Microstructure design for high IR sensitivity

Abstract

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.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows: 
     
       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 .Iadd.first .Iaddend.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.]. .Iadd.first .Iaddend.dielectric .Iadd.layer .Iaddend.supporting said upper microbridge detector plane structure above said lower section so that a thermal isolation gap exists between said upper .[.and.]. .Iadd.detector plane structure and said .Iaddend.lower .[.sections.]. .Iadd.section.Iaddend.; 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 claim 1 wherein said reflective thin film metal coating is selected from the group consisting of Au, Pt, and Al. 
     
     
       3. The microbridge structure according to claim 1 wherein said dielectric is of silicon nitride. 
     
     
       4. The microbridge structure according to claim 1 wherein said thin film resistive element is selected from the group consisting of vanadium oxide and titanium oxide. 
     
     
       5. The microbridge structure according to claim 1 wherein said thin film resistive element is V 2  O 3 . 
     
     
       6. The microbridge structure according to claim 1 wherein said gap between said lower section and said upper detector .Iadd.plane .Iaddend.structure is in the range of about 1-2 microns. 
     
     
       7. The microbridge structure according to claim 2 wherein the coating is about 50 nm in thickness. 
     
     
       8. The microbridge structure according to claim 1 and further comprising, in said planar sandwich structure, a second dielectric thin film layer and a thin film absorber layer. 
     
     
       9. The microbridge structure according to claim .[.3.]. .Iadd.8 .Iaddend.wherein the first .Iadd.supporting .Iaddend.dielectric .Iadd.thin film .Iaddend.layer .[.in.]. .Iadd.is .Iaddend.on the order of 100 nm in thickness and the second dielectric .Iadd.thin film .Iaddend.layer is on the order of 250 nm in thickness. 
     
     
       10. The microbridge structure according to claim 4 wherein the .[.resistive element film.]. .Iadd.thin film resistive element .Iaddend.is on the order of 50-75 nm in thickness. 
     
     
       11. The microbridge structure according to claim 8 wherein the absorber layer is on the order of 30 nm in thickness. 
     
     
       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.]. .Iadd.first .Iaddend.dielectric .Iadd.layer .Iaddend.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.]. .Iadd.detector plane structure and said .Iaddend.lower .[.sections.]. .Iadd.section.Iaddend.; and,   electrically conductive paths included in said downwardly extending leg portion means connecting said first and second terminals to said lower section. .Iadd.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. .Iaddend..Iadd.14.  The thermal detector means of claim 13 wherein said bridging dielectric layer comprises a first dielectric layer beneath said temperature responsive means and a second dielectric layer over said first dielectric layer and said temperature responsive means. .Iaddend..Iadd.15. The thermal detector means of claim 14 wherein said dielectric layers are of silicon nitride. .Iaddend..Iadd.16. The thermal detector means according to claim 15 wherein the first dielectric layer is on the order of 100 nm in thickness and the second dielectric layer is on the order of 250 nm in thickness. .Iaddend..Iadd.17. The two-level microbridge uncooled infrared thermal detector means of claim 13 wherein: 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. .Iaddend..Iadd.18. The thermal detector means according to claim 17 wherein the absorber means is a layer on the order of 30 nm in thickness. .Iaddend..Iadd.19. The thermal detector means of claim 13 wherein said infrared-reflective means is a thin film metal coating.   
     
     
        .Iaddend..Iadd.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. .Iaddend..Iadd.21. The thermal detector means according to claim 20 wherein the coating about 50 nm in thickness. .Iaddend..Iadd.22. The thermal detector means of claim 13 wherein said temperature responsive means is a thin film resistive element. .Iaddend..Iadd.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. .Iaddend..Iadd.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. .Iaddend..Iadd.25. The thermal detector means of claim 22 wherein said thin film resistive element is V 2  O 3 . .Iaddend..Iadd.26. The thermal detector means of claim 22 wherein said thin film resistive element is V 2  O 3  operated in its semiconductor phase. .Iaddend..Iadd.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. .Iaddend..Iadd.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. .Iaddend.