Highly sensitive solid-state image sensor

• US 7,550,705 B2
• Filed: 09/26/2005
• Issued: 06/23/2009
• Est. Priority Date: 09/29/2004
• Status: Expired due to Fees

• Current Assignee: CSEM Centre Suisse D'Electronique et de Microtechnique SA
• Original Assignee: CSEM Centre Suisse D'Electronique et de Microtechnique SA
• Inventors: Lustenberger, Felix, Seitz, Peter
• Primary Examiner(s): Porta; David P
• Assistant Examiner(s): BOOSALIS, FANI POLYZOS
• Application Number:
  US11/663,412
• Publication Number:
  US 20070267578A1
• Time in Patent Office: 1,366 Days
• Field of Search: 250/208.1, 250/395, 257/292, 257/443
• US Class Current: 250/208.1
• CPC Class Codes: H04N 25/616 involving a correlated sampling function, e.g. correlated double sampling [CDS] or triple sampling

Abstract

A solid-state image sensor (1) with very high sensitivity approaching the single-photon limit is realized with three modular building blocks: (a) a pixel (2.11, 2.12, . . . ) with a photo-site, intermediate photo-charge storage capability as used for correlated double sampling, and an electronic circuit for signal buffering or amplification, (b) a column or row signal line (3.1) to which a plurality of such pixels (2.11, 2.21, . . . ) is connected using transistor switches, incorporating a low-pass filter (30.1), and (c) a readout circuit (4) to which the row signal lines (3.1, 3.2, . . . ) are connected, consisting of a plurality of analog amplifiers (41.1, 41.2, . . . ) with an analog multiplexer (42). Photo-generated signals are read out and the reset level is subtracted either in the analog or in the digital domain, to implement a correlated-double-sampling method.

Claims

1. A solid-state image sensor comprising:

a plurality of photodetecting elements for generating electric charge carriers as a function of incident electromagnetic radiation,

a signal line to which two or more of the photodetecting elements are connected, and

a readout circuit to which the signal line is connected,

said readout circuit including

a low-pass-filter structure and an amplifier assigned to the signal line, wherein said low-pass filter structure is adapted to reduce statistical noise from photo-charge detection without impairing overall pixel readout speed of said photodetecting elements.

2. The image sensor according to claim 1, wherein said signal line is at least partly laid out as a metal-insulator-metal capacitance device, forming said low-pass-filter structure.

3. The image sensor according to claim 2, wherein

said signal line is at least partly laid out as a polysilicon-polysilicon capacitance device, forming a low-pass-filter structure;

a power line is stacked in parallel to the signal line, forming a low-pass-filter structure;

each photodetecting element includes intermediate photo-charge storage for intermediate storage of the electric charge carriers, to allow correlated double sampling;

each photodetecting element comprises a photogate pixel, a pinned photodiode or a dendritic-gate pixel;

the amplifier is a programmable-gain amplifier;

the readout circuit comprises an analog-to-digital converter assigned to said signal line; and

a plurality of signal lines are connected via an analog or digital multiplexer circuit to at least one output line.

4. A method for detecting incident electromagnetic radiation using the image sensor according to claim 3, comprising the steps of:

generating electric charge carriers as a function of incident electromagnetic radiation in a plurality of photodetecting elements,

transferring an electric signal characteristic of the generated electric charge carriers on a signal line, and

processing the electric signal in a readout circuit, wherein reducing signal-transfer bandwidth of the signal line by assigning a low-pass-filter structure and an amplifier to the signal line, and statistical noise of photo-charge detection is reduced without impairing overall pixel readout speed of said photodetecting elements.

5. The method according to claim 4, wherein said low-pass-filter structure is built up by exploiting a parasitic capacitance.

6. The image sensor according to claim 1, wherein said signal line is at least partly laid out as a polysilicon-polysilicon capacitance device, forming said low-pass-filter structure.

7. The image sensor according to claim 1, wherein a power line is stacked in parallel to said signal line, forming said low-pass-filter structure.

8. The image sensor according to claim 1, wherein each photodetecting element includes an intermediate photo-charge storage for intermediate storage of the electric charge carriers, to allow correlated double sampling.

9. The image sensor according to claim 1, wherein each photodetecting element comprises a photogate pixel, a pinned photodiode or a dendritic-gate pixel.

10. The image sensor according to claim 1, wherein said amplifier is a programmable-gain amplifier.

11. The image sensor according to claim 1, wherein said readout circuit comprises an analog-to-digital converter assigned to said signal line.

12. The image sensor according to claim 1, comprising a plurality of signal lines) which are connected via an analog or digital multiplexer circuit to at least one output line.

13. A method for detecting incident electromagnetic radiation using the image sensor according to claim 1, comprising the steps of:

generating electric charge carriers as a function of the incident electromagnetic radiation in said plurality of photodetecting elements,

transferring an electric signal characteristic of the generated electric charge carriers on a signal line,

processing the electric signal in a readout circuit, wherein reducing signal-transfer bandwidth of the signal line by assigning a low-pass-filter structure and an amplifier to the signal line and statistical noise of photo-charge detection is reduced without impairing overall pixel readout speed of said photodetecting elements.

14. The method according to claim 13, wherein said low-pass-filter structure is built up by exploiting a parasitic capacitance.

15. The solid-state imaging device of claim 1, wherein said low-pass-filter structure has a bandwidth limitation corresponding to less than half of a readout time of said signal line.

16. The solid-state imaging device of claim 1, the low-pass-filter structure having a bandwidth, wherein the statistical noise reduction is equal to the square root of the bandwidth of said low-pass-filter structure, to allow correlated double sampling.

17. The solid-state imaging device of claim 1, wherein said low-pass-filter structure is adapted to reduce white resistor or Johnson noise.

18. A solid-state imaging sensor comprising:

a plurality of photodetecting elements for generating electric charge carriers as a function of incident electromagnetic radiation,

a signal line to which two or more of the photodetecting elements are connected, and

a readout circuit to which the signal line is connected, said readout circuit including an amplifier and a power line that is stacked in parallel to said signal line to form a low-pass-filter structure, which are assigned to the signal line.