring the data for FIG. 5 the absorber film 23 was not included in the stack structure.
Referring now to FIG. 6 there is shown graphically how the overall absorption of the film structure varies across the IR wavelength of 8-14 microns as the thickness of the metal absorber film is increased to 3 mm nm and to 5 mm nm. In this film stack design the Si3 N4 layer 22 is 250 mm nm, the resistive film 21 is 75 nm and the Si3 N4 film 20 is 100 nm with an air gap of 1.5 microns and a reflective Pt layer 18 of 50 nm. This curve for 3 nm shows absorptance>90% between 8 and 14 microns.
The measured optical properties of reflectance R, transmissivity T, and absorptance A of the silicon nitride layers 20 and 22 (800A thick) are shown in FIG. 7 with percent of signal shown on the ordinate axis and IR wavelength along the abscissa. It can be seen that the transmissivity at 8 microns (about 90) and at 14 microns (about 80) is quite high and that the reflectance R at both 8 and 14 microns is well under ten.
Patent | Priority | Assignee | Title |
6441374, | Jul 26 1999 | NEC Corporation | Thermal type infrared ray detector with thermal separation structure for high sensitivity |
6541772, | Dec 26 2000 | Honeywell International Inc | Microbolometer operating system |
6559447, | Dec 26 2000 | Honeywell International Inc | Lightweight infrared camera |
6621083, | Dec 29 2000 | Honeywell International Inc | High-absorption wide-band pixel for bolometer arrays |
6661010, | Dec 26 2000 | Honeywell International Inc. | Microbolometer operating system |
6667479, | Jun 01 2001 | Raytheon Company | Advanced high speed, multi-level uncooled bolometer and method for fabricating same |
6924485, | Oct 01 2001 | NEC Corporation | Infrared ray detector having a vacuum encapsulation structure |
7145143, | Mar 18 2002 | Honeywell International Inc | Tunable sensor |
7365326, | Jan 17 2003 | Honeywell International Inc | Camera having distortion correction |
7442933, | Feb 03 2005 | DRS Network & Imaging Systems, LLC | Bolometer having an amorphous titanium oxide layer with high resistance stability |
7622717, | Dec 03 2007 | DRS Network & Imaging Systems, LLC | Pixel structure having an umbrella type absorber with one or more recesses or channels sized to increase radiation absorption |
7746236, | May 01 2007 | Honeywell International Inc. | Fire detection system and method |
7842533, | Jan 07 2009 | Robert Bosch GmbH | Electromagnetic radiation sensor and method of manufacture |
8314769, | Apr 28 2010 | Honeywell International Inc. | High performance detection pixel |
8502147, | Oct 04 2011 | Flir Systems, Inc.; FLIR SYSTEMS, INC | Microbolometer detector layer |
9250135, | Mar 16 2011 | Honeywell International Inc | MWIR sensor for flame detection |
Patent | Priority | Assignee | Title |
3484611, | |||
3619614, | |||
3629585, | |||
3693011, | |||
3851174, | |||
3896309, | |||
4009516, | Mar 29 1976 | Honeywell Inc. | Pyroelectric detector fabrication |
4029962, | Jun 23 1975 | Texas Instruments Incorporated | Arrays for infrared image detection |
4067104, | Feb 24 1977 | Rockwell International Corporation | Method of fabricating an array of flexible metallic interconnects for coupling microelectronics components |
4115692, | May 04 1977 | The United States of America as represented by the Secretary of the Army | Solid state readout device for a two dimensional pyroelectric detector array |
4169273, | Jun 26 1978 | Honeywell Inc. | Photodetector signal processing |
4239312, | Nov 29 1978 | Hughes Aircraft Company | Parallel interconnect for planar arrays |
4286278, | Sep 01 1977 | Honeywell Inc. | Hybrid mosaic IR/CCD focal plane |
4317126, | Apr 14 1980 | Motorola, Inc. | Silicon pressure sensor |
4354109, | Dec 31 1979 | Honeywell Inc. | Mounting for pyroelectric detecctor arrays |
4365106, | Aug 24 1979 | Efficient method and apparatus for converting solar energy to electrical energy | |
4378489, | May 18 1981 | Honeywell Inc. | Miniature thin film infrared calibration source |
4463493, | Oct 14 1981 | Tokyo Shibaura Denki Kabushiki Kaisha | Method for making mask aligned narrow isolation grooves for a semiconductor device |
4472239, | Oct 09 1981 | Honeywell, Inc. | Method of making semiconductor device |
4691104, | Jun 14 1984 | Murata Manufacturing Co., Ltd. | One-dimensional pyroelectric sensor array |
4750834, | Jan 07 1986 | D.O.M. Associates, Inc. | Interferometer including stationary, electrically alterable optical masking device |
4803360, | Sep 19 1984 | U.S. Philips Corp. | Infrared radiation detector with flanged semiconductor window |
5010251, | Aug 04 1988 | Utah State University Research Foundation | Radiation detector array using radiation sensitive bridges |
5017784, | Mar 11 1985 | INDIGO N V | Thermal detector |
5021663, | Aug 12 1988 | Raytheon Company | Infrared detector |
5455421, | Aug 13 1985 | Massachusetts Institute of Technology | Infrared detector using a resonant optical cavity for enhanced absorption |
DE2253214, | |||
JP1136035, | |||
JP341305, | |||
JP58131525, | |||
JP60119426, | |||
JP61170626, | |||
JP61195318, | |||
WO9116607, |
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