Pixel unit, TOF image sensor including the pixel unit, and imaging device
By symmetrically setting the voltage signal output module and microlens translation in the TOF image sensor, the problem of charge position deviation of pixel units is solved, ensuring the consistency of charge collection, and improving the accuracy of depth information measurement and measurement accuracy.
Patent Information
- Application Number
- CN201910996389.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2019-10-18
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2039-10-18
AI Technical Summary
In the TOF image sensor, the position of the charge generated by the pixel unit deviates from the center of the photosensitive surface, resulting in different charges collected at the same position at different phases, affecting the accuracy of depth information measurement, especially at a large incident angle, it is difficult to ensure that light is projected to The central position of the photosensitive surface leads to a decrease in measurement accuracy.
By setting the first voltage signal output module and the second voltage signal output module in the pixel unit symmetrically to the center of the pixel array, and setting the distance through the translation of the microlens, the photosensitive surface can obtain the maximum amount of light, ensuring that the charge is transferred from the photosensitive surface to the The time of the two modules is consistent, so as to ensure that the charges collected at different phases at the same position are the same.
It is achieved to ensure that the same number of electrons get the same charges under different taps under extremely short photon integration time, improving the accuracy of depth information measurement and phase measurement of the TOF image sensor.
Smart Images
Figure CN110729320B_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the TOF field, and in particular to a TOF image sensor and an imaging device having a pixel unit and including the pixel unit. Background Art
[0002] TOF is the abbreviation of time offlight. The working principle of TOF is that the transmitting module actively emits near-infrared light, which is reflected or scattered by an object during transmission, and then the reflected or scattered light is received by the TOF image sensor. The distance information of the measured object is obtained by calculating the phase difference or time difference between the emitted and received light.
[0003] The main working process of the TOF image sensor is as follows: First, the microlens gathers the light reflected and scattered by the measured object, and the light is transmitted through the empty area in the middle of the multilayer electrode, and the light will be projected onto the clamped photodiode. At this time, the optical signal is converted into an electrical signal. After processing, the required image is obtained.
[0004] Traditional pixels are composed of a clamped photodiode PPD, a transmission tube TG, a photocharge storage area FD, a source follower SF, a gate tube SEL, and a reset tube RST. The brief working principle is as follows: First, during the reset period of the pixel, the reset tube RST and the transmission tube TG are turned on at the same time, so that the electrons inside the N buried layer are depleted. At this time, the N buried layer will be in an empty well state, and the floating diffusion area FD will also be at a high potential.
[0005] At this time, the potential of the floating diffusion node is output to the bus as the first signal of the correlated double sampling CDS through the source follower SF and the gate tube SEL. Secondly, after the exposure time is completed, the transmission tube TG is turned on for the second time, so that the charge accumulated under the suspended inversion layer of the clamping photodiode PPD is transferred to the N-type photocharge storage area FD, and is maintained on the FD capacitor after TX is turned off, forming a voltage V FD . V FD The output voltage of the source follower SF is controlled by the gate tube SEL and transferred to the bus as the second signal of the correlated double sampling CDS. Finally, the input signals of the two correlated double sampling CDS are subtracted by the subsequent circuit to obtain the analog value representing the corresponding optical signal, which is converted into a digital value by the subsequent ADC and processed to obtain the required image.
[0006] Phase-type TOF uses a two-tap four-phase method or a two-tap two-phase method to collect charges and control the phase relationship between the infrared laser signal and the transmission tube TG. If the two-tap two-phase method is used, the demodulated signal FD1 in the first integration stage is in phase with the frequency modulation signal, that is, the stored charge with a phase of 0°, and FD2 collects and reads out the stored charge with a phase of 180°. The phase 0° photogenerated charge signal PS0 and the 180° photogenerated charge signal PS1 read out in this integration stage have the following ranging formula: T on It is the time that the FM signal is high within one cycle of the FM signal. If the two-tap four-phase method is used, the control phases are 0°, 90°, 180°, and 270°. Through two measurements, the accumulated charge of the four phases is calculated, the phase shift is calculated, and then the photon flight time is converted to obtain the depth value.
[0007] Because the imaging area has a certain area, the light must pass through the external lens group to converge and adjust before entering the single pixel area. When the pixel is at the center of the entire imaging area, the light is almost vertically incident. Figure 1 When a pixel is at the edge of the entire imaging area, the angle at which light is projected onto the pixel is large. Imaging sensors generally create a microlens above a single pixel to converge light, and the amount of light on the pixel can be increased through the microlens. For microlenses at the edge, the position where the charge is generated deviates from the center of the photosensitive surface. The paths of charge transfer for the two taps are different, and the same amount of charge at the same position may result in different amounts of charge collected in the two phases.
[0008] The position of the microlens relative to a single pixel can be translated laterally to correct the position of the light projected onto the photosensitive surface. However, for 3D depth sensors, the photon integration time is extremely short and the amount of light on the photosensitive surface is extremely low. If the incident angle is large, it is difficult to ensure that the light is projected onto the center of the photosensitive surface at the same time, so the accuracy of the depth information measurement cannot be guaranteed. Summary of the invention
[0009] The present application provides a TOF image sensor having a pixel unit, including the pixel unit, and an imaging device, which can solve the problem that the position of charge generation in the current pixel unit deviates from the center of the photosensitive surface, resulting in different amounts of charge collected at the same position in different phases, thereby affecting the accuracy of depth information measurement.
[0010] According to the first aspect of the present application, the present application provides a pixel unit, which forms a pixel array, comprising: a semiconductor substrate; a photosensitive surface arranged in the semiconductor substrate; a superimposed electrode group, which is arranged on the side of the photosensitive surface where light is incident, and includes at least two layers of electrodes; a microlens, which corresponds to the photosensitive surface and is arranged on the side of the superimposed electrode group away from the photosensitive surface; a first voltage signal output module, which is arranged on one side of the photosensitive surface; and a second voltage signal output module, which is symmetrical to the first voltage output module and is arranged on the other side of the photosensitive surface, wherein the microlens is offset by a set distance so that the photosensitive surface obtains a maximum amount of light, and the first voltage signal output module and the second voltage signal output module are symmetrically arranged relative to the center of the pixel array so that the time when the charge accumulated on the photosensitive surface is transferred from the photosensitive surface to the first voltage signal output module is consistent with the time when the charge is transferred from the photosensitive surface to the second voltage signal output module.
[0011] Preferably, the microlens offset setting distance is determined by simulation, wherein the microlens offset is translated along a line connecting the center of the pixel array and the center of the pixel unit.
[0012] Preferably, the first voltage signal output module or the second voltage signal output module includes: a transfer transistor, which is arranged on one side of the photosensitive surface; a photocharge storage area, which is arranged in the substrate and is used to store the charge transferred from the transfer transistor; a reset transistor, which is arranged in the semiconductor substrate and coupled to the photosensitive surface, and is used to reset the charge stored in the photocharge storage area; a source follower transistor, whose control end is connected to the photocharge storage area, and whose input end is connected to the reset transistor; and a selection transistor, whose input end is connected to the output end of the source follower transistor, and the output end of the selection transistor outputs a voltage signal; and a deep trench isolation area, which is arranged on the side of the photocharge storage area away from the photodiode.
[0013] Preferably, at least one layer of electrodes in the stacked electrode group extends toward the center of the photosensitive surface and bends toward the substrate to guide light into the semiconductor substrate.
[0014] Preferably, the electrode closest to the microlens in the stacked electrode group extends toward the center of the photosensitive surface and bends toward the substrate.
[0015] Preferably, at least one electrode layer in the stacked electrode group is transparent to infrared rays and extends to the transparent region to cover more than 90% of the area of the transparent region.
[0016] According to the second aspect of the present application, the present application provides a TOF image sensor, which is applied to an imaging device, comprising: the pixel unit as described above, wherein the pixel units are evenly distributed around the optical axis of the imaging device to form a pixel array including at least one layer of annular structure.
[0017] Preferably, a pixel unit is disposed at the center of the pixel array.
[0018] According to a third aspect of the present application, the present application provides an imaging device, which includes the TOF image sensor as described above.
[0019] The beneficial effects of the present application are as follows: by setting the first voltage signal module and the second signal voltage module symmetrically about the center of the pixel array, and by translating the microlens to set the distance so that the photosensitive surface obtains the maximum amount of light, the time when the charge is transferred to the first voltage signal module and the second voltage signal module can be made consistent, and the charges collected at the same position on the photosensitive surface in different phases can be ensured to be the same, thereby ensuring the accuracy of depth information measurement and improving the measurement accuracy of the TOF image sensor. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Figure 1 is a schematic diagram of the charge transfer path of edge pixels in a conventional TOF image sensor;
[0021] Figure 2 is a schematic structural diagram of a pixel unit of the present application;
[0022] Figure 3 is a schematic diagram of the electrode structure of the pixel unit of the present application;
[0023] Figure 4 is a schematic diagram of a first embodiment of a TOF image sensor of the present application;
[0024] Figure 5 is a schematic diagram of a second embodiment of a TOF image sensor of the present application;
[0025] Figure 6 is a schematic diagram of a third embodiment of a TOF image sensor of the present application.
[0026] Explanation of the figure symbols: semiconductor substrate 101 photosensitive surface PPD superimposed electrode group ME microlens ML first voltage signal output module 102 first transfer transistor TR1 first photocharge storage area FD1 first reset transistor RST1 first source follower transistor SF1 first selection transistor SEL1 first deep trench isolation area DT1 second voltage signal output module 103 second transfer transistor TG2 second photocharge storage area FD2 second reset transistor RST2 second source follower transistor SF2 second selection transistor SEL2 second deep trench isolation area DT2 anti-reflection film 104. DETAILED DESCRIPTION
[0027] The present application is further described in detail below through specific implementation methods in conjunction with the accompanying drawings.
[0028] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.
[0029] See also Figure 2 The pixel unit of the present application includes: a semiconductor substrate 101; a photosensitive surface PPD arranged in the semiconductor substrate 101; an overlay electrode group ME, which is arranged on the side of the photosensitive surface PPD where light is incident, and includes at least two layers of electrodes; a microlens ML, which corresponds to the photosensitive surface PPD and is arranged on the side of the overlay electrode group ME away from the photosensitive surface PPD; a first voltage signal output module 102, which is arranged on one side of the photosensitive surface PPD; and a second voltage signal output module 103, which is symmetrical to the first voltage output module and is arranged on the other side of the photosensitive surface PPD; wherein the microlens ML is offset by a set distance so that the photosensitive surface PPD obtains a maximum amount of light, and the first voltage signal output module 103 and the second voltage signal output module 104 are symmetrically arranged relative to the center of the pixel array, so that the time when the charge accumulated on the photosensitive surface PPD is transferred from the photosensitive surface PPD to the first voltage signal output module 102 is consistent with the time when the charge is transferred from the photosensitive surface PPD to the second voltage signal output module 103.
[0030] The semiconductor substrate 101 is used to form a device structure or a chip circuit. The semiconductor substrate 101 may be a semiconductor base, including a silicon substrate, a silicon germanium substrate, a silicon carbide substrate, a silicon on insulator (SOI) substrate, a germanium on insulator (GOI) substrate, a glass substrate, or a III-V compound substrate (such as silicon nitride or gallium arsenide, etc.). The semiconductor substrate 101 may also be a bulk substrate, i.e., a silicon substrate, a silicon germanium substrate, or a silicon carbide substrate. In other embodiments, the semiconductor substrate 101 may also be a silicon on insulator substrate or a germanium on insulator substrate.
[0031] The photosensitive surface PPD is arranged in the semiconductor substrate 101 and is formed by an ion implantation process. Moreover, 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 photosensitive surface PPD.
[0032] In this embodiment, the photosensitive surface PPD includes a clamped photodiode. The clamped photodiode is doped with N-type ions, and the N-type ions include phosphorus ions, arsenic ions or antimony ions.
[0033] Furthermore, the photosensitive surface PPD of this embodiment has an additional thin P+ layer (not shown) on the surface of the traditional photosensitive surface PPD. The N buried layer of the charge collection layer is isolated from the top surface of Si / SiO2 through the top P+ layer, thereby covering up the traps that are the main cause of the dark current. This makes the photosensitive surface PPD have a smaller dark current than traditional photodiodes on the one hand, and on the other hand, it can form a fully depleted accumulation area, thereby overcoming the problem of output image lag.
[0034] Please continue reading Figure 2 The first voltage signal output module 102 includes: a first transfer transistor TG1, a first photocharge storage area FD1, a first reset transistor RST1, a first source follower transistor SF1, a first gate transistor SEL1 and a first deep trench isolation area DT1.
[0035] The first transfer transistor TG1 outputs a first voltage signal when receiving a control signal; the first photocharge storage area FD1 is arranged in the semiconductor substrate 101 and on the side of the first transfer transistor TG1 away from the photosensitive surface PPD, wherein the first transfer transistor TG1 transfers the charge accumulated in the photosensitive surface PPD to the first photocharge storage area FD1 for storage; the first reset transistor RST1 is arranged in the semiconductor substrate 101 and coupled to the photosensitive surface PPD, and is used to reset the charge stored in the first photocharge storage area FD1; the control end of the first source follower transistor SF1 is connected to the first photocharge storage area FD1, and its input end is connected to the first reset transistor RST1; the input end of the first selection transistor SEL1 is connected to the output end of the first source follower transistor SF1, and the output end of the first selection transistor SEL1 outputs a voltage signal; the first deep trench isolation area DT1 is arranged on the side of the first photocharge storage area FD1 away from the photodiode.
[0036] The second voltage signal output module 103 includes: a second transfer transistor TG2, a second photocharge storage area FD2, a second reset transistor RST2, a second source follower transistor SF2, a second gate transistor SEL2 and a second deep trench isolation area DT2.
[0037] a second transfer transistor TG2 arranged symmetrically to the first transfer transistor, the second transfer transistor TG2 outputting a second voltage signal when receiving a control signal; a second photocharge storage area FD2 arranged in the semiconductor substrate 101 and arranged on a side of the second transfer transistor TG2 away from the photosensitive surface PPD, wherein the second transfer transistor TG2 transfers the second voltage signal of the photosensitive surface PPD to the second photocharge storage area FD2 for storage; a second reset transistor RST2 arranged on the semiconductor substrate 101 and coupled to the photosensitive surface PPD, for resetting the charge stored in the second photocharge storage area FD2; a second source follower transistor SF2, a control end of which is connected to the second photocharge storage area FD2, and an input end of which is connected to the second reset transistor RST2; a second selection transistor SEL2, an input end of which is connected to the output end of the second source follower transistor SF2, and the output end of the second selection transistor SEL2 outputs a voltage signal; and a second deep trench isolation area DT2, which is symmetrical to the first deep trench isolation area DT1 and arranged on a side of the second photocharge storage area FD2 away from the photodiode.
[0038] At least one layer of electrodes in the stacked electrode group ME extends toward the center of the photosensitive surface PPD and bends toward the substrate to guide light into the semiconductor substrate 101 .
[0039] In this embodiment, the electrode on the side closest to the microlens ML in the stacked electrode group ME extends toward the center of the photosensitive surface PPD and bends toward the substrate.
[0040] It should be noted here that the material of the superimposed electrode group ME is a metal material containing more than 90% copper, and the superimposed electrode group ME is made into a curved structure through a special manufacturing process. Since the sharp-angle bend or right-angle bend structure is prone to discharge at the bend tip, and impurities are easily accumulated in this area, the metal layer is prone to structural fracture after long-term operation, and the additional parasitic capacitance at the corner will also affect the transmission of the signal. In order to avoid the above-mentioned negative effects, the curved structure generally adopts an obtuse bend or an arc bend structure.
[0041] In this embodiment, the electrode is bent at an angle greater than or equal to 30 degrees toward the semiconductor substrate 101. The bending angle can be set according to actual conditions and is not limited here.
[0042] The present application reduces the interference effect between electrode structures by setting and adjusting the structure of the superimposed electrode group ME, thereby reducing the lateral crosstalk caused by multiple reflections of light between the multi-layer electrode structures.
[0043] Furthermore, the light-clearing aperture formed by the electrode in the transparent region is smaller than the light-clearing aperture formed by any other electrode in the superimposed electrode layer.
[0044] Furthermore, at least one layer of electrodes in the stacked electrode group ME can transmit infrared rays and extend to the transparent region to cover more than 90% of the area of the transparent region.
[0045] In this embodiment, the electrodes that can transmit infrared rays are electrodes that are closest to the semiconductor substrate 101 in the stacked electrode group ME.
[0046] In this embodiment, the infrared-transmissive electrode is made of a polysilicon thin film.
[0047] In other embodiments, the infrared-transmissive electrode is made of an alloy material mainly including ITO (indium tin oxide).
[0048] The transparent electrode can be used to apply a gate control voltage to control the performance of the charge potential well, and can also be used as a patch to connect electrodes. The role of the transparent electrode is not limited here.
[0049] Furthermore, the pixel unit further includes an anti-reflection film 104, which is disposed above or below the microlens ML or in the substrate of the pixel unit. Figure 4 , the anti-reflection film 104 is disposed below the microlens ML.
[0050] In this embodiment, the thickness of the antireflection film 104 is a uniform preset thickness, and the preset thickness is obtained by the following formula for the pixels in the TOF image sensor: Wherein, e is the preset thickness, θ is the main light angle of the edge pixel, λ is a single near-infrared light wavelength, n is the medium refractive index, and k is 0 and a positive integer.
[0051] In this embodiment, the microlens ML of the pixel unit is translated relative to the photosensitive surface PPD of the pixel unit by a set distance along the line connecting the center of the pixel array and the center of the pixel unit so that the photosensitive surface PPD receives the maximum light. The set translation distance is obtained by pre-simulation, such as simulating the incident light angle of the light through optical simulation software such as zemax, lighttools, tracepro, etc., and then simulating the microlens ML to translate the set distance along the direction of the line connecting the center of the pixel array and the center of the pixel unit, and detecting the amount of light irradiated on the photosensitive surface PPD. When the amount of light on the photosensitive surface PPD reaches the maximum value, the translation distance of the microlens ML of the pixel unit is determined. Because the incident angles of the light of the pixel units on the same circumference are consistent, as long as the translation distance of the microlens of one of the pixel units on the circumference is determined, the translation distance of the microlenses on the same circumference can be determined.
[0052] Because the translation amount of the microlens ML of the TOF image sensor is based on the standard of ensuring the maximum amount of light on the photosensitive surface PPD, the amount of light on each pixel is guaranteed, so that there can be enough photogenerated electrons under a very short photon integration time to ensure that the TOF image sensor can work normally. In this way, it can be ensured that the same number of electrons with the same integration time can obtain the same amount of charge under different taps, thereby ensuring the accuracy of phase measurement and improving the working accuracy of the phase-type TOF image sensor.
[0053] See also Figures 4 to 6 There are two ways in which the pixel unit structure of the present application realizes that the time when the charge of the photosensitive surface PPD is transferred from the photosensitive surface PPD to the first transfer transistor is consistent with the time when the charge is transferred from the photosensitive surface PPD to the second transfer transistor:
[0054] The first is that the microlens ML is offset by a set distance so that when light is incident on the photosensitive surface PPD, the photosensitive surface can obtain the maximum amount of light, and the first voltage signal output module 102 and the second voltage signal output module 103 are centrally symmetrical relative to the center of the pixel array, that is, the optical axis of the imaging device.
[0055] Please continue reading Figure 4 and Figure 5 In this embodiment, the angle between the first voltage signal output module 102 and the second voltage signal output module 103 relative to the center of the photosensitive surface PPD of the pixel unit has a set angle, and the set angle can be 180 degrees, 90 degrees or 45 degrees. The set angle can be set according to actual needs and is not limited here.
[0056] Please continue reading Figure 6 , the second is: the microlens ML is offset by a set distance so that when the incident light is incident on the photosensitive surface PPD, the photosensitive surface can obtain the maximum amount of light, the photosensitive surface PPD is a centrally symmetrical structure, and the first voltage signal output module and the second voltage signal output module are symmetrically arranged about the center position of the photosensitive surface PPD. In this embodiment, the photosensitive surface PPD of the pixel unit is a regular octagonal structure. The first voltage signal output module 102 is arranged on one side of the photosensitive surface PPD of the pixel unit, that is, on the rectangle on the left side of the regular octagonal structure; the second voltage signal output module 103 is symmetrical to the first voltage signal output module 102 and is arranged on the other side of the photosensitive surface PPD of the pixel unit, that is, on the rectangle on the right side of the regular octagonal structure. Of course, the photosensitive surface PPD of the pixel unit can be other centrally symmetrical structures, which is not limited here.
[0057] Please continue reading Figures 4 to 6 The present application also proposes a TOF image sensor, which includes: the pixel units as above, wherein the pixel units are evenly distributed around the optical axis of the imaging device to form a pixel array including at least one layer of annular structure.
[0058] In this embodiment, a pixel unit as described above may also be disposed at the center of the pixel array.
[0059] The present application also proposes an imaging device, which includes the TOF image sensor as described above.
[0060] Combine the following Figures 1 to 6 Here we will explain the working principle of this application.
[0061] Because the photosensitive surface PPD of the pixel unit is symmetrically distributed on a circle centered on the optical axis of the imaging device, the distance from the pixels on the same circle to the optical axis is consistent. Also, since the external optical lens is generally a circular lens, the angle at which light is projected onto each pixel on a specific circle is consistent.
[0062] We adopt the method of translating the microlens ML toward the optical axis of the imaging device along the line connecting the center of the imaging device and the center of the pixel unit, and optically calculate the different projection angles corresponding to the pixel unit at different circumferences, so that the light received by the photosensitive surface PPD reaches the maximum amount of light, and the projection point of the light is still the center of symmetrically distributed photocharge storage areas, deep trench isolation areas, transmission tubes and other symmetrical structures, so that the transmission time of the photogenerated charge to the first transmission transistor TG1 and the second crystal transmission tube is consistent, and when the same amount of photogenerated charge is generated, the number of electrons collected by the two taps is also consistent.
[0063] When the phase-type TOF image sensor is working, the first reset transistor RST1, the second reset transistor RST2 and the first transfer transistor TG1 and the second transfer transistor are turned on to reset the first photocharge storage area FD1, the second photocharge storage area FD2 and the photosensitive surface PPD, and discharge the residual charge in the photosensitive surface PPD to meet the condition of complete exhaustion, and no photogenerated charge is generated when no modulated light signal is incident on the photosensitive surface PPD.
[0064] At the same time, the first selection transistor SEL1 and the second selection transistor SEL2 are turned on so that the reset value is read out by the correlated double sampling circuit. Then the first transfer transistor TG1, the second transfer transistor TG2, the first reset transistor RST1 and the second reset transistor RST2 are turned off, and the photosensitive surface PPD starts to accumulate charges. The first transfer transistor TG1 and the second transfer transistor TG2 are turned on by the phase relationship between the demodulated pulse signal and the frequency modulation signal, and the signal charges accumulated in the photosensitive surface PPD are transferred to the first photocharge storage area FD1 and the second photocharge storage area FD2. After the first transfer transistor TG1 and the second transfer transistor TG2 are turned off, the signal charges are read out by turning on the first selection transistor SEL1 and the second selection transistor SEL2.
[0065] When the first transfer transistor TG1 is turned on, the accumulated charge is transferred to the first photocharge storage area FD1; when the second transfer transistor TG2 is turned on, the accumulated charge is transferred to the second photocharge storage area FD2; then the first selection transistor SEL1 and the second selection transistor are turned on, and the correlated double sampling module reads out the signal.
[0066] When the two-tap four-phase method is used for depth measurement, the control signal sent to the first transmission transistor TG1 is set to have the same phase as the modulated light, and the control signal sent to the second transmission transistor TG2 is set to be complementary to the phase of the control signal sent to the first transmission transistor TG1, and the modulated light is emitted to the object to be measured. After the pixel unit receives the reflected light reflected by the object to be measured after receiving the modulated light, the voltage output by the first voltage signal module is obtained as the first voltage signal PS0 output by the first voltage signal output module 102 when the phase of the reflected light is 0°, and the voltage signal output by the second voltage signal module is obtained as the second voltage signal PS1 output by the second voltage signal output module 103 when the phase of the reflected light is 180°; after the photosensitive surface PPD of the pixel unit receives the reflected light again, the voltage output by the first voltage signal module is obtained as the first voltage signal PS2 output by the first voltage signal output module 102 when the phase of the reflected light is 90°, and the voltage output by the second voltage signal module is obtained as the second voltage signal PS3 output by the second voltage signal output module 103 when the phase of the reflected light of the modulated light is 270°.
[0067] According to the formula: The flight time of the modulated light is calculated, where T tof is the round trip time of the frequency modulated light, T pluse is the period of the modulated optical signal, MODCLK is the frequency of the FM signal, Depth is the measured distance, and c is the speed of light.
[0068] Finally, the depth information of the measured object is restored by measuring the depth information of different pixel points.
[0069] The beneficial effects of the present application are as follows: by setting the first voltage signal module and the second signal voltage module symmetrically about the center of the pixel array, and by translating the microlens to set the distance so that the photosensitive surface obtains the maximum amount of light, the time when the charge is transferred to the first voltage signal module and the second voltage signal module can be made consistent, and the charges collected at the same position on the photosensitive surface in different phases can be ensured to be the same, thereby ensuring the accuracy of depth information measurement and improving the measurement accuracy of the TOF image sensor.
[0070] Those skilled in the art will appreciate that all or part of the steps of the various methods in the above-mentioned implementations may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which may include: a read-only memory, a random access memory, a disk or an optical disk, etc.
[0071] The above contents are further detailed descriptions of the present application in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present application is limited to these descriptions. For ordinary technicians in the technical field to which the present application belongs, several simple deductions or substitutions can be made without departing from the inventive concept of the present application.
Claims
1. A pixel unit, wherein the pixel unit forms a pixel array, It is characterized in that It includes: Semiconductor substrate; A photosensitive surface disposed in the semiconductor substrate; A stacked electrode group, which is arranged on the light incident side of the photosensitive surface and comprises at least two layers of electrodes; A microlens corresponding to the photosensitive surface and arranged on a side of the superimposed electrode group away from the photosensitive surface side; A first voltage signal output module, which is arranged on one side of the photosensitive surface; and A second voltage signal output module, symmetrically arranged at the other side of the photosensitive surface of the first voltage signal output module; The microlens is offset by a set distance so that the photosensitive surface obtains a maximum amount of light, and the first voltage signal output module and the second voltage signal output module are symmetrically arranged relative to the center of the pixel array so that the time when the charge accumulated on the photosensitive surface is transferred from the photosensitive surface to the first voltage signal output module is consistent with the time when the charge is transferred from the photosensitive surface to the second voltage signal output module; At least one layer of electrodes in the stacked electrode group extends toward the center of the photosensitive surface and bends toward the substrate to guide light into the semiconductor substrate.
2. The pixel unit according to claim 1, It is characterized in that The microlens offset setting distance is determined by simulation, wherein the microlens offset is translated along a line connecting the center of the pixel array and the center of the pixel unit.
3. The pixel unit according to claim 1, It is characterized in that The first voltage signal output module or the second voltage signal output module includes: A transmission transistor, which is arranged on one side of the photosensitive surface; A photocharge storage region, which is arranged in the substrate and is used to store the charge transferred from the transfer transistor; A reset transistor, which is arranged in the semiconductor substrate and coupled to the photosensitive surface, and is used to reset the charge stored in the photocharge storage area; a source follower transistor, a control terminal of which is connected to the photocharge storage area, and an input terminal of which is connected to the reset transistor; and a gating transistor, whose input terminal is connected to the output terminal of the source follower transistor, and the output terminal of the gating transistor outputs a voltage signal; and A deep trench isolation region is arranged on a side of the photocharge storage region away from the photodiode.
4. The pixel unit according to claim 1, It is characterized in that The electrode closest to the microlens in the stacked electrode group extends toward the center of the photosensitive surface and bends toward the substrate.
5. The pixel unit according to claim 1, It is characterized in that At least one electrode layer in the stacked electrode group can transmit infrared rays and extend to the transparent region to cover more than 90% of the area of the transparent region.
6. A TOF image sensor, It is characterized in that It is applied to an imaging device, comprising: a pixel unit as claimed in any one of claims 1 to 5, wherein the pixel units are evenly distributed around the optical axis of the imaging device to form a pixel array including at least one layer of annular structure.
7. The TOF image sensor according to claim 6, It is characterized in that A pixel unit is disposed at the center of the pixel array.
8. An imaging device, It is characterized in that It includes the TOF image sensor as claimed in claim 6.