CN209961904U

CN209961904U - Current-assisted photon demodulation type pixel unit, back-illuminated image sensor chip and imaging system

Info

Publication number: CN209961904U
Application number: CN201920248883.6U
Authority: CN
Inventors: 徐渊; 廖嘉雯; 杨俊伟; 黄志宇
Original assignee: Shenzhen City Light Micro Technology Co Ltd
Current assignee: Optical Micro Information Technology Hefei Co ltd
Priority date: 2018-11-14
Filing date: 2019-02-27
Publication date: 2020-01-17
Anticipated expiration: 2029-02-27

Abstract

The application provides a current-assisted photon demodulation type pixel unit, back-illuminated image sensor chip and imaging system, the pixel unit includes: a substrate; a photodetector; the first voltage signal output module comprises a first switch, and the first switch outputs a voltage signal when receiving the control signal; the second voltage signal output module comprises a second switch, and the second switch outputs a voltage signal when receiving the control signal; the phase of the control signal sent to the first switch is set to be the same as that of the modulated light, the phase of the control signal sent to the second switch is set to be complementary with that of the modulated light, voltage signals output by the first voltage signal output module and the second voltage signal output module in different phases are obtained after reflected light is received, and the flight time of the modulated light is calculated. The method and the device can improve the problems of low responsivity, low demodulation bandwidth and low measurement precision of the pixel unit, thereby meeting the requirements of specific occasions.

Description

Current-assisted photon demodulation type pixel unit, back-illuminated image sensor chip and imaging system

Technical Field

The present application relates to the field of image processing, and in particular, to a current-assisted photon demodulation type pixel unit, a back-illuminated image sensor chip, and an imaging system.

Background

Artificial three-dimensional (3D) vision has been seen as a bridge for intelligent systems to the outside world, enabling machines to see what we see in three-dimensional space, and many 3D acquisition systems have been developed over the years, including stereo vision, structured light projection and laser scanners, which unfortunately do not reliably collect real-time three-dimensional data. Ranging systems based on the time of flight (TOF) principle provide an elegant solution to instantly obtain complete three-dimensional information of an object by emitting modulated light and detecting its reflected light round trip time. Time of flight (TOF) ranging has a wide range of applications, such as in the 3D mouse, gesture-based remote control, entertainment, robotics, security systems, and automotive applications.

At present, among the sensor pixel structures of the phase TOF ranging system, the most common is the Active Pixel Sensor (APS) structure, wherein the most basic APS is composed of three transistors and one photodetector, and is denoted by the english abbreviation 3T-APS, and includes a reset switch transistor, a source follower, a selection switch transistor, and a photodetector for photoelectric conversion. More generally, 4T-APS pixels are formed by adding a transmission gate and a suspended N-type diffusion region on the basis of 3T-APS pixels, so that the signal-to-noise ratio of the pixels is improved.

The TOF ranging system is widely adopted and requires a pixel structure to have the following characteristics: low noise, high responsivity, high demodulation contrast, high demodulation bandwidth and low power consumption. Recently, in the creation of standard CMOS photonic demodulators, there have been many efforts in academia to provide a number of very constructive structures that enable 3D imaging systems fabricated on the time-of-flight principle, but there still remain challenges, and the responsivity, demodulation bandwidth and measurement accuracy of these detectors are too low to meet the requirements of specific situations.

Disclosure of Invention

The application provides a current-assisted photon demodulation type pixel unit, a back-illuminated image sensor chip and an imaging system, which can solve the problem that the 3D imaging system manufactured by the flight time principle at present has low responsivity, low demodulation bandwidth and low measurement precision and cannot meet the requirements of specific occasions.

According to a first aspect of the present application, there is provided a current assisted photon demodulation type pixel cell comprising: a substrate; a photodetector, comprising: a photodiode disposed within the substrate to accumulate charge in response to reflected light incident on the photodetector; the first voltage signal output module is used for converting the charges accumulated on the photodiode into a voltage signal and comprises a first switch, wherein the control end of the first switch receives a control signal, the input end of the first switch is connected with the photodiode, and the output end of the first switchThe output end outputs a first voltage signal when the control end of the first switch receives the control signal; the second voltage signal output module is used for converting the charges accumulated on the photodiode into a voltage signal and comprises a second switch, wherein the control end of the second switch receives a control signal, the input end of the second switch is connected with the photodiode, and the output end of the second switch outputs a second voltage signal when the control end of the second switch receives the control signal; when the two-tap two-phase method is adopted for measurement, after the photodiode of the pixel unit receives reflected light reflected by the object to be measured, the first voltage signal PS0 output by the first voltage signal output module when the phase of the reflected light is 0 DEG is obtained, and the second voltage signal PS1 output by the second voltage signal output module when the phase of the reflected light is 180 DEG is obtained; according to the formula:

calculating the time of flight of the modulated light, wherein T_onFor modulating the time during which the light level is high during a period.

Preferably, when the two-tap four-phase method is used for measurement, after the photodiode of the pixel unit receives the reflected light again, the first voltage signal PS2 output by the first voltage signal output module when the voltage output by the first voltage signal output module is the phase of the reflected light at 90 ° is obtained, and the second voltage signal PS3 output by the second voltage signal output module when the voltage output by the second voltage signal output module is the phase of the reflected light of the modulated light at 270 ° is obtained; according to the formula:

calculating the time of flight of the modulated light, wherein T_tofFor modulating the optical round-trip time, T_pluseFor adjustingThe period of light making.

Preferably, the substrate comprises a first region and a second region; the photodiode comprises a light-sensitive surface, and the light-sensitive surface is arranged at the central position of the first area of the substrate; the first switch of the first voltage signal output module includes: the first electrode is used for receiving a control signal and is connected with the control end of the first switch; a first acceleration region for accelerating a flow of charges in the substrate upon receiving a control signal, which is disposed in the second region of the substrate and at one side of the photodiode, and which is connected to an input terminal of the first switch; the first collecting region is used for receiving and storing the charges accumulated by the photodiode transmitted by the first accelerating region and is arranged on one side of the first accelerating region, which is far away from the photodiode; a third electrode for outputting the charge accumulated by the photodiode, which is connected to the first collecting region and the output terminal of the first switch; the second switch of the second voltage signal output module includes: the second electrode is used for receiving a control signal and is connected with the control end of the second switch; a second acceleration region for accelerating the flow of charges in the substrate upon receiving the control signal, which is disposed in the second region of the substrate and is symmetrically disposed to one side of the photodiode with respect to the first acceleration region, and which is connected to the input terminal of the second switch; the second collecting region is used for receiving and storing the charges accumulated by the photodiode transmitted by the second accelerating region, and the first collecting region is symmetrically arranged on one side of the second accelerating region, which is far away from the photodiode; a fourth electrode for outputting the charge accumulated by the photodiode, which is connected to the second collecting region and the output terminal of the second switch; when a voltage difference exists between an input voltage value received by the first electrode and an input voltage value received by the second electrode, an electric field is formed between the first acceleration region and the second acceleration region so that charges accumulated by the photodiode are transferred to the first collection region or the second collection region for storage.

Preferably, the pixel unit further includes: a first reset transistor for resetting the charges stored in the first collecting region, connected to the third electrode; a first source electrode following transistor, the control end of which is connected with the first collecting area, the input end of which is connected with the first reset transistor, and the output end of which outputs a first voltage signal; a second reset transistor for resetting the charges stored in the second collecting region, connected to the fourth electrode; and a second source follower transistor, the control end of which is connected with the second collecting area, the input end of which is connected with the second reset transistor, and the output end of which outputs a second voltage signal.

Preferably, the pixel cell further comprises a deep trench isolation structure for isolating active regions of adjacent pixel cells, which are disposed in the substrate around the periphery of the pixel cell.

Preferably, the pixel unit further comprises a micro lens for focusing and irradiating light onto the photosensitive surface of the photodiode, which is arranged above the photosensitive surface of the photodiode.

Preferably, the pixel unit further includes a light-shielding layer disposed above a peripheral position of the first region of the substrate.

According to a second aspect of the present application, there is provided a back-illuminated image sensor chip including: a pixel array including a plurality of current assisted photon demodulation type pixel cells as described above; the pixel driving unit is used for outputting a control signal to control the pixel units in the pixel array to work and is connected with the pixel array; the readout unit is used for reading and outputting voltage signals output by pixel units in the pixel array and is connected with the pixel array; a control unit which connects and controls the pixel array, the pixel driving unit, and the readout unit; the control unit controls the phase of a control signal sent to the first switch by the pixel driving unit to be the same as the phase of the modulated light, sets the phase of a control signal sent to the second switch to be complementary with the phase of the control signal sent to the first switch, and transmits the modulated light to an object to be measured, wherein the time length of modulation after each transmission is T_pulseWhen the two-tap two-phase method is adopted for measurement, after the pixel unit receives reflected light reflected by an object to be measured, the first voltage signal PS0 output by the first voltage signal output module when the voltage output by the first voltage signal module is the phase of the reflected light at 0 degree is obtained, and the second voltage signal PS0 output by the first voltage signal output module when the phase of the reflected light is 0 degree is obtainedThe voltage output by the voltage signal output module is a second voltage signal PS1 output by the second voltage signal output module when the phase of the reflected light is 180 degrees; according to the formula:calculating the time of flight of the modulated light, wherein T_onFor modulating the time during which the light level is high during a period.

calculating the time of flight of the modulated light, wherein T_tofFor modulating the optical round-trip time, T_pluseThe period of the modulated light.

According to a third aspect of the present application, there is provided an imaging system comprising an image sensing chip as described above and a laser emitter.

According to a fourth aspect of the present application, there is provided a method of forming a pixel unit, the method comprising: arranging a substrate; providing a photodetector comprising: a photodiode disposed within the substrate to accumulate charge in response to reflected light incident on the photodetector; the first voltage signal output module is used for converting the charges accumulated on the photodiode into a voltage signal and comprises a first switch, wherein the control end of the first switch receives a control signal, the input end of the first switch is connected with the photodiode, and the output end of the first switch outputs a first voltage signal when the control end of the first switch receives the control signal; the second voltage signal output module is used for converting the charges accumulated on the photodiode into a voltage signal and comprises a second switch, wherein the control end of the second switch receives a control signal, the input end of the second switch is connected with the photodiode, and the output end of the second switch outputs a second voltage signal when the control end of the second switch receives the control signal; when the two-tap two-phase method is adopted for measurement, after the photodiode of the pixel unit receives reflected light reflected by the object to be measured, the first voltage signal PS0 output by the first voltage signal output module when the phase of the reflected light is 0 DEG is obtained, and the second voltage signal PS1 output by the second voltage signal output module when the phase of the reflected light is 180 DEG is obtained; according to the formula:

Preferably, the method is carried out by adopting a two-tap four-phase methodDuring measurement, after the photodiode of the pixel unit receives the reflected light again, the first voltage signal PS2 output by the first voltage signal output module when the phase of the reflected light is 90 ° is obtained as the voltage output by the first voltage signal output module, and the second voltage signal PS3 output by the second voltage signal output module when the phase of the reflected light of the modulated light is 270 ° is obtained as the voltage output by the second voltage signal output module; according to the formula:

According to a fifth aspect of the present application, there is provided a depth information measuring and calculating method, including: providing a pixel array comprising a plurality of current assisted photon demodulation type pixel cells as described above; setting a pixel driving unit, which is used for outputting a control signal to control the pixel units in the pixel array to work and is connected with the pixel array; a readout unit is arranged, is used for reading and outputting voltage signals output by pixel units in the pixel array, and is connected with the pixel array; a setting control unit which is connected with and controls the pixel array, the pixel driving unit and the readout unit; the control unit controls the phase of a control signal sent to the first switch by the pixel driving unit to be the same as the phase of the modulated light, sets the phase of a control signal sent to the second switch to be complementary with the phase of the control signal sent to the first switch, and transmits the modulated light to an object to be measured, wherein the time length of modulation after each transmission is T_pulseWhen a two-tap two-phase method is used for measurement, after the pixel unit receives reflected light reflected by an object to be measured, a first voltage signal PS0 output by the first voltage signal output module when the phase of the reflected light is 0 degrees and a second voltage signal PS1 output by the second voltage signal output module when the phase of the reflected light is 180 degrees are obtained, wherein the voltage output by the first voltage signal output module is the first voltage signal PS0 output by the first voltage signal output module when the phase of the reflected light is 0 degrees; according to the formula:

The beneficial effect of this application lies in: the application arranges a first voltage signal output module and a second voltage signal output module in a current-assisted photon demodulation type pixel unit structure, the first voltage signal output module and the second voltage signal output module can convert charges accumulated by a photoelectric detector responding to reflected light into voltage signals after receiving control signals, and then the flight time of modulated light can be calculated by arranging the phase relation between a first switch of the first voltage signal output module and a second switch of the second voltage signal output module and the modulated light, acquiring the voltage signals output by the first voltage signal output module and the second voltage signal output module under different phases after receiving the reflected light, so that the reaction speed and the demodulation bandwidth of an imaging system can be improved, the measurement precision is higher, and the requirements of high-precision industries in the fields of safety detection and industrial control are met, the application range of the product is wider.

Drawings

FIG. 1 is a schematic structural diagram of a current-assisted photon demodulation pixel unit according to a first embodiment of the present application;

FIG. 2 is a schematic structural diagram of a current-assisted photon demodulation pixel unit according to a second embodiment of the present application;

FIG. 3 is a schematic top view of a current assisted photon demodulation pixel cell according to a second embodiment of the present application;

FIG. 4 is an equivalent circuit schematic of FIG. 2;

FIG. 5 is a timing diagram of a four phase measurement of the present application;

FIG. 6 is a schematic diagram of a back side illuminated image sensor chip in a third embodiment of the present application;

fig. 7 is a flowchart of a method of forming a pixel cell shown in a fifth embodiment of the present application; and

fig. 8 is a flowchart of a depth information measuring and calculating method according to a sixth embodiment of the present application.

Description of reference numerals: the first region 101 and the second region 102 of the substrate 10 the deep trench isolation structure 103 the photodetector 20 photodiode PD first voltage signal output module 201 first transfer transistor VMOD1 first electrode first acceleration region V1 first P-type doped region first collection region CLO1 second voltage signal output module 202 second transfer transistor VMOD2 second electrode second acceleration region V3 second P-type doped region second collection region CLO2 fourth electrode first reset transistor RST1 first capacitor C1 first source follower transistor SF1 second reset transistor RST2 second capacitor C2 second source follower transistor SF2 light shield layer 30 microlens 40.

Detailed Description

The present application will be described in further detail below with reference to the accompanying drawings by way of specific embodiments.

The conception of the application is as follows: the pixel unit structure capable of measuring ambient light and measuring reflected light of a measured object is arranged on the structure of the traditional 4T-APS, a drift electric field is generated through the potential difference of the two P + type doped regions to control the transfer position of photo-generated charges, the sensitivity is good, the DC modulation contrast ratio is close to 100%, the accuracy of measuring image depth information can be improved, and the application range of a product is wider.

The first embodiment is as follows:

referring to fig. 1 and 2, the current assisted photon demodulation pixel unit includes: a substrate 10 and a photodetector 20. The photodetector 20 includes: a photodiode PD, a first voltage signal output module 201, and a second voltage signal output module 202.

A photodiode PD disposed within the substrate 10 to accumulate charge in response to reflected light incident on the photodiode PD. The first voltage signal output module 201 is configured to convert the charges accumulated in the photodiode PD into a voltage signal, and includes a first switch, a control terminal of the first switch receives a control signal, an input terminal of the first switch is connected to the photodiode PD, and an output terminal of the first switch outputs the first voltage signal when the control terminal of the first switch receives the control signal. The second voltage signal output module 202 is configured to convert the charges accumulated in the photodiode PD into a voltage signal, and includes a second switch, a control terminal of the second switch receives the control signal, an input terminal of the second switch is connected to the photodiode PD, and an output terminal of the second switch outputs a second voltage signal when the control terminal of the second switch receives the control signal.

The substrate 10 is used to form a device structure or a chip circuit, and the substrate 10 may be a semiconductor base including a silicon substrate 10, a silicon germanium substrate 10, a silicon carbide substrate 10, a Silicon On Insulator (SOI) substrate 10, a Germanium On Insulator (GOI) substrate 10, a glass substrate 10, or a III-V compound substrate 10 (e.g., silicon nitride or gallium arsenide, etc.). The substrate 10 may also be a bulk base, i.e., a silicon substrate 10, a silicon germanium substrate 10, or a silicon carbide substrate 10. In other embodiments, the substrate 10 can also be a silicon-on-insulator substrate 10 or a germanium-on-insulator substrate 10. In other embodiments, the substrate 10 can further include a semiconductor base and an epitaxial layer formed on a surface of the semiconductor base through an epitaxial process.

In the present embodiment, the substrate 10 includes: a P-type single crystal silicon substrate 10(P-type substrate) and a P-type epitaxial layer (P-epitaxial layer).

The photodiode PD is disposed in the substrate 10, the photodiode PD is formed by an ion implantation process, and by controlling the energy and concentration of the ion implantation, the depth and implantation range of the ion implantation can be controlled, thereby controlling the depth and thickness of the photodiode PD.

In the present embodiment, the Photodiode PD is a Pinned Photodiode (PPD). The photodiode PD is doped with N-type ions, which include phosphorus ions, arsenic ions, or antimony ions. In addition, the photodiode PD can be additionally provided with a thin P + layer relative to the surface layer of the conventional photodetector 20, and the top P + layer isolates the N buried layer of the charge collection layer from the top surface of Si/SiO2, so that traps causing the main cause of dark current are covered, so that the photodiode PD has smaller dark current relative to the conventional photodetector 20 on one hand, and can form a fully depleted accumulation region on the other hand, thereby overcoming the problem of output image lag.

The photodiode PD is disposed in a central position of the substrate 10, the first switch of the first voltage signal output module 201 may be a first transfer transistor VMOD1, the first transfer transistor VMOD1 is disposed in the substrate 10 and disposed at one side of the photodiode PD, and the first transfer transistor VMOD1 is coupled with the photodiode PD to output the charge accumulated by the photodiode PD as a first voltage signal. The second switch of the second voltage signal output module 202 is a second transfer transistor VMOD2, the second transfer transistor VMOD2 is disposed in the substrate 10 and the symmetrical first transfer transistor VMOD1 is disposed at the other side of the photodiode PD, and the second transfer transistor VMOD2 is coupled with the photodiode PD to output the charges accumulated by the photodiode PD as a second voltage signal.

The operation principle of the present embodiment will be described with reference to fig. 1 to 5.

When the two-tap two-phase method is adopted for measurement, after the photodiode PD of the pixel unit receives reflected light reflected by the object to be measured, the first voltage signal PS0 output by the first voltage signal output module 201 when the phase of the reflected light is 0 ° is obtained, and the second voltage signal PS1 output by the second voltage signal output module 202 when the phase of the reflected light is 180 ° is obtained;

according to the formula:

Then according to the formula:

and calculating to obtain the image Depth information Depth of the object to be measured.

When the two-tap four-phase method is adopted for measurement, after the photodiode PD of the pixel unit receives the reflected light again, the first voltage signal PS2 output by the first voltage signal output module 201 when the phase of the reflected light is 90 ° is obtained, and the second voltage signal PS3 output by the second voltage signal output module 202 when the phase of the reflected light of the modulated light is 270 ° is obtained;

according to the formula:

Then according to the formula:

Example two:

referring to fig. 2 to 5, the current-assisted photon demodulation pixel unit includes: substrate 10, photodetector 20, light shielding layer 30, and microlens 40. The photodetector 20 includes: the photodiode PD, the first voltage signal output block 201, the second voltage signal output block 202, the first reset transistor RST1, the first capacitor C1, the first source follower transistor SF1, the second reset transistor RST2, the second capacitor C2, and the second source follower transistor SF 2.

With continued reference to fig. 2 and 3, the substrate 10 includes: a first region 101, a second region 102, and a deep trench isolation structure 103. Wherein the back side of the substrate 10 is provided in the first region 101 and the front side of the substrate 10 is provided in the second region 102.

In this embodiment, the current-assisted photon demodulation type pixel unit adopts a back-illuminated CMOS process, and a light-receiving surface of a structure of the back-illuminated current-assisted photon demodulation type pixel unit is located in the first region 101, which is also a "back surface" of the silicon wafer, in contrast to all devices and wires manufactured by a semiconductor process being located on a "front surface" of the silicon wafer. In order to allow light to impinge on the PN junction of the photodiode PD from the back side, the silicon wafer back side of the photodiode PD of the pixel unit must be thinned to the extent of being "transparent" to light. Because the metal layer of the backlit pixel is on the opposite side of the illumination, no "walls" or "wells" are formed for incident light. The back-illuminated pixel cell structure maximizes the fill factor, allows flexible transistor positioning, and makes the light path independent of the metal layer.

In this embodiment, the substrate 10 is used to form a device structure or a chip circuit, and the substrate 10 may be a semiconductor base including a silicon substrate 10, a silicon germanium substrate 10, a silicon carbide substrate 10, a silicon-on-insulator (SOI) substrate 10, a germanium-on-insulator (GOI) substrate 10, a glass substrate 10, or a III-V compound substrate 10 (e.g., silicon nitride or gallium arsenide, etc.). The substrate 10 may also be a bulk base, i.e., a silicon substrate 10, a silicon germanium substrate 10, or a silicon carbide substrate 10. In other embodiments, the substrate 10 can also be a silicon-on-insulator substrate 10 or a germanium-on-insulator substrate 10. In other embodiments, the substrate 10 can further include a semiconductor base and an epitaxial layer formed on a surface of the semiconductor base through an epitaxial process.

In the present embodiment, the substrate 10 includes: a P-type single crystal silicon substrate (P-type substrate) and a P-type epitaxial layer (P-epitaxial layer). The P-type single crystal silicon substrate is formed in the first region 101 of the substrate 10, i.e., the back surface of the substrate 10, and the P-type epitaxial layer is formed in the second region 102 of the substrate 10, i.e., the front surface of the substrate 10.

Since light is incident on the pixel cell from the back side of the substrate 10, i.e., from the P-type single crystal silicon substrate, this requires the P-type single crystal silicon substrate 10 of the substrate 10 to be relatively thin.

A deep trench isolation structure 103 for isolating active regions of adjacent said pixel cells, which is disposed in the substrate around the periphery of the pixel cells.

Referring to fig. 2 to 4, the photodiode PD is disposed in a center of the first region 101 of the substrate 10, and the photodiode PD includes a photosensitive surface disposed in the center of the first region 101 of the substrate 10.

The first voltage signal output module 201 is configured to convert the charges accumulated in the photodiode PD into a voltage signal, and includes a first switch, a control terminal of the first switch receives a control signal, an input terminal of the first switch is connected to the photodiode PD, and an output terminal of the first switch outputs the first voltage signal when the control terminal of the first switch receives the control signal. The second voltage signal output module 202 is configured to convert the charges accumulated in the photodiode PD into a voltage signal, and includes a second switch, a control terminal of the second switch receives the control signal, an input terminal of the second switch is connected to the photodiode PD, and an output terminal of the second switch outputs a second voltage signal when the control terminal of the second switch receives the control signal. A first reset transistor RST1 for resetting the charge held by the first switch is connected to the first switch. The first source follower transistor SF1 has a control terminal connected to the first switch, an input terminal connected to the first reset transistor RST1, and an output terminal outputting a first voltage signal. A second reset transistor RST2 to reset the charge held by the second switch, which is connected to the second switch. The second source follower transistor SF2 has a control terminal connected to the second switch, an input terminal connected to the second reset transistor RST2, and an output terminal outputting the second voltage signal.

Specifically, the first switch of the first voltage signal output module 201 is a first transfer transistor VMOD1, the first transfer transistor VMOD1 is disposed in the second region 102 of the substrate 10 and is disposed at one side of the photodiode PD, and the first transfer transistor VMOD1 is coupled to the photodiode PD to output the charges accumulated by the photodiode PD as the first voltage signal. The second switch of the second voltage signal output module 202 is a second transfer transistor VMOD2, the second transfer transistor VMOD2 is disposed in the second region 102 of the substrate 10 and the symmetrical first transfer transistor VMOD1 is disposed at the other side of the photodiode PD, and the second transfer transistor VMOD2 is coupled with the photodiode PD to output the charges accumulated by the photodiode PD as a second voltage signal.

The first transfer transistor VMOD1 of the first voltage signal output module 201 includes: a first electrode for receiving a control signal, which is connected to a control terminal of the first transfer transistor VMOD 1; a first acceleration region V1 for accelerating the flow of charges in the substrate 10 upon receiving a control signal, which is disposed in the second region 102 of the substrate 10 and on one side of the photodiode PD, and which is connected to an input terminal of the first transfer transistor VMOD 1; a first collection region CLO1 for receiving and storing the charges accumulated by the photodiode PD from the first acceleration region V1, which is disposed at a side of the first acceleration region V1 away from the photodiode PD; and a third electrode for outputting charges accumulated in the photodiode PD, which is connected to the first collection region CLO1 and the output terminal of the first transfer transistor VMOD 1.

The second pass transistor VMOD2 of the second voltage signal output module 202 includes: a second electrode for receiving a control signal, which is connected to a control terminal of the second pass transistor VMOD 2; a second acceleration region V3 disposed in the second region 102 of the substrate 10 and a symmetrical first acceleration region V1 disposed at one side of the photodiode PD, which is connected to the input terminal of the second transfer transistor VMOD 2; a second collection region CLO2 for receiving and storing the charges accumulated by the photodiode PD from the second acceleration region V3, wherein the second collection region CLO2 is disposed at a side of the second acceleration region V3 away from the photodiode PD; and a fourth electrode for holding and outputting the charges accumulated by the photodiode PD, which is connected to the second collection region CLO2 and the output terminal of the second transfer transistor VMOD 2.

A first reset transistor RST1 for resetting the charges stored in the first collecting region CLO1 is connected to the third electrode. The first source follower transistor SF1 has a control terminal connected to the first collection region CLO1, an input terminal connected to the first reset transistor RST1, and an output terminal outputting a first voltage signal. A second reset transistor RST2 for resetting the charges stored in the second collection region CLO2, which is connected to the fourth electrode. A second source follower transistor SF2 having a control terminal connected to the second collection region CLO2, an input terminal connected to the second reset transistor RST2, and an output terminal outputting a second voltage signal.

In this embodiment, the first transfer transistor VMOD1, the first reset transistor RST1, the first source follower transistor SF1, the second transfer transistor VMOD2, the second reset transistor RST2, and the second source follower transistor SF2 are MOS transistors.

In this embodiment, the first accelerating region V1 includes a first P-type recess region and a first P-type doped region formed in the first P-type recess region, and the second accelerating region V3 includes a second P-type recess region and a second P-type doped region formed in the second P-type recess region. Both the first collection region CLO1 and the second collection region CLO2 are N-type doped regions. The two P-type doped regions, the first P-type doped region and the second P-type doped region, are used for controlling the drift electric field of the substrate 10, and the two N-type doped regions, the first collection region CLO1 and the second collection region CLO2, are used for collecting photo-generated charges. The current-assisted photoelectric demodulator controls the VMOD1 and the VMOD2 to generate a drift electric field of the substrate 10, so that photo-generated electrons generate directional movement and have high modulation contrast.

In the present embodiment, the first capacitor C1 and the second capacitor C2 are used to provide a longer exposure time.

In this embodiment, the first electrode and the second electrode receive a control signal, the control signal is an input voltage, and when there is a voltage difference between the input voltage value received by the first electrode and the input voltage value received by the second electrode, an electric field is formed between the first acceleration region V1 and the second acceleration region V3 so that the charges accumulated in the photodiode PD are transferred to the first collection region CLO1 or the second collection region CLO2 for storage.

Further, with continued reference to fig. 2, the deep trench isolation structure 103 is used to isolate the active regions of adjacent pixel cells, which are disposed in the second region 102 of the substrate 10 around the periphery of the pixel cells. Specifically, the deep trench isolation structures 103 are formed in the P-type epitaxial layer, wherein one deep trench isolation structure 103 is formed at a side of the first collection region CLO1 away from the photodiode PD, and the other deep trench isolation structure 103 is formed at a side of the second collection region CLO2 away from the photodiode PD. The deep trench isolation structure 103(DTI) in the pixel serves to isolate the active region between pixels, which can suppress photons injected from adjacent pixels and suppress the generation of dark current and reduce crosstalk between pixels.

Further, referring to fig. 2, the light shielding layer 30 is disposed on the upper surfaces of the first voltage signal output module 201 and the second voltage signal output module 202 for blocking light from irradiating the region except the photodiode PD and shielding electrical interference.

In this embodiment, since the pixel unit includes the photodiode PD as a part for receiving light irradiation to obtain optical information and several active circuits, other active circuits such as the first voltage signal output module 201 and the second voltage signal output module 202 do not require light irradiation, and the parameter performance of the active transistor may be changed if the other active circuits are irradiated with light, so as to cause circuit failure. Therefore, after all processes are completed on the layout, the invention covers a light shielding layer 30 on all active transistor areas. It not only has the function of shielding and reflecting light, but also has the function of shielding and preventing electric interference after being grounded. The material of the light-shielding layer 30 in this embodiment is metal.

Further, a microlens 40 for condensing light to be irradiated onto a photosensitive region of the photodetector 20 is disposed on an upper surface of the pixel unit. In this embodiment, in order to further increase the fill factor FF (the ratio of the cross-sectional area of the photosensitive region to the pixel area), the peripheral blocked light is collected on the photosensitive region of the photodiode PD by the light-collecting effect of the microlens 40.

The operation of the present embodiment will be described with reference to fig. 2 to 5.

By irradiating light of a set frequency onto the photosensitive region of the photodiode PD to generate electron-hole pairs, which will be separated upon application of a voltage across the first transfer transistor VMOD1 and/or the second transfer transistor VMOD2, the photogenerated holes form a hole current with the majority carrier holes and start to move towards the first/second P-doped region with the lowest voltage, the electrons accelerate in the opposite direction and due to the built-in barrier of the substrate 10, are selected into the detector node first/second collection regions CLO 1/CLO 2. That is, when the voltage on the first transfer transistor VMOD 1-the voltage on the second transfer transistor VMOD2 >0, the photo-generated electrons are guided by the electric field to be transferred to the first collection region CLO1, and vice versa to be transferred to the second collection region CLO 2. Based on the two-phase/four-phase method, the complementary phase information can be obtained by the first collection region CLO1 and the second collection region CLO2 by strictly controlling the on or off of the first transfer transistor VMOD1 and the second transfer transistor VMOD 2.

The specific process is as follows: first, the first collection region CLO1 and the second collection region CLO2 are reset by turning on the first reset transistor RST1 and the second reset transistor RST2 before exposure, residual charges within the photodiode PD are drained so as to satisfy a condition of complete depletion, and photo-generated charges are not generated when no modulated light is incident on the photodiode PD.

Then, the first measurement is carried out, the modulated light emitting source is turned on to send modulated light, the control unit controls the pixel driving unit to send a control signal to the first transmission switch, the phase of the control signal is the same as that of the modulated light, the control signal sent to the second transmission switch is set to be complementary with that of the control signal sent to the first transmission switch, namely, the phase of the control signal is shifted by 180 degrees relative to the modulated light, the modulated light is sent to an object to be measured, if the distance of the object to be measured is 0 meter, all photo-generated electrons enter the first collecting area CLO1, however, if the object to be measured has a certain distance, because the propagation of the light needs a certain time, the reflected light is necessarily delayed when irradiating the sensor. When the reflected light irradiates the photosensitive region of the photodiode PD, if the voltage signal of the first transfer transistor VMOD1 is greater than the voltage signal of the second transfer transistor VMOD2, the photo-generated electrons enter the first collecting region CLO1, and if the voltage signal of the second transfer transistor VMOD2 is greater than the voltage signal of the first transfer transistor VMOD1, the photo-generated electrons enter the second collecting region CLO2, and the electron quantities in the first collecting region CLO1 and the second collecting region CLO2 are all the electron quantities generated by the primary light pulse, which is the complementary relationship between the first collecting region CLO1 and the second collecting region CLO 2.

Referring to fig. 4, Q0 is the charge amount entering the first collection area CLO1 when the voltage signal applied to the first transfer crystal VMOD1 is shifted by 0 ° with respect to the modulated light, and Q180 is the charge amount entering the second collection area CLO2 when the voltage signal applied to the second transfer crystal VMOD2 is shifted by 180 ° with respect to the modulated light, and the charge amount can be removed by the capacitor to calculate the voltage. Therefore, the phase 0 ° photo-generated voltage signal read out in the first integration phase is PS0, and the phase 180 ° photo-generated voltage signal read out in the second integration phase is PS 1.

When a two-tap two-phase method is adopted for measurement, according to the formula:

calculating the time of flight of the modulated light, wherein T_onFor modulating light during a period T_pluseThe time when the internal level is high.

Then according to the formula:

In the second measurement, the voltage signal applied to the first transfer crystal VMOD1 is shifted 90 ° relative to the modulated light, the voltage signal applied to the second transfer crystal VMOD2 is shifted 270 ° relative to the modulated light, and accordingly the charge Q90 of the first collection area CLO1 and the charge Q180 of the second collection area CLO2 are obtained, and finally the voltage signals in the first collection area CLO1 and the second collection area CLO2 are read out through the reading circuit.

Therefore, in the first integration stage, after the pixel unit receives the reflected light reflected by the object to be measured after receiving the modulated light, the voltage signal PS0 when the phase of the reflected light is 0 ° output by the first voltage signal output module 201 is obtained, and the voltage signal output by the second voltage signal output module 202 is obtained as the voltage signal PS1 when the phase of the reflected light is 180 °; in the second integration stage, after the pixel unit receives the reflected light again, the voltage output by the first voltage signal output module 201 is obtained as the voltage signal PS2 when the phase of the reflected light is 90 °, and the voltage output by the second voltage signal output module 202 is obtained as the voltage signal PS3 when the phase of the reflected light of the modulated light is 270 °.

When the two-tap four-phase method is adopted for measurement, according to the formula:calculating the time of flight of the modulated light, wherein T_tofFor modulating the optical round-trip time, T_pluseThe period of the modulated light.

Then according to the formula:

Example three:

referring to fig. 1 to 6, the back side illuminated image sensor chip includes: a pixel array 601, a pixel driving unit 602, a readout unit 603, and a control unit 604.

A pixel array 601 for outputting a voltage signal; a pixel driving unit 602, configured to output a control signal to control operation of pixel units in the pixel array 601, and connected to the pixel array 601; a readout unit 603 for reading and outputting voltage signals output by pixel units in the pixel array 601, which is connected to the pixel array 601; a control unit 604 which connects and controls the pixel array 601, the pixel driving unit 602, and the readout unit 603.

The current assisted photon demodulation type pixel unit includes: substrate 10, photodetector 20, light shielding layer 30, and microlens 40. The photodetector 20 includes: the photodiode PD, the first voltage signal output block 201, the second voltage signal output block 202, the first reset transistor RST1, the first capacitor C1, the first source follower transistor SF1, the second reset transistor RST2, the second capacitor C2, and the second source follower transistor SF 2.

In this embodiment, the pixel unit adopts a back-illuminated CMOS process, and the light-receiving surface of the structure of the back-illuminated current-assisted photon demodulation type pixel unit is located in the first region 101, which is also the "back surface" of the silicon wafer, compared to the case that all devices and wires manufactured by a semiconductor process are located on the "front surface" of the silicon wafer. In order to allow light to impinge on the PN junction of the photodiode PD from the back side, the silicon wafer back side of the photodiode PD of the pixel unit must be thinned to the extent of being "transparent" to light. Because the metal layer of the backlit pixel is on the opposite side of the illumination, no "walls" or "wells" are formed for incident light. The back-illuminated pixel cell structure maximizes the fill factor, allows flexible transistor positioning, and makes the light path independent of the metal layer.

Referring to fig. 2 and 3, the photodiode PD is disposed in the center of the first region 101 of the substrate 10, and the photodiode PD includes a photosensitive surface disposed in the center of the first region 101 of the substrate 10.

It should be noted that the pixel unit of the present application can be used to form a Video Graphics Array (VGA) with 640 × 480 pixels, or a quartevga with 320 × 240 pixels, or an SVGA with 240 × 160 pixels, or an array with 120 × 160 pixels, etc., and has wide application in the market. The pixel array may also be composed of pixel units of other specifications to implement different applications, and the specific specification is set according to the actual needs of the user, which is not limited in this way.

The operation of the present embodiment will be described with reference to fig. 2 to 6.

The main working principle of this embodiment is: by irradiating light of a set frequency onto the photosensitive region of the photodiode PD to generate electron-hole pairs, which will be separated upon application of a voltage across the first transfer transistor VMOD1 and/or the second transfer transistor VMOD2, the photogenerated holes form a hole current with the majority carrier holes and start to move towards the first/second P-doped region with the lowest voltage, the electrons accelerate in the opposite direction and due to the built-in barrier of the substrate 10, are selected into the detector node first/second collection regions CLO 1/CLO 2. That is, when the voltage on the first transfer transistor VMOD 1-the voltage on the second transfer transistor VMOD2 >0, the photo-generated electrons are guided by the electric field to be transferred to the first collection region CLO1, and vice versa to be transferred to the second collection region CLO 2. Based on the two-phase/four-phase method, the complementary phase information can be obtained by the first collection region CLO1 and the second collection region CLO2 by strictly controlling the on or off of the first transfer transistor VMOD1 and the second transfer transistor VMOD 2.

According to the formula:

Then according to the formula:and calculating to obtain the image Depth information Depth of the object to be measured.

The readout unit 603 transmits the readout voltage signals PS0, PS1, PS2 and PS3 to the CPU/FPGA through the parallel port.

The operation unit of the CPU/FPGA is according to the formula:

The operation unit of the CPU/FPGA is further according to the formula:

Example four:

the application provides an imaging system, which comprises the image sensing chip and a laser transmitter.

The imaging system of the embodiment can be applied to the fields of 3D imaging, gesture recognition, entertainment, robots, safety systems, automobiles and the like.

Example five:

referring to fig. 7, the present application provides a method for forming a pixel unit, the method comprising:

step S701: providing a substrate 10;

step S702: a photodetector 20 is provided, which includes: a photodiode PD disposed within the substrate 10 to accumulate charge in response to reflected light incident on the photodiode PD. The first voltage signal output module 201 is configured to convert the charges accumulated in the photodiode PD into a voltage signal, and includes a first switch, a control terminal of the first switch receives a control signal, an input terminal of the first switch is connected to the photodiode PD, and an output terminal of the first switch outputs the first voltage signal when the control terminal of the first switch receives the control signal. A second voltage signal output module 202, configured to convert the charges accumulated in the photodiode PD into a voltage signal, where the second voltage signal output module includes a second switch, a control terminal of the second switch receives the control signal, an input terminal of the second switch is connected to the photodiode PD, and an output terminal of the second switch outputs a second voltage signal when the control terminal of the second switch receives the control signal;

step S703: setting the phase of a control signal sent to the first switch to be the same as that of the modulated light, setting the phase of a control signal sent to the second switch to be complementary with that of the control signal sent to the first switch, and transmitting the modulated light to an object to be measured;

step S704: when the two-tap two-phase method is used for measurement, after the photodiode PD of the pixel unit receives the reflected light reflected by the object to be measured, the first voltage signal PS0 output by the first voltage signal output module 201 when the phase of the reflected light is 0 ° is obtained as the voltage output by the first voltage signal output module, and the second voltage signal output module when the phase of the reflected light is 180 ° is obtained as the voltage output by the second voltage signal output module202 output a second voltage signal PS 1; according to the formula:

calculating the time of flight of the modulated light, wherein T_onA time during which the level is high in one period for modulating light;

step S705: when the two-tap four-phase method is adopted for measurement, after the photodiode PD of the pixel unit receives the reflected light again, the first voltage signal PS2 output by the first voltage signal output module 201 when the phase of the reflected light is 90 ° is obtained, and the second voltage signal PS3 output by the second voltage signal output module 202 when the phase of the reflected light of the modulated light is 270 ° is obtained; according to the formula:

In the pixel unit of the present embodiment, reference is made to the current-assisted photon demodulation pixel unit described in the second embodiment and the third embodiment, and thus, the description is not repeated.

Example six:

referring to fig. 8, a depth information measuring method includes:

step S801: providing a pixel array comprising a plurality of current assisted photon demodulation type pixel cells as described above;

step S802: setting a pixel driving unit, which is used for outputting a control signal to control the pixel units in the pixel array to work and is connected with the pixel array;

step S803: a readout unit is arranged, is used for reading and outputting voltage signals output by pixel units in the pixel array, and is connected with the pixel array;

step S804: a setting control unit which is connected with and controls the pixel array, the pixel driving unit and the readout unit;

step S805: turning on a modulated light emitting source to send modulated light, controlling a control signal sent to a first switch by a pixel driving unit to be the same as the phase of the modulated light by a control unit, setting the phase of the control signal sent to the first switch to be the same as the phase of the modulated light, setting the phase of the control signal sent to a second switch to be complementary with the phase of the control signal sent to the first switch, and sending the modulated light to an object to be measured;

step S806: when the two-tap two-phase method is used for measurement, after the photodiode PD of the pixel unit receives reflected light reflected by an object to be measured, the first voltage signal PS0 output by the first voltage signal output module 201 when the phase of the reflected light is 0 ° is obtained as the voltage output by the first voltage signal output module, and the second voltage signal PS1 output by the second voltage signal output module 202 when the phase of the reflected light is 180 ° is obtained as the voltage output by the second voltage signal output module; according to the formula:

step S807: when the two-tap four-phase method is adopted for measurement, after the photodiode PD of the pixel unit receives the reflected light again, the first voltage signal PS2 output by the first voltage signal output module 201 when the phase of the reflected light is 90 ° is obtained, and the second voltage signal PS3 output by the second voltage signal output module 202 when the phase of the reflected light of the modulated light is 270 ° is obtained; according to the formula:

The beneficial effect of this application lies in: the application arranges a first voltage signal output module and a second voltage signal output module in a current-assisted photon demodulation type pixel unit structure, the first voltage signal output module and the second voltage signal output module can convert charges accumulated by a photoelectric detector responding to reflected light into voltage signals after receiving control signals, and then the flight time of modulated light can be calculated by arranging the phase relation between a first switch of the first voltage signal output module and a second switch of the second voltage signal output module and the modulated light, acquiring the voltage signals output by the first voltage signal output module and the second voltage signal output module under different phases after receiving the reflected light, so that the reaction speed of the pixel unit can be improved, different distances can be measured, the measurement precision is higher, and the requirements of high-precision industries in the fields of safety detection and industrial control are met, the application range of the product is wider, and the pixel structure generates a drift electric field through the potential difference of the two P + type doped regions to control the transfer position of photo-generated charges, so that the pixel structure has good sensitivity and DC modulation contrast close to 100%, and the pixel structure is not a surface device, and the modulation electric field in the measuring device is not limited on the surface of the detector by adopting a back-illuminated CMOS process, so that the pixel structure has higher responsivity and a higher modulation band.

Those skilled in the art will appreciate that all or part of the steps of the various methods in the above embodiments may be implemented by instructions associated with hardware via a program, which may be stored in a computer-readable storage medium, and the storage medium may include: read-only memory, random access memory, magnetic or optical disk, and the like.

The foregoing is a more detailed description of the present application in connection with specific embodiments thereof, and it is not intended that the present application be limited to the specific embodiments thereof. It will be apparent to those skilled in the art from this disclosure that many more simple derivations or substitutions can be made without departing from the inventive concepts herein.

Claims

1. A current assisted photon demodulation type pixel cell, comprising:

a substrate;

a photodetector, comprising:

a photodiode disposed within the substrate to accumulate charge in response to reflected light incident on the photodetector;

the first voltage signal output module is used for converting the charges accumulated on the photodiode into a voltage signal and comprises a first switch, wherein a control end of the first switch receives a control signal, an input end of the first switch is connected with the photodiode, and an output end of the first switch outputs a first voltage signal when the control end of the first switch receives the control signal; and

the second voltage signal output module is used for converting the charges accumulated on the photodiode into a voltage signal and comprises a second switch, wherein a control end of the second switch receives a control signal, an input end of the second switch is connected with the photodiode, and an output end of the second switch outputs a second voltage signal when the control end of the second switch receives the control signal;

when the two-tap two-phase method is adopted for measurement, after the photodiode of the pixel unit receives reflected light reflected by the object to be measured, the voltage output by the first voltage signal module is obtained as a first voltage signal PS0 output by the first voltage signal output module when the phase of the reflected light is 0 degrees, and the voltage output by the second voltage signal output module is obtained as a second voltage signal PS1 output by the second voltage signal output module when the phase of the reflected light is 180 degrees;

according to the formula:

calculating a time of flight of the modulated light, wherein T_onThe time during which the level of the modulated light is high in one period.

2. The pixel cell of claim 1, wherein when the two-tap four-phase method is used for measurement, after the photodiode of the pixel cell receives the reflected light again, the first voltage signal output by the first voltage signal output module is obtained as the first voltage signal PS2 output by the first voltage signal output module when the phase of the reflected light is 90 °, and the second voltage signal output by the second voltage signal output module is obtained as the second voltage signal PS3 output by the second voltage signal output module when the phase of the reflected light of the modulated light is 270 °;

according to the formula:

calculating a time of flight of the modulated light, wherein T_tofFor said modulated light round trip time, T_pluseIs the period of the modulated light.

3. The current assisted photon demodulation type pixel cell of claim 1,

the substrate comprises a first region and a second region;

the photodiode comprises a light-sensitive surface, and the light-sensitive surface is arranged at the central position of the first area of the substrate;

the first switch of the first voltage signal output module includes: a first electrode for receiving the control signal, connected to a control terminal of the first switch; a first acceleration region for accelerating a flow of charges in the substrate upon receiving the control signal, disposed in the second region of the substrate and disposed at one side of the photodiode, which is connected to an input terminal of the first switch; the first collecting region is used for receiving and storing the charges accumulated by the photodiode transmitted by the first accelerating region and is arranged on one side of the first accelerating region, which is far away from the photodiode; a third electrode for outputting the charge accumulated by the photodiode, which is connected to the first collecting region and the output terminal of the first switch;

the second switch of the second voltage signal output module includes: a second electrode for receiving the control signal, connected to a control terminal of the second switch; a second acceleration region for accelerating the flow of charges in the substrate upon receiving the control signal, which is disposed in a second region of the substrate and symmetrically to the first acceleration region disposed at one side of the photodiode, which is connected to the input terminal of the second switch; the second collecting region is used for receiving and storing the charges accumulated by the photodiode transmitted by the second accelerating region, and the second collecting region is arranged on one side of the second accelerating region far away from the photodiode in a symmetrical mode with the first collecting region; a fourth electrode for outputting the charge accumulated by the photodiode, which is connected to the second collecting region and the output terminal of the second switch;

when a voltage difference exists between an input voltage value received by the first electrode and an input voltage value received by the second electrode, an electric field is formed between the first acceleration region and the second acceleration region so that charges accumulated by the photodiode are transferred to the first collection region or the second collection region for storage.

4. The current assisted photon demodulation type pixel cell of claim 3, wherein said pixel cell further comprises:

a first reset transistor for resetting the charge stored in the first collection region, the first reset transistor being connected to the third electrode;

a first source follower transistor, the control end of which is connected with the first collecting area, the input end of which is connected with the first reset transistor, and the output end of which outputs the first voltage signal;

a second reset transistor for resetting the charges stored in the second collecting region, connected to the fourth electrode; and

and the control end of the second source electrode following transistor is connected with the second collecting area, the input end of the second source electrode following transistor is connected with the second reset transistor, and the output end of the second source electrode following transistor outputs the second voltage signal.

5. The current assisted photon demodulation type pixel cell of claim 1 further comprising a deep trench isolation structure for isolating active regions of adjacent said pixel cells disposed in the substrate around a periphery of said pixel cell.

6. The pixel cell of claim 1, further comprising a microlens for condensing light onto the photo-sensing surface of the photodiode, disposed above the photo-sensing surface of the photodiode.

7. The current assisted photon demodulation pixel cell of claim 1 further comprising a light blocking layer disposed over a peripheral location of the first region of the substrate.

8. A back-illuminated image sensor chip, comprising:

a pixel array comprising a plurality of current assisted photon demodulation type pixel cells according to claim 1;

the pixel driving unit is used for outputting the control signal to control the pixel units in the pixel array to work and is connected with the pixel array;

the readout unit is used for reading and outputting voltage signals output by pixel units in the pixel array and is connected with the pixel array;

a control unit which connects and controls the pixel array, the pixel driving unit, and the readout unit;

the control unit controls the phase of a control signal sent to the first switch by the pixel driving unit to be the same as that of the modulated light, sets the phase of a control signal sent to the second switch to be complementary with that of a control signal sent to the first switch, and transmits the modulated light to an object to be measured, wherein the time length of modulation after each transmission is T_pulseWhen a two-tap two-phase method is used for measurement, after the pixel unit receives reflected light reflected by the object to be measured, a first voltage signal PS0 output by the first voltage signal output module when the voltage output by the first voltage signal output module is at a phase of 0 ° of the reflected light is obtained, and a second voltage signal PS1 output by the second voltage signal output module when the voltage output by the second voltage signal output module is at a phase of 180 ° of the reflected light is obtained;

according to the formula:

9. The back-illuminated image sensor chip of claim 8, wherein when the two-tap four-phase method is used for measurement, after the photodiode of the pixel unit receives the reflected light again, the first voltage signal PS2 output by the first voltage signal output module when the voltage output by the first voltage signal output module is 90 ° in phase of the reflected light is obtained, and the second voltage signal PS3 output by the second voltage signal output module when the voltage output by the second voltage signal output module is 270 ° in phase of the reflected light of the modulated light is obtained;

according to the formula:calculating a time of flight of the modulated light, wherein T_tofFor said modulated light round trip time, T_pluseIs the period of the modulated light.

10. The back-illuminated image sensor chip of claim 8,

the substrate comprises a first region and a second region;

11. The back-illuminated image sensor chip of claim 10, wherein the pixel cell further comprises:

12. The back-illuminated image sensor chip of claim 8, wherein the pixel cells further comprise deep trench isolation structures for isolating active regions of adjacent ones of the pixel cells disposed in the substrate around a periphery of the pixel cells.

13. The back-illuminated image sensor chip of claim 8, wherein the pixel unit further comprises a microlens for condensing light onto the photosensitive surface of the photodiode, which is disposed above the photosensitive surface of the photodiode.

14. The back-illuminated image sensor chip of claim 8, wherein the pixel unit further comprises a light-shielding layer disposed over a peripheral position of the first region of the substrate.

15. An imaging system comprising a back-illuminated image sensor chip as claimed in any one of claims 8 to 14 and a laser emitter.