Bolometric focal plane array

• US 6,249,002 B1
• Filed: 08/24/1998
• Issued: 06/19/2001
• Est. Priority Date: 08/30/1996
• Status: Expired due to Term

• Current Assignee: Lockheed Martin IR Imaging Systems, Inc. (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin IR Imaging Systems, Inc. (Martin Marietta Corporation)
• Inventors: Butler, Neal R.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US09/011,942
• Time in Patent Office: 1,030 Days
• Field of Search: 250/338.4, 250/370.08, 250/332
• US Class Current: 250/338.4
• CPC Class Codes: G01J 5/22 Electrical features thereof
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 25/671 for non-uniformity detection or correction
• CPC Class Codes: H04N 25/673 by using reference sources
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

An array of infrared sensitive bolometric detectors. The bolometers are connected across row and column readout lines. Integrated on the array are column signal processors that measure the resistance of each bolometer. Each column signal processor stores the output of a bolometer on an integrator. The array is temperature stabilized to a predetermined temperature to keep bolometer response within a predetermined bandwith.

Claims

1. Apparatus comprising:

a semiconductor substrate including an upper level and a lower level;

a plurality of sensors, fabricated on the upper level, to detect radiation and to output image signals based on the detected radiation; and

a plurality of switches, fabricated on the lower level, to select at least some of the plurality of sensors,

wherein a number of electrical connections connecting the plurality of sensors to the plurality of switches is less than two times a number of sensors.

2. The apparatus of claim 1, wherein the number of electrical connections connecting the plurality of sensors to the plurality of switches is equal to the number of sensors plus one.

3. The apparatus of claim 1, further including a vacuum package to seal the semiconductor substrate.

4. The apparatus of claim 1, wherein the sensors are thermal sensors.

5. The apparatus of claim 1, wherein the sensors are resistive microbolometer elements.

6. The apparatus of claim 5, wherein the sensors are constructed and arranged as an uncooled focal plane array.

7. The apparatus of claim 1, wherein the plurality of switches includes a plurality of switch pairs, each switch pair responsive to a sensor control signal to select one sensor of the plurality of sensors.

8. The apparatus of claim 7, wherein the number of electrical connections connecting the plurality of sensors to the plurality of switch pairs is equal to the number of sensors plus one.

9. The apparatus of claim 7, wherein the plurality of switch pairs includes CMOS switches.

10. The apparatus of claim 7, wherein each switch pair includes:

a first switch connected between a common supply bus and a first terminal of the one sensor; and

a second switch connected between an image signal output bus to provide the image signals and a second terminal of the one sensor.

11. The apparatus of claim 10, further including processing circuitry coupled to the image signal output bus to process the image signals and to output processed image data based on the image signals.

12. The apparatus of claim 11, wherein the processing circuitry includes offset correction circuitry to compensate errors in the image signals and to output corrected image signals.

13. The apparatus of claim 12, wherein the offset correction circuitry includes means for providing a time-varying compensation signal to compensate errors in the image signals.

14. The apparatus of claim 12, wherein the offset correction circuitry includes means for providing a compensation signal to compensate changes in the image signals due to current-induced heating of the sensors.

15. The apparatus of claim 12, wherein:

the sensors are resistive microbolometer elements; and

the offset correction circuitry compensates resistance non-uniformities of the sensors.

16. The apparatus of claim 12, wherein the processing circuitry further includes an analog to digital converter to output the processed image data based on the corrected image signals.

17. The apparatus of claim 16, wherein the processing circuitry is monolithically integrated on the semiconductor substrate.

18. The apparatus of claim 1, further including:

a temperature sensing element to sense a temperature of the plurality of sensors; and

a thermoelectric stabilizer to stabilize the temperature at a predetermined value.

19. The apparatus of claim 18, wherein the temperature sensing element is monolithically integrated on the semiconductor substrate with the plurality of sensors.

20. The apparatus of claim 19, wherein the temperature sensing element includes at least one sensor of the plurality of sensors.

21. The apparatus of claim 20, wherein the predetermined value is based on an average temperature of at least some of the plurality of sensors.

22. The apparatus of claim 21, further including means for determining the average temperature.

23. The apparatus of claim 19, further including a vacuum package to seal the semiconductor substrate and the thermoelectric stabilizer.

24. Apparatus comprising:

a semiconductor substrate including an upper level and a lower level;

a plurality of sensors, fabricated on the upper level and arranged as a two-dimensional grid, to detect radiation and to output image signals based on the detected radiation;

a plurality of switch pairs, fabricated on the lower level, each switch pair responsive to a sensor control signal to select one sensor of the plurality of sensors; and

processing circuitry including row circuitry and column circuitry to provide the sensor control signal to each sensor to output an image signal,

wherein a number of electrical connections connecting the plurality of sensors to the plurality of switch pairs is equal to a number of sensors plus one.

25. The apparatus of claim 24, wherein the two-dimensional grid includes a plurality of basic unit cells, each basic unit cell comprising:

one sensor of the plurality of sensors;

one switch pair of the plurality of switch pairs; and

a test transistor, connected in parallel with the one sensor, to output a test signal that emulates the image signal output by the one sensor.

26. The apparatus of claim 25, wherein the processing circuitry includes test circuitry to activate the test transistor of each basic unit cell to output the test signal, the processing circuitry outputting processed image data based on the test signal from each basic unit cell when the test transistor is activated.

27. The apparatus of claim 26, wherein:

the one sensor has a sensor resistance; and

the activated test transistor has an on-resistance that is substantially equal to the sensor resistance.

28. The apparatus of claim 25, wherein the two-dimensional grid includes columns of basic unit cells, each column having a column output to provide the image signals and the test signals from the basic unit cells, the one switch pair of each basic unit cell connecting the one sensor and the test transistor between a common supply bus and the column output in response to the sensor control signal.

29. The apparatus of claim 28, wherein the common supply bus is the ground.

30. The apparatus of claim 28, wherein for each column of basic unit cells, the processing circuitry includes:

an amplifier to receive the image signals and the test signals from the column output and to output an amplified column signal;

an integrator to integrate the amplified column signal; and

an analog to digital converter to convert the integrated amplified column signal to processed image data.

31. The apparatus of claim 30, wherein the amplifier is a buffered direct injection amplifier comprising:

a lateral bipolar input stage to receive the column output;

a current source load; and

a pass transistor, coupled to the lateral bipolar input stage and the current source load, to output the amplified column signal.

32. The apparatus of claim 30, wherein the analog to digital converter includes:

a converter circuit to convert the integrated amplified column signal to a digital signal, the converter circuit including a first register to store the digital signal during a conversion period; and

a metastability resolving circuit, coupled to the converter circuit so as to receive the digital signal, to store the digital signal at a predetermined time after the conversion period and output a metastability resolved digital signal based on the digital signal as the processed image data.

33. The apparatus of claim 32, wherein the apparatus is monolithically formed on the semiconductor substrate within a single integrated circuit chip.

34. An array of N sensors, each sensor of the array being connected to at least one other sensor of the array and at least one switch of a plurality of switches, such that a number of electrical connections between the array and the plurality of switches is less than 2N, wherein each sensor of the array is connected to the at least one other sensor and the at least one switch at a common node.

35. An array of N sensors, each sensor of the array being connected to at least one other sensor of the array and at least one switch of a plurality of switches, such that a number of electrical connections between the array and the plurality of switches is less than 2N, wherein:

the sensors are fabricated on an upper level of a semiconductor substrate; and

the plurality of switches are fabricated on a lower level of the semiconductor substrate.