# US 2019/0379844 A1 · Pixel cell with multiple photodiodes

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- Number: US 2019/0379844 A1
- Document ID: US20190379844A1
- Status: Published application
- Kind: A1
- Application number: 16/436,049
- Filed: 2019-06-10
- Published: 2019-12-12
- Earliest claimed: 2018-06-11
- Assignees: Facebook Technologies, LLC
- Applicants: Facebook Technologies, LLC
- Inventors: Song CHEN; Xinqiao LIU
- Web page: https://patentgrep.com/patent/US20190379844A1

## CPC

- H04N 25/70: SSIS architectures; Circuits associated therewith
- H10F 39/1847: {Multispectral infrared image sensors having a stacked structure, e.g. NPN, NPNPN or multiple quantum well [MQW] structures}
- H04N 25/705: Pixels for depth measurement, e.g. RGBZ
- H04N 25/77: Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
- H04N 25/772: comprising A/D, V/T, V/F, I/T or I/F converters
- H10F 39/802: {Geometry or disposition of elements in pixels, e.g. address-lines or gate electrodes}
- H10F 39/80373: {characterised by the gate of the transistor}
- H10F 39/812: {Arrangements for transferring the charges in the image sensor perpendicular to the imaging plane, e.g. buried regions used to transfer generated charges to circuitry under the photosensitive region}
- H04N 23/20: for generating image signals from infrared radiation only
- H10F 39/182: {Colour image sensors}
- H10F 39/184: {Infrared image sensors}
- H10F 39/1865: {Overflow drain structures}
- H10F 39/199: {Back-illuminated image sensors}
- H10F 39/8033: {Photosensitive area}
- H10F 39/8053: {Colour filters}
- H10F 39/8063: {Microlenses}
- H10F 39/807: {Pixel isolation structures}
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

In one example, a method comprises: transmitting a first signal to transfer a first portion of a first charge from a first photodiode to a first charge sensing unit to obtain a first measurement result and transmitting a second signal to transfer a second portion of the first charge from the first photodiode to a second charge sensing unit to obtain a second measurement result. The timing of transmission of the first signal and the second signal are based on the indirect time-of-flight measurement operation. The method further comprises performing the indirect time-of-flight measurement operation based on the first measurement result and the second measurement result; transmitting a third signal to transfer a second charge from a second photodiode to the second charge sensing unit via the first photodiode to obtain a third measurement result; and performing a 2D sensing operation based on the third measurement result.

## Claims

### Claim 1

An apparatus comprising:
a first photodiode;
a second photodiode;
a first charge sensing unit;
a second charge sensing unit;
a first polysilicon gate;
a second polysilicon gate; and
a controller configured to:
enable the first photodiode to generate a first charge;
enable the second photodiode to generate a second charge;
transmit, via the first polysilicon gate, a first signal to transfer a first portion of the first charge from the first photodiode to the first charge sensing unit to obtain a first measurement result, a timing of transmission of the first signal being based on an indirect time-of-flight measurement operation;
transmit, via the second polysilicon gate, a second signal to transfer a second portion of the first charge from the first photodiode to the second charge sensing unit to obtain a second measurement result, a timing of transmission of the second signal being based on the indirect time-of-flight measurement operation;
perform the indirect time-of-flight measurement operation based on the first measurement result and the second measurement result;
transmit, via the second polysilicon gate, a third signal to transfer the second charge from the second photodiode to the second charge sensing unit via the first photodiode to obtain a third measurement result; and
perform a 2D sensing operation based on the third measurement result.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein:
the first photodiode and the second photodiode are in a semiconductor substrate having a front side surface;
the semiconductor substrate comprises:
a first drain region configured as the first charge sensing unit,
a first channel region connected between the first drain region and the first photodiode,
a second drain region configured as the second charge sensing unit; and
a second channel region connected between the second drain region and the second photodiode;
and wherein the first polysilicon gate and the second polysilicon gate are on the front side surface and over, respectively, the first channel region and the second channel region.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein the first photodiode comprises a pinning layer; and
wherein the pinning layer is connected to the first channel region and the second channel region.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein:
the first polysilicon gate extends over a first region of the first photodiode connected to the first channel region;
the second polysilicon gate extends over a second region of the first photodiode connected to the second channel region;
the first signal is configured to modulate electrical potentials of the first region of the first photodiode and of the first channel region; and
the second signal is configured to modulate electrical potentials of the second region of the first photodiode and of the second channel region.

### Claim 5 (depends on 4)

The apparatus of claim 4, further comprising:
a third drain region configured as a third charge sensing unit to measure a third portion of the first charge;
a third channel region connected between the third drain region and the first photodiode; and
a third polysilicon gate on the front side surface and over the third channel region to transmit a fourth signal to transfer the third portion of the first charge to the third drain region via the third channel region,
wherein the controller is configured to control a timing of transmission of the fourth signal based on the indirect time-of-flight measurement operation and to perform the indirect time-of-flight measurement operation based on the third portion of the first charge.

### Claim 6 (depends on 5)

The apparatus of claim 5, further comprising:
a fourth drain region configured as a charge sink to reset at least one of the first photodiode or the second photodiode;
a fourth channel region connected between the fourth drain region and the first photodiode; and
a fourth polysilicon gate on the front side surface and over the fourth channel region to transmit a fifth signal to reset the first photodiode.

### Claim 7 (depends on 6)

The apparatus of claim 6, further comprising a barrier layer sandwiched between the first photodiode and the second photodiode;
wherein the barrier layer is configured to block the first charge from flowing into the second photodiode; and
wherein the barrier layer is controllable by a sixth signal to control a flow of the second charge from the second photodiode to the first photodiode.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein the apparatus further comprises an infra-red illuminator to transmit a first infra-red light pulse;
wherein the first photodiode is configured to generate the first charge based on detecting a second infra-red light pulse from reflection of the first infra-red light pulse; and
wherein the controller is configured to:
control the infra-red illuminator to transmit the first infra-red light pulse between a first time and a second time; and
synchronize the timing of transmission of the first signal and the second signal based on the second time to measure a phase difference between the first infra-red light pulse and the second infra-red light pulse for the indirect time-of-flight measurement operation.

### Claim 9 (depends on 8)

The apparatus of claim 8, wherein the controller is configured to:
stop the transmission of the first signal at the second time to measure, based on the first portion of the first charge, a first width of the second infra-red light pulse before the second time;
start the transmission of the second signal at the second time to measure, based on the second portion of the first charge, a second width of the second infra-red light pulse after the second time; and
determine the phase difference based on a ratio between the second width and a total width of the second infra-red light pulse, and based on a width of the first infra-red light pulse.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein the controller is configured to:
transmit the fourth signal to measure, based on the third portion of the first charge, an ambient infra-red light;
measure, based on a first difference between the first portion of the first charge and the third portion of the first charge, the first width of the second infra-red light pulse before the second time; and
measure, based on a second difference between the second portion of the first charge and the third portion of the first charge, the second width of the second infra-red light pulse before the second time.

### Claim 11 (depends on 10)

The apparatus of claim 10, wherein the controller is configured to transmit the fifth signal to reset the first photodiode before and after the transmission of the first signal and the second signal.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the second photodiode is configured to generate the second charge based on detecting visible light; and
wherein the controller is configured to:
transmit the fifth signal to reset the first photodiode; and
transmit the sixth signal and the third signal to transfer the second charge from the second photodiode to the second drain region via the reset first photodiode.

### Claim 13 (depends on 12)

The apparatus of claim 12, wherein the controller is configured to obtain the third measurement result of the visible light based on the second charge and a first infra-red crosstalk component introduced by the second infra-red light pulse, the first infra-red crosstalk component being based on the first charge and a ratio between a spectral response of the first photodiode and a spectral response of the second photodiode within a frequency range of the first infra-red light pulse.

### Claim 14 (depends on 13)

The apparatus of claim 13, wherein the controller is configured to generate the measurement of the visible light based on a second infra-red crosstalk component introduced by the ambient infra-red light.

### Claim 15 (depends on 14)

The apparatus of claim 14, wherein the first infra-red crosstalk component and the second infra-red crosstalk component are determined based on the width of the first infra-red light pulse and an integration period in which the second photodiode generates the second charge in response to the visible light.

### Claim 16

A method comprising:
enabling a first photodiode to generate a first charge;
enabling a second photodiode to generate a second charge;
transmitting a first signal to transfer a first portion of the first charge from the first photodiode to a first charge sensing unit to obtain a first measurement result, a timing of transmission of the first signal being based on an indirect time-of-flight measurement operation;
transmitting a second signal to transfer a second portion of the first charge from the first photodiode to a second charge sensing unit to obtain a second measurement result, a timing of transmission of the second signal being based on the indirect time-of-flight measurement operation;
performing the indirect time-of-flight measurement operation based on the first measurement result and the second measurement result;
transmitting a third signal to transfer the second charge from the second photodiode to the second charge sensing unit via the first photodiode to obtain a third measurement result; and
performing a 2D sensing operation based on the third measurement result.

### Claim 17 (depends on 16)

The method of claim 16, wherein the first signal is transmitted to modulate an electrical potential of a first region of the first photodiode; and
wherein the second signal is transmitted to modulate an electrical potential of a second region of the first photodiode.

### Claim 18 (depends on 16)

The method of claim 16, further comprising:
controlling an infra-red illuminator to transmit a first infra-red light pulse between a first time and a second time;
enabling the first photodiode to generate the first charge based on detecting a second infra-red light pulse from reflection of the first infra-red light pulse within an integration period; and
synchronizing the timing of transmission of the first signal and the second signal based on the second time to measure a phase difference between the first infra-red light pulse and the second infra-red light pulse for the indirect time-of-flight measurement operation.

### Claim 19 (depends on 18)

The method of claim 18, further comprising:
stopping the transmission of the first signal at the second time to measure, based on the first portion of the first charge, a first width of the second infra-red light pulse before the second time;
starting the transmission of the second signal at the second time to measure, based on the second portion of the first charge, a second width of the second infra-red light pulse after the second time; and
determining the phase difference based on a ratio between the second width and a total width of the second infra-red light pulse, and based on a width of the first infra-red light pulse.

### Claim 20 (depends on 19)

The method of claim 19, further comprising:
transmitting a fourth signal to transfer a third portion of the first charge from the first photodiode to a third charge sensing unit, the third portion of the first charge being generated by the first photodiode in response to an ambient infra-red light;
measuring, based on a difference between the first portion of the first charge and the third portion of the first charge, the first width of the second infra-red light pulse before the second time; and
measuring, based on a difference between the second portion of the first charge and the third portion of the first charge, the second width of the second infra-red light pulse before the second time.