An image sensor and its reading method

Abstract

This invention discloses an image sensor and a readout method. The image sensor includes several pixel units, each pixel unit comprising a first reset transistor and a source follower transistor connected to a floating diffuse active region, a second reset transistor, and several pixels connected in series. One end of each pixel is connected to the floating diffuse active region, and the other end is connected to a power supply through the second reset transistor. Each pixel includes interconnected charge transport transistors and photosensitive units. The charge transport transistors of several pixels are connected in series between the floating diffuse active region and the second reset transistor, and the photosensitive units of several pixels are connected between their respective charge transport transistors and ground. Correspondingly, this invention also provides a readout method for the image sensor. The image sensor and readout method of this invention improve pixel photosensitive quantum efficiency and simultaneously increase pixel photoelectric conversion gain, effectively reducing pixel signal noise.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to an image sensor and a reading method. Background Technology

[0002] With the development of technology, computing devices have been gradually applied to all aspects of modern society and have made significant contributions to its development. These include, but are not limited to, digital cameras, camcorders, smartphones, and navigation systems. In particular, in recent years, devices with image acquisition capabilities, such as digital cameras, have become increasingly popular, and the requirements for their image quality have become increasingly stringent.

[0003] The working principle of existing CMOS image sensors is as follows: a photosensitive element converts the received light signal into a photoelectric charge signal. This photoelectric charge signal is then transmitted to a floating diffuse active region, where a source follower transistor in the pixel converts the photoelectric charge signal back into a photoelectric signal for output by the subsequent signal processing system. The photoelectric signal output by the pixel contains signal noise, with random noise from the transistor device being one of the main sources. The magnitude of its equivalent input noise is related to the total parasitic capacitance of the floating diffuse active region, which is equal to the sum of the capacitances contributed by the active region, the metal, and the polysilicon interconnects. The smaller the total parasitic capacitance of the floating diffuse active region, the higher the photoelectric conversion gain of the pixel, and the lower its equivalent input noise.

[0004] However, to improve pixel photosensitivity, especially for small pixels, image sensor pixels often employ a shared structure, where multiple pixels share a reset transistor, source follower transistor, and pixel selection transistor. The aim is to increase the fill rate of the pixel's photosensitive element, thereby improving quantum efficiency, as illustrated in the pixel structure disclosed in patent number CN102956660A. However, this shared structure increases the parasitic capacitance of the floating active region, thus reducing photoelectric conversion gain. Therefore, existing designs for improving pixel quantum efficiency and increasing pixel photoelectric conversion gain are mutually restrictive and contradictory. Summary of the Invention

[0005] The purpose of this invention is to provide an image sensor and reading method that solves the technical problem of how to simultaneously improve pixel photosensitive quantum efficiency and increase pixel photoelectric conversion gain.

[0006] This invention provides an image sensor comprising a plurality of pixel units. Each pixel unit includes a first reset transistor and a source follower transistor connected to a floating diffuse active region. The pixel unit further includes a second reset transistor and a plurality of pixels connected in series, one end of which is connected to the floating diffuse active region, and the other end is connected to a power supply through the second reset transistor. Each pixel includes a charge transport transistor and a photosensitive unit connected in series. The charge transport transistors of the plurality of pixels are connected in series between the floating diffuse active region and the second reset transistor, and the photosensitive units of the plurality of pixels are connected between the corresponding charge transport transistors and ground.

[0007] In one embodiment, an auxiliary polysilicon gate is further disposed on one side of the photosensitive unit of the plurality of pixels.

[0008] In one embodiment, the auxiliary polysilicon gate is used to receive a negative potential to accelerate the removal of residual charge.

[0009] In one embodiment, the auxiliary polysilicon gate is used to receive a first negative voltage to an Nth negative voltage, wherein the potential of the first negative voltage to the Nth negative voltage decreases sequentially to ensure that the charge of the plurality of pixels is fully output.

[0010] In one embodiment, the vertical projection of the auxiliary polysilicon gate onto the photosensitive unit is a polygon or an ellipse.

[0011] In one embodiment, the surface area of ​​the auxiliary polysilicon gate near the photosensitive unit is 0.2 to 0.8 times the surface area of ​​the cathode end of the photosensitive unit.

[0012] In one embodiment, the auxiliary polysilicon gate is coaxially arranged with the photosensitive unit in a first direction.

[0013] In one embodiment, the drain of the first reset transistor and the drain of the source follower transistor are both connected to a power supply, and the source of the first reset transistor and the gate of the source follower transistor are both connected to the floating diffuse active region; the source of the source follower transistor is connected to the output terminal; the first reset transistor is used to reset the charge signal of the floating diffuse active region and the source follower transistor before the pixel is exposed; the source follower transistor is used to receive the charge signal transmitted by the pixel and amplify and output it.

[0014] In one embodiment, the image sensor further includes a row selection transistor, and the source follower transistor is connected to the output terminal through the row selection transistor.

[0015] In one embodiment, the image sensor further includes a dual-conversion gain control module connected between the first reset transistor and the floating diffused active region. The dual-conversion gain control module includes at least one dual-conversion gain control transistor and a capacitor. The dual-conversion gain control module is used to switch between a low conversion gain mode and a high conversion gain mode.

[0016] This invention also discloses a method for reading images from a sensor, comprising:

[0017] In the first reset, the second reset transistor is turned on, and the Nth to Xth charge transport transistors are turned on. The pixels are reset sequentially along the direction away from the floating diffused active region to clear the charge of the pixels sequentially. Wherein, X is a natural number and 2≤X≤N.

[0018] Pixel exposure involves sequentially turning off the Xth charge transport transistor and exposing any pixel after performing a first reset operation.

[0019] The second reset involves turning off the second reset transistor, turning on the first reset transistor, and turning on the first to the Xth charge transport transistors to perform a reset operation on the floating diffused active region.

[0020] Reset signal reading: After performing a second reset operation on the floating diffusion active region, the potential signal of the floating diffusion active region is output, and the reset signals from the first pixel to the Xth pixel are obtained sequentially.

[0021] Charge transfer: turn off the first reset transistor and turn on the first charge transfer transistor to the Xth charge transfer transistor, so that after outputting the potential signal of the floating diffuse active region, the photoelectric charge stored in the photosensitive unit in the pixel is transferred to the floating diffuse active region, and the image signals of the first and Xth pixels are acquired sequentially.

[0022] Charge readout: The source follower transistor transfers photoelectric charge readout to the floating diffuse active region.

[0023] In one embodiment, the pixel further includes an auxiliary polysilicon gate, which is disposed parallel to one side of the cathode end of the photosensitive unit, wherein the first reset step includes:

[0024] Turn off the first charge transport transistor and set the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor from the initial potential to the first negative potential, thereby resetting the potential of the first photosensitive unit corresponding to the first charge transport transistor.

[0025] The Xth charge transport transistor is turned off in sequence, exposing the X-1 photosensitive unit corresponding to the X-1th charge transport transistor; and the potential of the Xth auxiliary polysilicon gate corresponding to the Xth charge transport transistor is set from the initial potential to the first negative potential, thus resetting the potential of the Xth photosensitive unit corresponding to the Xth charge transport transistor.

[0026] After the X-1 photosensitive unit is exposed, the potential of the X-1 auxiliary polysilicon gate corresponding to the X-1 photosensitive unit is set from the first negative potential to the initial potential.

[0027] In one embodiment, when X=N, the first reset step further includes:

[0028] After the X-1 photosensitive unit is exposed, the potential of the X auxiliary polysilicon gate corresponding to the X charge transport transistor is set from the initial potential to the first negative potential, and the second reset transistor is turned off, so that the X photosensitive unit corresponding to the X charge transport transistor is exposed.

[0029] After the Xth photosensitive unit is exposed, the potential of the Xth auxiliary polysilicon gate is set from the first negative potential to the initial potential.

[0030] In one embodiment, the initial potential is -0.5V to 0.5V, and the first negative potential is set to -1.5V to -0.5V.

[0031] In one embodiment, the time interval between the step of turning off the first charge transport transistor and the step of setting the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor from the initial potential to the first negative potential is 50ns to 150ns; the time interval between the step of turning off the Xth charge transport transistor and the step of setting the potential of the Xth auxiliary polysilicon gate corresponding to the Xth charge transport transistor from the initial potential to the first negative potential is 50ns to 150ns; the time interval between the step of turning off the Xth charge transport transistor and the step of setting the potential of the (X-1)th auxiliary polysilicon gate from the first negative potential to the initial potential is 50ns to 150ns; and the time interval between the step of turning off the second reset transistor and the step of setting the potential of the Xth auxiliary polysilicon gate from the first negative potential to the initial potential is 50ns to 150ns.

[0032] In one embodiment, the charge transfer step includes:

[0033] Turn on the first charge transport transistor to the Xth charge transport transistor;

[0034] Negative voltages are applied to the first auxiliary polysilicon gate to the Xth auxiliary polysilicon gate respectively to ensure that the charge of the plurality of pixels is fully output; along the direction away from the floating diffused active region, the potential of the negative voltage received by the first auxiliary polysilicon gate to the potential of the negative voltage received by the Nth auxiliary polysilicon gate decreases sequentially.

[0035] In one embodiment, during the charge transfer step:

[0036] The time interval between the steps of turning on the first charge transport transistor to the Xth charge transport transistor and the steps of applying negative voltages to the first auxiliary polysilicon gate to the Xth auxiliary polysilicon gate is 50 ns to 150 ns.

[0037] In one embodiment, the expression for the photoelectric signal read from the first pixel is: Wherein, Sig1 is the photoelectric signal read out by the first pixel, R1 is the reset signal of the first pixel, and S1 is the image signal of the first pixel;

[0038] The expression for the photoelectric signal read from the Xth pixel is: Among them, Sig x R is the photoelectric signal read from the Xth pixel. x S is the reset signal for the Xth pixel. x For the image signal of the Xth pixel, Sig x-1 Δt is the photoelectric signal read from the (X-1)th pixel, Δt is the time interval between the second reset step and the charge transfer step, T is the exposure period, and X is a natural number where 2≤X≤N.

[0039] This invention discloses an image sensor and its readout method. The image sensor employs a pixel-sharing approach, saving the number of transistors and increasing the area occupancy of the photosensitive units within each pixel. This effectively improves the photoelectric conversion quantum efficiency of the photosensitive units, making it particularly suitable for the design layout of small-area pixel image sensors. Furthermore, the pixels in the pixel group are arranged in series, which, compared to the parallel sharing layout of existing technologies, significantly improves the photoelectric conversion gain of the floating diffuse active region, thereby effectively reducing pixel signal noise. Therefore, the image sensor pixels and readout method of this invention improve pixel photosensitive quantum efficiency and simultaneously increase pixel photoelectric conversion gain, effectively reducing pixel signal noise. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the pixel-sharing structure of an image sensor provided by existing technology;

[0041] Figure 2This is a circuit diagram of a pixel unit in an image sensor provided in an embodiment of the present invention;

[0042] Figure 3 This is a schematic diagram of the planar structure of the photosensitive unit in an image sensor according to an embodiment of the present invention;

[0043] Figure 4 This is a schematic diagram of the cross-sectional structure of the photosensitive unit in a pixel of an image sensor according to an embodiment of the present invention;

[0044] Figure 5 This is a schematic diagram of the timing control of a pixel unit in an image sensor according to an embodiment of the present invention;

[0045] Figure 6 The pixel unit in the image sensor provided in one embodiment of the present invention is... Figure 5 A schematic diagram of the device potential well at time t16;

[0046] Figure 7 This is a schematic diagram of the photoelectric signals of each pixel in an image sensor provided in an embodiment of the present invention. Detailed Implementation

[0047] To further illustrate the technical methods and effects of the present invention in order to achieve the intended purpose, the specific implementation methods, structure, features and effects of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0048] To demonstrate the advantages of the pixel units of the image sensor in the embodiments of the present invention, it is necessary to first understand the pixel-sharing structure of the image sensor in the prior art. Figure 1 This is a schematic diagram of the pixel-sharing structure of an image sensor provided by existing technology, such as... Figure 1 As shown, the pixel-sharing structure of existing image sensors is a parallel shared pixel structure, comprising multiple photosensitive units 001 to 00m, multiple charge transport transistors 011 to 01m, a reset transistor 02, a source follower transistor 03, a row selection transistor 04, and a floating diffused active region FD0. In this prior art, the value of m is a natural number, and the parasitic capacitance of the floating diffused active region FD0 is related to the value of m; the larger the value of m, the higher the parasitic capacitance of FD0. Although the parallel shared pixel structure of the prior art can increase the occupied area of ​​the photosensitive units, the parasitic capacitance of FD0 is much higher than that of the non-shared pixel structure. Therefore, the photoelectric conversion gain decreases, leading to a deterioration and increase in the equivalent signal noise of the pixel output, thereby reducing the image quality of the image sensor.

[0049] The image sensor of this invention adopts a structure in which multiple pixels are shared to form a pixel unit. The pixel unit includes a first reset transistor 103 and a source follower transistor 104 connected to the floating diffuse active region. Figure 2 This is a circuit diagram of a pixel unit in an image sensor provided by an embodiment of the present invention, as shown below. Figure 2 As shown, a pixel unit includes several pixels, for example Figure 2 As shown, there are n pixels, where n is a natural number greater than or equal to 2, and the n pixels are connected in series. Several pixels are connected in series, with one end connected to the floating diffuse active region FD and the other end connected to the power supply Vdd through the second reset transistor 106. Further, each pixel includes a charge transport transistor and a photosensitive unit connected in series. The charge transport transistors of several pixels are connected in series between the floating diffuse active region FD and the second reset transistor 106, and the photosensitive units of several pixels are connected between the corresponding charge transport transistor and ground.

[0050] It is understood that the drain of the first reset transistor 103 and the drain of the source follower transistor 104 are both connected to the power supply Vdd, and the source of the first reset transistor 103 and the gate of the source follower transistor 104 are both connected to the floating diffused active region FD; the source of the source follower transistor 104 is connected to the output terminal; the first reset transistor 103 is used to reset the charge signal of the floating diffused active region FD and the source follower transistor 104 before pixel exposure; the source follower transistor 104 is used to receive the charge signal transmitted by the pixel and amplify it for output.

[0051] In some embodiments, the image sensor further includes a row selection transistor 105, and a source follower transistor 104 is connected to the output terminal via the row selection transistor 105.

[0052] It is understandable that, such as Figure 2As shown, the pixel unit includes a first reset transistor 103 and a source follower transistor 104 connected to the floating diffuse active region FD, a row selection transistor 105 connected to the source follower transistor 104, and a second reset transistor 106 connected to the power supply Vdd. The n pixels of the pixel unit share the first reset transistor 103, the source follower transistor 104, the row selection transistor 105, and the second reset transistor 106. The n pixels are connected in series between the floating diffuse active region FD and the source terminal of the second reset transistor 106. The source terminal of the first reset transistor 103 and the gate terminal of the source follower transistor 104 are connected to the floating diffuse active region FD, and the source terminals of the first reset transistor 103 and the source terminal of the source follower transistor 104 are connected to the power supply Vdd. The source terminal of the source follower transistor 104 is connected to the drain terminal of the row selection transistor 105. The source terminal of the row selection transistor 105 is connected to the signal output line output. The output signal of the signal output line output can be read by an external circuit to obtain the potential signal of the floating diffuse active region FD when the row selection transistor 105 is turned on. The source terminal of the second reset transistor 106 is connected to the first terminal of the nth photosensitive unit 101n and the source terminal of the nth charge transport transistor 102n, and the drain terminal of the second reset transistor 106 is connected to the power supply Vdd.

[0053] See Figure 2 An auxiliary polysilicon gate is also disposed on one side of each photosensitive unit of several pixels. This auxiliary polysilicon gate is used to receive a negative potential to accelerate the removal of residual charge. Specifically, it is used to receive a first negative voltage to an Nth negative voltage, wherein the potential of the first negative voltage to the Nth negative voltage decreases sequentially to ensure complete charge output of the several pixels. For example, as... Figure 2 As shown, the x-th pixel includes the x-th photosensitive unit 101x, the x-th auxiliary polysilicon gate 1x, and the x-th charge transport transistor 102x, where x is a natural number less than or equal to n. The gate terminal of the x-th auxiliary polysilicon gate 1x is CGx, the gate terminal of the x-th charge transport transistor 102x is TXx, the gate terminal of the first reset transistor 103 is RST, the gate terminal of the row selection transistor 105 is RS, and the gate terminal of the second reset transistor 106 is RST2. The nth pixel includes an nth charge transport transistor 102n, an nth auxiliary polysilicon gate 1n, and an nth photosensitive unit 101n; the drain terminal of the nth charge transport transistor 102n is connected to the source terminal of the (x-1)th charge transport transistor, and the gate terminal TXn of the nth charge transport transistor 102n receives the nth transmission control signal; the first terminal of the nth photosensitive unit 101n is connected to the source terminal of the nth charge transport transistor 102n and the nth auxiliary polysilicon gate 1n, and the second terminal of the nth photosensitive unit 101n is grounded; wherein, the source terminal of the nth charge transport transistor 102n is connected to the source terminal of the second reset transistor 106.

[0054] In one embodiment of the invention, in a first direction, an auxiliary polysilicon gate is coaxially disposed with the photosensitive unit. The first direction can be a direction perpendicular to the upper surface of the photosensitive unit, or it can be understood as the auxiliary polysilicon gate being located above the middle surface of the photosensitive unit. Figure 3 As shown, the first auxiliary polysilicon gate 11 is located above the middle surface of the first photosensitive unit 1011, where the planar structure of 11 is square. Similarly, the second auxiliary polysilicon gate 12 is located above the middle surface of the second photosensitive unit 1012, and so on. The nth auxiliary polysilicon gate 1n is located above the middle surface of the nth photosensitive unit 101n, that is, the Nth auxiliary polysilicon gate 1N is located above the middle surface of the Nth photosensitive unit 101N, where N is a natural number less than or equal to n.

[0055] In one embodiment of the invention, the planar shape of the auxiliary polysilicon gate can be a polygon or an ellipse. The polygon can be a regular shape such as a regular polygon or a rhombus, and the ellipse can be a circle.

[0056] In one embodiment of the invention, the planar area of ​​the auxiliary polysilicon gate is 0.2 to 0.8 times the planar area of ​​the photosensitive unit.

[0057] Optionally, the photosensitive unit can be any one of a photodiode, a PIN photodiode, a partial PIN photodiode, or a polysilicon gate photodiode.

[0058] Figure 3 This is a schematic diagram of the planar structure of the photosensitive unit in an image sensor according to an embodiment of the present invention; please also refer to... Figure 2 and Figure 3 .like Figure 2 As shown, the component within the dashed box marked 100 represents the component of the first pixel. The corresponding components for the remaining pixels are the same as those within the dashed box marked 100. The following diagram illustrates the planar representation of the component within the 100 portion. Figure 3 As shown.

[0059] In one embodiment, the photosensitive unit includes an N-type region, a P+ pin layer, and a P-type epitaxial layer. The N-type region of the photosensitive unit is the first end of the photosensitive unit, and the P+ pin layer of the photosensitive unit is connected to the xth auxiliary polysilicon gate. Figure 4 This is a schematic diagram of the cross-sectional structure of the photosensitive unit in a pixel of an image sensor according to an embodiment of the present invention, as shown below. Figure 4 As shown Figure 3 Please also refer to the vertical cross-section diagram at the marked AB positions. Figure 3 and Figure 4The first photosensitive unit 1011 has the same structure as the x-th photodiode of the remaining pixels, where x is a natural number greater than 1 and less than or equal to n. Taking the structure of the first photosensitive unit 1011 as an example, in the first photosensitive unit 1011, 401 is an N-type region, 402 is a P+ pin layer, and P-epi is a P-type epitaxial layer. In one embodiment of the invention, the x-th photosensitive unit can be a front-facing light-receiving unit or a back-facing light-receiving unit.

[0060] In one embodiment of the invention, the gate terminal RST of the first reset transistor 103, the gate terminal RS of the row selection transistor 105, the gate terminal RST2 of the second reset transistor 106, the gate terminals of each charge transport transistor, and each auxiliary polysilicon gate are respectively connected to the timing control line of the decoder to realize the switching action of each transistor in this embodiment and perform signal acquisition operation.

[0061] In some optional embodiments, the image sensor further includes a dual conversion gain control module connected between the first reset transistor and the floating diffused active region. The dual conversion gain control module includes at least one dual conversion gain control transistor and a capacitor, and is used to switch between a low conversion gain mode and a high conversion gain mode. Specifically, this configuration allows for increased conversion gain with a smaller integrating capacitor under low illumination conditions to improve sensitivity; and increased stored charge with a larger integrating capacitor under high illumination conditions to decrease conversion gain and improve dynamic range.

[0062] The image sensor of this invention employs a pixel-sharing approach, saving the number of transistors and increasing the area occupancy of photosensitive units within each pixel. This effectively improves the photoelectric conversion quantum efficiency of the photosensitive units, making it particularly suitable for the design layout of small-area pixel image sensors. Furthermore, the pixels in the pixel unit are arranged in series, which, compared to the parallel sharing layout of existing technologies, significantly increases the photoelectric conversion gain of the floating diffuse active region, thereby effectively reducing pixel signal noise. Therefore, the image sensor pixels and readout method of this invention improve pixel photosensitive quantum efficiency and simultaneously increase pixel photoelectric conversion gain, effectively reducing pixel signal noise.

[0063] Based on the same inventive concept, this embodiment also provides a method for reading the image sensor described in the above embodiments. Figure 5 This is a schematic diagram of the timing control of pixel units in an image sensor according to an embodiment of the present invention. Figure 5The diagram illustrates the gate control timing of each device in a pixel unit, including the timing of the gate terminals RST2 of the second reset transistor 106, RST of the first reset transistor 103, RS of the row selection transistor 105, TX1 of the first charge transport transistor 1021, CG1 of the first auxiliary polysilicon gate 11, TX2 of the second charge transport transistor 1022, CG2 of the second auxiliary polysilicon gate 12, TXn of the nth charge transport transistor 102n, and CGn of the nth auxiliary polysilicon gate 1n. "Read" can represent, for example, reading the output signal from the signal output line "output" via an external circuit to obtain the potential signal of the floating diffuse active region FD when the row selection transistor 105 is turned on. In this embodiment, a high gate terminal potential indicates that the transistor is in the on state, and a low gate terminal potential indicates that the transistor is in the off state. However, this invention is not limited to this; in one embodiment, a low gate terminal potential may indicate that the transistor is in the on state, and a high gate terminal potential may indicate that the transistor is in the off state, etc.

[0064] Please refer to Figure 5 The image sensor reading method of this embodiment includes:

[0065] The first reset activates the second reset transistor 106 and the Nth to xth charge transfer transistors, and performs a reset operation on several pixels sequentially along the direction away from the floating diffused active region to clear the charge of several pixels in sequence; where x is a natural number and 2≤x≤N;

[0066] The purpose of the first reset is to clear the charge from the first to the nth photosensitive units. For example... Figure 5 Before the time t1 shown, the gate terminal RST2 of the second reset transistor 106 is set to a high potential, so the second reset transistor 106 is in the turn-on state. The gate terminals of the Nth to xth charge transport transistors are simultaneously set to a high potential, so the xth to Nth charge transport transistors are also in the turn-on state, and the floating diffuse active region FD performs the first reset.

[0067] Pixel exposure involves sequentially turning off the xth charge transfer transistor and exposing any pixel after performing the first reset operation; the purpose is to sequentially expose the first to the nth pixels of a pixel unit.

[0068] In one embodiment of the invention, exposure is performed after the second reset of the first to the nth pixels, and the exposure sequence is the first photosensitive unit 1011, the second photosensitive unit 1012 up to the nth photosensitive unit 101n, and the exposure period T of each pixel is the same.

[0069] In the second reset, the second reset transistor is turned off, the first reset transistor is turned on, and the first to xth charge transport transistors are turned on to perform a reset operation on the floating diffused active region. In the second reset step, after the second reset transistor 106 is turned off, the first reset transistor 103 is turned on. Subsequently, the first reset transistor 103 is turned on, and the first to xth charge transport transistors are turned on.

[0070] Reset signal reading: After performing a second reset operation on the floating diffusion active region FD, the potential signal of the floating diffusion active region FD is output, and the reset signals from the first pixel to the xth pixel are obtained sequentially.

[0071] Furthermore, after the floating diffusion active region FD is reset a second time, the potential signal of the first pixel is obtained by reading the potential signal of the floating diffusion active region FD; the charge of the first pixel is transferred to the floating diffusion active region FD, the exposure of the first pixel ends, and the potential signal of the floating diffusion active region FD is read to obtain the second potential signal of the first pixel; and so on, the floating diffusion active region FD is reset a second time, the potential signal of the floating diffusion active region FD is read to obtain the first potential signal of the nth pixel; the charge of the nth pixel is transferred to the floating diffusion active region FD, the exposure of the nth pixel ends, and the potential signal of the floating diffusion active region FD is read to obtain the second potential signal of the nth pixel; accordingly, the reset signals of the first pixel to the xth pixel are obtained sequentially.

[0072] Charge transfer: turn off the first reset transistor 103 and turn on the first charge transfer transistor to the xth charge transfer transistor, so that after outputting the potential signal of the floating diffuse active region FD, the photoelectric charge stored in the photosensitive unit in the pixel is transferred to the floating diffuse active region FD, and the image signals of the first and xth pixels are acquired in sequence.

[0073] Charge readout: The source follower transistor 104 reads out the photoelectric charge transferred to the floating diffuse active region FD. In embodiments including a row select transistor RS, the photoelectric charge transferred to the floating diffuse active region FD can also be read out by the select transistor RS via the source follower transistor 104.

[0074] For example, taking the transfer of charge of the first pixel to the floating diffusion active region FD as an example, the method includes: turning on the first charge transfer transistor 1021, transferring the charge of the first pixel to the floating diffusion active region, and then turning off the first charge transfer transistor 1021; turning on the first to xth charge transfer transistors, transferring the charge of the xth pixel to the floating diffusion active region FD, and then turning off the first to xth charge transfer transistors.

[0075] It is understood that in the reading method provided in the embodiments of this application, the photosensitive units in each pixel are read sequentially. That is, after each pixel is exposed, the steps of second reset, reset signal reading, charge transfer, and charge readout are performed sequentially.

[0076] As an example, the second reset step of the first pixel begins by turning on the first reset transistor 103 to perform a second reset of the floating diffusion active region FD. Next, a reset signal readout operation for the first pixel is performed, that is, the potential signal of the floating diffusion active region FD is read to obtain the first potential signal R1 of the first pixel. Then, a charge transfer operation for the first pixel is performed, turning on the first charge transfer transistor 1021, and after the first pixel's exposure ends and the charge of the first pixel is transferred to the floating diffusion active region, the first charge transfer transistor 1021 is turned off. Finally, an initial photoelectric signal readout operation for the first pixel is performed, reading the potential signal of the floating diffusion active region to obtain the second potential signal of the first pixel.

[0077] In a further example, the steps of the second pixel performing a second reset, reset signal reading, charge transfer, and charge readout are as follows: For the second reset, the first reset transistor 103 is turned on to perform a second reset on the floating diffusion active region FD, and then the first and second charge transfer transistors are turned on; the potential signal of the floating diffusion active region FD is read to obtain the first potential signal of the second pixel; for the charge transfer operation of the second pixel, the first and second charge transfer transistors are turned on, and after the first pixel finishes exposure, the charge of the second pixel is transferred to the floating diffusion active region FD, and the first and second charge transfer transistors are turned off; the potential signal of the floating diffusion active region FD is read to obtain the second potential signal of the second pixel.

[0078] Similarly, for the nth pixel, the first reset transistor 103 is turned on to perform a second reset of the floating diffuse active region FD, and the first to nth charge transfer transistors are turned on. The reset signal reading operation for the nth pixel can be performed by reading the potential signal of the floating diffuse active region FD and obtaining the first potential signal of the nth pixel. The charge transfer operation for the nth pixel can be performed by: turning on the first to nth charge transfer transistors; after the nth pixel's exposure ends, transferring the charge of the nth pixel to the floating diffuse active region FD, and then turning off the first to nth charge transfer transistors. Finally, the initial photoelectric signal reading of the nth pixel is performed, and the potential signal of the floating diffuse active region FD is read to obtain the second potential signal of the nth pixel.

[0079] In one embodiment of the invention, the pixel further includes an auxiliary polysilicon gate, which is disposed parallel to one side of the cathode end of the photosensitive unit. Accordingly, the first reset step should further include: turning off the first charge transport transistor and setting the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor from the initial potential to the first negative potential, thereby resetting the potential of the first photosensitive unit corresponding to the first charge transport transistor.

[0080] At this time, the potentials of the first to nth auxiliary polysilicon gates can be set to a first negative potential V1. In one embodiment of the invention, the potential of the first auxiliary polysilicon gate 11 can be set from an initial potential to a first negative potential V1. In one embodiment of the invention, the preferred range of the initial potential is -0.5V to 0.5V, and the preferred range of the first negative potential V1 is -1.5V to -0.5V.

[0081] The xth charge transport transistor is turned off in sequence, exposing the x-1th photosensitive unit corresponding to the x-1th charge transport transistor; and the potential of the xth auxiliary polysilicon gate corresponding to the xth charge transport transistor is set from the initial potential to the first negative potential, thus resetting the potential of the xth photosensitive unit corresponding to the xth charge transport transistor.

[0082] After the (x-1)th photosensitive unit is exposed, the potential of the (x-1)th auxiliary polysilicon gate corresponding to the (x-1)th photosensitive unit is set from the first negative potential to the initial potential.

[0083] When x=n, that is, when the x-th pixel is actually the n-th pixel, after the x-1-th photosensitive unit is exposed, the potential of the x-th auxiliary polysilicon gate corresponding to the x-th charge transport transistor is set from the initial potential to the first negative potential, and the second reset transistor is turned off, so that the x-th photosensitive unit corresponding to the x-th charge transport transistor is exposed; after the x-th photosensitive unit is exposed, the potential of the x-th auxiliary polysilicon gate is set from the first negative potential to the initial potential.

[0084] For example, the potential of the first auxiliary polysilicon gate 11 is set to a first negative potential; the second charge transport transistor 1022 is turned off, the first photosensitive unit 1011 is controlled to start exposure, and the potential of the first auxiliary polysilicon gate 11 is set to an initial potential; the potential of the second auxiliary polysilicon gate 12 is set to a first negative potential; the third charge transport transistor 1023 is turned off, the second photosensitive unit 1012 is controlled to start exposure, and the potential of the second auxiliary polysilicon gate 12 is set to an initial potential. Similarly, the potential of the (x-1)th auxiliary polysilicon gate is set to a first negative potential; the nth charge transport transistor 102n is turned off, the (x-1)th photosensitive unit is controlled to start exposure, and the potential of the (x-1)th auxiliary polysilicon gate is set to an initial potential; the potential of the nth auxiliary polysilicon gate 1n is set to a first negative potential, the second reset transistor 106 is turned off, the nth photosensitive unit 101n is controlled to start exposure, and the potential of the nth auxiliary polysilicon gate 1n is set to an initial potential.

[0085] Furthermore, in one embodiment of the invention:

[0086] The time interval between the start time of the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor from the initial potential to the first negative potential and the start time of turning off the first charge transport transistor is 50ns~150ns.

[0087] The time interval between the start time of the potential of the xth auxiliary polysilicon gate corresponding to the xth charge transport transistor from the initial potential to the first negative potential and the start time of turning off the xth charge transport transistor is 50ns~150ns.

[0088] The time interval between setting the potential of the (x-1)th auxiliary polysilicon gate to the initial potential and the time interval between turning off the xth charge transport transistor is 50ns to 150ns.

[0089] The time interval between setting the potential of the xth auxiliary polysilicon gate to the initial potential and the time interval between setting the initial potential and turning off the second reset transistor 106 is preferably in the range of 50ns to 150ns.

[0090] For example, the time interval between the start time of setting the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor as the initial potential and the start time of turning off the second charge transport transistor 1022 is preferably in the range of 50ns to 150ns; the time interval between setting the potential of the second auxiliary polysilicon gate as the initial potential and the start time of turning off the third charge transport transistor 1023 is preferably in the range of 50ns to 150ns; the time interval between setting the potential of the nth auxiliary polysilicon gate as the initial potential and the start time of turning off the second reset transistor 106 is preferably in the range of 50ns to 150ns.

[0091] In the charge transfer step, after turning on the first charge transfer transistor to the xth charge transfer transistor, negative voltages can be applied to the first auxiliary polysilicon gate to the xth auxiliary polysilicon gate respectively to ensure that the charge of several pixels is fully output; along the direction away from the floating diffusion active region, the potential of the negative voltage received by the first auxiliary polysilicon gate to the potential of the negative voltage received by the nth auxiliary polysilicon gate decreases sequentially: in other words, there is a gradient relationship between the highest potential of the potential well from the nth photosensitive unit 101n to the first photosensitive unit 1011, the highest potential of the potential well of the nth photosensitive unit 101n is the lowest, and the highest potential of the potential well of the first photosensitive unit 1011 is the highest. The nth photosensitive unit 101n, which is farthest from the FD, does not have a charge residue problem after the charge transfer is completed, and the image sensor does not have a ghosting problem.

[0092] It is understandable that, in the charge transfer step, the time interval between the step of turning on the first charge transfer transistor to the xth charge transfer transistor and the step of applying negative voltages to the first auxiliary polysilicon gate to the xth auxiliary polysilicon gate is 50ns to 150ns.

[0093] Figure 7 This is a schematic diagram of the photoelectric signals of each pixel in an image sensor according to an embodiment of the present invention. In this embodiment, the image sensor reading method includes: obtaining the photoelectric signal Sig1 of the first pixel based on the first potential signal R1 and the second potential signal S1 of the first pixel; obtaining the photoelectric signal Sig2 of the second pixel based on the first potential signal R2, the second potential signal S2, the photoelectric signal Sig1 of the first pixel, the time difference Δt, and the exposure period T, wherein the time difference between the end time of charge transfer of the Nth pixel and the end time of the second reset of the Nth pixel is set as the time difference Δt, N is a natural number less than or equal to n, and the exposure period T of the photosensitive unit of any pixel is set to be the same; and so on, obtaining the photoelectric signal Sign of the nth pixel based on the difference between the first potential signal Rn of the nth pixel, the difference Sn of the second potential signal of the nth pixel, the photoelectric signals Sig1 to SigX-1 of the first to (x-1)th pixels, the time difference Δt, and the exposure period T.

[0094] Specifically, this embodiment corrects the photoelectric signals of pixels. Please refer to... Figures 5 to 7 ,like Figure 5 As shown, when reading the data after exposure of n pixels in a pixel unit, each pixel first undergoes a second reset, then the first potential of the pixel is read, followed by charge transfer, and finally the second potential of the pixel is read; as... Figure 6As shown, when reading the photoelectric signal of a pixel, it is necessary to calculate based on the potential well of the floating diffuse active region (FD). During the calculation, the influence of charge transfer from previous pixels to the FD needs to be removed. For example... Figure 7 As shown, when calculating the photoelectric signal of each pixel, it is necessary to correct for the time interval Δt between the end time of the second reset of the Nth pixel and the end time of the charge transfer at the end of the exposure of the Nth pixel. Specifically, the photoelectric signal Sign of the Nth pixel is obtained based on the difference between the first potential signal Rn of the Nth pixel, the second potential signal Sn of the Nth pixel, the photoelectric signals Sig1 to SigX-1 of the first to (x-1)th pixels, the time interval Δt, and the exposure period T. Here, the time difference between the end time of the charge transfer of the Nth pixel and the end time of the second reset of the Nth pixel can be set as the time interval, where N is a natural number less than or equal to n. Figure 5 As shown, the time interval Δt can be t7~t10 or t12 to t17. That is, the end time of the second reset of the second pixel can be the time when the first reset transistor 103 is turned off, and the end time of the charge transfer of the second pixel can be the time when the first to second charge transfer transistors 1021 and 1022 are turned off; the end time of the second reset of the nth pixel can be the time when the first reset transistor 103 is turned off, and the end time of the charge transfer of the nth pixel can be the time when the first charge transfer transistor 1021 to the nth charge transfer transistor 102n are turned off.

[0095] In one embodiment, the photoelectric signal Sig1 of the first pixel is expressed as: Wherein, Sig1 is the photoelectric signal read from the first pixel, R1 is the reset signal of the first pixel, and S1 is the image signal of the first pixel.

[0096] In one embodiment, the expression for the photoelectric signal read from the x-th pixel is: Wherein, Sigx is the photoelectric signal read from the x-th pixel, Rx is the reset signal of the x-th pixel, Sx is the image signal of the x-th pixel, Sigx-1 is the photoelectric signal read from the (x-1)-th pixel, ΣSigx-1 is the sum of the photoelectric signals read from Sig1 to Sigx-1, Δt is the time interval between the second reset step and the charge transfer step, T is the exposure period, and x is a natural number where 2≤x≤N.

[0097] Therefore, the expression for the photoelectric signal of the second pixel is: Wherein, Sig2 is the photoelectric signal read out of the second pixel, R2 is the reset signal of the second pixel, S2 is the image signal of the second pixel, Sig2 is the photoelectric signal read out of the second pixel, ΣSig2 is actually the sum of the photoelectric signals read out from Sig1 to Sig2, Δt is the time interval between the second reset step and the charge transfer step, and T is the exposure period.

[0098] The image sensor pixels of this invention employ a pixel unit sharing method, saving the number of transistors and increasing the area occupancy of photosensitive units within the pixel. This effectively improves the photoelectric conversion quantum efficiency of the photosensitive units, making it particularly suitable for the design layout of small-area pixel image sensors. The pixel units of this invention are arranged in a series configuration, which, compared to the parallel sharing layout of existing technologies, significantly improves the photoelectric conversion gain of the floating diffuse active region, thereby effectively reducing pixel signal noise. Therefore, the image sensor and readout method of this invention improve pixel photosensitive quantum efficiency and simultaneously increase pixel photoelectric conversion gain, effectively reducing pixel signal noise.

[0099] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. An image sensor comprising a plurality of pixel units, said pixel unit including a first reset transistor and a source follower transistor connected to a floating diffuse active region, characterized in that, The pixel unit further includes a second reset transistor and several pixels connected in series, with one end connected to the floating diffusion active region and the other end connected to a power supply through the second reset transistor. Each pixel includes interconnected charge transport transistors and photosensitive units. The charge transport transistors of the several pixels are connected in series between the floating diffusion active region and the second reset transistor, and the photosensitive units of the several pixels are connected between the corresponding charge transport transistors and ground. The pixels of the pixel unit are arranged in series, and the pixel unit includes n pixels, where n is a natural number greater than or equal to 2. The source terminal of the second reset transistor is connected to the first terminal of the nth photosensitive unit and the source terminal of the nth charge transport transistor. All n pixels are used for imaging, and each pixel is used for first reset, pixel exposure, second reset, reset signal readout, and charge readout.

2. The image sensor as described in claim 1, characterized in that, An auxiliary polysilicon gate is also provided on one side of the photosensitive unit of the plurality of pixels.

3. The image sensor as described in claim 2, characterized in that, The auxiliary polysilicon gate is used to receive a negative potential to accelerate the removal of residual charge.

4. The image sensor as described in claim 2, characterized in that, The auxiliary polysilicon gate is used to receive a first negative voltage to an Nth negative voltage, wherein the potential of the first negative voltage to the Nth negative voltage decreases sequentially to ensure that the charge of the plurality of pixels is fully output.

5. The image sensor as described in claim 2, characterized in that, The vertical projection of the auxiliary polysilicon gate onto the photosensitive unit is a polygon or an ellipse.

6. The image sensor as described in claim 2, characterized in that, The surface area of ​​the auxiliary polysilicon gate near the photosensitive unit is 0.2 to 0.8 times the surface area of ​​the cathode end of the photosensitive unit.

7. The image sensor as described in claim 2, characterized in that, In the first direction, the auxiliary polysilicon gate is coaxially arranged with the photosensitive unit.

8. The image sensor according to claim 1, characterized in that, The drain of the first reset transistor and the drain of the source follower transistor are both connected to a power supply, and the source of the first reset transistor and the gate of the source follower transistor are both connected to the floating diffuse active region; the source of the source follower transistor is connected to the output terminal; the first reset transistor is used to reset the charge signal of the floating diffuse active region and the source follower transistor before the pixel is exposed; the source follower transistor is used to receive the charge signal transmitted by the pixel and amplify and output it.

9. The image sensor according to claim 8, characterized in that, The image sensor also includes a row selection transistor, and the source follower transistor is connected to the output terminal through the row selection transistor.

10. The image sensor according to claim 1, characterized in that, The image sensor also includes a dual-conversion gain control module connected between the first reset transistor and the floating diffused active region. The dual-conversion gain control module includes at least one dual-conversion gain control transistor and a capacitor. The dual-conversion gain control module is used to switch between a low conversion gain mode and a high conversion gain mode.

11. The image sensor reading method according to any one of claims 1 to 10, characterized in that, include: In the first reset, the second reset transistor is turned on, and the Nth to Xth charge transport transistors are turned on. The pixels are reset sequentially along the direction away from the floating diffused active region to clear the charge of the pixels sequentially. Wherein, X is a natural number and 2≤X≤N. Pixel exposure involves sequentially turning off the Xth charge transport transistor and exposing any pixel after performing a first reset operation. The second reset involves turning off the second reset transistor, turning on the first reset transistor, and turning on the first to the Xth charge transport transistors to perform a reset operation on the floating diffused active region. Reset signal reading: After performing a second reset operation on the floating diffusion active region, the potential signal of the floating diffusion active region is output, and the reset signals from the first pixel to the Xth pixel are obtained sequentially. Charge transfer: turn off the first reset transistor and turn on the first charge transfer transistor to the Xth charge transfer transistor, so that after outputting the potential signal of the floating diffuse active region, the photoelectric charge stored in the photosensitive unit of the pixel is transferred to the floating diffuse active region, and the image signals of the first and Xth pixels are acquired sequentially. Charge readout: The source follower transistor transfers photoelectric charge readout to the floating diffuse active region.

12. The image sensor reading method according to claim 11, characterized in that, The pixel further includes an auxiliary polysilicon gate, which is disposed parallel to one side of the cathode end of the photosensitive unit, wherein the first reset step includes: Turn off the first charge transport transistor and set the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor from the initial potential to the first negative potential, thereby resetting the potential of the first photosensitive unit corresponding to the first charge transport transistor. The Xth charge transport transistor is turned off in sequence, exposing the X-1 photosensitive unit corresponding to the X-1th charge transport transistor; and the potential of the Xth auxiliary polysilicon gate corresponding to the Xth charge transport transistor is set from the initial potential to the first negative potential, thus resetting the potential of the Xth photosensitive unit corresponding to the Xth charge transport transistor. After the X-1 photosensitive unit is exposed, the potential of the X-1 auxiliary polysilicon gate corresponding to the X-1 photosensitive unit is set from the first negative potential to the initial potential.

13. The image sensor reading method according to claim 12, characterized in that, When X=N, the first reset step further includes: After the X-1 photosensitive unit is exposed, the potential of the X auxiliary polysilicon gate corresponding to the X charge transport transistor is set from the initial potential to the first negative potential, and the second reset transistor is turned off, so that the X photosensitive unit corresponding to the X charge transport transistor is exposed. After the Xth photosensitive unit is exposed, the potential of the Xth auxiliary polysilicon gate is set from the first negative potential to the initial potential.

14. The image sensor reading method according to any one of claims 12 and 13, characterized in that, The initial potential is -0.5V to 0.5V, and the first negative potential is set to -1.5V to -0.5V.

15. The image sensor reading method according to any one of claims 12 and 13, characterized in that: The time interval between the step of turning off the first charge transport transistor and the step of setting the potential of the first auxiliary polysilicon gate corresponding to the first charge transport transistor from the initial potential to the first negative potential is 50 ns to 150 ns. The time interval between the step of turning off the Xth charge transport transistor and the step of setting the potential of the Xth auxiliary polysilicon gate corresponding to the Xth charge transport transistor from the initial potential to the first negative potential is 50 ns to 150 ns. The time interval between the step of turning off the Xth charge transport transistor and the step of setting the potential of the (X-1)th auxiliary polysilicon gate from the first negative potential to the initial potential is 50 ns to 150 ns; The time interval between the step of turning off the second reset transistor and the step of setting the potential of the Xth auxiliary polysilicon gate from the first negative potential to the initial potential is 50 ns to 150 ns.

16. The image sensor reading method according to claim 12, characterized in that, The charge transfer steps include: Turn on the first charge transport transistor to the Xth charge transport transistor; Negative voltages are applied to the first auxiliary polysilicon gate to the Xth auxiliary polysilicon gate respectively to ensure that the charge of the plurality of pixels is fully output; along the direction away from the floating diffused active region, the potential of the negative voltage received by the first auxiliary polysilicon gate to the potential of the negative voltage received by the Nth auxiliary polysilicon gate decreases sequentially.

17. The image sensor reading method according to claim 12, characterized in that, In the charge transfer step: The time interval between the steps of turning on the first charge transport transistor to the Xth charge transport transistor and the steps of applying negative voltages to the first auxiliary polysilicon gate to the Xth auxiliary polysilicon is 50 ns to 150 ns.

18. The image sensor reading method according to claim 11, characterized in that: The expression for the photoelectric signal read from the first pixel is: Wherein, Sig1 is the photoelectric signal read out by the first pixel, R1 is the reset signal of the first pixel, and S1 is the image signal of the first pixel; The expression for the photoelectric signal read from the Xth pixel is: Among them, Sig x R is the photoelectric signal read from the Xth pixel. x S is the reset signal for the Xth pixel. x For the image signal of the Xth pixel, Sig x-1 Δt is the photoelectric signal read from the (X-1)th pixel, Δt is the time interval between the second reset step and the charge transfer step, T is the exposure period, and X is a natural number where 2≤X≤N.

Images