Imager pixel with capacitance for boosting reset voltage

• US 7,446,807 B2
• Filed: 12/03/2004
• Issued: 11/04/2008
• Est. Priority Date: 12/03/2004
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Hong, Sungkwon C.
• Primary Examiner(s): Ometz; David
• Assistant Examiner(s): Giles; Nicholas G
• Application Number:
  US11/002,281
• Publication Number:
  US 20060119720A1
• Time in Patent Office: 1,432 Days
• Field of Search: 348/308, 348/312, 348/313, 348/314
• US Class Current: 348/308
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 25/779 Circuitry for scanning or addressing the pixel array
• CPC Class Codes: H04N 3/1512 for MOS image-sensors, e.g. MOS-CCD H04N3/1581 takes precedence
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

A pixel cell in which a capacitance is coupled between a storage node and a row select transistor and another capacitance is coupled between a storage node and a voltage supply or ground source potential to boost a reset voltage.

Claims

1. A pixel circuit comprising:

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

a first capacitance circuit coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a readout circuit for reading out a signal based on charges stored at said floating diffusion region and said first capacitance circuit; and

a voltage boost circuit operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state wherein said voltage boost circuit comprises a second capacitance circuit.

2. The pixel circuit of claim 1, wherein said voltage boost circuit is coupled between said floating diffusion region and said readout circuit.

3. The pixel circuit of claim 1, wherein said second capacitance circuit comprises a capacitor.

4. The pixel circuit of claim 1, further comprising a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region.

5. The pixel circuit of claim 1, further comprising a row select transistor acting as a switching device coupled to said voltage boost circuit.

6. The pixel circuit of claim 1, further comprising a source follower transistor coupled to said floating diffusion region.

7. The pixel circuit of claim 1, wherein said photo-conversion device comprises a photodiode.

8. The pixel circuit of claim 1, wherein said first capacitance circuit is further coupled to a pixel supply voltage.

9. The pixel circuit of claim 1, wherein said first capacitance circuit is further coupled to a reset supply voltage.

10. The pixel circuit of claim 1, wherein said first capacitance circuit is further coupled to a ground source potential.

11. A pixel of an imaging device comprising:

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

a first capacitor coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a readout circuit for reading out a signal based on charges stored at said floating diffusion region and said first capacitance circuit; and

a second capacitor operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state,

said first and second capacitors having a common first electrode and respective second electrodes.

12. The pixel of claim 11, wherein said first and second capacitors are at least partially formed over a pixel isolated region.

13. A method of fabricating an integrated circuit comprising:

forming a photo-conversion device;

forming a floating diffusion region for receiving and storing charge from said photo-conversion device;

forming a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

forming a first capacitance circuit coupled to said floating diffusion region for storing charge received from said photo-conversion device;

forming a readout circuit for reading out a signal based on charges stored at said floating diffusion region and said first capacitance circuit; and

forming a voltage boost circuit operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state wherein said step of forming a voltage boost circuit comprises forming a second capacitance circuit.

14. The method of claim 13, wherein said step of forming a voltage boost circuit comprises coupling said voltage boost circuit to said floating diffusion region and to said readout circuit.

15. The method of claim 13, wherein step of forming said second capacitance circuit comprises forming a capacitor.

16. The method of claim 13, further comprising a step of forming a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region.

17. The method of claim 13, further comprising a step of forming a row select transistor coupled to said voltage boost circuit.

18. The method of claim 13, further comprising a step of forming a source follower transistor coupled to said floating diffusion region.

19. A method of operating a pixel comprising the steps of:

receiving light in a photo-conversion device, said photo-conversion device converting said light into electrical charge;

resetting a floating diffusion region to a predetermined reset voltage state;

boosting a voltage on said floating diffusion region above said predetermined reset voltage state with a capacitance circuit operating in response to a switching state of a switching device;

reading out said boosted reset voltage;

storing charge from said photo-conversion device in said floating diffusion region and in another capacitance circuit coupled to said floating diffusion region; and

reading out a signal based on stored charge at said floating diffusion region from said photo-conversion device.

20. The method of claim 19, further comprising a step of delivering said charge from said photo-conversion device through a transfer transistor to said floating diffusion region.

21. The method of claim 19, further comprising operating a row select transistor to generate a boosted voltage at said floating diffusion region.

22. A pixel circuit comprising:

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region;

a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

a first capacitor coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a source follower transistor coupled to said floating diffusion region for providing pixel output signals;

a row select transistor for selectively operating said source follower transistor; and

a voltage boost circuit operating in response to a switching state of said row select transistor for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state wherein said voltage boost circuit comprises a second capacitor.

23. The pixel circuit of claim 22, wherein said voltage boost circuit is coupled between said floating diffusion region and a source of said row select transistor.

24. The pixel circuit of claim 22, wherein said photo-conversion device comprises a photodiode.

25. A pixel circuit comprising:

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a transfer transistor coupled between the photo-conversion device and the floating diffusion region for delivering said charge from said photo-conversion device to said floating diffusion region;

a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

a first capacitor coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a second capacitor operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state;

a row select transistor coupled to said second capacitor; and

a source follower transistor coupled to said second capacitor for reading out a signal based on charges stored at said floating diffusion region and said first capacitor.

26. An imager comprising:

an array of pixel circuits, at least one pixel circuit of said array comprising;

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

a first capacitance circuit coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a readout circuit for reading out a signal based on charges stored at said floating diffusion region and said first capacitance circuit; and

a voltage boost circuit operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state wherein said voltage boost circuit comprises a second capacitance circuit.

27. The imager of claim 26, wherein said voltage boost circuit is coupled between said floating diffusion region and said readout circuit.

28. The imager of claim 26, wherein said second capacitance circuit comprises a capacitor.

29. The imager of claim 26, further comprising a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region.

30. The imager of claim 26, further comprising a row select transistor coupled to said voltage boost circuit.

31. The imager of claim 26, further comprising a source follower transistor coupled to said floating diffusion region.

32. The imager of claim 26, wherein said photo-conversion device comprises a photodiode.

33. A processing system comprising:

a processor; and

an imager electronically coupled to said processor, said imager comprising an array of pixel circuits, at least one pixel circuit of said array comprising;

a photo-conversion device;

a floating diffusion region for receiving and storing charge from said photo-conversion device;

a reset transistor for resetting said floating diffusion region to a predetermined reset voltage state;

a first capacitance circuit coupled to said floating diffusion region for storing charge received from said photo-conversion device;

a readout circuit for reading out a signal based on charges stored at said floating diffusion region and said first capacitance circuit; and

a voltage boost circuit operating in response to a switching state of a switching device of said pixel circuit for boosting a reset voltage on said floating diffusion region above said predetermined reset voltage state wherein said voltage boost circuit comprises a second capacitance circuit.

34. The processing system of claim 33, wherein said voltage boost circuit is coupled between said floating diffusion region and said readout circuit.

35. The processing system of claim 33, wherein said second capacitance circuit comprises a capacitor.

36. The processing system of claim 33, further comprising a transfer transistor for delivering said charge from said photo-conversion device to said floating diffusion region.

37. The processing system of claim 33, further comprising a row select transistor coupled to said voltage boost circuit.

38. The processing system of claim 33, further comprising a source follower transistor coupled to said floating diffusion region.

39. The processing system of claim 33, wherein said photo-conversion device comprises a photodiode.