Pixel-level optical elements for uncooled infrared detector devices

• US 20110266443A1
• Filed: 04/28/2010
• Published: 11/03/2011
• Est. Priority Date: 04/28/2010
• Status: Active Grant

• Current Assignee: DRS Network & Imaging Systems, LLC (Leonardo S.p.A.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Fagan, Thomas P. III, Syllaios, Athanasios J., Schimert, Thomas R.
• Granted Patent: US 8,610,070 B2
• Time in Patent Office: Days
• US Class Current: 250/338.4
• CPC Class Codes: G01J 1/02 Details
• CPC Class Codes: G01J 1/0204 Compact construction
• CPC Class Codes: G01J 1/04 Optical or mechanical part supplementary adjustable parts
• CPC Class Codes: G01J 1/0411 using focussing or collimating elements, i.e. lenses or mirrors; Aberration correction
• CPC Class Codes: G01J 1/0429 using polarisation elements
• CPC Class Codes: G01J 1/0488 with spectral filtering
• CPC Class Codes: G01J 4/04 Polarimeters using electric detection means G01J4/02 takes precedence
• CPC Class Codes: G01J 5/02 Constructional details
• CPC Class Codes: G01J 5/0215 Compact construction
• CPC Class Codes: G01J 5/023 Particular leg structure or construction or shape; Nanotubes
• CPC Class Codes: G01J 5/024 Special manufacturing steps or sacrificial layers or layer structures
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0802 Optical filters
• CPC Class Codes: G01J 5/0806 Focusing or collimating elements, e.g. lenses or concave mirrors
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: G01J 5/59 using polarisation; Details thereof

Abstract

Pixel-level monolithic optical element configurations for uncooled infrared detectors and focal plane arrays in which a monolithically integrated or fabricated optical element may be suspended over a microbolometer pixel membrane structure of an uncooled infrared detector element A monolithic optical element may be, for example, a polarizing or spectral filter element, an optically active filter element, or a microlens element that is structurally attached by an insulating interconnect to the existing metal interconnects such that the installation of the optical element substantially does not impact the thermal mass or thermal time constant of the microbolometer pixel structure, and such that it requires little if any additional device real estate area beyond the area originally consumed by the microbolometer pixel structure interconnects.

Claims

1. An uncooled infrared detector element, comprising:

a substrate;

a microbolometer pixel membrane structure configured to absorb infrared radiation, the microbolometer pixel membrane structure comprising a membrane material supported at a position spaced above the substrate; and

a monolithically fabricated optical element suspended over and above the membrane material of the microbolometer pixel membrane structure.

2. The uncooled infrared detector element of claim 1, wherein the microbolometer pixel membrane structure has a thermal mass value;

and wherein the monolithically fabricated optical element is suspended over and above the membrane material of the microbolometer pixel membrane structure in a manner such that the thermal mass value of the microbolometer pixel membrane structure is substantially unchanged by the presence of the optical element.

3. The uncooled infrared detector element of claim 1, wherein the membrane material comprises electrically conductive material;

wherein the membrane material is supported at a position spaced above the substrate by at least two spaced electrically conductive interconnects; and

wherein the monolithically fabricated optical element is suspended over and above the membrane material of the microbolometer pixel membrane structure by at least two optical element support interconnects that are at least partially aligned to and supported by the at least two electrically conductive interconnects.

4. The uncooled infrared detector element of claim 3, wherein the substrate includes read out integrated circuitry (ROIC);

and wherein the at least two spaced electrically conductive interconnects are electrically coupled to the ROIC.

5. The uncooled infrared detector element of claim 1, wherein the optical element comprises an optical filter element.

6. The uncooled infrared detector element of claim 1, wherein the optical element comprises a polarizing filter element.

7. The uncooled infrared detector element of claim 1, wherein the optical element comprises a spectral filter element.

8. The uncooled infrared detector element of claim 1, wherein the optical element comprises an optically active filter element.

9. The uncooled infrared detector element of claim 1, wherein the optical element comprises at least one microlens.

10. The uncooled infrared detector element of claim 1, further comprising one or more radiation detectors provided within or below the substrate and a reflector layer disposed on an upper surface of the substrate between the substrate and the microbolometer pixel structure, one or more openings being defined in the reflector layer corresponding to and vertically aligned with the one or more radiation detectors;

wherein one or more openings are defined in the membrane structure corresponding to and vertically aligned with the one or more openings defined in the reflector layer; and

wherein the optical element comprises one or more microlenses that are each configured to focus radiation onto a corresponding one of the radiation detectors through a corresponding opening in the membrane structure and a corresponding opening in the reflector layer.

11. The uncooled infrared detector element of claim 10, wherein the one or more radiation detectors comprise radiation detectors capable of detecting radiation ranging from visible to short infrared wavelengths;

and wherein the optical element comprises one or more microlenses that are each configured to focus VNS radiation onto a corresponding one of the VNS radiation detectors through a corresponding opening in the membrane structure and a corresponding opening in the reflector layer.

12. A focal plane array assembly, comprising:

a plurality of uncooled infrared detector elements arranged as an array, each of the plurality of uncooled infrared detector elements comprising;

a substrate including read out integrated circuitry (ROIC), and

a microbolometer pixel membrane structure configured to absorb infrared radiation, the microbolometer pixel membrane structure comprising an electrically conductive membrane material supported at a position spaced above the substrate by at least two spaced electrically conductive interconnects electrically coupled to the ROIC;

where at least a portion of the plurality of uncooled infrared detector elements of the array further comprise a monolithically fabricated optical element suspended over and above the membrane material of the microbolometer pixel membrane structure by at least two optical element support interconnects that are at least partially aligned to and supported by the at least two electrically conductive interconnects.

13. The focal plane array of claim 12, wherein the microbolometer pixel membrane structure of each of the plurality of uncooled infrared detector elements has a thermal mass value;

and wherein at least a portion of the plurality of uncooled infrared detector elements of the array each further comprises a monolithically fabricated optical element suspended over and above the membrane material of the microbolometer pixel membrane structure by at least two optical element support interconnects that are at least partially aligned to and supported by the at least two electrically conductive interconnects in a manner such that the thermal mass value of the microbolometer pixel membrane structure is substantially unchanged by the presence of the optical element.

14. The focal plane array of claim 12, wherein at least a portion of the optical elements of the array each comprises an optical filter element.

15. The focal plane array of claim 12, wherein at least a portion of the optical elements of the array each comprises a polarizing filter element.

16. The focal plane array of claim 12, wherein the array comprises a first type of polarizing filter element suspended over and above the membrane material of at least one microbolometer pixel membrane structure and a second and different type of polarizing filter element suspended over and above the membrane material of at least one other microbolometer pixel membrane structure.

17. The focal plane array of claim 12, wherein the array comprises a first type of polarizing filter element suspended over and above the membrane material of at least one microbolometer pixel membrane structure and no optical element suspended over and above the membrane material of at least one other microbolometer pixel membrane structure.

18. The focal plane array of claim 12, wherein at least a portion of the optical elements of the array each comprises a spectral filter element.

19. The focal plane array of claim 12, wherein the array comprises a first type of spectral filter element suspended over and above the membrane material of at least one microbolometer pixel membrane structure and a second and different type of spectral filter element suspended over and above the membrane material of at least one other microbolometer pixel membrane structure.

20. The focal plane array of claim 12, wherein the array comprises a first type of spectral filter element suspended over and above the membrane material of at least one microbolometer pixel membrane structure and no optical element suspended over and above the membrane material of at least one other microbolometer pixel membrane structure.

21. The focal plane array of claim 12, wherein the array comprises a first type of spectral filter element suspended over and above the membrane material of at least one microbolometer pixel membrane structure and a second and different type of spectral filter element suspended over and above the membrane material of at least one other microbolometer pixel membrane structure, the second type of spectral filter being configured to substantially block the underlying microbolometer pixel membrane structure substantially completely from incoming radiation so as to form a reference pixel for the array.

22. The focal plane array of claim 12, wherein the uncooled infrared detector elements of the array each comprises one or more radiation detectors provided within or below the substrate and a reflector layer disposed on an upper surface of the substrate between the substrate and the microbolometer pixel structure, one or more openings being defined in the reflector layer corresponding to and vertically aligned with the one or more radiation detectors;

wherein one or more openings are defined in the membrane structure corresponding to and vertically aligned with the one or more openings defined in the reflector layer; and

wherein the optical element comprises one or more microlenses that are each configured to focus radiation onto a corresponding one of the radiation detectors through a corresponding opening in the membrane structure and a corresponding opening in the reflector layer.

23. The focal plane array of claim 22, wherein the one or more radiation detectors comprise radiation detectors capable of detecting radiation ranging from visible to short infrared wavelengths;

and wherein each optical element comprises one or more microlenses that are each configured to focus VNS radiation onto a corresponding one of the VNS radiation detectors through a corresponding opening in the membrane structure and a corresponding opening in the reflector layer.

24. A wafer-level packaged focal plane array assembly, comprising:

a device wafer, the device wafer comprising the focal plane array assembly of claim 12; and

a lid wafer, the lid wafer being at least partially transmissive of incident infrared radiation and being assembled to the device wafer such that the lid wafer allows the incident infrared radiation to reach the focal plane array assembly through the lid wafer.

25. A method of making a focal plane array assembly, comprising:

providing a substrate;

forming read out integrated circuitry (ROIC) for the substrate;

forming a plurality of uncooled infrared detector elements arranged as an array, each of the plurality of uncooled infrared detector elements comprising;

a substrate including read out integrated circuitry (ROIC); and

a microbolometer pixel membrane structure configured to absorb infrared radiation, the microbolometer pixel membrane structure comprising an electrically conductive membrane material supported at a position spaced above the substrate by at least two spaced electrically conductive interconnects electrically coupled to the ROIC, the microbolometer pixel membrane structure having a thermal mass value; and

monolithically fabricating an optical element suspended over and above the membrane material of the microbolometer pixel membrane structure of at least a portion of the plurality of uncooled infrared detector elements of the array by at least two optical element support interconnects that are at least partially aligned to and supported by the at least two electrically conductive interconnects.

26. The method of claim 25, wherein the microbolometer pixel membrane structure of each of the plurality of uncooled infrared detector elements has a thermal mass value;

and wherein the method further comprises monolithically fabricating an optical element suspended over and above the membrane material of the microbolometer pixel membrane structure of each of at least a portion of the plurality of uncooled infrared detector elements of the array by at least two optical element support interconnects that are at least partially aligned to and supported by the at least two electrically conductive interconnects in a manner such that the thermal mass value of the microbolometer pixel membrane structure is substantially unchanged by the presence of the optical element.

27. The method of claim 25, wherein at least a portion of the optical elements of the array each comprises an optical filter element.

28. The method of claim 25, wherein at least a portion of the optical elements of the array each comprises a polarizing filter element.

29. The method of claim 25, wherein at least a portion of the optical elements of the array each comprises a spectral filter element.

30. The method of claim 25, wherein at least a portion of the optical elements of the array each comprises an optically active filter element.

31. The method of claim 25, wherein at least a portion of the optical elements of the array each comprises a spectral filter element configured to substantially block the underlying microbolometer pixel membrane structure substantially completely from incoming radiation so as to form a reference pixel for the array.

32. The method of claim 25, wherein at least a portion of the optical elements of the array each comprises at least one microlens.

33. The method of claim 25, further comprising:

providing a device wafer and forming the forming the plurality of individual detector elements arranged as an array on the device wafer;

providing a lid wafer, the lid wafer being at least partially transmissive of incident infrared radiation; and

assembling the lid wafer to the device wafer such that the lid wafer allows the incident infrared radiation to reach the focal plane array assembly through the lid wafer.

34. The method of claim 33, sealingly assembling the lid wafer to the device wafer with a vacuum therebetween to form a wafer-level packaged focal plane array assembly.