Photoelectric sensor, pixel circuit, image sensor and photoelectric sensing method

Abstract

The present application provides a photoelectric sensor, including a photosensitive unit, configured to receive incident light and generate photogenerated current during an exposure phase, which has a photomemory function, that is, the photogenerated current is still maintained in the photosensitive unit after the incident light is removed; and a storage unit, coupled to the photosensitive unit, configured to convert the photogenerated current into photogenerated charge or photogenerated voltage during an integration phase and store or maintain it, wherein the integration phase at least includes a preset time period after the end of the exposure phase. The present application also provides a pixel circuit including such a photoelectric sensor, an image sensor and an electronic device including such a pixel array, and a corresponding photoelectric sensing method.

Description

Technical Field

[0001] The present application relates to an image sensor, and in particular to a photoelectric sensor of a photosensitive unit with a light memory function, a pixel circuit, an image sensor, and a corresponding photoelectric sensing method. Background Art

[0002] Photoelectric sensors and image sensors play an extremely important role in many medical electronics, consumer electronics, and military electronic equipment. For example, X-ray images are the golden criterion for diagnosing various diseases such as orthopedics, lung diseases, and cardiovascular and cerebrovascular diseases; fingerprint recognition has become a standard security lock for smartphones; hyperspectral and multispectral imaging are important modern military detection methods. In these applications, high-sensitivity and high-resolution photoelectric sensors and image sensors for weak light signals and transient photoelectric signals have always been the focus of research.

[0003] Take X-ray imaging equipment, which is indispensable in modern medicine, as an example. For more than 100 years since the discovery of X-rays, image sensors have been the core components of medical X-ray imaging systems that use the penetrating power of X-rays to capture images of tissues in the human body. Low-dose, high-resolution, and dynamic imaging are the main development directions of modern X-ray imaging, and the requirements for image sensors are high sensitivity, high signal-to-noise ratio, and fast response speed. Existing image sensor technologies can be divided into the following categories: imaging technologies based on charge-coupled devices (CCDs) and complementary metal oxide (CMOS) transistors, and flat-panel detection imaging technologies based on hydrogenated amorphous silicon (a-Si:H) photodiodes. At present, the most mainstream X-ray image sensors are based on a-Si:H photodiode technology. Although this technology is constantly improving, there are still many problems. One of the most important research directions in the application of X-ray medical imaging today is to improve the sensitivity of image sensors to reduce the X-ray radiation dose and reduce the harm to the human body. For example, in military applications such as missile tail flame detection, the long detection distance causes the intensity of the photoelectric signal that can be used for imaging to be extremely weak, while the fast change speed of the event requires the photoelectric imaging to respond extremely fast.

[0004] How to detect weak, transient photoelectric signals is a difficult problem in the design of photosensitive sensors and image sensors. As the intensity of the incident photoelectric signal decreases, the output signal intensity of the traditional image sensor readout array is greatly reduced, so the imaging quality will be affected by the dark current and signal noise and drop sharply. Furthermore, when the resolution of the image sensor is increased, the pixel area is also reduced accordingly, and the signal-to-noise ratio and sensitivity of the imaging unit will be greatly reduced, which is also a limiting factor for traditional image sensors to achieve high resolution. Summary of the invention

[0005] In response to the problems of the prior art, the present application proposes a photoelectric sensor, comprising a photosensitive unit, configured to receive incident light and generate photogenerated current during an exposure phase, and having a photomemory function, that is, the photogenerated current is still maintained in the photosensitive unit after the incident light is removed; and a storage unit, coupled to the photosensitive unit, configured to convert the photogenerated current into photogenerated charge or photogenerated voltage during an integration phase and store or maintain the photogenerated current, wherein the integration phase at least includes a preset time period after the end of the exposure phase.

[0006] Particularly, the photosensitive unit with a photo-memory function comprises a metal oxide semiconductor device or an organic semiconductor device with a photo-memory function.

[0007] Particularly, the photosensitive unit at least comprises a phototransistor, a photodiode or a photoresistor.

[0008] In particular, the storage unit includes a storage capacitor coupled to the photosensitive unit, and the storage capacitor is configured to perform an integration operation of converting the photogenerated current into the photogenerated charge or the photogenerated voltage.

[0009] In particular, the storage unit further comprises an integration control unit, which is coupled between the photosensitive unit and the storage capacitor and is configured to control the time of performing the integration operation under the influence of an integration control signal.

[0010] Particularly, the integration control unit comprises an integration transistor, a first electrode and a second electrode of which are respectively coupled to the storage capacitor and the photosensitive unit, or respectively coupled to the photosensitive unit and a power supply, and a control electrode of which is configured to receive an integration control signal.

[0011] Particularly, the storage unit further includes an amplification unit, which is coupled to the storage capacitor and configured to amplify the photogenerated charge or voltage.

[0012] Particularly, the duration of the integration phase is longer than the duration of the exposure phase.

[0013] Particularly, the integration phase also includes a time period that overlaps with the exposure phase.

[0014] The present application also provides a pixel circuit, comprising a photoelectric sensor as described in any of the foregoing, and a scanning unit, which is coupled to a storage unit of the photoelectric sensor and is configured to output the photogenerated current signal or voltage signal or the corresponding electrical signal to the outside of the pixel circuit under the control of a scanning signal.

[0015] Particularly, in the case where the photosensor includes an amplifying unit, the amplifying unit includes an N-type amplifying transistor, a first electrode of which is coupled to the scanning unit, and a control electrode and a second electrode of which are respectively coupled to the first and second plates of the storage capacitor.

[0016] In particular, in the case where the photoelectric sensor includes an amplifying unit, the amplifying unit includes a P-type amplifying transistor, whose control electrode is coupled to the first plate of the storage capacitor, the second plate of the capacitor is coupled to the first reference potential, its first electrode is coupled to the second reference potential, and its second electrode is coupled to the scanning unit, wherein the second reference potential is higher than the first reference potential and the power supply voltage.

[0017] The present application also provides an image sensor, including a pixel array, and a scanning control circuit and a readout circuit coupled thereto; wherein the pixel array includes one or more pixel circuits as described above.

[0018] Particularly, the devices in the scanning control circuit and the readout circuit are made of metal oxide semiconductor or organic semiconductor technology.

[0019] The present application also provides an electronic device, which includes a photoelectric sensor as described in any of the above or an image sensor as described in any of the above.

[0020] The present application also provides a photoelectric sensing method, including sensing incident light and generating photogenerated current by a photosensitive unit with a photomemory function during an exposure phase; and converting the photogenerated current into photogenerated charge or voltage during an integration phase, and storing or maintaining the photogenerated charge or voltage, wherein the integration phase at least includes a preset time period after the end of the exposure phase.

[0021] Particularly, the duration of the integration phase is longer than the duration of the exposure phase.

[0022] Particularly, the integration phase also includes a time period that overlaps with the exposure phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The embodiments of the present application will be further described in detail below with reference to the accompanying drawings, wherein:

[0024] Figure 1 The figure is a schematic diagram of the working mode of a phototransistor with a light memory function according to an embodiment of the present application;

[0025] FIG. 2( a ) is a modular schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to an embodiment of the present application;

[0026] FIG2( b ) is a timing diagram showing the operation of the photoelectric sensor and the image sensor shown in FIG2( a );

[0027] FIG. 3( a ) is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to an embodiment of the present application;

[0028] FIG3( b ) is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application;

[0029] FIG3( c ) is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application;

[0030] Figure 4 Shown is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application;

[0031] Figure 5 Shown are included Figure 4 Schematic diagram of the working timing of the image sensor including the photoelectric sensor and pixel circuit;

[0032] Figure 6 Shown is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application;

[0033] Figure 7 FIG. 1 is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application;

[0034] Figure 8 FIG. 1 is a schematic diagram of the structure of an image sensor according to an embodiment of the present application; and

[0035] Fig. 9 FIG. 4 is an image sensing method according to an embodiment of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] The transistor in the present application can be a bipolar transistor or a field effect transistor. The transistor includes a control electrode, a first electrode and a second electrode, the control electrode is coupled to a control metal layer, the first electrode and the second electrode are coupled to an active layer with a light memory function, and a dielectric layer is provided between the control metal layer and the semiconductor layer. The conductivity characteristics of the active layer with a light memory function of the phototransistor are modulated by the input light and change. When the transistor is a bipolar transistor, the control electrode refers to the base of the bipolar transistor, the first electrode refers to the collector or emitter of the bipolar transistor, and the corresponding second electrode is the emitter or collector of the bipolar transistor; when the transistor is a field effect transistor, the control electrode refers to the gate of the field effect transistor, the first electrode can be the drain or source of the field effect transistor, and the corresponding second electrode can be the source or drain of the field effect transistor. Usually in an N-type transistor, the voltage of the drain should be greater than or equal to the voltage of the source, so the position of the source and drain will change with the different bias states of the transistor. Since the transistors used in the display are generally thin film transistors (TFTs), the embodiments of the present application may be described using thin film transistors as an example, and the drain and source of the transistor in the embodiments of the present application may vary depending on the bias state of the transistor.

[0038] The present application proposes a photoelectric sensor, a pixel circuit and an image sensor that is based on a photosensitive unit with a light memory function to improve the imaging quality under transient and low-dose light input conditions. The so-called light memory function of the photosensitive unit means that after the exposure is completed, the photosensitive unit receives the input light and generates a photocurrent; and after the exposure is completed, even if the incident light is removed, the photosensitive unit still maintains the photocurrent within a preset time period.

[0039] Studies have shown that materials with photomemory function and can be used as active layers or photosensitive functional layers include metal oxide semiconductors in inorganic semiconductors (for example, due to the narrow band gap and high oxygen vacancy concentration, the photoelectric response intensity of indium zinc oxide IZO is high and has good photomemory function), and some organic semiconductors. Specifically, under the action of external light, the photosensitive unit with photomemory function can generate photogenerated carriers like other types of photosensitive units, and then have input light modulated conductivity or current. But the difference is that due to the lattice relaxation process, the photosensitive unit based on this material has significant photomemory. For example, it takes a very long time for the recombination and disappearance of photogenerated carriers in metal oxide semiconductor phototransistors, so the photogenerated current in this photosensitive unit can be maintained for a long time. For another example, the value of the photogenerated current of a reverse biased metal oxide semiconductor photodiode can last for more than several hours, far exceeding the time required for photoelectric readout detection. For example, under the action of light, the resistance value of a metal oxide semiconductor photoresistor will change, and it has the ability to maintain this resistance state continuously.

[0040] In the solution of the present application, the optical memory characteristics of metal oxide semiconductors and organic semiconductor materials are used to enhance the photoelectric conversion capability of the photosensitive unit and improve the signal-to-noise ratio and sensitivity of the photoelectric sensor or image sensor. In applications where the incident photoelectric signal is weak or the exposure time is short, such as in X-ray medical imaging equipment, the optical memory characteristics of the metal oxide semiconductor photosensitive unit can be used to reduce the X-ray exposure time to avoid harm to the human body while ensuring a clear image.

[0041] Figure 1 The figure shows a schematic diagram of the working mode of a phototransistor with a light memory function according to an embodiment of the present application. Of course, in addition to phototransistors, there may also be other forms of photosensitive units with a light memory function, such as photodiodes or photoresistors, etc. Here, the characteristics of the photosensitive unit with a light memory function are further introduced by taking the phototransistor as an example. In the dark state, the output current of the phototransistor is Idk; in the exposure time period, due to the input of incident light, the output current of the phototransistor rises to Iph0. In the subsequent time period after the incident light stops, the output current of the phototransistor is Iph1, which is lower than Iph0, but the decrease is limited. It can be basically considered that the photogenerated current remains unchanged before and after the exposure stage. Therefore, in the following introduction, the current in the photosensitive unit in the exposure stage and the integration stage or the photoelectric signal accumulation stage is the photogenerated current.

[0042] FIG. 2( a ) is a schematic diagram showing a modular structure of a photosensor and an image sensor pixel according to an embodiment of the present application.

[0043] As shown in FIG2(a), the photoelectric sensor 102 may include a photosensitive unit 1022 having a light memory function, and a storage unit 1024 coupled to the photosensitive unit 1022. The photoelectric sensor may be applied to different devices, for example, the sensed photoelectric signal may be used for image capture, photoelectric switch, light intensity detection, touch recognition, time of flight ranging, etc.

[0044] According to one embodiment, as shown in FIG. 2( a), when the photoelectric sensor is used for image capture, the image sensor pixel circuit 104 may include a photoelectric sensor 102 and a scanning unit 1042 coupled thereto. According to other embodiments, the image sensor including such a pixel circuit may include a column / row readout amplifier circuit. According to one embodiment, the positive input terminal of the readout amplifier circuit may be coupled to a reference voltage, and the negative input terminal may be coupled to the output terminal via a charge amplification capacitor and a reset switch. According to other embodiments, the pixel may also include a signal amplification unit, and / or a reset unit and other functional units before the readout signal is output to the pixel.

[0045] FIG. 2( b ) is a timing diagram showing the operation of the photoelectric sensor and the image sensor shown in FIG. 2( a ).

[0046] For both photosensors and image sensors, there is an exposure phase and an integration phase / photogenerated signal accumulation phase.

[0047] In the exposure stage t1 , incident light is irradiated, and the photosensitive unit 1022 with a light memory function can detect the input light and generate a corresponding photocurrent.

[0048] In the integration stage / photogenerated signal accumulation stage t2, the incident light stops irradiating, but due to the photomemory effect, the photogenerated current still continues to exist in the photosensitive unit. According to one embodiment, the duration of the photogenerated current (which can be in the order of milliseconds) is much longer than the duration of the incident light (which can be in the order of microseconds). In this stage, the photogenerated current can be converted into a photogenerated voltage or charge, and maintained in the storage unit 1024 after updating. According to other embodiments, the integration stage t2 can also be started before the exposure stage t1 ends. The so-called integration means the operation of accumulating the photogenerated signal, and is not limited to any specific operation method or circuit structure.

[0049] For the image sensor, as shown in FIG2(b), it also includes a readout stage, in which the scanning unit can be opened row by row, so that the charge / voltage held by the storage unit can be transmitted row by row to the readout amplifier circuit for further filtering, noise reduction, digital processing, etc. Of course, the change of the readout method and the position of the readout amplifier circuit belongs to the well-known scheme, and any change belongs to the scope of protection of this application.

[0050] In existing photoelectric sensors or image sensors, the integration time is less than or equal to the exposure time, or in other words, the integration operation is performed synchronously with the exposure. This is because the photocurrent of the traditional phototransistor only exists during the exposure time period, so the integration operation must also be performed during the exposure stage. It is worth noting that in the present application, whether the integration operation starts during the exposure time period or at a certain time point after the exposure time period, the integration operation will continue after the exposure ends. In the present application, the integration time will be much longer than the exposure time. For example, the integration time length is in the order of milliseconds, while the exposure time can be in the order of microseconds. This is precisely because, for a photosensitive unit with a light memory function, the photocurrent can still be maintained or memorized after the incident light is removed. Therefore, the pixel circuit can obtain a longer time to perform the integration operation, which will significantly improve the effective photoelectric signal strength, suppress the influence of dark current and other noise amounts, and thus obtain clear image data.

[0051] FIG3(a) is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to an embodiment of the present application. The photoelectric sensor 302 may include a photosensitive unit 3022, which is connected in series between a power supply and a node P; and a storage unit. According to an embodiment, the storage unit may include a storage capacitor C px , its upper plate is coupled to node P, and its lower plate receives a reference potential or is coupled to other nodes. According to one embodiment, the image sensor 304 may include a photoelectric sensor 302, and may also include a scanning unit 3042 coupled between node P and a readout line. The working principle of the photoelectric sensor and pixel circuit in FIG3(a) is similar to that shown in FIG2(a), and will not be described in detail here.

[0052] In this embodiment, the capacitor C px It plays two roles: (1) during the integration period, it uses the photomemory effect of the photosensitive unit to convert the photogenerated current into the internal node voltage; (2) in the subsequent readout process, it maintains the photogenerated voltage and suppresses the influence of leakage current and voltage feedthrough effect on the readout voltage.

[0053] FIG3( b ) is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application. The storage unit in the photoelectric sensor 302 may include a storage capacitor C px and amplifier transistor M1. Here the photocurrent still flows through C px is converted into a voltage and controls the transconductance of the amplifier transistor M1. px and M1 is converted into the drain-source current of M1. The larger the value of the photogenerated current is, the larger the value of the drain-source current converted to M1 is. And due to the light memory effect, the photogenerated current continues to act on C px The time is much longer than the exposure time, so through C px The drain-source current of M1 obtained by converting the photogenerated current into M1 will be significantly increased, thereby achieving the amplification of the photogenerated current.

[0054] According to one embodiment, the image sensor 304 may include a photosensor 302 and a scanning unit 3042. When the scanning unit 3042 (eg, a scanning transistor) is in an off state, C px It only modulates the transconductance of M1, and the drain-source current of M1 is almost 0; when the scanning unit 3042 is turned on, it is C px The output current of M1 is controlled and output to the external amplifier circuit through the scanning unit 3042.

[0055] FIG3( c ) is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application. In this embodiment, the amplifying transistor M2 included in the storage unit of the photoelectric sensor 302 is a P-type. According to one embodiment, the image sensor 304 may include the photoelectric sensor 302 and may also include a scanning unit 3042.

[0056] During the integration phase, the photocurrent flows through C px is converted into a voltage on node P, thereby modulating the transconductance of the P-type transistor M2. When the scanning unit 306 is turned on, the transistor M2 outputs a signal current to the external amplifier circuit. In the structure shown in FIG3(c), the capacitor C px The upper plate of transistor M2 is coupled to the internal node P, and the lower plate thereof receives the reference potential 1; the gate of transistor M2 is coupled to the internal node P, the source thereof receives the reference potential 2, and the drain thereof is coupled to the scanning unit 306. In order for transistor M2 to be normally turned on, both the reference potential 1 and the power supply voltage should be smaller than the value of the reference potential 2.

[0057] According to different embodiments, in addition to the transistors M1 and M2 shown in FIG. 3( b ) and FIG. 3( c ), other types of internal amplification units may also be included. However, no matter what amplification means or method is used to amplify the signal corresponding to the photogenerated charge or photogenerated voltage, it is a conventional means and still falls within the protection scope of this application.

[0058] Figure 4 The photosensitive unit of the photoelectric sensor 402 may include at least a phototransistor T having a light memory function. ph , the memory cell may include an integral control transistor T int and storage capacitor C px According to one embodiment, the image sensor pixel circuit 404 may include a photosensor 402 and may also include a scanning unit such as a scanning transistor T s .

[0059] Specifically, the phototransistor T ph The drain is coupled to the power supply and the gate is configured to receive the control signal V B , whose source is coupled to the integral control transistor T int of the drain.

[0060] like Figure 4 As shown, the integral control transistor T int The gate is configured to receive the integral control signal Int, T int The source of is coupled to the internal node P. The storage capacitor C px The upper plate is also coupled to the internal nodes P, Cpx The lower plate receives a reference potential or is coupled to other nodes.

[0061] like Figure 4 As shown, the scanning transistor T in the image sensor pixel circuit 404 s A gate thereof is configured to receive a scan signal Scan, a drain thereof is coupled to an internal node P, and a source thereof is coupled to a readout line.

[0062] Figure 4 In the illustrated photoelectric sensor or image sensing pixel circuit, the storage unit is not limited to the C px Implementation. Various circuit changes can be implemented by referring to the different storage unit structures shown in Figures 3(a)-(c). No further description is given here. In addition, Figure 4 Only N-type transistor technology is used as an example to illustrate the implementation method of the image sensing pixel, but the pixel circuit can also be implemented entirely with P-type transistors, or include both N-type transistors and P-type transistors. Since these different circuit variations do not require creative work for those skilled in the art, they also fall within the scope of protection of this application.

[0063] Figure 5 Shown are included Figure 4 Schematic diagram of the working sequence of the photoelectric sensor and image sensor of the pixel circuit. In the exposure stage t1, the phototransistor T ph Photogenerated carriers are generated by the incident light, and the photogenerated current I ph The value of increases. When the Int signal is at a high level, it corresponds to the integration stage t2, and the integration control transistor T int is turned on, so the phototransistor T ph The photocurrent flows through T int To the storage capacitor C px After that, the Int signal becomes low level, and the integral control transistor T int The voltage converted from the photocurrent is stored in the capacitor C px During the readout phase, the voltage value corresponding to the photocurrent will be always maintained by C px Keep until the scanning signals Scan1, Scan2, Scan3, etc. jump to high level line by line, then the storage capacitor C px The charge is transferred out of the pixel circuit.

[0064] Depend on Figure 5It can be seen that there may be a time interval between the integration time t2 and the exposure time t1. In practical applications, the rise of the photocurrent generated in the photosensitive unit requires a certain amount of time. Therefore, a specific time interval can be set after the exposure time to start the integration. This is also to allow the photocurrent to rise to a more stable value after a sufficient response time, thereby improving the accuracy of the integration operation. For image sensors, Figure 5 The integral control signal Int is shared by the entire panel. When the integral control signal Int jumps to a high level, the integral control transistors T int Therefore, the global integration time is shorter than the line-by-line readout process.

[0065] According to one embodiment, the scanning transistor T of each pixel of the image sensor s They are all turned off during the integration time period, so the integration and readout process of each pixel is carried out in time. This readout process can effectively expand the scope of use of image sensors. For example, in consumer electronic products, image sensors such as touch, fingerprint recognition, and palmprint recognition often rely on flat-panel display platforms, and the actual finished products have high integration and rich functions. However, due to the increase in integration and the smaller physical distance, signal crosstalk inevitably exists between different functional modules such as display and sensing. In order to suppress the crosstalk between the display drive signal and the image sensor, it is generally necessary to carry out the display and image sensor readout processes in time. Therefore, in the integration stage of the image sensor, the display drive can be performed; and in the readout stage of the image sensor, the display drive can be stopped. Therefore, the drive timing of the image sensor of the present application is not only conducive to picking up images under weak and instantaneous input light conditions, but also can be flexibly coordinated with other optoelectronic devices such as the drive of the flat-panel display.

[0066] The photoelectric sensor and image sensing pixel circuit provided by the present application have high reliability. Capacitor C px The amount of charge accumulated on the phototransistor is proportional to the ph The amount of photocurrent and the integration time are determined by the integration control transistor T int For the image sensor pixel, the amount of charge obtained by the external amplifier circuit is also determined solely by the storage capacitor C px The accumulated charge on the px The ratio of the capacitance value of the external amplifier circuit is determined. Therefore, the photoelectric conversion relationship between the photoelectric sensor and the pixel circuit in this application has almost nothing to do with the electrical performance of the transistor. int and T s Even if the electrical performance of the pixel circuit is uneven or drifts, the output voltage value of the pixel circuit remains constant.

[0067] In addition, the output signal strength of the photoelectric sensor and the image sensing pixel circuit provided by the present application is relatively high, and can have a better response to weak input light signals. ph Due to the light memory effect, even if the incident light duration is short and the input photoelectric signal strength is weak, the photosensitive unit can still provide a constant photocurrent after the incident light is removed. Therefore, the actual photocurrent integral intensity can be greatly improved by adjusting the pulse length of the integral control signal Int.

[0068] Furthermore, the photoelectric sensor and image sensing pixel circuit provided by the present application are less affected by the dark state current. px The photogenerated charge on the surface may be affected by leakage current. The paths that may cause the impact include T int Branch, T s Branch and C px The leakage itself. Considering T int The number of branch series transistors is large, and the leakage current value is small; for the pixel circuit, T s The branch can suppress leakage by adjusting the low level value of the Scan signal (i.e., the value of the shutoff voltage); C px Due to factors such as the low leakage current itself, the dark state noise of the pixel circuit in the embodiment of the present application is low, which is conducive to the detection of weak light signals.

[0069] According to different embodiments, the photosensitive unit of the photoelectric sensor and the image sensor pixel is not limited to the phototransistor with a light memory function. Other devices such as photodiodes and photoresistors with a light memory function can also be used to construct the photosensitive unit in the present application. The following introduces several other embodiments of the image sensor pixel circuit.

[0070] Figure 6 The schematic diagram of the photoelectric sensor and the image sensor pixel circuit according to another embodiment of the present application is shown. The photosensitive unit of the photoelectric sensor 602 may include, for example, a photodiode D having a light memory function. ph , whose cathode receives the supply voltage and whose anode is coupled to the integral control transistor T int The other circuit connections are similar to Figure 4 The pixel circuits shown are similar and will not be described again. According to one embodiment, the image sensor pixel circuit 604 may include the photoelectric 602 and may also include a scanning unit.

[0071] The above circuit mainly uses the photodiode D phThe reverse leakage current is modulated by the incident light. In order to enhance the optical memory effect of the photodiode, the anode or cathode metal material can be appropriately selected so that a Schottky junction diode is formed between the anode metal and, for example, the metal oxide / organic semiconductor layer active layer or between the metal oxide / organic semiconductor layer active layer and the cathode metal layer.

[0072] According to another embodiment, the photodiode D ph And integral control tube T int The series relationship of may also have other configurations (not shown in the figure). For example, the integral control tube T int The gate can receive the Int signal, the drain can receive the power supply voltage, and the source can be coupled to the photodiode D ph The cathode, D ph The anode of the device is coupled to the internal node P, and other connections can be Figure 6 The embodiments shown are similar.

[0073] Figure 7 FIG. 1 is a schematic diagram of a photoelectric sensor and an image sensor pixel circuit according to another embodiment of the present application. The photosensitive unit of the photoelectric sensor 702 may include a photoresistor R having a light memory function. ph According to one embodiment, the image sensor pixel circuit 604 may include a photoresistor 602 and may further include a scanning unit. ph The first terminal can receive the power supply voltage, R ph The second terminal is coupled to the integration control transistor T int In addition, the photoresistor R ph and the integral control transistor T int There may also be other changes in the connection mode (not shown in the figure). For example, the integral control transistor T int The gate receives the integral control signal Int, the drain receives the power supply voltage, and the source is coupled to the photoresistor R ph The first terminal of the photoresistor R ph The second terminal is coupled to the internal node P of the pixel circuit. Other circuit connection methods are similar to Figure 4 The pixel circuit shown is similar and will not be described again here.

[0074] Figure 8 The figure shows a schematic diagram of the structure of an image sensor according to an embodiment of the present application. The image sensor may include a pixel array, a scanning control circuit, and a readout circuit. The scanning circuit may be used to provide corresponding line-by-line scanning control signals, integral control signals, bias voltages required by photosensitive units, etc. The readout circuit may include not only the operational amplifier circuit, reset transistor, coupling capacitor, etc. illustrated in the aforementioned embodiments, but may also include an analog-to-digital conversion module, a filtering module, etc.

[0075] According to one embodiment, part or all of the scanning control circuit and the readout circuit can also be implemented by metal oxide semiconductor transistors or organic semiconductor devices. In other words, the peripheral driving circuit and the pixel array can be prepared by the same process as the photosensitive unit to reduce the number of connection lines around the image sensor module and improve the integration and reliability of the image sensor.

[0076] For example, for a conventional image sensor including an N-row*M-column pixel array, when the scanning unit of the i-th row of pixels is turned on, the image sensing data in the M pixels of the i-th row can be picked up by the readout amplifier circuits of the corresponding columns and converted into output voltage signals. Where i is an integer greater than or equal to 1 and less than or equal to N. For the j-th readout line, where j is an integer greater than or equal to 1 and less than or equal to M, there is a non-negligible parasitic capacitance C on it. P This is because the jth readout line is coupled to the scanning units of N pixel circuits, and the parasitic capacitance of the transistors of these scanning units has an influence on the parasitic capacitance C of the jth readout line. P Contribute; and the jth readout line and the N scan lines may overlap, and the overlapping capacitance has an influence on the parasitic capacitance C P Also contributes. Parasitic capacitance C P The value of the readout voltage of the conventional image sensor pixel circuit is reduced.

[0077] However, when the image sensor with optical memory function proposed in the present application or the electronic device including such an image sensor is used, the light output current can be continuously and stably provided under weak light illumination / short light input conditions, so that the storage unit is programmed and stores a strong photogenerated charge / photogenerated voltage signal, which can reduce the parasitic capacitance C P Impact on image sensors.

[0078] Fig. 9 FIG. 4 is a diagram showing a photoelectric sensing method according to an embodiment of the present application.

[0079] At 902, incident light is sensed by a photosensitive unit with a light memory function and a photocurrent is generated during an exposure phase. According to one embodiment, the photosensitive unit with a light memory function may include a metal oxide semiconductor or organic semiconductor photosensitive unit with a light memory function.

[0080] At 904, the photogenerated current is converted into a photogenerated charge or voltage during an integration phase, and the photogenerated charge or voltage is stored or maintained, wherein the integration phase at least includes a preset time period after the end of the exposure phase. According to one embodiment, the photogenerated charge or voltage may also be amplified using a storage unit. According to one embodiment, the integration phase may also include a time period overlapping with the exposure phase.

[0081] The duration of the integration phase is longer than that of the exposure phase. In particular, the integration phase also includes a time period that overlaps with the exposure phase.

[0082] By utilizing the photoelectric sensor, image sensor and corresponding method provided in the present application, a clear image can still be reliably obtained in application scenarios with short exposure time and relatively weak incident light intensity, while also reducing the impact of negative factors such as dark current and parasitic capacitance on the quality of the captured photoelectric signal.

[0083] The above embodiments are only used to illustrate the present application, and are not intended to limit the present application. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the scope of the present application. Therefore, all equivalent technical solutions should also fall within the scope of the present application.

Claims

1. A photoelectric sensor, comprising: A photosensitive unit configured to receive incident light and generate photocurrent during an exposure phase, and having a photomemory function, that is, the photocurrent is still maintained in the photosensitive unit after the incident light is removed; and The storage unit is coupled to the photosensitive unit and is configured to convert the photocurrent into photocharge or photovoltage and store or maintain it during an integration phase, wherein the integration phase at least includes a preset time period after the exposure phase ends. 2 . The photoelectric sensor according to claim 1 , wherein the photosensitive unit with a photo-memory function comprises a metal oxide semiconductor device or an organic semiconductor device with a photo-memory function.

3. The photosensor according to claim 2, wherein the photosensitive unit comprises at least a phototransistor, a photodiode or a photoresistor.

4. The photosensor of claim 1, wherein the storage unit comprises a storage capacitor coupled to the photosensitive unit, the storage capacitor being configured to perform an integration operation of converting the photo-generated current into the photo-generated charge or the photo-generated voltage.

5. The photosensor according to claim 4, wherein the storage unit further comprises an integration control unit, which is coupled between the photosensitive unit and the storage capacitor and is configured to control the time for performing the integration operation under the influence of an integration control signal.

6. The photoelectric sensor as claimed in claim 5, wherein the integration control unit comprises an integration transistor, a first electrode and a second electrode of which are respectively coupled to the storage capacitor and the photosensitive unit, or respectively coupled to the photosensitive unit and a power supply, and a control electrode of which is configured to receive an integration control signal. 7 . The photosensor according to claim 4 , wherein the storage unit further comprises an amplification unit coupled to the storage capacitor and configured to amplify the photogenerated charge or voltage.

8. The photosensor according to any one of claims 1 to 7, wherein the duration of the integration phase is longer than the duration of the exposure phase.

9. The photosensor of claim 8, wherein the integration phase further includes a time period that coincides with the exposure phase.

10. A pixel circuit, comprising a photoelectric sensor as described in any one of claims 1 to 9, and a scanning unit, which is coupled to a storage unit of the photoelectric sensor and is configured to output the photogenerated current signal or voltage signal or the corresponding electrical signal to the outside of the pixel circuit under the control of a scanning signal.

11. The pixel circuit of claim 10, wherein when the photosensor includes an amplifying unit, the amplifying unit includes an N-type amplifying transistor, a first electrode of which is coupled to the scanning unit, and a control electrode and a second electrode of which are respectively coupled to a first plate and a second plate of the storage capacitor.

12. The pixel circuit of claim 10, wherein when the photosensor includes an amplifying unit, the amplifying unit includes a P-type amplifying transistor, a control electrode of which is coupled to a first plate of the storage capacitor, a second plate of the capacitor is coupled to a first reference potential, a first electrode of which is coupled to a second reference potential, and a second electrode of which is coupled to the scanning unit, wherein the second reference potential is higher than the first reference potential and the power supply voltage.

13. An image sensor comprising a pixel array, and a scanning control circuit and a readout circuit coupled thereto; wherein the pixel array comprises one or more pixel circuits as claimed in any one of claims 10 to 12.

14. The image sensor according to claim 13, wherein the devices in the scanning control circuit and the readout circuit are made of metal oxide semiconductor or organic semiconductor process.

15. An electronic device comprising the photoelectric sensor according to any one of claims 1 to 9, the pixel circuit according to any one of claims 10 to 12, or the image sensor according to any one of claims 13 to 14.

16. A photoelectric sensing method, comprising: During the exposure phase, the photosensitive unit with a light memory function senses the incident light and generates a photocurrent; and The photogenerated current is converted into a photogenerated charge or voltage, and the photogenerated charge or voltage is stored or maintained during an integration phase, wherein the integration phase at least includes a preset time period after the exposure phase ends. The method of claim 16 , wherein the integration phase is longer than the exposure phase.

18. The method of claim 17, wherein the integration phase further includes a time period that coincides with the exposure phase.

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