Methods for Transferring Charge in an Image Sensor

• US 20170373106A1
• Filed: 08/21/2017
• Published: 12/28/2017
• Est. Priority Date: 03/06/2013
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Li, Xiangli, Fan, Xiaofeng, Wan, Chung Chun
• Granted Patent: US 10,943,935 B2
• Time in Patent Office: Days
• 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 27/14616 characterised by the channel of the transistor, e.g. channel having a doping gradient
• CPC Class Codes: H04N 25/587 acquired sequentially, e.g. using the combination of odd and even image fields
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• 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 25/771 comprising storage means other than floating diffusion
• CPC Class Codes: H04N 25/78 Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
• CPC Class Codes: H04N 25/79 Arrangements of circuitry being divided between different or multiple substrates, chips or circuit boards, e.g. stacked image sensors

Abstract

Apparatuses and methods for charge transfer in image sensors are disclosed. One example of an image sensor pixel may include a first charge storage node and a second charge storage node. A transfer circuit may be coupled between the first and second charge storage nodes, and the transfer circuit may have a first region proximate the first charge storage node and configured to have a first potential. The transfer circuit may also have a second region proximate the second charge storage node configured to have a second, higher potential. An input node may be configured to control the first and second potentials based on a transfer signal provided to the input node.

Claims

1. A method of transferring charge from a first storage node to a second storage node in an integrated circuit (IC), the method comprising:

applying, at a transfer gate, a first applied potential to a first region of the IC and to a second region of the IC, wherein;

the first region of the IC is between the first storage node and the second region of the IC, the first region and the second region being positioned adjacent to the transfer gate;

the first region is configured to maintain a first variable potential less than a second variable potential of the second region;

a virtual barrier region of the IC is between the second region and the second storage node, and is configured to have a virtual barrier potential less than a potential of the second storage node; and

the first applied potential causes the first variable potential to be less than a potential of the first storage node;

accumulating a quantity of charge in the first storage node;

applying, at the transfer gate, a second applied potential to the first region and to the second region so that;

the first variable potential is greater than the potential of the first storage node; and

a portion of the accumulated charge of the first storage node is transferred into the second region;

applying, at the transfer gate, a third applied potential so that the second variable potential is less the virtual barrier potential; and

transferring the portion of the accumulated charge from the second region into the second storage node.

2. The method of claim 1, further comprising initially depleting the first storage node of an initial charge.

3. The method of claim 1, wherein accumulating the quantity of charge includes receiving charge from a photodiode of an image sensor.

4. The method of claim 1, wherein the portion of accumulated charge is a first portion of the accumulated charge, and further comprising repeating the operations of claim 1 so that a second portion of the accumulated charge is transferred from the first storage node into the second storage node.

5. The method of claim 4, further comprising iteratively repeating the operations of claim 1 until a final portion of the accumulated charge has been transferred to the second storage node.

6. The method of claim 1, further comprising iteratively repeating the operations of claim 1 for a fixed time period.

7. The method of claim 1, wherein the first potential of the first storage node is greater than a second potential of the second storage node.

8. A method of operating an image sensor pixel having a photodiode, the method comprising:

turning off a first transfer gate to electrically isolate the photodiode, wherein;

the photodiode is linked to a first storage node, the link controlled by the first transfer gate;

a first region and a second region of the image sensor pixel are configured between the first storage node and a second storage node so that the first storage node, the first region, the second region and the second storage node form a sequence in the image sensor pixel; and

a second transfer gate is configured to control transfer of charge between the first storage node and the second storage node;

accumulating charge in the photodiode during an integration time;

transferring the accumulated charge from the photodiode to the first storage node by turning on the first transfer gate;

electrically isolating the first storage node by turning off the first transfer gate; and

applying a pulse at the second transfer gate to alter a first variable potential of the first region and a second variable potential of the second region to cause a portion of the transferred accumulated charge in the first storage node to flow to the second storage node;

wherein;

during the pulse the portion of the transferred accumulated charge flows through the first region into the second region; and

after completion of the pulse, the portion of the transferred accumulated charge in the second region flows into the second storage node.

9. The method of claim 8, further comprising initially depleting a first initial charge in the photodiode and a second initial charge in the first storage node.

10. The method of claim 8, further comprising repeatedly applying one or more subsequent pulses at the second transfer gate to cause subsequent portions of the transferred accumulated charge in the first storage node to flow to the second storage node.

11. The method of claim 10, wherein the subsequent pulses are applied until the transferred accumulated charge in the first storage node is substantially completely transferred to the second storage node.

12. The method of claim 8, wherein:

the image sensor pixel is configured so that the second variable potential of the second region remains greater than the first variable potential of the first region; and

the pulse alters the first variable potential of the first region to be greater than a potential of the first storage node.

13. The method of claim 12, wherein the image sensor pixel comprises a virtual barrier region between the second region and the second storage node, and the method further comprises maintaining a virtual barrier potential of the virtual barrier region to be less than a potential of the second storage node.

14. The method of claim 8, further comprising:

after completion of the pulse, transferring the portion of the transferred accumulated charge that flowed into the second storage node to a third storage node.

15. The method of claim 14, wherein transferring the portion of the transferred accumulated charge that flowed into the second storage node to a third storage node includes applying a transfer signal to a third transfer gate configured to isolate the second storage node from the third storage node.

16. The method of claim 14, further comprising generating an output signal based on the portion of the transferred accumulated charge that flowed into the second storage node and was transferred to the third storage node.

17. A method of controlling charge flow in an image sensor pixel having a photodiode, a first storage node, a second storage node, a first region, a second region and a third storage node, the method comprising:

isolating the photodiode during a first time interval;

accumulating charge in the photodiode during a second time interval following the first time interval;

during a final subinterval of the second time interval;

removing the isolation of the photodiode;

isolating the first storage node from a second storage node;

resetting the second storage node; and

transferring the accumulated charge from the photodiode to the first storage node;

during a third time interval following the second time period;

removing the isolation of the first storage node from the second storage node;

isolating the second storage node from the third storage node;

transferring a portion of the transferred accumulated charge in the first storage node from the first storage node into the second region, wherein;

the first region and the second region of the image sensor pixel are configured between the first storage node and the second storage node, the first region being adjacent to the first storage node and the second storage node being adjacent to the second storage node;

the portion of the transferred accumulated charge initially flows through the first region into the second region during an initial part of the third time interval; and

the portion of the transferred accumulated charge flows from the second region into the second transfer node during a second part of the third time interval that follows the first part of the third time interval;

and

during a fourth time interval following the third time interval;

removing the isolation of second storage node from the third storage node;

moving into the third storage region the portion of the transferred accumulated charge that was transferred into the second storage node.

18. The method of claim 17, further comprising repeatedly transferring further portions of the transferred accumulated charge in the first storage node from the first storage node into the second storage node during the third time interval.

19. The method of claim 17, further comprising using the portion of the transferred accumulated charge in the third storage region to generate an output signal from the image sensor pixel.

20. The method of claim 17, further comprising depleting an initial charge in the photodiode during an initial time interval before the first time interval.