Photoconductive bolometer infrared detector

• US 20060202120A1
• Filed: 03/14/2005
• Published: 09/14/2006
• Est. Priority Date: 03/14/2005
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Kauffman, Christopher L., Beystrum, Timothy R., Yoo, Sung-Shik
• Granted Patent: US 7,262,413 B2
• Time in Patent Office: Days
• US Class Current: 250/338.400
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices

Abstract

A photoconductive bolometer infrared detector using a detector material that has a resistance changed due to photo-excitation and thermal-excitation from an incident radiation in the infrared range. The resistance changes caused by photo-excitation and the thermal excitation are additive for this detector material. The detector material is suspended over a substrate by a gap of one quarter wavelength of the incident radiation, such that the thermal absorption of the incident radiation can be enhanced. Preferably, the detector material is lead selenide that has a thermal coefficient of resistance as high as 3.45%° C.⁻¹, which is about 60% higher than that of vanadium oxide that has been widely used as the detector material in the conventional microbolometers. This detector structure allows dual band uncooled or moderately cooled operation. In the case of the use of PbSe as the detector material, largely enhanced MWIR operation is enabled over a standard uncooled micro-bolometer tuned to the LWIR, and high temperature dual band MWIR and LWIR operation is enabled as compared to quantum well or HgCdTe detectors that must be cooled to cryogenic temperatures.

Claims

1. A photoconductive microbolometer detector, comprising:

a detector layer suspended over a substrate; and

a readout circuit formed in the substrate for supplying a bias current to the detector layer and to read resistance change of the detector layer when an incident radiation impinges on the detector layer, wherein the resistance change is caused by both photo-excitation and thermal excitation of the detector layer by the incident radiation.

2. The detector of claim 1, wherein the detector layer is fabricated from photoconductive semiconductor.

3. The detector of claim 2, wherein the detector layer is fabricated from lead selenide (PbSe).

4. The detector of claim 2, wherein the detector layer is fabricated from amorphous silicon.

5. The detector of claim 2, wherein the detector layer is sensitized.

6. The detector of claim 1, wherein the detector layer suspends over the substrate by an air cavity of one quarter wavelength of the incident radiation.

7. The detector of claim 1, further comprising an absorber or structural support layer attached to the detector layer.

8. The detector of claim 1, wherein the substrate further comprises a reflective layer aligned under the detector layer.

9. The detector of claim 1, further comprising at least one leg extending from the substrate to support the detector layer suspending over the substrate.

10. The detector of claim 9, further comprising a pair of conductive contacts extending from two opposite edges of the detector layer for connecting the leg.

11. A photoconductive microbolometer detector, comprising:

a lead selenide detector layer suspended over a substrate;

at least two legs supporting the detector layer to suspend over the substrate; and

a readout circuit formed in the substrate for supplying a bias current to the detector layer and to read resistance change of the detector layer when incident radiation impinges thereon.

12. The detector of claim 11, wherein the detector layer is suspending over the substrate by a vacuum or air gap of one quarter wavelength of the incident radiation.

13. The detector of claim 11, further comprising an absorber or structural support layer attached to a bottom surface of the detector layer.

14. The detector of claim 11, wherein the lead selenide detector layer is sensitized.

15. A photoconductive microbolometer detection device, comprising:

a substrate;

a plurality of photoconductive microbolometer detector units suspended over the substrate, each of the detector units includes a detector layer; and

a read out circuit formed in the substrate for supplying a bias current to and to detect an electrical resistance change of each photoconductive microbolometer detector units, wherein the electrical resistance change of each photoconductive microbolometer detector units is caused by both photo-excitation and thermal-excitation of each detector layer by an incident radiation.

16. The device of claim 15, wherein the detector layer is fabricated from lead selenide.

17. The device of claim 15, wherein each of the photoconductive microbolometer detector units comprises at least two legs extending from the substrate to for supporting the detector unit to suspend over the substrate.

18. The device of claim 15, wherein each of the photoconductive microbolometer detector units comprises an absorber attached to the detector layer.

19. The device of claim 15, wherein the substrate includes a silicon substrate.

20. The device of claim 15, wherein the incident radiation includes infrared radiation.

21. The device of claim 15, wherein the detector layers of the photoconductive microbolometer detector units are selectively sensitized.

22. The device of claim 21, wherein the sensitized photoconductive microbolometer detector units and the non-sensitized photoconductive microbolometer detector units are arranged in a checkerboard pattern over the substrate.

23. The device of claim 15, wherein a plurality of medium-wavelength infrared absorbers is attached to the detector layers of a portion of the photoconductive microbolometer detector units.

24. The device of claim 15, wherein the detector layers of the photoconductive microbolometer detector units are sensitized.

25. The device of claim 24, further comprising a plurality of high pass filter for filtering outputs of a selective portion of the photoconductive microbolometer detector units.

26. A photoconductive microbolometer infrared detector, comprising a detector layer made of lead selenide, wherein an infrared signal incident on the photoconductive microbolometer is detected by measuring an electric resistance change of the detector.

28. The device of claim 26, wherein the lead selenide layers are selectively sensitized to detector both long-wavelength infrared radiation and medium-wavelength infrared radiation.

30. The device of claim 26, further comprising a plurality of medium-wavelength infrared absorbers attached to a selective portion of the lead selenide layers.

31. The device of claim 26, wherein the lead selenide layers are sensitized to detect both medium- and long-wavelength infrared radiations.

32. The device of claim 26, further comprising a plurality of high pass filters for filtering outputs of a selective portion of the lead selenide layers.

27. A photoconductive microbolometer infrared detector device, comprising:

a substrate; and

a plurality of lead selenide layers suspending over the substrate.

29. The device of claim 27, wherein the unsensitized lead selenide layers are operative to detector long-wavelength infrared radiation only.