Photoelectric sensors, random readout active pixel circuits, image sensors and camera devices

Abstract

The present invention provides a photoelectric sensor, a randomly readable active pixel circuit, an image sensor and a camera device. The photoelectric sensor includes a doped region, a substrate, a doped source region, a doped drain region and two isolation regions; the doped region is arranged on the bottom surface of the substrate to form a photodiode with the substrate; and the doped region forms a cathode of the photodiode, and the cathode is used to connect a positive voltage to make the photodiode work in a reverse bias region; the doped source region and the doped drain region are arranged at intervals on the top of the substrate to form a field effect transistor with the substrate; the top surface of the doped source region forms a source electrode, and the top surface of the doped drain region forms a drain electrode; the two isolation regions are respectively located on opposite sides of the substrate, and extend from the doped source region and the doped drain region to the doped region from top to bottom; the top surface of the substrate is sequentially formed with a gate insulating layer and a gate electrode arranged between the doped source region and the doped drain region from bottom to top; the gate electrode is used to connect a voltage to select the working state of the field effect transistor to be in a wide dynamic response range mode or a high gain mode.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and in particular to a photoelectric sensor, a randomly readable active pixel circuit, an image sensor and a camera device. Background Art

[0002] Phototransistor is a commonly used integrated photoelectric sensor, which includes two parts: photoelectric sensor and photocurrent amplifier. Traditional phototransistors are prepared using bipolar process and front side illumination (FSI). Since the incident light needs to pass through the passivation layer, interconnection insulation layer and metal wiring layer to reach the photosensitive area and be absorbed. In this process, the light will be reflected by the insulating medium or metal and cause loss, or refracted through multiple layers of insulating medium and change the light path. These factors will reduce the quantum efficiency.

[0003] In addition, Figure 1 and Figure 2 As shown, the conventional phototransistor can be either NPN or PNP. When the phototransistor is used, the collector of the phototransistor is connected to a fixed positive potential VDD, the emitter is grounded, and the base is suspended for light sensing. When light is irradiated on the base, a photocurrent is generated between the base and the collector, and is amplified by the phototransistor to generate current gain. However, compared with CMOS devices, conventional phototransistors are larger in size and incompatible with CMOS processes, and cannot be used in high-resolution image sensors. Summary of the invention

[0004] Based on this, in order to solve the problems that phototransistors have low quantum efficiency, large size, and cannot be applied to image sensors, the present invention provides a photoelectric sensor, a randomly readable active pixel circuit, an image sensor, and a camera device.

[0005] According to a first aspect of an embodiment of the present invention, the present invention provides a photoelectric sensor, comprising a doped region, a substrate, a doped source region, a doped drain region and two isolation regions;

[0006] The doped region is arranged on the bottom surface of the substrate to form a photodiode with the substrate; and the doped region forms a cathode of the photodiode, and the cathode is used to connect a positive voltage to make the photodiode work in a reverse bias region;

[0007] The doped source region and the doped drain region are arranged at intervals on the top of the substrate to form a field effect transistor with the substrate; a source electrode is formed on the top surface of the doped source region, and a drain electrode is formed on the top surface of the doped drain region;

[0008] The two isolation regions are respectively located at opposite sides of the substrate and extend from the doped source region and the doped drain region to the doped region from top to bottom, respectively, to isolate adjacent pixels or adjacent sensors;

[0009] The top surface of the substrate is sequentially formed with a gate insulating layer and a gate arranged between the doped source region and the doped drain region from bottom to top; the gate is used to connect a voltage to make the working state of the field effect transistor in a wide dynamic response range mode or a high gain mode.

[0010] According to the second aspect of an embodiment of the present invention, the present invention provides an active pixel circuit that can be randomly read, characterized in that it includes a gate tube and the above-mentioned photoelectric sensor; the drain of the gate tube is electrically connected to the source of the photoelectric sensor, and the source of the gate tube serves as the circuit output end; in the photoelectric sensor, the cathode and the drain are connected in series.

[0011] According to a third aspect of the embodiments of the present invention, the present invention provides an image sensor, wherein the image sensor comprises the above-mentioned randomly readable active pixel circuit.

[0012] According to a fourth aspect of the embodiments of the present invention, the present invention provides a camera device, which includes the above-mentioned image sensor.

[0013] Compared with the prior art, the present invention produces at least the following beneficial technical effects:

[0014] The present invention forms a doped source region, a doped drain region, a gate insulating layer and a gate on the top surface of a substrate, and forms a doped region and a cathode on the bottom surface of the substrate to form a back-illuminated integrated photoelectric sensor of a photodiode and a field effect transistor on a common substrate. Thus, by utilizing the advantages of the back-illuminated type and the above-mentioned structure, the technical problems of low quantum efficiency, large volume and inability to be applied to image sensors in the related art of photosensitive triodes can be solved. It can also be compatible with the preparation process of back-illuminated CMOS image sensors and can be prepared into a small-size device for use in image sensors. In addition, in subsequent applications, it may be necessary to apply multiple photoelectric sensors to integrate the required photosensitive devices, such as image sensors or cameras or display devices, but not limited thereto. In this way, multiple photoelectric sensors are generally arranged in an array, so there will inevitably be a situation where photoelectric sensors are arranged adjacent to each other, and a certain amount of crosstalk will be generated between adjacent photoelectric sensors. Therefore, by setting the two isolation regions, adjacent pixels or adjacent sensors can be isolated to avoid crosstalk between adjacent pixels or adjacent sensors.

[0015] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a schematic diagram of the structure of a traditional phototransistor;

[0017] Figure 2 It is the equivalent circuit diagram of the traditional phototransistor;

[0018] Figure 3 is a schematic structural diagram of a photoelectric sensor according to an exemplary embodiment of the present invention;

[0019] Figure 4 is an equivalent circuit diagram of a photoelectric sensor according to an exemplary embodiment of the present invention;

[0020] Figure 5 is a schematic diagram of a curve showing a change in output current of a photoelectric sensor with the intensity of incident light according to an exemplary embodiment of the present invention;

[0021] Figure 6 is a schematic diagram of a curve showing a relationship between gain and gate voltage of a photoelectric sensor under different light intensities according to an exemplary embodiment of the present invention;

[0022] Figure 7 is a schematic diagram of a simulation effect of light gain of a photoelectric sensor when it works in an off-state region according to an exemplary embodiment of the present invention;

[0023] Figure 8 It is a schematic diagram of the circuit structure of a conventional random read logarithmic active pixel circuit;

[0024] Fig. 9 It is a schematic diagram of the circuit structure of a conventional back-illuminated active pixel circuit;

[0025] Fig.10 is a schematic diagram of a circuit structure of a randomly readable active pixel circuit according to an exemplary embodiment of the present invention;

[0026] Fig.11 yes Fig.10 The equivalent circuit diagram of the random readout active pixel circuit is shown. DETAILED DESCRIPTION

[0027] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Instead, they are merely examples of devices and methods consistent with some aspects of the present invention as detailed in the appended claims.

[0028] The terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates their meaning. It should also be understood that the term "and / or" used in the present invention refers to any or all possible combinations of one or more associated listed items.

[0029] In order to at least solve the technical problems in the related art that the phototransistor has low quantum efficiency, large size, and cannot be applied to image sensors, the present invention provides a photoelectric sensor, which forms a doped source region, a doped drain region, a gate insulating layer, and a gate on the top surface of a substrate, and forms a doped region and a cathode on the bottom surface of the substrate to form a back-illuminated integrated photoelectric sensor of a photodiode and a field effect transistor on a common substrate. Thus, by utilizing the advantages of the back-illuminated type and the above-mentioned structure, the technical problems in the related art that the phototransistor has low quantum efficiency, large size, and cannot be applied to image sensors can be solved. It can also be compatible with the preparation process of the back-illuminated CMOS image sensor and can be prepared into a small-sized device for use in image sensors. The photoelectric sensor provided by the present invention is described below:

[0030] like Figure 3 As shown, the photoelectric sensor provided in the embodiment of the present invention includes a doped region, a substrate, a doped source region, a doped drain region and two isolation regions. The doped region is arranged on the bottom surface of the substrate to form a photodiode with the substrate; and the doped region forms a cathode of the photodiode, and the cathode is used to connect a positive voltage to make the photodiode work in the reverse bias region. The doped source region and the doped drain region are arranged at intervals on the top of the substrate to form a field effect transistor with the substrate; a source is formed on the top surface of the doped source region, and a drain is formed on the top surface of the doped drain region. The two isolation regions are respectively located on opposite sides of the substrate, and extend from the doped source region and the doped drain region to the doped region from top to bottom, respectively, to isolate adjacent pixels or adjacent sensors. The top surface of the substrate is sequentially formed with a gate insulating layer and a gate arranged between the doped source region and the doped drain region from bottom to top; the gate is used to connect a voltage to make the working state of the field effect transistor in a wide dynamic response range mode or a high gain mode.

[0031] Thus, the doped region and substrate on the back of the photoelectric sensor of the embodiment of the present invention jointly form a photodiode for detecting incident light and converting visible light into photocharges; at the same time, the doped source region, doped drain region and substrate on the front of the photoelectric sensor jointly form a field effect transistor (Metal-Oxide-Semiconductor Field-EffectTransistor, MOSFET) for amplifying the photocurrent generated by the photodiode. Among them, the doped source region, doped drain region and substrate on the front of the photoelectric sensor respectively constitute the source region, drain region and channel region of the field effect transistor, and the gate insulating layer and gate on the top surface of the substrate are the gate insulating layer and gate of the field effect transistor respectively; at the same time, the source electrode formed on the top surface of the doped source region and the drain electrode formed on the top surface of the doped drain region are the source electrode and drain electrode of the field effect transistor respectively. In addition, in subsequent applications, it may be necessary to apply multiple photoelectric sensors to integrate the required photosensitive devices, such as image sensors or cameras or display devices, but not limited to this. In this way, multiple photoelectric sensors are generally arranged in an array, so there will inevitably be a situation where photoelectric sensors are arranged adjacent to each other, and a certain amount of crosstalk will be generated between adjacent photoelectric sensors. Therefore, by providing the two isolation regions, adjacent pixels or adjacent sensors can be isolated to avoid crosstalk between adjacent pixels or adjacent sensors.

[0032] In the above, the isolation region may be prepared by deep trench isolation technology or capacitor deep trench isolation technology, but is not limited thereto.

[0033] In the above, the substrate may be a lightly doped P-type substrate or a lightly doped N-type substrate. Based on this, in the embodiment where the substrate is a P-type substrate, the doped region, the doped source region and the doped drain region are all N-type heavily doped regions; in the embodiment where the substrate is an N-type substrate, the doped region, the doped source region and the doped drain region are all P-type heavily doped regions.

[0034] The working principle of the photoelectric sensor of the embodiment of the present invention is described below by taking the substrate as a lightly doped P-type silicon substrate as an example:

[0035] In order to keep the photoelectric sensor in working state, a constant positive voltage is connected to the cathode to make the photodiode work in the reverse bias region.

[0036] When the photoelectric sensor is in working state, after the incident light enters the photodiode, it is converted into photogenerated electron-hole pairs by the photodiode. Under the action of the built-in electric field of the photodiode, the holes in the photogenerated electron-hole pairs are swept into the substrate, causing the potential of the substrate to increase, generating a substrate forward bias on the field effect transistor, thereby adjusting the working threshold voltage of the field effect transistor. When the field effect transistor works in the off-state region, the inversion layer channel is not formed. At this time, the doped source region-substrate-doped drain region of the field effect transistor can be equivalent to a (N+)P(N+) bipolar transistor (Bipolar Junction Transistor, BJT); among them, the drain of the field effect transistor can be regarded as the collector of the BJT, the substrate can be regarded as the base of the BJT, and the source can be regarded as the emitter of the BJT; the photogenerated current generated by the photodiode can be regarded as the forward hole current flowing into the base of the BJT. At this time, the BJT working in the amplification region amplifies the forward hole current to obtain the output current I DS :

[0037]

[0038] In formula (1), β is the magnification factor of the BJT collector current to the base current, I PD is the photocurrent of the photodiode, I s is the reverse saturation current of the photodiode, k is the Boltzmann constant, T is the absolute temperature, q is the charge constant, η is the internal quantum efficiency, R is the reflection loss of the device to the incident light, α is the absorption coefficient of the substrate material to light, d is the depth of the edge of the P-type region of the photodiode depletion region, A is the area of ​​the photodiode, P in is the incident light power, h is Planck's constant, v is the incident light frequency, D E 、N E , L E are respectively the minority carrier diffusion coefficient of the source region, the impurity doping concentration, the minority carrier diffusion coefficient, and D B 、N B , L B are the minority carrier diffusion coefficient, doping concentration, and minority carrier diffusion length of the substrate region, and L is the channel length between the source region and the drain region. BS is the substrate voltage, which varies with the intensity of the incident light on the photodiode:

[0039]

[0040] When the gate voltage is increased to make the field effect transistor work in the subthreshold region, as the substrate potential increases, the working threshold voltage of the field effect transistor decreases and the output current increases. At this time, the relationship between the output current and the intensity of the incident light is:

[0041]

[0042] In formula (3), μ N is the field effect mobility of the field effect transistor, C ox is the gate insulation capacitance, W and L are the channel width and length of the field effect transistor respectively, V GS is the gate voltage, γ is the body effect coefficient, Φ fp is the potential difference between the Fermi level and the intrinsic Fermi level, n is the reverse slope of the subthreshold current, and its relationship with the subthreshold swing S is:

[0043] Therefore, if Figures 5 to 7 As shown in the figure, the photoelectric sensor provided by the embodiment of the present invention can realize that when the photoelectric sensor works in the off-state region, its output current is linearly related to the light intensity of the incident light, and has a dynamic range of 160dB, which is higher than that of the traditional CMOS photoelectric sensor. At this time, the photoelectric sensor is in a wide dynamic response range mode. When the photoelectric sensor works in the subthreshold region, its output current tends to be linearly related to the light intensity of the incident light, and the optical gain can be as high as 10 6 -10 7 , at this time, the photoelectric sensor is in the working state of the high gain mode. Among them, the working area of ​​the photoelectric sensor can be adjusted by adjusting the gate voltage to select the wide dynamic response range mode or the high gain mode.

[0044] In one embodiment, the substrate may be a lightly doped silicon wafer substrate or a silicon epitaxial layer substrate.

[0045] In one embodiment, in order to further reduce the volume of the entire photoelectric sensor and to increase the photosensitive area of ​​the photodiode to a certain extent, the cathode is formed by an electrode layer plated on the bottom surface of the doped region. Based on this, in order to reduce the loss of the photodiode when absorbing incident light, in one embodiment, the electrode layer is a transparent electrode layer.

[0046] It should be noted that the various technical features in the above implementations can be combined arbitrarily as long as there is no conflict or contradiction between the combinations of features. However, due to space limitations, they are not described one by one.

[0047] Based on the above-mentioned embodiment of the photoelectric sensor, the embodiment of the present invention further provides an active pixel circuit capable of random reading, so as to at least solve the following problems of the conventional active pixel circuit:

[0048] (a) If Figure 8As shown, for a conventional random read logarithmic active pixel circuit with a wide dynamic response range, it includes three field effect transistors and a conventional photodiode. The three field effect transistors are respectively a reset transistor Trst, a source follower Tsf and a gate tube Tsel. The conventional random read logarithmic active pixel circuit has a random read type, and its output signal changes logarithmically with the change of light intensity, so it has a wide dynamic response range, which can generally reach more than 100dB. In addition, the conventional random read logarithmic active pixel circuit does not need to be reset, so the pixel fill factor is large, the operation is fast and simple. At the same time, each pixel in the conventional random read logarithmic active pixel circuit works independently and does not need to perform time integration of the photogenerated charge during the photoelectric conversion process, so it can be read randomly in space and time. The random readability in space allows important signals to be read and processed independently, making the sensor more intelligent, and the random readability in time allows the signal to be read out and processed more quickly, so the random readability in space and time makes the reading speed of effective signals faster. However, the device connection method inside the pixel of the traditional random read logarithmic active pixel circuit makes the output signal decrease as the light intensity increases, so the back-end signal readout and processing circuit needs to be redesigned. Moreover, it is precisely because the output and input of the traditional random read logarithmic active pixel circuit are logarithmically related that the sensor has low sensitivity under weak light intensity. The design using three transistors also makes it difficult to reduce the pixel size, so the spatial resolution is also limited.

[0049] (ii) Fig. 9 As shown, for the traditional back-illuminated active pixel circuit, it is a structure of an active pixel circuit (4T-APS) containing four transistors, including a pinned photodiode (PPD), a transmission tube Tx, a reset switch field effect transistor Trst, a source follower Tsf, and a gate tube Tsel. Among them, the incident light illuminates the PPD from the back. Compared with the front-illuminated (FSI) structure, this back-illuminated structure has a larger photosensitive area and fill factor, thereby improving quantum efficiency and sensitivity. However, this 4T-APS circuit structure is complex, and the timing operation of resetting-integrating-reading the pixel is required, and it does not have random readability. In addition, it is necessary to compromise on the indicators of high sensitivity and wide dynamic response range.

[0050] From the above, it can be seen that the randomly readable active pixel circuit in the embodiment of the present invention solves at least the following technical problems: the signal isolation and processing circuit at the back end of the traditional random read logarithmic active pixel circuit in the related technology needs to be redesigned, the sensitivity is low under weak light intensity, the pixel size is difficult to reduce and the spatial resolution is limited due to the use of three transistors, and the back-illuminated active pixel circuit of the 4T-APS structure has a complex structure, does not have random readability, and is not compatible with high sensitivity and a wide dynamic response range.

[0051] In response to the above technical issues, such as Fig.10 and Fig.11 As shown, the randomly readable active pixel circuit provided by the embodiment of the present invention includes a gate tube and a photoelectric sensor in any of the above embodiments. The drain of the gate tube is electrically connected to the source of the photoelectric sensor, the source of the gate tube serves as the circuit output end, and the gate of the gate tube is used to connect a positive voltage to turn on the circuit or connect a negative voltage to turn off the circuit; in the photoelectric sensor, the cathode is connected in series with the drain.

[0052] From the embodiment of the photoelectric sensor, it can be seen that when the field effect transistor in the photoelectric sensor works in the off-state region, its output current is linearly related to the incident light intensity, and the dynamic range can reach more than 160dB. When the field effect transistor in the photoelectric sensor works in the subthreshold region, its output current is linearly related to the incident light intensity, and the optical gain can reach 10 6 ~10 7 Therefore, the purpose of selecting the working mode of the photoelectric sensor can be achieved by adjusting the gate voltage of the field effect transistor of the photoelectric sensor. Based on this, the randomly readable active pixel circuit made by using the photoelectric sensor in the above embodiment of the present invention can at least produce the following beneficial technical effects:

[0053] On the one hand, the dynamic range of the randomly readable active pixel circuit of the embodiment of the present invention can be as high as 160dB, which is much higher than the traditional randomly readable logarithmic active pixel circuit. It can generate a resolvable output signal even under very weak light intensity. Therefore, when performing photodetection, there is no need to integrate the photogenerated charge and reset the photodiode, which is conducive to simplifying the device timing and realizing the random readability of the device.

[0054] On the other hand, compared with the conventional random read logarithmic active pixel circuit and the back-illuminated active pixel circuit of the 4T-APS structure, the random read active pixel circuit of the embodiment of the present invention can realize the functions of photodetection, amplification and readout with only two transistors, which can reduce the pixel size and improve the spatial resolution. At the same time, it has the characteristics of high gain and wide dynamic response range.

[0055] It can be seen from the above that the working modes of the random reading active pixel circuit in the embodiment of the present invention include a wide dynamic response range mode and a high gain mode.

[0056] The following describes how to implement the selection of the working mode of the random read active pixel circuit according to the embodiment of the present invention:

[0057] (I) Wide dynamic response range mode

[0058] The driving process of implementing the circuit in a wide dynamic response range mode includes:

[0059] Applying a voltage to the cathode of the photoelectric sensor so that the photodiode operates in a reverse saturation region;

[0060] adjusting the voltage applied to the gate of the photosensor so that the field effect transistor operates in the off-state region;

[0061] When light is incident on the back side of the substrate of the photoelectric sensor, a photocurrent is generated in the photodiode, and the output current at the output end of the circuit is linearly related to the light intensity of the light. The working mode of the circuit is a wide dynamic response range mode.

[0062] (II) High gain mode

[0063] The driving process of implementing the circuit in high gain mode includes:

[0064] Applying a voltage to the cathode of the photoelectric sensor so that the photodiode operates in a reverse saturation region;

[0065] adjusting the voltage applied to the gate of the photosensor so that the field effect transistor operates in a subthreshold region;

[0066] When light enters the back side of the substrate of the photoelectric sensor, a photocurrent is generated in the photodiode, and the output current at the output end of the circuit tends to be linearly related to the light intensity of the light, and the working mode of the circuit is a high gain mode. The tendency to be linear can be understood as being approximately linear.

[0067] It should be noted that when the randomly readable active pixel circuit is in any of the above working modes, it is in the on state, and at this time, the gate of the gate tube is connected to a positive voltage to turn on the gate tube as a switch, thereby turning on the circuit. When it is necessary to turn off the random active pixel circuit, a negative voltage can be connected to the gate of the gate tube to turn off the gate tube as a switch, thereby turning off the circuit.

[0068] In one embodiment, the gate transistor is a field effect transistor.

[0069] Corresponding to the embodiment of the aforementioned randomly readable active pixel circuit, the present invention further provides an image sensor. The image sensor includes the aforementioned randomly readable active pixel circuit. In addition to the randomly readable active pixel circuit, the image sensor also includes other structures necessary for image sensors in the related art, which will not be described in detail here.

[0070] Corresponding to the above-mentioned embodiment of the image sensor, the present invention further provides a camera device. The camera device includes the above-mentioned image sensor. In addition to the image sensor, the camera device also includes other necessary structures of the camera in the related art, such as a lens and a display screen, which will not be described in detail here.

[0071] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications to the present invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims and equivalent technologies of the present invention, the present invention is also intended to include these changes and modifications.

Claims

1. A randomly readable active pixel circuit, characterized in that: It includes a gate tube and a photoelectric sensor; the photoelectric sensor includes a doping region, a substrate, a doping source region, a doping drain region and two isolation regions; The doped region is arranged on the bottom surface of the substrate to form a photodiode with the substrate; and the doped region forms a cathode of the photodiode, and the cathode is used to connect a positive voltage to make the photodiode work in a reverse bias region; The doped source region and the doped drain region are arranged at intervals on the top of the substrate to form a field effect transistor with the substrate; a source electrode is formed on the top surface of the doped source region, and a drain electrode is formed on the top surface of the doped drain region; The two isolation regions are respectively located at opposite sides of the substrate and extend from the doped source region and the doped drain region to the doped region from top to bottom, respectively, to isolate adjacent pixels or adjacent sensors; The top surface of the substrate is formed with a gate insulating layer and a gate electrode arranged between the doped source region and the doped drain region in sequence from bottom to top; The gate is used to access a voltage to select the working state of the field effect transistor to be in a wide dynamic response range mode or a high gain mode; The drain of the gate tube is electrically connected to the source of the photoelectric sensor, the source of the gate tube serves as the circuit output end, and the gate of the gate tube is used to connect a positive voltage to turn on the circuit or connect a negative voltage to turn off the circuit; in the photoelectric sensor, the cathode and the drain are connected in series.

2. The randomly readable active pixel circuit according to claim 1, characterized in that: The working mode of the circuit includes a wide dynamic response range mode; The driving process of implementing the circuit in a wide dynamic response range mode includes: Applying a voltage to the cathode of the photoelectric sensor so that the photodiode operates in a reverse saturation region; adjusting the voltage applied to the gate of the photosensor so that the field effect transistor operates in the off-state region; When light is incident on the back side of the substrate of the photoelectric sensor, a photocurrent is generated in the photodiode, and the output current at the output end of the circuit is linearly related to the light intensity of the light. The working mode of the circuit is a wide dynamic response range mode.

3. The randomly readable active pixel circuit according to claim 2, characterized in that: The working mode of the circuit also includes a high-gain mode; the driving process of implementing the circuit in the high-gain mode includes: Applying a voltage to the cathode of the photoelectric sensor so that the photodiode operates in a reverse saturation region; adjusting the voltage applied to the gate of the photosensor so that the field effect transistor operates in a subthreshold region; When light is incident on the back side of the substrate of the photoelectric sensor, a photocurrent is generated in the photodiode, the output current at the output end of the circuit tends to be linearly related to the light intensity of the light, and the working mode of the circuit is a high gain mode.

4. The randomly readable active pixel circuit according to claim 1, characterized in that: The cathode is formed by an electrode layer plated on the bottom surface of the doping region.

5. The randomly readable active pixel circuit according to claim 4, characterized in that: The electrode layer is a transparent electrode layer.

6. The randomly readable active pixel circuit according to claim 1, characterized in that: The substrate is a P-type substrate, and the doped region, doped source region and doped drain region are all N-type heavily doped regions; or, the substrate is an N-type substrate, and the doped region, doped source region and doped drain region are all P-type heavily doped regions.

7. The randomly readable active pixel circuit according to claim 1, characterized in that: The substrate is a lightly doped silicon wafer substrate or a silicon epitaxial layer substrate.

8. An image sensor, characterized in that: The randomly readable active pixel circuit comprises the one described in any one of claims 1 to 7.

9. A camera device, characterized in that: Comprising the image sensor as claimed in claim 8.

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