Pixel cell with high storage capacitance for a CMOS imager

• US 7,199,405 B2
• Filed: 10/20/2004
• Issued: 04/03/2007
• Est. Priority Date: 02/25/2000
• Status: Expired due to Term

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Rhodes, Howard E.
• Primary Examiner(s): Louie; Wai-Sing
• Application Number:
  US10/968,289
• Publication Number:
  US 20050077554A1
• Time in Patent Office: 895 Days
• Field of Search: None
• US Class Current: 257/184
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• 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 27/14636 Interconnect structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers

Abstract

A pixel sensor cell for use in a CMOS imager exhibiting improved storage capacitance. The source follower transistor is formed with a large gate that has an area from about 0.3 μm² to about 10 μm². The large size of the source follower gate enables the photocharge collector area to be kept small, thereby permitting use of the pixel cell in dense arrays, and maintaining low leakage levels. Methods for forming the source follower transistor and pixel cell are also disclosed.

Claims

1. A method of operating a pixel device comprising:

receiving a plurality of photons at a first doped semiconductor region;

converting at least a portion of the plurality of photons to a plurality of charges in the first doped semiconductor region;

accumulating the plurality of charges in a second doped semiconductor region;

transferring the plurality of charges through an electrically conductive path to a gate of a source follower transistor, the gate having an area of from between about 0.3 μ

m² to about 25 μ

m²; and

conducting an electrical current through the transistor, the electrical current having a magnitude related to a quantity of the plurality of photons.

2. A method of operating a pixel device as defined in claim 1 further comprising receiving the plurality of photons at the first semiconductor region through a photo gate.

3. A method of operating a pixel device as defined in claim 1 wherein the electrically conductive path comprises a transfer transistor.

4. A method operating a pixel device as defined in claim 1 wherein the transferring the plurality of charges through an electrically conductive path comprises transferring the plurality of charges through an interconnect.

5. A method of operating a pixel device as defined in claim 4 wherein the interconnect comprises a doped semiconductor material.

6. A method of operating a pixel device as defined in claim 4 wherein the interconnect comprises a metal material.

7. A method of operating a pixel device as defined in claim 6 wherein the metal material comprises a refractory metal material.

8. A method of forming a photosensitive device comprising:

forming photosensitive region disposed at a first portion of a semiconductor substrate, the photosensitive region being adapted to receive a flux of photons and responsively generate a plurality of charges;

forming a transistor gate disposed at a second portion of the semiconductor substrate, the transistor gate being adapted to receive and store a portion of the plurality of charges, the transistor gate having an areal dimension of between about 0.3 μ

m² and about 25 μ

m²; and

forming an electrically conductive path between the photosensitive region and the transistor gate, the electrically conductive path being adapted to share charges between the photosensitive region and the transistor gate.

9. A method of forming a photosensitive device as defined in claim 8 wherein the conductive path comprises a transfer transistor disposed in a third region of the semiconductor substrate.

10. A method of forming a photosensitive device as defined in claim 8 wherein the conductive path comprises a metal material.

11. A method of forming a photosensitive device as defined in claim 10 wherein the metal material comprises copper.

12. A method of forming a photosensitive device as defined in claim 10 wherein the conductive path comprises a refractory metal material.

13. A method of forming a photosensitive device as defined in claim 12 wherein the refractory metal material comprises tungsten.