A detector pixel unit, image sensor

Abstract

The application provides a detector pixel unit, comprising: a photodiode for receiving detection light and generating electrons; a modulation grid for receiving the electrons with different phase delays; a floating diffusion node for storing the electrons received by the modulation grid; and a background light elimination grid for eliminating background light electrons in the pixel unit during non-operation of the modulation grid, the background light elimination grid storing the background light electrons.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection, in particular to a detector pixel unit and an image sensor. BACKGROUND

[0002] In the field of detection, more and more technologies are being developed. In order to ensure efficient and rapid detection of target information in application fields such as image or ranging, the efficiency of obtaining detection information is also attracting more and more attention. The light absorption rate of the pixel unit of the detector will directly affect the image quality obtained by the detector or the accuracy of the data in the ranging process. Generally, this type of detector contains a photoelectric conversion element that can convert incident light into an electrical signal. It can be roughly divided into two types: charge-coupled device (CCD) and complementary metal-oxide semiconductor (CMOS). Among them, CMOS converts charge into voltage per unit pixel and outputs signals from the signal line through switching operation. The photo-generated charge formed by at least one of the above two photoelectric conversion devices needs to be transmitted inside the device to the floating diffusion node for output. In recent years, with the progress of semiconductor technology, the miniaturization of ranging modules for measuring the distance to an object has made progress. Therefore, for example, it has been realized to install a ranging module in a mobile terminal such as a so-called smart phone, which is a small-sized information processing apparatus having a communication function. With the progress of technology, in the process of distance or depth information detection, the method frequently used is the time of flight (TOF) ranging method. The principle is to send a light pulse to the target object continuously, and then use a sensor to receive the light returned from the object. The distance of the target object is obtained by detecting the flight (round trip) time of the light pulse. In the TOF technology, the technology that directly measures the flight time of light is called DTOF (direct-TOF). The measurement technology that modulates the transmitted light signal periodically, measures the phase delay of the reflected light signal relative to the transmitted light signal, and then calculates the flight time from the phase delay is called ITOF (Indirect-TOF) technology. According to the difference in modulation and demodulation type, it can be divided into continuous wave (CW) modulation and demodulation mode and pulse modulation (PM) modulation and demodulation mode. Further, the ITOF scheme can also obtain a high-precision and high-sensitivity distance detection scheme, so the ITOF scheme has also obtained more widely application.

[0003] In order to obtain high efficiency measurement results and higher integration of chips, two taps or more are usually used to realize distance measurement, and distance information of a target object can be obtained according to a phase distance measurement algorithm, for example, a two-phase method, or a three-phase, four-phase method or even a 5-phase scheme can be used to obtain distance information. Here, a four-phase algorithm is taken as an example, but it is not limited to the four-phase algorithm.

[0004] When the modulation grid is not working, background light will generate charges, so the background light charges of the modulation grid need to be eliminated before working, which requires introducing a special device structure in the semiconductor device to eliminate the background light charges of the modulation grid. Usually, a special gate is designed at the top of one side of the semiconductor device, and a large voltage is applied to the gate when the modulation grid is not working, so that the background light charges can be transmitted out to the charge storage part through the transmission gate. In order to eliminate the background light charges of the modulation grid, a special transmission gate and charge storage part are needed, which makes the available area of the device smaller, the fill factor smaller, and the miniaturization of the device not useful. Therefore, it is a technical problem to be solved to design a device that can eliminate the background light when the modulation grid is not working and improve the fill factor of the device. SUMMARY

[0005] The purpose of the present application is to solve the technical problem of reducing the fill factor caused by eliminating the background light of the modulation grid when the modulation grid is not working in the existing detection unit.

[0006] To achieve the above purpose, the technical solutions adopted by the embodiments of the present application are as follows:

[0007] In a first aspect, the embodiments of the present application provide a detector pixel unit, comprising: a photodiode for receiving detection light and generating electrons; a modulation grid for receiving the electrons with different phase delays; a floating diffusion node for storing the electrons received by the modulation grid; and a background light elimination gate for eliminating background light electrons in the pixel unit during non-working period of the modulation grid, wherein the background light elimination gate stores the background light electrons.

[0008] Optionally, when the modulation grid is not working, the background light elimination gate absorbs the background light electrons in the detector pixel unit to the background light elimination gate and stores them.

[0009] Optionally, when the detector pixel unit is reset, the background light elimination gate releases the stored background light electrons of the detector pixel unit to the inside of the detector pixel unit.

[0010] Optionally, the reset of the detector pixel unit includes the reset of the background light electrons.

[0011] Optionally, the background light elimination gate is at a high level above 2.8V.

[0012] Optionally, the background light elimination gate is at a low level below 0V.

[0013] Optionally, the background light elimination gate is located in the middle of the detector pixel unit.

[0014] Optionally, the background light elimination gate is located at the top of one side of the detector pixel unit.

[0015] In a second aspect, the embodiments of the present application provide an image sensor comprising a receiving array of the detector pixel unit of the first aspect, and the receiving array comprises a plurality of the detector pixel unit of claim 1.

[0016] Optionally, when the modulation gate is not working, the background light elimination gate attracts and stores the background light electrons in the detector pixel unit.

[0017] The beneficial effects of the present application are:

[0018] A detector pixel unit comprises: a photodiode for receiving detection light and generating electrons; a modulation gate for receiving the electrons with different phase delays; a floating diffusion node for storing the electrons received by the modulation gate; and a background light elimination gate for eliminating background light in the pixel unit during non-working period of the modulation gate, and the background light elimination gate stores the background light electrons. In this way, the background light of the pixel unit can be eliminated while the fill factor of the pixel unit is improved, which is conducive to the miniaturization of the pixel unit. In actual use, a detector array comprising M*N pixel units is used for detection, and the miniaturization of each pixel unit is conducive to the miniaturization of the detector array and the miniaturization of the image sensor. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0020] Figure 1 A pixel unit structure schematic diagram provided by the embodiments of the present application;

[0021] Figure 2 A timing diagram of a pixel unit provided by the embodiments of the present application;

[0022] Figure 3A top view of a pixel unit provided for an embodiment of the present application;

[0023] Figure 4 A working timing diagram of a pixel unit provided for an embodiment of the present application;

[0024] Figure 5 A sectional view of a pixel unit provided for an embodiment of the present application;

[0025] Figure 6 An equivalent circuit diagram of a pixel unit provided for an embodiment of the present application;

[0026] Figure 7 A layout diagram of a pixel unit provided for an embodiment of the present application;

[0027] Figure 8 A layout diagram of a pixel unit provided for an embodiment of the present application;

[0028] Figures 9a-9d A charge movement schematic diagram of a pixel unit provided for an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0030] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative labor are within the scope of protection of the present application.

[0031] It should be noted that: similar reference numerals and letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0032] Figure 1 A pixel unit structure schematic diagram provided for an embodiment of the present application, wherein the pixel unit 10 comprises: a background light elimination gate (TD) 101 for eliminating the background light in the pixel unit during non-working period of the modulation gate, 1011 is a storage area of the background light electrons collected by the TD, PGA 103, PGB 102 is a modulation gate, MN 104 is used for collecting the photo-generated electrons modulated by the modulation gate, TX 105 is a transfer gate, and FD 106 is a floating diffusion node.

[0033] Figure 2 A timing diagram of a pixel unit provided by an embodiment of the present application, Figure 2 The working timing diagram of the pixel unit shown is applicable to Figure 1 The pixel unit shown. Figure 1 With Figure 2 The pixel unit shown is a two-tap pixel unit, which is only illustrative and not limited to two taps. As Figure 2 The RST signal is used to reset the pixel unit before the pixel unit works. In the RST reset stage, TD, TX, PGA, and PGB are all reset. After the RST reset ends, the integration period starts. In the integration period, PGA and PGB work, and TD is at a low level. In the two-tap pixel unit structure, for example, 0° and 90° share one tap, and 180° and 270° share one tap. The light source emits probe light, which is reflected by the object to be detected. PGA and PGB receive the probe light with two phase delays, for example, 0° and 180° in the four phases. As Figure 2 The integration working timing diagram shown transfers the photo-generated electrons in the 0° and 180° phases in the pixel unit to the photoelectric conversion module and outputs the electrons to the floating diffusion node FD 106 via the transfer gate TX. The working process of PGA and PGB in the 90° and 270° phases is similar to that of 0° and 180°, which will not be described here.

[0034] After the electrons reach the floating diffusion node FD 106, they are read out by the readout circuit for subsequent processing in the readout period as Figure 2 The PGA and PGB do not work in the readout period, the transfer gate TX is at a low level, and TD is at a high level. The background light electrons collected in the readout period are transmitted by TD and stored in 1011. In this way, the background light is eliminated by TD when the pixel unit works next time, avoiding the influence of residual charge of the background light on the ranging accuracy and improving the ranging accuracy. However, the pixel unit has a dedicated storage area 1011 to eliminate the influence of the background light, and TD is a transfer gate. Then the background light charge is read out from 1011. Because of the existence of 1011, the fill factor of the pixel unit is low, which is not conducive to the miniaturization of the pixel unit. Figure 1 Figure 2

[0035] Figure 3 A top view of a pixel unit provided by an embodiment of the present application is shown in FIG. 10. As Figure 3 TD is located in the middle of the pixel unit, Figure 3 ​​The TD of the pixel unit shown in the figure is not connected with a corresponding charge storage area. Figure 3 The TGA and TGB in the figure delay the reception of the electrons of the pixel unit in four phases and transmit the received electrons to the FDA and FDB.

[0036] Figure 4 Another working timing diagram of a pixel unit provided by the embodiment of the present application is shown in the figure. Figure 4 For Figure 3 The working timing diagram of the pixel unit shown in the figure is as follows: Figure 4 In the RST period, the Pixle_RST signal is at high level to reset the pixel unit, the TD is at low level, and the TGA and TGB are at high level. In the integration period, the Pixle_RST and TD are both at low level, the TGA and TGB delay the reception of the electrons of the pixel unit in four phases and transmit the received electrons to the FDA and FDB. In the readout period, the Pixle_RST is at low level, the TD is at high level (generally, 2.8V is used, but in order to improve the storage capacity under the gate of the TD, a level greater than 2.8V can also be used), and the TGA and TGB are both at low level and do not work. In the readout period, because the TD is at high level, the background light electrons of the pixel unit are attracted to the under-gate of the TD. Then, in the RST period of the next frame, the TD is at low level (generally, 0V is used), the background light charge under the gate of the TD is released into the pixel unit, and the residual charge of the pixel unit is reset together with the TGA and TGB. Through this design, the effect of eliminating the background light can be achieved even without the storage area connected with the TD, and the fill factor of the pixel unit can be improved, which is conducive to the miniaturization of the pixel unit.

[0037] Figure 5 A sectional view of a pixel unit provided by the embodiment of the present application is shown in the figure, and the section is along the A-A' direction shown in the figure. Figure 3 The sectional view along the A-A' direction shown in the figure is as follows: Figure 5 As shown in the figure, the P-type epitaxial layer 501 contains a P-well 502, the FDA 504 and the FDB 503 are arranged in the P-well, and the gate TGA 505, the TD 506 and the gate TGB 507 are arranged on the top of the pixel unit. Figure 5 The working principle of the pixel unit shown in the figure is similar to the above-mentioned embodiment, which will not be described here.

[0038] Figure 6 An equivalent circuit diagram of a pixel unit provided by the embodiment of the present application is shown in the figure, Figure 6 The equivalent circuit diagram of the pixel unit shown in the figure is as follows: Figure 3 The equivalent circuit diagram of the pixel unit shown in the figure is as follows: Figure 6The middle RST signal resets the FDA and the FDB, the SEL is opened to read, and the TD, TGA and TGB reset the PD. Figure 6 The working principle of the equivalent circuit diagram of the pixel unit shown is similar to the above embodiment, and thus will not be described here.

[0039] Figure 7 A layout diagram of a pixel unit provided by the embodiment of the application is shown in Figure 7 A layout diagram of a pixel unit provided by the embodiment of the application is shown in Figure 3 The layout diagram of the pixel unit shown is similar to the working principle of the pixel unit shown in Figure 7 As shown in the figure, 701 can be used as TD, and 703, 705, 707 and 709 can be used as FD, wherein 703, 705, 707 and 709 can be combined in any two to form FDA and FDB. 702, 704, 706 and 708 can be used as TG, wherein 702, 704, 706 and 708 can be combined in any two to form TGA and TGB. Figure 7 The layout diagram of the pixel unit shown is similar to the working principle of the pixel unit shown in Figure 3 The layout diagram of the pixel unit shown is similar to the working principle of the pixel unit shown in

[0040] Figure 8 A layout diagram of a pixel unit provided by the embodiment of the application is shown in Figure 8 As shown in the figure, 801 can be used as TD, 802 and 804 can be used as FDA and FDB respectively, and 803 and 805 can be used as TGA and TGB respectively. Figure 8 The layout diagram of the pixel unit shown is similar to the working principle of the pixel unit shown in Figure 3 The layout diagram of the pixel unit shown is similar to the working principle of the pixel unit shown in

[0041] Figures 9a-9d A charge movement schematic diagram of a pixel unit provided by the embodiment of the application is shown in Figure 9a In the figure, TGA is at a high level, TGA is opened, TGB is at a low level, and TD is at a low level. At this time, the charge of PD is transmitted to FDA after being received by TGA modulation. Figure 9b In the figure, TGB is at a high level, TGB is opened, TGA is at a low level, and TD is at a low level. At this time, the charge of PD is transmitted to FDB after being received by TGB modulation. Figure 9c In the figure, TGA and TGB are both at a low level, and TD is at a high level. At this time, TGA and TGB do not work, and the background photocharge in PD is attracted to the gate of TD, that is, the read period in the above embodiment. In Figure 9d In the figure, TD is at a low level, and TGA and TGB are both at a high level. At this time, the background light saved in the gate of TD is released into PD, and then transmitted out through TGA and TGB, thereby completing the elimination of the background photocharge in PD.

[0042] It can be seen from the above embodiments that the design of the present application can eliminate the PD background light while improving the fill factor of the pixel unit, which is conducive to the miniaturization of the pixel unit. In actual use, a detector array composed of M*N pixel units is used for detection, and the miniaturization of each pixel unit is conducive to the miniaturization of the detector array and the miniaturization of the image sensor.

[0043] It should be noted that, in this document, relational terms such as“first” and“second”, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms“comprises”,“comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by“comprises a...” does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0044] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application. It should be noted that similar reference numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. The above only describes the preferred embodiments of the present application and is not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A detector pixel cell, comprising: A photodiode for receiving probe light and generating electrons; a modulation gate on top of one side of the pixel cell for receiving the electrons with different phase delays; floating A floating diffusion node for holding the electrons received by the modulation gate; a background light elimination gate on top of one side of the pixel cell, spaced apart from the modulation gate and the floating diffusion node without a corresponding charge storage area; the background light elimination gate for eliminating background light electrons in the pixel cell during non-operation of the modulation gate, the background light elimination gate storing the background light electrons, specifically as follows: When the modulation gate is not in operation, the background light elimination gate attracts the background light electrons in the detector pixel cell to the background light elimination gate and stores them; When the detector pixel cell is reset, the background light elimination gate releases the stored background light electrons of the detector pixel cell to the inside of the detector pixel cell; The reset of the detector pixel cell includes the reset of the background light electrons.

2. The detector pixel unit of claim 1, wherein, When the modulation gate is not in operation, the background light elimination gate is at a high level of 2.8V or above to attract the background light electrons in the detector pixel cell to the background light elimination gate and store them.

3. The detector pixel unit of claim 1, wherein, When the detector pixel cell is reset, the background light elimination gate is at a low level of 0V or below, and the background light elimination gate releases the stored background light electrons of the detector pixel cell to the inside of the detector pixel cell.

4. The detector pixel unit of claim 1, wherein, The background light elimination gate is located in the middle of the detector pixel cell.

5. An image sensor comprising a receiving array composed of a plurality of detector pixel cells as claimed in claim 1.

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