PIXEL SENSOR CELL WITH FRAME STORAGE CAPABILITY

• US 20100013972A1
• Filed: 07/16/2008
• Published: 01/21/2010
• Est. Priority Date: 07/16/2008
• Status: Active Grant

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Krishnasamy, Rajendran, Rassel, Richard J., Ellis-Monaghan, John J., Adkisson, James W., Musante, Charles F., Mulugeta, Solomon
• Granted Patent: US 8,009,215 B2
• Time in Patent Office: Days
• US Class Current: 348/308
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion

Abstract

A set of frame transfer transistors are provided between a hold gate transistor and a transfer gate transistor of a CMOS image sensor to enable storage of charge generate in the photosensitive diode after exposure. The readout of the charges from the set of frame transfer transistors may be performed after a plurality of exposures of the CMOS image sensor, between each of which charges are shifted toward the transfer gate transistor within the set of frame transfer transistors. Useful operation modes are enabled including a burst mode operation for rapid capture of successive images and high dynamic range operations in which multiple images are taken with different exposure times or a large capacitance is provided by ganging the diffusions of the set of frame transfer transistors.

Claims

1. A method of operating a semiconductor circuit of an array of image sensor pixels, said method comprising:

providing an array of image sensor pixels, wherein each image sensor pixel includes a plurality of frame transfer transistors in a serial connection and electrically connected to a photosensitive diode; and

exposing an entirety of said array at least twice prior to reading data from said array, wherein a plurality of frames is stored in said plurality of frame transfer transistors, and wherein each of said plurality of frames corresponds to one of said multiple exposures.

2. The method of claim 1, further comprising shifting said plurality of frames within said plurality of frame transfer transistors away from said photosensitive diode.

3. The method of claim 2, further comprising applying a common gate voltage to gate electrodes of every third frame transfer transistor among said plurality of frame transfer transistors or to gate electrodes of every fourth frame transfer transistor among said plurality of frame transfer transistors during said shifting of said plurality of frames.

4. The method of claim 1, further comprising transferring said plurality of frames to a pixel sensing circuit after said multiple exposures.

5. The method of claim 4, wherein said pixel sensing circuit senses each of said plurality of frames sequentially.

6. The method of claim 4, wherein said multiple exposures are performed sequentially with different exposure times prior to sensing any of said plurality of frames.

7. The method of claim 4, wherein said multiple exposures are performed sequentially with a same exposure time prior to sensing any of said plurality of frames.

8. The method of claim 4, wherein said plurality of frames is transferred to said pixel sensing circuit row by row.

9. A method of operating a semiconductor circuit comprising:

providing a semiconductor circuit for an array of image sensor pixels, wherein each of said image sensor pixels comprises;

a photosensitive diode;

a first transistor, wherein a source of said first transistor is directly connected to a terminal of said photosensitive diode;

a second transistor, wherein a channel of the said second transistor is electrically coupled to a channel of the first transistor;

a plurality of frame transfer transistors serially connected to said second transistor; and

exposing an entirety of said array at least twice prior to reading data from said array, wherein a plurality of frames is stored in said plurality of frame transfer transistors, and wherein each of said plurality of frames corresponds to one of said multiple exposures.

10. The method of claim 9, further comprising shifting said plurality of frames within said plurality of frame transfer transistors away from said photosensitive diode.

11. The method of claim 10, further comprising applying a common gate voltage to gate electrodes of every third frame transfer transistor among said plurality of frame transfer transistors or to gate electrodes of every fourth frame transfer transistor among said plurality of frame transfer transistors during said shifting of said plurality of frames.

12. The method of claim 9, further comprising transferring said plurality of frames to a pixel sensing circuit after said multiple exposures.

13. The method of claim 12, wherein said pixel sensing circuit senses each of said plurality of frames sequentially.

14. The method of claim 12, wherein said multiple exposures are performed sequentially with different exposure times prior to sensing any of said plurality of frames.

15. The method of claim 12, wherein said multiple exposures are performed sequentially with a same exposure time prior to sensing any of said plurality of frames.

16. The method of claim 12, wherein said plurality of frames is transferred to said pixel sensing circuit row by row.

17. The method of claim 12, wherein a channel of one of said plurality of frame transfer transistors is electrically connected to said channel of said second transistor and a channel of each of the rest of said plurality of frame transfer transistors is electrically connected to a channel of another of said plurality of frame transfer transistors, wherein all of said plurality of frame transfer transistors are connected in a serial connection thereamongst.

18. The method of claim 12, wherein gates of every fourth frame transfer transistor among said plurality of frame transfer transistors are electrically shorted, and wherein gates of adjoining frame transfer transistors are electrically disconnected.

19. The method of claim 12, wherein gates of every third frame transfer transistor among said plurality of frame transfer transistors are electrically shorted, and wherein gates of adjoining frame transfer transistors are electrically disconnected.

20. The method of claim 12, wherein said semiconductor circuit further comprises a global reset transistor, wherein a source of said global reset transistor is directly connected to said terminal of said photosensitive diode and a drain of said global reset transistor drain is directly connected to a power supply source.