Infrared-responsive photoconductive array and method of making

• US 5,561,295 A
• Filed: 07/29/1994
• Issued: 10/01/1996
• Est. Priority Date: 07/29/1994
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Litton Systems Incorporated
• Inventors: Jacksen, Niels F., Preis, Mark K.
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US08/283,394
• Time in Patent Office: 795 Days
• Field of Search: 250/338.4, 250/330, 250/332, 250/338.1
• US Class Current: 250/338.4
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: H01L 27/14649 Infrared imagers
• CPC Class Codes: H01L 31/0324 comprising only AIVBVI or AIIBIVCVI chalcogenide compounds, e.g. Pb Sn Te
• CPC Class Codes: H01L 31/09 Devices sensitive to infrared, visible or ultraviolet radiation H01L31/101 takes precedence

Abstract

A photoconductive detector array which is responsive to infrared light to provide an electrical output response includes a substrate which is transparent to infrared light. A continuous layer of photoconductive material is disposed upon the substrate, and a conductive grid disposed on the continuous layer of photoconductive material divides the photoconductive material electrically but not physically into plural detector areas. Electrical connection structure is provided for individual electrical contact with a central region of each one of the plural detector areas. A method of making a detector array according to the invention includes forming plural perforations through the continuous layer of photoconductive material to expose the substrate. The electrical connection structure includes contacts which are secured to the substrate through the photoconductive material and which effect electrical connection with this material for each one of the plural detector areas.

Claims

1. An edge-less photodetector comprising:

a substrate;

a continuous layer of material which is responsive to photons of light to change an electrical characteristic of the material, said continuous layer of material being disposed upon said substrate;

a conductive grid disposed on the continuous layer of material and electrically but not physically dividing a detector area of said material from the remainder of said continuous layer of material; and

electrical means for making electrical contact with a central region of said detector area.

2. The photodetector of claim 1 wherein said electrical means for making electrical contact with a central region of said detector area includes a contact structure secured to said layer of material.

3. The photodetector of claim 2 wherein said contact structure is secured to said layer of material by a layer of metallic material also bonding to said substrate.

4. The photodetector of claim 3 wherein said layer of metallic material includes a metal selected from the group including chromium, titanium, and tungsten.

5. The photodetector of claim 3 wherein said continuous layer of material defines an opening centrally of said detector area, said opening exposing a surface of said substrate, and said layer of metallic material bonding with said surface of said substrate within said opening.

6. The photodetector of claim 3 wherein said contact structure further includes a column of conductive material carried upon said layer of metallic material and extending outwardly of said photodetector.

7. The photodetector of claim 6 wherein said column of conductive material includes indium metal.

8. The photodetector of claim 6 wherein said contact structure further includes a layer of interface metal interposing between said metallic material and said column of conductive material.

9. The photodetector of claim 8 wherein said layer of interface metal includes gold metal.

10. The photodetector of claim 9 wherein a layer of palladium metal is interposed between said interface layer of gold metal and said column of conductive material.

11. The photodetector of claim 1 wherein said conductive grid defines plural openings, each one of said plural openings of said conductive grid substantially defining one of a respective plurality of detector areas.

12. The photodetector of claim 11 wherein said conductive grid defines openings having a shape selected from the group including rectangular, square, octagonal, and round.

13. The photodetector of claim 11 further including means for electrically connecting said conductive grid to electrical circuitry external of said photodetector.

14. The photodetector of claim 13 wherein said means for electrically connecting said conductive grid to electrical circuitry external of said photodetector includes a contact pad carried by said substrate.

15. The photodetector of claim 11 further including means for electrically connecting each one of said plural detector areas individually to electrical circuitry externally of said detector.

16. The photodetector of claim 15 wherein said means for electrically connecting each one of said plural detector areas individually to electrical circuitry externally of said detector array includes a plurality of contact structures individually secured to said continuous layer of material in electrical contact centrally of respective ones of said plurality of detector areas.

17. The photodetector of claim 15 wherein each of said plurality of contact structures is also secured to said continuous layer of material by a respective bond layer of metallic material also bonding to said substrate.

18. The photodetector of claim 17 wherein said bond layer of metallic material includes a metal selected from the group including chromium, titanium, and tungsten.

19. The photodetector of claim 17 wherein said continuous layer of material defines an opening centrally of each one of said plurality of detector areas, said openings exposing a respective portion of a surface of said substrate, and said bond layer of metallic material extending through said respective opening to bond with said surface of said substrate.

20. The photodetector of claim 19 wherein each of said plurality of contact structures further includes a respective column of indium metal carried upon said layer of metallic material and extending outwardly of said detector, a respective layer of interface metal interposing between said column of indium metal and said bond layer of metallic material.

21. The photodetector of claim 20 wherein said layer of interface metal includes a layer of gold metal.

22. The photodetector of claim 21 wherein a layer of palladium metal is interposed between said interface layer of gold metal and said column indium metal.

23. An edge-less photoconductive lead selenide (PbSe) detector array for receiving infrared light and providing an electrical output response, said detector array comprising:

a substrate of quartz material having a window portion which is transparent to infrared light;

a continuous layer of photoconductive PbSe material disposed upon said substrate congruent with said window portion;

a conductive metallic grid disposed on said continuous layer of photoconductive PbSe material, said conductive metallic grid electrically dividing said continuous layer of PbSe material into plural detector areas;

a layer of passivating material overlying said layer of PbSe material and said conductive metallic grid thereon; and

a respective plurality of electrical contact structures extending through said layer of passivating material and each making individual electrical contact with a central region of a respective one of the plural detector areas.

24. The edge-less photoconductive lead selenide detector array of claim 23 wherein said continuous layer of PbSe material defines a respective plurality of holes therethrough centrally of said detector areas, each one of said plurality of holes receiving a portion of a respective one of said plurality of contact structures.

25. The edge-less photoconductive lead selenide detector array of claim 24 further including a respective plurality of bonding pads disposed respectively one in each one of said plurality of holes and bonding to said substrate.

26. The edge-less photoconductive lead selenide detector array of claim 25 wherein each of said plurality of bonding pads is interposed between said contact structure and said substrate and bonds to each.

27. The edge-less photoconductive lead selenide detector array of claim 26 wherein said bonding pads includes a metal selected from the group including chromium, titanium, and tungsten.

28. The edge-less photoconductive lead selenide detector array of claim 26 further including an interface layer of metallic gold interposed between each of said plurality of bonding pads and said contact structure.

29. The edge-less photoconductive lead selenide detector array of claim 28 wherein said interface layer of metallic gold is generally hat-shaped to include a lower wall bonding with a respective one of said bonding pads, a side wall contacting said layer of PbSe material, and a flange portion extending radially outwardly around the respective one of said plural holes in said layer of PbSe material.

30. The edge-less photoconductive lead selenide detector array of claim 29 further including a layer of metallic palladium interposed between said interface layer of gold metal and said contact structure, said layer of metallic palladium also interposing between said layer of passivating material and said contact structure.

31. The edge-less photoconductive lead selenide detector array of claim 23 wherein said contact structure includes a column of metallic palladium.

32. A method of making an edge-less photoconductive lead selenide (PbSe) detector array for receiving infrared light and responsively providing an electrical output signal, said method comprising the steps of:

providing a substrate of quartz material having a portion which is transparent to infrared light;

providing a continuous layer of photoconductive PbSe material upon said substrate congruent with said transparent portion thereof;

providing a conductive metallic grid disposed on said continuous layer of photoconductive PbSe material;

utilizing said conductive metallic grid to electrically divide said continuous layer of PbSe material into plural detector areas; and

providing a respective plurality of electrical contact structures each making individual electrical contact with a central region of a respective one of said plural detector areas.

33. The method of claim 32 further including the step of providing a layer of passivating material overlying said layer of PbSe material and said conductive metallic grid.

34. The method of claim 33 further including the step of defining a respective plurality of holes through said layer of PbSe material, locating each one of said plurality of through holes centrally of a respective one of said plurality of detector areas, and receiving a portion of a respective one of said plurality of contact structures into each one of said plurality of through holes.

35. The method of claim 34 further including the step of including a respective plurality of bonding pads each disposed respectively in one of said plurality of through holes, and employing said plurality of bonding pads to secure said plurality of contact structures to said substrate.

36. The method of claim 35 further including the step of interposing said plurality of bonding pads between said contact structure and said substrate, and bonding each one of said plurality of bonding pads to each of said substrate and to a respective one of said plurality of contact structures.

37. The method of claim 36 further including the step of forming said plurality of bonding pads from a metal selected from the group including chromium, titanium, and tungsten.

38. The method of claim 36 further including the step of providing an interface layer of metallic gold interposed between each of said plurality of bonding pads and the respective one of said plurality of contact structures.

39. The method of claim 38 further including the steps of providing a layer of metallic palladium interposed between said interface layer of gold metal and the respective one of said plurality of contact structures, and also interposing said layer of metallic palladium also interposing between said layer of passivating material and respective ones of said plurality of contact structures.

40. The method of claim 32 further including the step of providing a column of metallic palladium as part of each one of said plurality of contact structures.

41. An edge-less lead selenide (PbSe) photodetector for receiving infrared light and responsively providing an electrical output signal, said photodetector comprising:

a substrate of quartz material which is transparent to infrared light;

a layer of photoconductive PbSe material disposed on said substrate, said layer of PbSe material being continuous over an area of said substrate which is larger than said photodetector, said layer of PbSe material being responsive to photons of infrared light to change in electrical conductivity;

a conductive metallic grid disposed on said layer of PbSe material and electrically but not physically dividing said photodetector from the remainder of said layer of PbSe material;

a layer of passivating material overlying said layer of PbSe material and said conductive metallic grid; and

an electrical contact structure extending through said layer of passivating material and making electrical contact with a central region of said detector area.

42. The photodetector of claim 41 wherein said conductive grid defines plural openings, each one of said plural openings of said conductive grid substantially defining one of a respective plurality of photodetectors.

43. The photodetector of claim 41 wherein said electrical contact structure is secured to said layer of PbSe material and to said substrate of quartz material.

44. The photodetector of claim 43 wherein said electrical contact structure is secured to said layer of PbSe material and to said substrate of quartz material by a layer of metallic material bonding to both said substrate quartz material and to said layer of PbSe material.

45. The photodetector of claim 44 wherein said layer of metallic material includes a metal selected from the group including chromium, titanium, and tungsten.

46. The photodetector of claim 43 wherein said continuous layer of PbSe material defines an opening centrally of said photodetector, said opening exposing a surface of said quartz substrate material, and said layer of metallic material bonding with said surface of said quartz substrate material within said opening.

47. The photodetector of claim 44 wherein said contact structure further includes a column of conductive material carried upon said layer of metallic material and extending outwardly of said photodetector through said layer of passivating material.

48. The photodetector of claim 47 wherein said column of conductive material includes indium metal.

49. The photodetector of claim 47 wherein said contact structure further includes a layer of interface metal interposing between said metallic material and said column of conductive material.

50. The photodetector of claim 49 wherein said layer of interface metal includes gold metal.

51. The photodetector of claim 50 wherein a layer of palladium metal is interposed between said interface layer of gold metal and said column of conductive material.