Thermal sensor

• US RE36,136 E
• Filed: 04/04/1996
• Issued: 03/09/1999
• Est. Priority Date: 07/16/1986
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Johnson, Robert G., Higashi, Robert E., Holmen, James O.
• Primary Examiner(s): Walberg, Teresa J.
• Assistant Examiner(s): EASTHOM, KARL D
• Application Number:
  US08/627,598
• Time in Patent Office: 1,069 Days
• Field of Search: 338/15, 338/17, 338/18, 338/22 R, 29/612, 257/443, 250/338.3, 250/338.4, 250/332, 250/338.1
• US Class Current: 338/18
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: H01L 27/16 including thermoelectric components with or without a junction of dissimilar materials; including thermomagnetic components using the Peltier effect only for cooling of semiconductor or other solid state devices H01L23/38
• CPC Class Codes: Y10T 29/49085 Thermally variable

Abstract

A two-level IR detector imaging array of high fill-factor design. The upper microbridge detector level is spaced above and overlie the integrated circuit and bus lines on the substrate surface below.

Claims

1. A two-level microbridge bolometer imaging array comprising:

an array of bolometer pixels on a semiconductor substrate, each one of said pixels having a lower section on the surface of the substrate and a microbridge upper detector plane spaced from and immediately above the lower section;

said lower section including a semiconductor diode, x and y bus lines and x and y pads;

said microbridge upper detector plane comprising a bridging dielectric layer having embedded throughout a temperature responsive resistive element having first and second terminals, said microbridge upper detector plane being supported above the lower section by dielectric leg portions which are downward extending continuation of the bridging dielectric layer;

said first and second terminals being continued down said leg portions to said diode and one of said bus lines.

2. The imaging array according to claim 1 wherein said dielectric layer is of silicon nitride.

3. The imaging array according to claim 2 wherein said silicon nitride layer comprises a first layer beneath said temperature responsive resistive element and a second layer over said first layer and said element.

4. The imaging array according to claim 1 wherein said temperature responsive resistive element is of a nickel-iron alloy.

5. The imaging array according to claim 1 wherein the microbridge upper detector plane is raised about 3 microns above the lower section.

6. The method of fabricating a two-level microbridge bolometer imaging array comprising the steps of:

forming on a silicon substrate a lower level of diodes and other components, column and row bus conductors, and x and y contact pads covered by a first dielectric;

opening contact areas through the first dielectric to one of said bus conductors and to one of said diodes contact areas in each pixel of the array, and to said x and y contact pads at the ends of the bus lines;

coating said first dielectric with a layer of glass;

cutting narrow valleys through the glass along the array column conductors and removing the glass from outside the area of the array, and sloping the edges of the remaining glass ridges to accept further coating;

coating the glass ridges and edges with a first thin film layer of silicon nitride;

opening contact areas through the first layer of silicon nitride to one of said bus conductors, and one of said diodes in each pixel of the array, and to the x and y pads;

patterning on the first layer of silicon nitride on each pixel and between the bus line contact area and the diode contact area on each pixel, a separation path of resistive metal which has a substantial temperature coefficient of resistance;

adding a second layer of silicon nitride over the first and over the resistive metal path to passify it, said silicon nitride layers forming an elevated plane;

cutting a narrow slit through the silicon nitride to the glass between adjoining pixels, and cutting additional narrow slits in each pixel area to provide further access to the glass, and cutting the nitride from the x and y pad areas; and

dissolving the glass beneath the silicon nitride layers to leave a cavity between the lower level and the elevated plane.

7. The method according to claim 6 wherein said first dielectric is of silicon nitride.

8. The method according to claim 6 wherein the resistive metal is an alloy of nickel-iron.

9. The method according to claim 6 wherein the layer thickness of the glass is about three microns.

11. temperature responsive means. .Iaddend..Iadd.20. The detector array according to claim 17 wherein said temperature responsive means is a nickel-iron alloy type resistive element. .Iaddend..Iadd.21. The detector array according to claim 17 wherein the microbridge upper detector section is a plane raised about 3 microns above the lower section. .Iaddend..Iadd.22. The detector array according to claim 17 wherein said upper detector section includes an infrared absorber coating over said temperature responsive means. .Iaddend..Iadd.23. The method of fabricating an array of two-level microbridge bolometer pixels comprising the steps of:

forming on a silicon substrate a lower level of integrated circuit means having at least two contacts per pixel covered by a first dielectric;

opening contact areas for each pixel through said first dielectric to said two contacts of said integrated circuit means;

coating said first dielectric with a layer of dissolvable material;

cutting narrow valleys through said dissolvable material to form ridges, removing the dissolvable material from said contacts and from outside the areas of the array, and sloping the edges of the remaining dissolvable material ridges to accent further coating;

coating the dissolvable material ridges and edges with a first thin film dielectric bridging layer;

opening contact areas through the first dielectric bridging layer to said contacts;

depositing on said first dielectric bridging layer of each pixel a thin film layer of resistive material which has a substantial temperature coefficient of resistance;

patterning a separation path having two ends in said thin film layer of resistive material including connecting, via said sloping edges, said ends of said path respectively, to said contacts;

adding a second thin film layer of dielectric material over said first bridging layer and over said patterned resistive material path to passify it, said dielectric layers and said resistive material forming an elevated plane;

cutting a narrow slit through said dielectric layers to the dissolvable material between adjoining pixels, cutting additional narrow slits in each pixel area to provide further access to the dissolvable material; and

dissolving the dissolvable material beneath said dielectric layers to leave a cavity between said lower level and said elevated plane.

10. The method according to claim 6 wherein the cavity is about three microns high. .Iadd.11. A two-level microbridge infrared thermal detector apparatus comprising:

a pixel on a semiconductor substrate, said pixel having a lower section on the surface of said substrate and a microbridge upper detector plane section spaced from and immediately above the lower section;

said lower section including integrated circuit means;

said microbridge upper detector section comprising a bridging dielectric layer having mounted thereon a temperature responsive detector 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; and

said first and second terminals being continued down said leg portions to said integrated circuit means. .Iaddend..Iadd.12. The detector apparatus according to claim 11 wherein said dielectric layer is of silicon nitride. .Iaddend..Iadd.13. The detector apparatus according to claim 12 wherein said silicon nitride layer comprises a first layer beneath said temperature responsive means and a second layer over said first layer and said temperature responsive means. .Iaddend..Iadd.14. The detector apparatus according to claim 11 wherein said temperature responsive means is of a nickel-iron alloy type resistive element. .Iaddend..Iadd.15. The detector apparatus according to claim 11 wherein the microbridge upper detector section is raised about 3 microns above said lower section. .Iaddend..Iadd.16. The detector apparatus according to claim 11 wherein said upper detector plane section includes an infrared absorber coating over said temperature responsive means. .Iaddend..Iadd.17. A two-level microbridge uncooled infrared thermal detector array comprising;

an array of pixels on a semiconductor substrate, each one of said pixels 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;

said microbridge upper detector section comprising a bridging dielectric layer having mounted thereon a temperature responsive detector 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; and

said first and second terminals being continued down said leg portions to said integrated circuit means. .Iaddend..Iadd.18. The detector array according to claim 17 wherein said dielectric layer is of silicon nitride. .Iaddend..Iadd.19. The detector array according to claim 18 wherein said silicon nitride layer comprises a first layer beneath said temperature responsive means and a second layer over said first layer and said

12. Iaddend..Iadd. 4. The method according to claim 23 wherein said first dielectric and said bridging dielectric layers are of silicon nitride. .Iaddend..Iadd.25. The method according to claim 23 wherein the resistive material is an alloy of nickel-iron. .Iaddend..Iadd.26. The method according to claim 23 wherein the layer thickness of the dissolvable material is about three microns. .Iaddend..Iadd.27. The method according to claim 23 wherein said cavity is about three microns high. .Iaddend..Iadd.28. The method according to claim 23 wherein an absorber thin film coating is deposited and delineated on said elevated plane prior to said cutting. .Iaddend..Iadd.29. The method according to claim 23 wherein said dissolvable material is glass. .Iaddend..Iadd.30. The method of fabricating an array of two-level microbridge infrared thermal detector pixels comprising the steps of:

forming on a silicon substrate a lower level of integrated circuit means having at least two contacts per pixel covered by a first dielectric;

opening contact areas for each pixel through said first dielectric to said two contacts of said integrated circuit means;

coating said first dielectric with a layer of dissolvable material;

cutting narrow valleys through said dissolvable material to form ridges, removing the dissolvable material from said contacts and from outside the areas of the array and sloping the edges of the remaining dissolvable material ridges to accept further coating;

coating the dissolvable material ridges and edges with a first thin film dielectric bridging layer;

opening contact areas through the first dielectric bridging layer to said contacts;

depositing on said first dielectric bridging layer of each pixel a thin film layer of resistive material which has a substantial temperature coefficient of resistance;

depositing on said first dielectric bridging layer of each pixel a thermal detector means which has (i) a significant change in characteristics as a function of temperature, and (ii) two contacts electrically connected via said sloping edges, respectively, to said two contacts of each pixel;

adding a second thin film layer of dielectric material over said temperature responsive means and said first bridging layer, said dielectric layers and said temperature responsive means forming an elevated plane;

cutting a narrow slit through said dielectric layers to the dissolvable material between adjoining pixels, cutting additional narrow slits in each pixel area to provide further access to the dissolvable material; and

dissolving the dissolvable material beneath said dielectric layers to leave a cavity between said lower level and said elevated plane.

13. Iaddend..Iadd. 1. The method according to claim 30 wherein the layer thickness of the dissolvable material is about three microns. .Iaddend..Iadd.32. The method according to claim 30 wherein said cavity is about three microns high. .Iaddend..Iadd.33. The method according to claim 30 wherein an absorber thin film coating is deposited and delineated on said elevated plane prior to said cutting. .Iaddend..Iadd.34. The method according to claim 30 wherein said dissolvable material is glass. .Iaddend.