Optical detectors using nulling for high linearity and large dynamic range

• US 6,420,706 B1
• Filed: 01/07/2000
• Issued: 07/16/2002
• Est. Priority Date: 01/08/1999
• Status: Expired due to Fees

• Current Assignee: Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: Sarnoff Corporation (SRI International, Inc.)
• Inventors: Pantuso, Francis P., Amantea, Robert, Lurie, Michael J.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US09/479,636
• Time in Patent Office: 921 Days
• Field of Search: 250/338.1
• US Class Current: 250/338.1
• CPC Class Codes: G01J 5/20 using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• CPC Class Codes: G01J 5/24 Use of specially adapted circuits, e.g. bridge circuits
• CPC Class Codes: G01J 5/40 using bimaterial elements

Abstract

An infrared radiation detector includes a bolometer or micro-cantilever detector device which functions as a null detector in conjunction with electronic circuitry. The electronic circuitry senses a change in an output signal of the detector as the detector responds to infrared radiation incident upon the detector and provides a signal to a control element which provides a stimulus to the detector device to maintain the detector output signal at the same level. The element may be a piezoelectric element, a heater or a pair of electrodes and the corresponding stimulus may be stress, heat, or electrostatic change. The stimulus compensates for the effect of the infrared radiation and maintains the chosen detector output level at the same level. The nulling circuitry improves the linearity and dynamic range of the detector device.

Claims

1. An infrared imager formed on a semiconductor substrate, comprising:

a plurality of infrared sensors, each infrared sensor forming a picture element (pixel) of the infrared image, each of said infrared sensors separately comprising;

a deflectable bi-material micro-cantilever, said micro-cantilever being deflectable in response to each of incident infrared radiation and a further stimulus, and having a reference position relative to the substrate when not exposed to said infrared radiation and said further stimulus;

a control element integral to the semiconductor substrate responsive to a control signal for providing said further stimulus to said deflectable bi-material micro-cantilever; and

an electronic circuit coupled to each of said micro-cantilever and said control element, capable of reading a position of said micro-cantilever including said reference position, and capable of determining and providing said control signal to said control element sufficient to maintain said micro-cantilever substantially at said reference position when said micro-cantilever is exposed to infrared radiation.

2. The infrared imager as in claim 1, wherein said control element comprises one of a heat generating element, a pair of conductive plates coupled to an electronic circuit and capable of providing an electrostatic change therebetween, and a piezoelectric element.

3. A method for converting infrared radiation to a visible image comprising the steps of:

(a) providing a bi-material micro-cantilever on a semiconductor substrate, said micro-cantilever including a deflectable plate and a heat generating element coupled to said micro-cantilever, said micro-cantilever being bendable responsive to each of incident infrared radiation and heat from said heat generating element;

(b) providing a control signal to said heat generating element thereby generating heat, said control signal having a first value;

(c) measuring a reference position of said micro-cantilever;

(d) exposing said bi-material micro-cantilever to incident infrared radiation;

(e) adjusting said control signal to said heat generating element sufficient to maintain said micro-cantilever substantially at said reference position, said adjusted control signal having a second value; and

(f) providing an output signal proportional to a difference between said first value and said second value.

4. The method as in claim 3, wherein said step (c) comprises optically measuring said reference position of said micro-cantilever.

5. The method as in claim 3, wherein said step (a) includes said deflectable plate including a conductive film forming an upper electrode of a capacitor and further includes a lower electrode of said capacitor formed within said substrate beneath said first electrode;

step (c) comprises measuring capacitance of said capacitor; and

step (e) includes adjusting said control signal to said heat generating element to maintain said capacitance substantially at a constant value.

6. The method as in claim 3, wherein said heat generating element comprises a resistor formed on said micro-cantilever, step (b) comprises providing a current to said resistor, and said step (e) includes adjusting said current provided to said resistor.

7. A method for converting infrared radiation to a visible image comprising the steps of:

(a) providing a plurality of infrared sensors arranged as a matrix of pixel elements (pixels), each of said infrared sensors separately comprising a bi-material micro-cantilever on a semiconductor substrate, said micro-cantilever including a deflectable plate and a piezoelectric element formed on said micro-cantilever, said micro-cantilever being bendable responsive to each of incident infrared radiation and stress from said piezoelectric element;

(b) measuring a reference position of said micro-cantilever;

(c) exposing said bi-material micro-cantilever to incident infrared radiation;

(d) providing a control signal to said piezoelectric element sufficient to maintain said micro-cantilever substantially at said reference position; and

(e) successively providing an output signal proportional to said control signal from each of the plurality of infrared sensors as a signal representing the visible image.

8. The method as in claim 7, wherein said step (d) includes supplying a voltage to electrically bias said piezoelectric element thereby forming a stress within said piezoelectric element, said stress causing said micro-cantilever to bend and wherein said step (e) comprises providing said output signal proportional to said voltage from each of the plurality of infrared sensors as a signal representing the visible image.

9. The method as in claim 7, wherein said piezoelectric element is formed of barium titanate.

10. The method as in claim 7, wherein said step (a) includes said deflectable plate including a conductive film forming an upper electrode of a capacitor and further includes a lower electrode of said capacitor formed within said substrate beneath said first electrode;

step (b) comprises measuring capacitance of said capacitor; and

step (d) includes further measuring said capacitance and providing said control signal to said piezoelectric element sufficient to maintain said capacitance at a substantially constant value.

11. A method for converting infrared radiation to a visible image comprising the steps of:

(a) providing a plurality of infrared sensors arranged as a matrix of pixel elements (pixels), each of said infrared sensors separately comprising a bi-material micro-cantilever coupled to a semiconductor substrate, said micro-cantilever including a deflectable first conductive plate, and a second conductive plate formed within said substrate beneath said micro-cantilever, said micro-cantilever being bendable responsive to each of incident infrared radiation and an electrostatic charge formed between said first conductive plate and said second conductive plate;

(b) measuring a reference position of said micro-cantilever;

(c) exposing said bi-material micro-cantilever to incident infrared radiation;

(d) providing an electrostatic charge between said first conductive plate and said second conductive plate sufficient to maintain said micro-cantilever substantially at said reference position; and

(e) successively providing an output signal proportional to said electrostatic charge from each of the plurality of infrared sensors as a signal representing the visible image.

12. The method as in claim 11, wherein said step (b) comprises optically measuring said reference position of said micro-cantilever.

13. The method as in claim 11, wherein each of said steps (b) and (d) include measuring a capacitance between said first and second conductive plates using an alternating current (AC) supply, and said step (d) includes providing an electrostatic charge using a (DC) direct current supply.

14. A method for converting infrared radiation to a visible image comprising the steps of:

(a) providing an array of bi-material micro-cantilevers on a semiconductor substrate, each micro-cantilever including a deflectable plate and a control element coupled to said micro-cantilever, each micro-cantilever being deflectable responsive to each of incident infrared radiation and a stimulus provided by said corresponding control element;

(b) measuring a reference position of each micro-cantilever of said array of bi-material micro-cantilevers relative to the substrate;

(c) exposing said array to incident infrared radiation;

(d) for each micro-cantilever of said array of micro-cantilevers, supplying a control signal to said control element capable of producing a stimulus sufficient to maintain said micro-cantilever substantially at said reference position; and

(e) providing a visible image having an array of pixels corresponding to said array of micro-cantilevers, each pixel including an intensity being proportional to said corresponding control signal supplied to said respective control element.

15. An infrared imager array formed on a semiconductor substrate, comprising:

a plurality of infrared sensors, each infrared sensor forming a picture element (pixel) on an infrared image, each of said infrared sensors seperately arranged in rows and columns, each of said infrared sensors separately comprising;

a deflectable bi-material micro-cantilever, said micro-cantilever being deflectable in response to each of incident infrared radiation and a further stimulus, and having a reference position when not exposed to said infrared radiation or said further stimulus;

a control element integral to the semiconductor substrate responsive to a control signal for providing said further stimulus to said deflectable bi-material micro-cantilever; and

an electronic circuit coupled to each of said micro-cantilever and said control element, capable of reading a position of said micro-cantilever including said reference position, and capable of determining and providing said control signal to said control element sufficient to maintain said micro-cantilever substantially at said reference position when said array is exposed to infrared radiation, wherein said control element provides said stimulus in response to said control signal.

16. The infrared imager array as in claim 15, wherein said control element comprises a piezoelectric material and said further stimulus comprises stress.

17. The infrared imager array as in claim 15, wherein said control element comprises a pair of electrodes and said further stimulus comprises electrostatic charge formed between said pair of electrodes.

18. An infrared imager array formed on a semiconductor substrate, comprising:

a plurality of infrared sensors arranged in rows and columns, each of said infrared sensors separately comprising;

a deflectable bi-material micro-cantilever, said micro-cantilever being deflectable in response to each of incident infrared radiation and a further stimulus, and having a reference position when not exposed to said infrared radiation or said further stimulus;

a heat generating control element responsive to a control signal for providing said further heating stimulus to said deflectable bi-material micro-cantilever; and

an electronic circuit coupled to each of said micro-cantilever and said control element, capable of reading a position of said micro-cantilever including said reference position, and capable of determining and providing said control signal to said control element sufficient to maintain said micro-cantilever substantially at said reference position when said array is exposed to infrared radiation,

wherein said heat generating control element provides said heating stimulus in response to said heat generating control signal.

19. An infrared imager array formed on a semiconductor substrate, comprising:

a plurality of infrared sensors arranged in rows and columns, each of said infrared sensors separately comprising;

a bottom electrically conductive plate formed within said substrate;

a capacitor comprising a top electrically conductive plate and said bottom electrically conductive plate, said top electrically conductive plate being formed above said bottom electrically conductive plate;

a bi-material element comprising a top layer and a bottom layer;

an absorber element formed on a portion of said top electrically conductive plate; and

a thermal isolation support element, a first side contacting said bi-material element and a second side contacting said substrate for anchoring said bi-material element, said absorber element, and said top electrically conductive plate to said substrate,

wherein said bi-material element, said absorber element, and said top electrically conductive plate form a bendable member;

a corresponding plurality of control elements, each coupled to a corresponding infrared sensor and capable of urging said bendable member to bend; and

an electronic circuit capable of measuring a capacitance of each capacitor and further capable of supplying a control signal to each corresponding control element to maintain each respective capacitance at a substantially constant value when said array is exposed to infrared radiation.