Infrared imager using room temperature capacitance sensor

• US 5,844,238 A
• Filed: 03/27/1996
• Issued: 12/01/1998
• Est. Priority Date: 03/27/1996
• Status: Expired due to Term

• Current Assignee: Sarnoff Corporation (SRI International, Inc.)
• Original Assignee: David Sarnoff Research Center, Inc.
• Inventors: Amantea, Robert, Levine, Peter Alan, Sauer, Donald Jon, Martinelli, Ramon Ubaldo
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US08/622,263
• Time in Patent Office: 979 Days
• Field of Search: 250/332, 250/338.4, 250/338.1
• US Class Current: 250/332
• CPC Class Codes: C07D 405/06 linked by a carbon chain containing only aliphatic carbon atoms
• CPC Class Codes: G01J 5/34 using capacitors, e.g. pyroelectric capacitors
• CPC Class Codes: G01J 5/40 using bimaterial elements
• 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 infrared imager includes an array of capacitance sensors that operate at room temperature. Each infrared capacitance sensor includes a deflectable first plate which expands due to absorbed thermal radiation relative to a non-deflectable second plate. In one embodiment each infrared capacitance sensor is composed of a bi-material strip which changes the position of one plate of a sensing capacitor in response to temperature changes due to absorbed incident thermal radiation. The bi-material strip is composed of two materials with a large difference in thermal expansion coefficients.

Claims

1. A transducer formed on a monolithic semiconductor integrated circuit substrate comprising:

a first electrically conductive plate formed on the substrate substantially parallel to a second electrically conductive plate along the xy plane;

a dielectric layer formed on the first plate, the first and second electrically conductive plates and the dielectric layer forming a capacitor;

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

an absorber element formed on a portion of the second electrically conductive plate;

a thermal conduction layer connecting the second electrically conductive plate and the bi-material element; and

a thermal isolation support element having a first side which is coupled to said bi-material element and a second side which is coupled to the substrate, the thermal isolation support element anchoring the bi-material element, the absorber element, the second electrically conductive plate and the thermal conduction layer to the substrate,

wherein the bi-material element, the absorber element, the second electrically conductive plate and the thermal conduction layer form a deflectable member.

2. A transducer of claim 1, wherein each of said first and second electrically conductive plates are formed from one of a metal, polysilicon and indium-tin oxide.

3. An infrared sensor formed on a monolithic semiconductor integrated circuit substrate comprising:

a reference capacitor comprising a top electrically conductive plate and a bottom electrically conductive plate;

a dielectric layer formed on the top electrically conductive plate of the reference capacitor;

a sense capacitor comprising a top electrically conductive plate and a bottom electrically conductive plate, said top electrically conductive plate being formed above said dielectric layer and said bottom electrically conductive plate being the top electrically conductive plate of the reference capacitor;

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

an absorber element formed on a portion of the top electrically conductive plate of the sense capacitor;

a thermal conduction layer connecting the top electrically conductive plate of the sense capacitor and the bi-material element; and

a thermal isolation support element having a first side which is coupled to said bi-material element and a second side which is coupled to the substrate for anchoring the bi-material element, the absorber element, the top electrically conductive plate of the sense capacitor and the thermal conduction layer to the substrate,

wherein the bi-material element, the absorber element, the top electrically conductive plate of the sense capacitor and the thermal conduction layer form a deflectable member.

4. An infrared sensor of claim 3, wherein each of said top and bottom electrically conductive plates of the sense capacitor and said top and bottom electrically conductive plates of the reference capacitor are formed from one of a metal, polysilicon and indium-tin oxide.

5. An infrared sensor of claim 3, wherein the bottom layer of the bi-material element is co-planar with the top electrically conductive plate of the sense capacitor.

6. An infrared sensor of claim 3, wherein the top electrically conductive plate and bottom electrically conductive plate of the reference capacitor and the top electrically conductive plate and bottom electrically conductive plate of the sense capacitor are aluminum.

7. An infrared sensor of claim 3, wherein the top layer and the bottom layer of the bi-material element have respectively different thermal expansion coefficients.

8. An infrared sensor of claim 7, wherein the thermal coefficient of expansion of the bottom layer of the bi-material element is greater than the thermal coefficient of expansion of the top layer of the bi-material element.

9. An infrared sensor of claim 3, wherein the absorber element has an emissivity of approximately 1.

10. An infrared sensor of claim 3, wherein the absorber element is one of black platinum and carbon.

11. An infrared sensor of claim 3, further comprising capacitance measurement means for measuring the capacitance of the sense capacitor.

12. An infrared sensor of claim 3, wherein the deflectable member changes its position in response to a temperature change due to absorbed incident thermal radiation.

13. An infrared imager array including a monolithic semiconductor integrated circuit substrate, comprising:

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

a first electrically conductive plate formed on the substrate substantially parallel to a second electrically conductive plate along the xy plane;

a dielectric layer formed on the first plate, the first and second electrically conductive plates and the dielectric layer forming a capacitor;

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

an absorber element formed on a portion of the second electrically conductive plate;

a thermal conduction layer connecting the second electrically conductive plate and the bi-material element; and

a thermal isolation support element having a first side coupled is to the bi-material element and a second side coupled to the substrate for anchoring the bi-material element, the absorber element, the second electrically conductive plate and the thermal conduction layer to the substrate,

wherein the bi-material element, the absorber element, the second electrically conductive plate and the thermal conduction layer form a deflectable member; and

a readout circuit comprising a plurality of source follower amplifiers, each source follower amplifier respectively coupled to the second electrically conductive plate of each transducer.

14. An infrared imager array of claim 13, wherein said first and second electrically conductive plates are formed from one of a metal, polysilicon and indium-tin oxide.

15. An infrared imager array of claim 13, wherein said readout circuit further comprises:

a reset transistor for clamping the first electrically conductive plate in each transducer to a reset potential;

a current mirror for providing a pixel load current to one of the plurality of source follower amplifiers;

a column driver circuit for providing a potential to each respective column of transducers, comprising a controller connected to the second electrically conductive plate for applying the potential to the transducer; and

a horizontal scanning shift register and a vertical scanning shift register for selecting one of the plurality of transducers to read out.

16. An infrared imager array of claim 15, wherein said readout circuit further comprises:

a correlated double sampling (CDS) circuit, connected to said column driver circuit, for sampling and holding an output signal of each source follower amplifier and for suppressing kTC noise and 1/f noise of the transducers.

17. An infrared imager array of claim 16, wherein each output signal is readout twice during a clock period.

18. An infrared imager array including a monolithic semiconductor integrated circuit substrate, comprising:

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

a reference capacitor comprising a top electrically conductive plate and a bottom electrically conductive plate;

a dielectric layer formed on the top electrically conductive plate of the reference capacitor;

a sense capacitor comprising a top electrically conductive plate and a bottom electrically conductive plate, said top electrically conductive plate being formed above said dielectric layer and said bottom electrically conductive plate being the top electrically conductive plate of the reference capacitor;

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

an absorber element formed on a portion of the top electrically conductive plate of the sense capacitor;

a thermal conduction layer connecting the top electrically conductive plate of the sense capacitor and the bi-material element; and

a thermal isolation support element, a first side contacting the bi-material element and a second side contacting the substrate for anchoring the bi-material element, the absorber element, the top electrically conductive plate of the sense capacitor and the thermal conduction layer to the substrate,

wherein the bi-material element, the absorber element, the top electrically conductive plate of the sense capacitor and the thermal conduction layer form a deflectable member; and

a readout circuit comprising at least a plurality of source follower amplifiers, each source follower amplifier respectively coupled to the top electrically conductive plate of each sense capacitor.

19. An infrared imager array of claim 18, wherein said readout circuit further comprises:

a reset transistor for clamping the top electrically conductive plate of the reference capacitor in each capacitance sensor to a reset potential;

a current mirror for providing a pixel load current to the plurality of source follower amplifiers;

a column driver circuit for multiplexing a first potential and a second potential onto each respective column of capacitance sensors, comprising;

a first controller connected to the top electrically conductive plate of the sense capacitor for applying the first potential to the sense capacitor; and

a second controller connected to the bottom electrically conductive plate of the reference capacitor for applying the second potential to the reference capacitor, the first and second potentials having respectively different polarities; and

a horizontal scanning shift register and a vertical scanning shift register for selecting one of the sense capacitors to be read out.

20. An infrared imager array of claim 19, wherein said readout circuit further comprises:

a correlated double sampling circuit, connected to said column driver circuit, for sampling and holding an output signal of each source follower amplifier and for suppressing kTC noise and 1/f noise of the sense capacitors.

21. An infrared imager array of claim 20, wherein each output signal is readout twice during a clock period.

22. A method of fabricating a transducer on a monolithic semiconductor integrated circuit substrate comprising the steps of:

forming a first electrically conductive plate on the surface of the integrated circuit substrate;

depositing a dielectric layer;

depositing a release layer over the dielectric layer;

forming a connection layer over a first portion of the release layer;

forming a bi-material element over a portion of the connection layer and over a second portion of the release layer;

forming a second electrically conductive plate over a third portion of the release layer;

forming a via through the release layer and the dielectric layer, said via contacting the connection layer and avoiding contact with the bi-material element;

forming an absorber layer over the second electrically conductive plate;

forming a thermal conduction layer between the second electrically conductive plate and the bi-material element;

forming a thermal isolation support element over the connection layer and the via and contacting the bi-material element; and

chemically removing the release layer.

23. A method of fabricating an infrared sensor on a monolithic semiconductor integrated circuit substrate comprising the steps of:

forming a first capacitive electrically conductive plate on the surface of the integrated circuit substrate;

forming an insulating layer over the first capacitive electrically conductive plate;

forming a second capacitive electrically conductive plate over the insulating layer;

depositing a dielectric layer;

depositing a release layer over the dielectric layer;

forming a connection layer over a first portion of the release layer;

forming a bi-material element over a portion of the connection layer and over a second portion of the release layer;

forming a third capacitive electrically conductive plate over a third portion of the release layer;

forming a via through the release layer and the dielectric layer, said via contacting the connection layer and avoiding contact with the bi-material element;

forming an absorber layer over the third capacitive electrically conductive plate;

forming a thermal conduction layer between the third capacitive electrically conductive plate and the bi-material element;

forming a thermal isolation support element over the connection layer and the via and contacting the bi-material element; and

chemically removing the release layer.

24. A method of reading an output signal provided by an infrared imager array which comprises a plurality of infrared capacitance sensors, each capacitance sensor comprising a sense capacitor and a reference capacitor coupled to a source follower amplifier, the method comprising the steps of:

clamping a top electrically conductive plate of each reference capacitor to a reset potential;

providing a load current to each source follower amplifier;

selecting, using a horizontal scanning shift register and a vertical scanning shift register, one capacitance sensor from the plurality of capacitance sensors to be read out; and

driving the sense capacitor of the selected capacitance sensor with a first potential and driving the reference capacitor of the selected capacitance sensor with a second potential, said first potential differing in polarity from said second potential;

reading a difference in potential between said sense capacitor and said reference capacitor as said output signal.

25. A method of readout of an infrared imager array of claim 24 further comprising the step of:

reducing the 1/f noise and dc offset of the capacitance sensors by using a correlated double sampling (CDS) readout circuit which uses switching of the first potential and the second potential.

26. A method of readout of an infrared imager array of claim 25, further comprising the step of:

two times oversampling the output of the CDS readout circuit.

27. A infrared sensor formed on a monolithic semiconductor integrated circuit substrate comprising:

a reference capacitor comprising a top electrically conductive plate and a bottom electrically conductive plate;

a dielectric layer formed on the top electrically conductive plate of the reference capacitor;

a sense capacitor comprising a top electrically conductive plate and a bottom electrically conductive plate, said top electrically conductive plate being formed above said dielectric layer and said bottom electrically conductive plate being the top electrically conductive plate of the reference capacitor;

an absorber element formed on a portion of the top electrically conductive plate of the sense capacitor;

a thermal conduction layer connecting the top electrically conductive plate of the sense capacitor to the absorber element, a thermal isolation support element having a first side which is coupled to said thermal conduction layer and a second side which is coupled to the substrate for anchoring the absorber element, the second electrically conductive plate and the thermal conduction layer to the substrate,

wherein the absorber element, the second electrically conductive plate and the thermal conduction layer form a deflectable member.

28. An infrared sensor of claim 27, wherein the top electrically conductive plate and bottom electrically conductive plate of the reference capacitor and the top electrically conductive plate and bottom electrically conductive plate of the sense capacitor are formed from one of a metal, polysilicon and indium-tin oxide.

29. An infrared sensor of claim 27, wherein the top electrically conductive plate and bottom electrically conductive plate of the reference capacitor and the top electrically conductive plate and bottom electrically conductive plate of the sense capacitor are aluminum.

30. An infrared sensor of claim 27, wherein the absorber element has an emissivity of approximately 1.

31. An infrared sensor of claim 27, wherein the absorber element is one of black platinum and carbon.

32. An infrared sensor of claim 27, further comprising capacitance measurement means for measuring the capacitance of the sense capacitor.

33. An infrared sensor of claim 27, wherein the deflectable member changes its position in response to a temperature change due to absorbed incident thermal radiation.