A global shutter image sensor pixel unit and working method

Abstract

The present invention discloses a global shutter image sensor pixel unit and working method. The pixel unit includes a photosensitive collection storage area and a signal reading area. The photosensitive collection storage area includes a substrate photosensitive collection area, a first-level capacitor, a signal storage area, a second-level capacitor and a global shutter switch; the global shutter switch includes a first shutter port, a second shutter port and a third shutter port, and the first shutter port is connected to the signal storage area; the photosensitive collection storage area is also provided with an external voltage interface, including a pixel gate, a pixel substrate, a shutter drive and a shutter power supply. The pixel gate is connected to the second port of the second-level capacitor, the pixel substrate is connected to the substrate photosensitive collection area, the shutter drive is connected to the second shutter port, and the shutter power supply is connected to the third shutter port; the signal reading area includes a reading field effect transistor for outputting the signal stored in the signal storage area. The present invention can realize the global exposure function of the image sensor through a simplified structure of only two transistors.

Description

Technical Field

[0001] The present invention relates to the field of image sensors, and in particular to a small-size global shutter image sensor pixel unit and a working method thereof. Background Art

[0002] CMOS image sensors (CIS) have been continuously developing and are now widely used in many fields such as smartphone imaging, security and surveillance, biometrics, automotive, depth sensing, and ranging. Generally speaking, CMOS image sensors often use two exposure methods: rolling shutter and global shutter. When imaging high-speed moving objects, global exposure is usually required to avoid image distortion. Compared with rolling exposure, global exposure requires not only timing adjustments but also a device-level global shutter structure. Usually, the simplest global shutter pixel is to add a field-effect transistor as a shutter structure (5T) on the basis of the classic 4T pixel structure, such as Figure 11 As shown, its work mainly includes the following processes: first, after the reset tube (RST) resets the pixel, the photogenerated charge is collected by the signal collection diode (PD); secondly, the charge signal is transferred from the signal collection diode to the storage node (FD) through the transfer tube (TX); next, the transfer tube is turned off to keep the storage node signal unchanged; then the shutter field effect tube (SH) is turned on to prevent the signal collected by the signal collection diode from overflowing and affecting the storage node signal; finally, the storage node voltage signal in the selected pixel is read out row by row through the source follower (SF) through the row selection tube (Row).

[0003] In application scenarios with high image resolution requirements, pixel size reduction has become an inevitable trend. However, since a single pixel of a CMOS global shutter image sensor includes many transistors, even if a transistor-sharing method is adopted between pixels, it is difficult to further reduce the pixel size while ensuring sufficient signal collection diode and storage node well depth capacity. Currently, with the application of back-illuminated (BSI) technology, the pixel size of CMOS global shutter image sensors can be reduced to 2.2um (Sergey Velichko, "Overview of CMOS Global Shutter Pixels," IEEE Transactions On Electron Devices, 2022, 69(6): 2806-2814), but there is still a distance from submicron.

[0004] Therefore, further reduction in the pixel size of global shutter image sensors depends on the design of a more streamlined pixel structure. At the same time, the pixels must also have a high fill factor and larger collection node and storage node capacitance to ensure quantum efficiency and full well capacity requirements, thereby not affecting the imaging quality while reducing the pixel size. Summary of the Invention

[0005] The purpose of the present invention is to address the problems encountered in the current global shutter image sensor pixel size reduction and propose a new global shutter image sensor pixel unit structure, which realizes the global exposure function of the image sensor through a simplified structure that only requires two transistors (2T).

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the pixel unit of the present invention is as follows:

[0007] A global shutter image sensor pixel unit includes a photosensitive collection storage area and a signal reading area, wherein the photosensitive collection storage area includes a substrate photosensitive collection area, a first-level capacitor, a signal storage area, a second-level capacitor and a global shutter switch, wherein the substrate photosensitive collection area is connected to the first port of the first-level capacitor; the second port of the first-level capacitor is connected to the first port of the second-level capacitor, and the connected area forms the signal storage area; the global shutter switch includes a first shutter port, a second shutter port and a third shutter port, wherein the second shutter port is an enable port for controlling the conduction between the first shutter port and the third shutter port, and the first shutter port is connected to the signal storage area; the photosensitive collection storage area is also provided with an external voltage interface, including A pixel gate, a pixel substrate, a shutter drive and a shutter power supply, wherein the pixel gate is connected to the second port of the second-level capacitor, the pixel substrate is connected to the substrate photosensitive collection area, the shutter drive is connected to the second port of the shutter, and the shutter power supply is connected to the third port of the shutter; and the substrate photosensitive collection area is used to sense light signals and collect photogenerated charges, and the global shutter switch is used to control the coupling of the signal amount of the signal storage area and the photogenerated charge amount collected by the substrate photosensitive collection area; and the signal reading area includes a reading field effect transistor for outputting the signal stored in the signal storage area; the doping type of the substrate of the reading field effect transistor is opposite to the doping type of its source and drain, and the gate of the reading field effect transistor is connected to the signal storage area.

[0008] Furthermore, the signal storage area behaves as a conductor when storing signals.

[0009] Furthermore, the substrate of the readout field effect transistor is connected to the substrate light-sensitive collection area, and both have the same doping type.

[0010] Furthermore, the shutter power supply is connected to the drain of the read field effect transistor.

[0011] Further, the global shutter switch is a field effect transistor, whose gate serves as the shutter second port, one of its source and drain is connected to the signal storage area as the shutter first port, and the other serves as the shutter third port; or the global shutter switch is a bipolar transistor, whose base region serves as the shutter second port, its collector region is connected to the signal storage area as the shutter first port, and its emitter region serves as the shutter third port.

[0012] Furthermore, a bottom insulating dielectric layer, a bottom gate, a top insulating dielectric layer and a top gate are sequentially provided on the substrate photosensitive collection area; the bottom insulating dielectric layer, the bottom gate and the top insulating dielectric layer are each an integral structure, and the top gate is composed of a first top gate and a second top gate that are not connected to each other; the bottom insulating dielectric layer constitutes the first-level capacitor, and the lower side of the bottom insulating dielectric layer serves as the first port of the first-level capacitor, and the upper side thereof serves as the second port of the first-level capacitor; the top insulating dielectric layer constitutes the second-level capacitor, and the lower side of the top insulating dielectric layer serves as the first port of the second-level capacitor, and the upper side thereof serves as the second port of the second-level capacitor connected to the first top gate; the signal storage area is located in the bottom gate, and the global shutter switch is a field-effect transistor, whose gate is composed of the second top gate, and whose source, drain and substrate are all located in the bottom gate.

[0013] Furthermore, a bottom insulating dielectric layer, a bottom gate, a top insulating dielectric layer and a top gate are sequentially provided on the substrate photosensitive collection area; the bottom insulating dielectric layer, the bottom gate, the top insulating dielectric layer and the top gate are each an integral structure; the bottom insulating dielectric layer constitutes the first-level capacitor, the lower side of the bottom insulating dielectric layer serves as the first port of the first-level capacitor, and the upper side thereof serves as the second port of the first-level capacitor; the top insulating dielectric layer constitutes the second-level capacitor, the lower side of the top insulating dielectric layer serves as the first port of the second-level capacitor, and the upper side thereof serves as the second port of the second-level capacitor connected to the top gate; the signal storage area is located in the bottom gate, and the global shutter switch is a bipolar transistor, whose base region, emitter region and collector region are all located in the bottom gate.

[0014] The present invention also provides a method for operating a pixel unit of a global shutter image sensor, comprising the following steps:

[0015] (1) Resetting the substrate photosensitive collection area: by applying an appropriate voltage difference between the pixel gate and the pixel substrate, the charge originally located in the substrate photosensitive collection area is discharged;

[0016] (2) Generation and collection of photogenerated charges: By changing the voltage difference between the pixel gate and the pixel substrate, a photogenerated charge collection well is formed in the area where the substrate's photosensitive collection area is connected to the first-stage capacitor. Under the action of light, the substrate's photosensitive collection area stimulates photogenerated charges, which then diffuse into the collection well and are collected.

[0017] (3) Opening of the global shutter: Before or during the collection of photogenerated charges, a voltage is applied through the second port of the shutter, so that the global shutter switch is turned on, and the shutter power supply transmits the external voltage to the signal storage area. The amount of photogenerated charge collected by the substrate photosensitive collection area is coupled with the signal amount stored in the signal storage area through the first-stage capacitor, that is, the signal amount stored in the signal storage area corresponds one-to-one to the amount of photogenerated charge collected by the substrate photosensitive collection area;

[0018] (4) Closing the global shutter: applying pressure to the second port of the shutter turns off the global shutter switch, and the signal storage area becomes a floating node, and the stored signal quantity no longer changes;

[0019] (5) Photoelectric signal reading: keep the global shutter switch in the off state, and first perform the operation of resetting the substrate photosensitive collection area in step (1). At this time, the voltage of the signal storage area depends on the amount of signal stored therein. When the pixel array is read out row by row, the pixel gate voltage is set and the voltage signal of the signal storage area of ​​the current row pixel is read out using the reading field effect transistor.

[0020] Furthermore, the specific implementation of the photoelectric signal reading in step (5) is a source follower method: the drain of the reading field effect tube is an external voltage interface, and the source of the reading field effect tube is externally connected to a current source. When the pixels are read out row by row, a fixed voltage is applied to the pixel gate of the corresponding pixel, so that the reading field effect tube acts as a source follower, converts the signal quantity of the signal storage area into its source voltage value and reads it out.

[0021] Furthermore, the specific implementation of the photoelectric signal reading in step (5) is a scanning voltage method: the source of the reading field effect tube and the drain of the reading field effect tube are both voltage interfaces, and a non-zero fixed voltage difference is applied to the two interfaces. When the pixels are read out row by row, the voltage of the pixel gate of the corresponding pixel is scanned, and by monitoring the current flowing through the reading field effect tube, the threshold voltage of the reading field effect tube is extracted as the mapping readout result of the signal quantity of the signal storage area.

[0022] The present invention provides a global shutter image sensor pixel structure that requires only two transistors (2T). This minimal number of transistors allows the pixel to maintain a fill factor exceeding 60% even when the pixel size is reduced to 0.7 μm. In contrast, conventional global shutter pixel structures typically have a fill factor of less than 50% when the pixel size is less than 5 μm. The fill factor determines the utilization rate of the light signal. Therefore, the global shutter image sensor pixel structure of the present invention effectively maintains high image quality even when the pixel size is reduced, providing a solution for shrinking global shutter image sensor pixels to sub-micron sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the circuit of the present invention;

[0024] Figure 2 This is a timing diagram of the image sensor of the present invention in source follower mode;

[0025] Figure 3 This is a timing diagram of the image sensor of the present invention working in a scanning voltage mode;

[0026] Figure 4 This is a circuit schematic diagram of a global shutter switch module according to embodiment 1 of the present invention;

[0027] Figure 5 This is a schematic top view of the image sensor structure according to embodiment 1 of the present invention;

[0028] Figure 6 Schematic diagram of the cross section along a-a' of the image sensor structure according to embodiment 1 of the present invention;

[0029] Figure 7 This is a circuit schematic diagram of a global shutter switch module according to embodiment 2 of the present invention;

[0030] Figure 8 This is a schematic top view of the image sensor structure according to embodiment 2 of the present invention;

[0031] Figure 9 Schematic diagram of the cross section along a-a' of the image sensor structure according to embodiment 2 of the present invention;

[0032] Figure 10 This is the layout of the 0.7um image sensor in the embodiment of the present invention;

[0033] Figure 11 This is a schematic diagram of the circuit of a 5T global shutter image sensor in the prior art. DETAILED DESCRIPTION

[0034] To make the content of the present invention more clear and understandable, the content of the present invention is further described below in conjunction with the accompanying drawings. Of course, the present invention is not limited to this specific embodiment, and general replacements known to those skilled in the art are also included in the scope of protection of the present invention.

[0035] like Figure 1 As shown, the small-size global shutter image sensor pixel unit provided by the present invention includes a photosensitive collection and storage area 100 and a signal reading area 101. The photosensitive collection and storage area 100 includes a substrate photosensitive collection area 102, a first-level capacitor 103, a signal storage area 104, a second-level capacitor 105, and a global shutter switch 106. Its external voltage interface includes a pixel gate 108a, a shutter power supply 108b, a shutter drive 108c, and a pixel substrate 108d. The connection relationship is shown in the figure: the substrate photosensitive collection area 102 is connected to the first port of the first-level capacitor 103, the second port of the first-level capacitor 103 is connected to the signal storage area 104, and the signal storage area 104 is respectively connected to the first ports of the global shutter switch 106 and the second-level capacitor 105. The pixel gate 108a is connected to the second port of the second-stage capacitor 105, the pixel substrate 108d is connected to the substrate photosensitive collection area 102, the global shutter switch 106 includes a first shutter port, a second shutter port and a third shutter port, the shutter drive 108c is connected to the second shutter port, the second shutter port is an enable port, used to control whether the first shutter port and the third shutter port are connected, the shutter power supply 108b is connected to the third shutter port, the signal storage area 104 is connected to the first shutter port, when the first shutter port and the third shutter port are connected, the voltage signal of the shutter power supply is transmitted to the signal storage area 104, at this time, the signal amount of the signal storage area 104 is coupled with the amount of photogenerated charge collected by the substrate photosensitive collection area 102, when the first shutter port and the third shutter port are no longer connected, the signal amount of the signal storage area 104 will no longer change, the substrate photosensitive collection area 102 is used to sense light signals and collect photogenerated charges, and it can be equivalent to a photodiode when working. The global shutter switch 106 is used to control the coupling between the signal amount of the signal storage area 104 and the amount of photogenerated charge collected by the substrate photosensitive collection area 102 .

[0036] The signal reading area 101 includes a reading field effect transistor 107, which is used to output the signal stored in the signal storage area 104. The doping type of its substrate is opposite to the doping type of its source and drain. Its gate is connected to the signal storage area 104, and its reading field effect transistor source 108e and reading field effect transistor drain 108f serve as the external interface of the signal reading area 101.

[0037] In an embodiment, the signal storage area 104 behaves as a conductor when storing signals to ensure that its overall potential is consistent, specifically including forming the signal storage area 104 material through highly doped silicon, highly doped polysilicon or metal, and also including forming a high concentration carrier accumulation or inversion layer in the signal storage area by applying pressure to maintain a low resistance state; the substrate of the reading field effect transistor 107 is connected to the substrate photosensitive collection area 102, and the two have the same doping type, so that the charge signal collected in the substrate photosensitive collection area 102 is discharged from the source and drain of the reading field effect transistor 107 when reset; the shutter power supply 108b is connected to the drain 108f of the reading field effect transistor, which can reduce the number of ports to reduce the difficulty of wiring.

[0038] The shutter drive 108c is pressurized to control whether the signal storage area 104 maintains the same potential as the shutter power supply 108b through the global shutter switch 106; when the global shutter switch 106 is turned off, the pixel gate 108a can indirectly regulate the potential of the signal storage area 104 through the second-level capacitor 105, and then reset the substrate photosensitive collection area 102 through the first-level capacitor 103. When entering the reading stage, the pixel gate 108a can also realize the row selection of the required reading pixel.

[0039] The working mode of the pixel unit of the small-size global shutter image sensor provided by the present invention includes five steps: resetting the substrate photosensitive collection area, generating and collecting photogenerated charges, opening the global shutter, closing the global shutter, and reading the photoelectric signal. Figure 2 、 Figure 3 The timing diagram of the embodiment of the two working modes of the present invention is shown in FIG. 1 , and the difference between the two is mainly in the last step of reading the photoelectric signal. Figure 2 、 Figure 3 As shown:

[0040] The first step is to reset the substrate photosensitive collection area 102 after the pixel is powered on, keep the voltage of the pixel substrate 108d unchanged, and apply a negative voltage signal to the pixel gate 108a to discharge the charge signal in the substrate photosensitive collection area 102;

[0041] In the second step, the voltage of the pixel gate 108a is raised to greater than or equal to 0V, and the pixel enters the exposure stage. Under external light, the photogenerated charges are collected by the substrate photosensitive collection area 102 through diffusion;

[0042] In the third step, after the pixel enters the exposure phase, a positive voltage signal is applied to the shutter driver 108c, turning on the global shutter switch 106. At this time, the potential of the signal storage area 104 remains consistent with the shutter power supply 108b. The amount of charge stored there changes with the change of the charge stored in the substrate photosensitive collection area 102 through the coupling effect of the first-stage capacitor 103, which is equivalent to transferring the photogenerated charge signal to the signal storage area 104.

[0043] In the fourth step, when the pixel needs to stop collecting light signals, a negative voltage signal is applied to the shutter driver 108c, turning off the global shutter switch 106. At this time, the signal storage area 104 becomes a floating node, and the signal stored therein no longer changes with changes in external light. When designing the pixel array, the same shutter driver 108c voltage can be used across the entire chip to simultaneously end the exposure phase for all pixels, thereby realizing the global shutter shutdown function.

[0044] The fifth step is to repeat the operation of the first step before reading out the charge signal stored in the pixel signal storage area 104, that is, to apply a negative voltage signal to the pixel gate 108a to return the substrate photosensitive collection area 102 to the initial state. At this time, the potential of the signal storage area 104 depends on the amount of signal stored therein. When the photoelectric signal is read out row by row, the pixel gate 108a can play the role of a row selection tube. The pixels that are not selected are in the waiting readout stage, and their pixel gates 108a maintain a negative voltage signal. The reading field effect tube 107 is in the off state, and the signal reading area 101 has no current output to the external interface. The selected pixel is in the readout stage, and the present invention provides two readout methods:

[0045] like Figure 2 The figure shows a source-follower approach: the drain 108f of the pixel readout FET is an external voltage interface, and the source 108e of the readout FET is connected to a current source. When the pixel enters the readout phase, a voltage in the range of 1.8V-3.3V is applied to the pixel gate 108a, causing the readout FET 107 to act as a source follower, converting the signal in the signal storage area 104 into its source voltage value and reading it out from the readout FET source 108e.

[0046] like Figure 3 The figure shows the method of scanning voltage: the drain 108f of the pixel read field effect transistor and the source 108e of the read field effect transistor are both external voltage interfaces, and the two interfaces maintain a non-zero fixed voltage difference. When the pixel enters the readout stage, the voltage of the pixel gate 108a is scanned, and by monitoring the current flowing through the read field effect transistor 107, the threshold voltage of the read field effect transistor 107 is extracted as the mapping readout result of the signal quantity of the signal storage area 104.

[0047] The present invention below provides two implementation structures of a small-size global shutter image sensor pixel unit.

[0048] Example 1

[0049] In this embodiment, the global shutter switch 106 of the pixel unit is composed of a field effect transistor, such as Figure 4 As shown, the shutter driver is connected to the gate of the field effect tube to control its conduction and shutdown, and the source and drain of the field effect tube are respectively connected to the signal storage area and the shutter power supply. Figure 5 、 Figure 6 The top view and cross-sectional view of this pixel unit are respectively given: a bottom insulating dielectric layer 606, a bottom gate 502, a top insulating dielectric layer 607 and a top gate are sequentially provided on the pixel substrate photosensitive collection area 604; wherein the bottom gate 502, the bottom insulating dielectric layer 606 and the top insulating dielectric layer 607 are each a whole in the pixel without being split, and the top gate is composed of a first top gate 500 and a second top gate 501 which are not connected to each other, and the bottom insulating dielectric layer 606 constitutes a first-level capacitor, and the lower side of the bottom insulating dielectric layer 606 is connected to the substrate photosensitive collection area 604 as the first port of the first-level capacitor, and the upper side of the bottom insulating dielectric layer 606 is connected to the bottom as the second port of the first-level capacitor. The top insulating dielectric layer 607 forms a second-level capacitor. The bottom side of the top insulating dielectric layer 607 serves as the first port of the second-level capacitor connected to the bottom gate 502, and the top side of the top insulating dielectric layer 607 serves as the second port of the second-level capacitor connected to the first top gate 500. The signal storage area is located within the bottom gate 502. The global shutter switch is composed of a field-effect transistor (FET), whose gate is formed by the second top gate 501 and serves as the second port of the shutter. Its source 603, drain 601, and substrate 602 are all located within the bottom gate 502. The source 603 serves as the first port of the shutter connected to the signal storage area, and the drain 601 serves as the third port of the shutter connected to the external voltage interface. The substrate of the readout FET is connected to the substrate photosensitive collection area 604 and can be electrically isolated at the top by a trench 503. The readout FET source 504 and drain 505 are arranged on the same substrate material as the substrate photosensitive collection area 604 and serve as an external interface. The shutter power supply 608 a is connected to the third port of the shutter, the shutter drive 608 b is connected to the second port of the shutter, and the pixel gate 608 c is connected to the first top gate 500 .

[0050] Example 2

[0051] In this embodiment, the global shutter switch 106 of the pixel unit is composed of a bipolar transistor, such as Figure 7 As shown, the shutter driver is connected to the base region of the bipolar transistor to control its conduction and cutoff. The collector region and the emitter region of the bipolar transistor are respectively connected to the signal storage region and the shutter power supply. Figure 8 、 Figure 9The top view and cross-sectional view of this pixel unit are respectively given: a bottom insulating dielectric layer 905, a bottom gate 801, a top insulating dielectric layer 906, and a top gate 800 are sequentially provided on the pixel substrate photosensitive collection area 903; the bottom insulating dielectric layer 905 constitutes a first-level capacitor, and the lower side of the bottom insulating dielectric layer 905 is connected to the substrate photosensitive collection area 903 as the first port of the first-level capacitor, and the upper side of the bottom insulating dielectric layer 905 is connected to the bottom gate 801 as the second port of the first-level capacitor; the top insulating dielectric layer 906 constitutes a second-level capacitor, and the top insulating dielectric layer 906 is connected to the bottom gate 801 as the second port of the first-level capacitor. The bottom side of 06 serves as the first port of the second-stage capacitor connected to the bottom gate 801. The top side of the top insulating dielectric layer 906 serves as the second port of the second-stage capacitor connected to the top gate 800. The signal storage area is located within the bottom gate 801. The global shutter switch is composed of a bipolar transistor, whose base region 901, emitter region 900, and collector region 902 are all located within the bottom gate 801. The base region 901 serves as the second port of the shutter, the emitter region 900 serves as the third port of the shutter, and is connected to different external voltage interfaces. The collector region 902 serves as the first port of the shutter and is connected to the signal storage area. The substrate of the readout field-effect transistor is connected to the substrate photosensitive collection area 903 and can be electrically isolated at the top by trench 802. The readout field-effect transistor source 803 and drain 804 are arranged on the same substrate material as the substrate photosensitive collection area 903 and serve as external interfaces. The shutter power supply 907 a is connected to the third port of the shutter, the shutter drive 907 b is connected to the second port of the shutter, and the pixel gate 907 c is connected to the top gate 800 .

[0052] In Examples 1 and 2, the bottom gate adopts a thin layer structure with a thickness of several nanometers to tens of nanometers to ensure a smaller bottom gate volume, which is used to reduce the parasitic light response introduced into the signal storage area by external light directly irradiating the bottom gate, thereby increasing the global shutter efficiency.

[0053] Figure 10 This is a layout design scheme based on the 0.7um pixel structure using the existing Nor-Flash 65 process in Example 1. The figure uses a symmetrical arrangement of four adjacent pixels and a shared readout field effect transistor source and global shutter switch to further increase the substrate's photosensitive collection area. The area of ​​a single pixel in the figure is 0.49um. 2 (0.70×0.70), the substrate photosensitive collection area is 0.30um 2 (0.48×0.63), a rough calculation shows that the single pixel filling factor can reach 61%.

[0054] Although the present invention has been disclosed above with reference to preferred embodiments, the aforementioned embodiments are merely examples for the purpose of illustration and are not intended to limit the present invention. Those skilled in the art may make various modifications and alterations without departing from the spirit and scope of the present invention. The scope of protection claimed by the present invention shall be subject to the claims.

Claims

1. A global shutter image sensor pixel unit, comprising a light-collecting storage area and a signal reading area, characterized in that: The photosensitive collection storage area includes a substrate photosensitive collection area, a first-level capacitor, a signal storage area, a second-level capacitor and a global shutter switch, wherein the substrate photosensitive collection area is connected to the first port of the first-level capacitor; the second port of the first-level capacitor is connected to the first port of the second-level capacitor, and the connected area forms the signal storage area; the global shutter switch includes a first shutter port, a second shutter port and a third shutter port, wherein the second shutter port is an enable port for controlling the conduction between the first shutter port and the third shutter port, and the first shutter port is connected to the signal storage area; the photosensitive collection storage area is also provided with an external voltage interface, including a pixel gate, a pixel substrate, a shutter drive and a shutter power supply, wherein the pixel gate is connected to the second port of the second-level capacitor, the pixel substrate is connected to the substrate photosensitive collection area, the shutter drive is connected to the second shutter port, and the shutter power supply is connected to the third shutter port; and, The substrate photosensitive collection area is used to sense light signals and collect photogenerated charges, and the global shutter switch is used to control the coupling of the signal quantity of the signal storage area and the photogenerated charge quantity collected by the substrate photosensitive collection area; and the signal reading area includes a reading field effect transistor for outputting the signal stored in the signal storage area; the substrate doping type of the reading field effect transistor is opposite to the doping type of its source and drain, and the gate of the reading field effect transistor is connected to the signal storage area.

2. A global shutter image sensor pixel unit according to claim 1, characterized in that: The signal storage area behaves as a conductor when storing a signal.

3. The global shutter image sensor pixel unit according to claim 1, wherein: The substrate of the readout field effect transistor is connected to the substrate light-sensitive collection area, and the two have the same doping type.

4. The global shutter image sensor pixel unit according to claim 1, wherein: The shutter power supply is connected to the drain of the readout field effect transistor.

5. The global shutter image sensor pixel unit according to claim 1, wherein: The global shutter switch is a field effect transistor, whose gate serves as the shutter second port, one of its source and drain is connected to the signal storage area as the shutter first port, and the other serves as the shutter third port; or the global shutter switch is a bipolar transistor, whose base serves as the shutter second port, its collector region is connected to the signal storage area as the shutter first port, and its emitter region serves as the shutter third port.

6. The global shutter image sensor pixel unit according to claim 5, characterized in that: A bottom insulating dielectric layer, a bottom gate, a top insulating dielectric layer and a top gate are sequentially provided on the substrate photosensitive collection area; the bottom insulating dielectric layer, the bottom gate and the top insulating dielectric layer are each an integral structure, and the top gate is composed of a first top gate and a second top gate that are not connected to each other; the bottom insulating dielectric layer constitutes the first-level capacitor, and the lower side of the bottom insulating dielectric layer serves as the first port of the first-level capacitor, and the upper side serves as the second port of the first-level capacitor; the top insulating dielectric layer constitutes the second-level capacitor, and the lower side of the top insulating dielectric layer serves as the first port of the second-level capacitor, and the upper side serves as the second port of the second-level capacitor connected to the first top gate; the signal storage area is located in the bottom gate, and the global shutter switch is a field-effect transistor, whose gate is composed of the second top gate, and its source, drain and substrate are all located in the bottom gate.

7. The global shutter image sensor pixel unit according to claim 5, characterized in that: The substrate photosensitive collection area is provided with a bottom insulating dielectric layer, a bottom gate, a top insulating dielectric layer and a top gate in sequence; the bottom insulating dielectric layer, the bottom gate, the top insulating dielectric layer and the top gate are each an integral structure; the bottom insulating dielectric layer constitutes the first-level capacitor, the lower side of the bottom insulating dielectric layer serves as the first port of the first-level capacitor, and the upper side serves as the second port of the first-level capacitor; the top insulating dielectric layer constitutes the second-level capacitor, the lower side of the top insulating dielectric layer serves as the first port of the second-level capacitor, and the upper side serves as the second port of the second-level capacitor connected to the top gate; the signal storage area is located in the bottom gate, and the global shutter switch is a bipolar transistor, whose base region, emitter region and collector region are all located in the bottom gate.

8. The method for operating a pixel unit of a global shutter image sensor according to any one of claims 1 to 7, characterized in that: The steps include: (1) Resetting the substrate photosensitive collection area: by applying an appropriate voltage difference between the pixel gate and the pixel substrate, the charge originally located in the substrate photosensitive collection area is discharged; (2) Generation and collection of photogenerated charges: By changing the voltage difference between the pixel gate and the pixel substrate, a photogenerated charge collection well is formed in the area where the substrate's photosensitive collection area is connected to the first-stage capacitor. Under the action of light, the substrate's photosensitive collection area stimulates photogenerated charges, which then diffuse into the collection well and are collected. (3) Opening of the global shutter: Before or during the collection of photogenerated charges, a voltage is applied through the second port of the shutter, so that the global shutter switch is turned on, and the shutter power supply transmits the external voltage to the signal storage area. The amount of photogenerated charge collected by the substrate photosensitive collection area is coupled with the signal amount stored in the signal storage area through the first-stage capacitor, that is, the signal amount stored in the signal storage area corresponds one-to-one to the amount of photogenerated charge collected by the substrate photosensitive collection area; (4) Closing the global shutter: applying pressure to the second port of the shutter turns off the global shutter switch, and the signal storage area becomes a floating node, and the stored signal quantity no longer changes; (5) Photoelectric signal reading: keep the global shutter switch in the off state, and first perform the operation of resetting the substrate photosensitive collection area in step (1). At this time, the voltage of the signal storage area depends on the amount of signal stored therein. When the pixel array is read out row by row, the pixel gate voltage is set and the voltage signal of the signal storage area of ​​the current row pixel is read out using the reading field effect transistor.

9. The working method according to claim 8, characterized in that: The specific implementation of the photoelectric signal reading in step (5) is a source follower method: the drain of the reading field effect tube is an external voltage interface, and the source of the reading field effect tube is externally connected to a current source. When the pixels are read out row by row, a fixed voltage is applied to the pixel gate of the corresponding pixel, so that the reading field effect tube acts as a source follower, converts the signal quantity of the signal storage area into its source voltage value and reads it out.

10. The working method according to claim 8, characterized in that: The specific implementation of the photoelectric signal reading in step (5) is a scanning voltage method: the source and the drain of the reading field effect tube are both voltage interfaces, and a non-zero fixed voltage difference is applied to the two interfaces. When the pixels are read out row by row, the voltage of the pixel gate of the corresponding pixel is scanned, and by monitoring the current flowing through the reading field effect tube, the threshold voltage of the reading field effect tube is extracted as the mapping readout result of the signal quantity of the signal storage area.

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