CN111355901A

CN111355901A - Photoelectric sensor, pixel circuit, image sensor and photoelectric sensing method

Info

Publication number: CN111355901A
Application number: CN202010184227.1A
Authority: CN
Inventors: 张盛东; 廖聪维; 周晓梁; 彭志超; 梁键; 安军军
Original assignee: Peking University Shenzhen Graduate School
Current assignee: Peking University Shenzhen Graduate School
Priority date: 2020-03-14
Filing date: 2020-03-14
Publication date: 2020-06-30
Also published as: WO2021184634A1

Abstract

The application provides a photoelectric sensor, which comprises a photosensitive unit, a photoelectric conversion unit and a photoelectric conversion unit, wherein the photosensitive unit is configured to receive incident light and generate a photo-generated current in an exposure stage, and has an optical memory function, namely the photo-generated current is still kept 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 photo-generated current into photo-generated charge or photo-generated voltage in an integration phase and store or maintain the photo-generated charge or the photo-generated voltage, wherein the integration phase at least comprises a preset time period after the exposure phase is finished. The application also provides a pixel circuit comprising such a photosensor, an image sensor and an electronic device comprising such a pixel array, and a corresponding photo-sensing method.

Description

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

Technical Field

The present invention relates to an image sensor, and more particularly, to a photosensor having a photosensitive cell with a light memory function, a pixel circuit, an image sensor, and a corresponding photo sensing method.

Background

Photosensors and image sensors play an extremely important role in numerous medical electronics, consumer electronics, and military electronics. For example, X-ray images are the gold criterion for diagnosing various diseases such as orthopedics, lung diseases, heart and cerebral vessels and the like; fingerprint identification has become a standard security lock for smart phones; hyperspectral and multispectral camera shooting are important modern military detection means. In these applications, high-sensitivity, high-resolution photosensors and image sensors for weak optical signals and transient photoelectric signals have been the focus of research.

Taking an X-ray imaging apparatus which is indispensable for modern medical treatment as an example, since over 100 years since X-ray discovery, an image sensor is a core component in a medical X-ray imaging system which takes an image of a tissue in a human body by means of the penetrating power of X-rays. Low dose, high resolution, dynamic imaging is a major development direction of modern X-ray imaging, where the requirements for image sensors are high sensitivity, high signal-to-noise ratio, fast response speed, etc. Existing image sensor technologies can be classified into the following categories: charge Coupled Device (CCD) and Complementary Metal Oxide (CMOS) transistor based imaging technologies, and hydrogenated amorphous silicon (a-Si: H) photodiode based flat panel detection imaging technologies. Currently, the most prevalent X-ray image sensors are based on a-Si: H photodiode technology. While this technology is constantly advancing, 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 the image sensor to reduce the X-ray irradiation dose and reduce the harm to the human body. For example, in military applications such as missile tail flame detection, the photoelectric signal intensity for imaging is very weak due to the long detection distance, and the response speed of photoelectric imaging is required to be very high due to the fast change speed of events.

How to detect weak and transient photoelectric signals is a difficult problem in the design of photosensitive sensors and image sensors. With the decrease of the intensity of the incident light electric signal, the intensity of the output signal of the conventional image sensor readout array is greatly reduced, and therefore, the imaging quality is sharply reduced by the influence of the dark-state current and the signal noise. Further, when the resolution of the image sensor is increased, the pixel area is also correspondingly reduced, the signal-to-noise ratio and the sensitivity of the imaging unit are greatly reduced, which is also a limiting factor in achieving high resolution of the conventional image sensor.

Disclosure of Invention

In view of the problems of the prior art, the present application provides a photosensor, including a photosensitive unit configured to receive incident light and generate a photo-generated current during an exposure period, and having a light memory function, i.e., the photo-generated current 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 photo-generated current into photo-generated charge or photo-generated voltage in an integration phase and store or maintain the photo-generated charge or the photo-generated voltage, wherein the integration phase at least comprises a preset time period after the exposure phase is finished.

In particular, the photosensitive unit with the optical memory function comprises a metal oxide semiconductor device or an organic semiconductor device with the optical memory function.

In particular, the light sensitive unit comprises at least a phototransistor, a photodiode or a photoresistor.

In particular, the storage unit comprises a storage capacitor coupled to the light sensitive unit, the storage capacitor being configured to perform an integration operation of converting the photo-generated current into the photo-generated charge or photo-generated voltage.

In particular, the storage unit further comprises an integration control unit, coupled between the light sensitive unit and the storage capacitor, configured to control the time for performing the integration operation under the influence of an integration control signal.

In particular, the integration control unit comprises an integration transistor having a first and a second pole coupled to the storage capacitor and the light sensitive unit, respectively, or to the light sensitive unit and a power supply, respectively, and a control pole configured to receive an integration control signal.

In particular, the storage unit further comprises an amplifying unit coupled to the storage capacitor and configured to amplify the photo-generated charge or voltage.

In particular, the integration phase is longer in time than the exposure phase.

In particular, the integration phase further comprises a time period coinciding with the exposure phase.

The present application further provides a pixel circuit comprising a photosensor according to any of the preceding claims, and a scanning unit, coupled to the storage unit of the photosensor, configured to output the photo-generated current signal or voltage signal or the corresponding electrical signal out of the pixel circuit under control of a scanning signal.

In particular, in case the photosensor comprises an amplifying unit, the amplifying unit comprises an N-type amplifying transistor, a first pole of which is coupled to the scanning unit, and a control pole and a second pole of which are coupled to the first and second plates of the storage capacitor, respectively.

In particular, in case the photosensor comprises an amplifying cell, the amplifying cell comprises a P-type amplifying transistor, the control electrode of which is coupled to the first plate of the storage capacitor, the second plate of the capacitor is coupled to a first reference potential, the first plate of the capacitor is coupled to a second reference potential, the second plate of the capacitor is coupled to the scanning cell, wherein the second reference potential is higher than the first reference potential and the supply voltage.

The present application also provides an image sensor comprising a pixel array, and a scan control circuit and a readout circuit coupled thereto; wherein the pixel array comprises one or more pixel circuits as described in any of the preceding.

In particular, the devices in the scan control circuit and the readout circuit are made by metal oxide semiconductor or organic semiconductor processes.

The present application further provides an electronic device comprising a photosensor according to any of the preceding claims or an image sensor according to any of the preceding claims.

The application also provides a photoelectric sensing method, which comprises the steps that in an exposure phase, a photosensitive unit with an optical memory function senses incident light and generates photo-generated current; and converting the photo-generated current into photo-generated charge or voltage in an integration phase, and storing or maintaining the photo-generated charge or voltage, wherein the integration phase at least comprises a preset time period after the exposure phase is finished.

In particular, the integration phase is longer in time than the exposure phase.

Drawings

Embodiments of the present application will be described in further detail below with reference to the attached drawing figures, wherein:

FIG. 1 is a schematic diagram illustrating an operation mode of a phototransistor with an optical memory function according to an embodiment of the present application;

FIG. 2(a) is a modular schematic diagram of a photosensor and image sensor pixel circuit according to one embodiment of the present application;

FIG. 2(b) is a timing diagram illustrating the operation of the photosensor and the image sensor shown in FIG. 2 (a);

FIG. 3(a) is a schematic diagram of a photosensor and image sensor pixel circuit according to one embodiment of the present application;

FIG. 3(b) is a schematic diagram of a photosensor and image sensor pixel circuit according to another embodiment of the present application;

FIG. 3(c) is a schematic diagram of a photosensor and image sensor pixel circuit according to yet another embodiment of the present application;

FIG. 4 is a schematic diagram of a photosensor and image sensor pixel circuit according to another embodiment of the present application;

FIG. 5 is a schematic diagram of the timing of the operation of an image sensor including the photosensor and pixel circuit of FIG. 4;

FIG. 6 is a schematic diagram of a photosensor and image sensor pixel circuit according to another embodiment of the present application;

FIG. 7 is a schematic diagram of a photosensor and image sensor pixel circuit according to yet another embodiment of the present application;

FIG. 8 is a schematic diagram of an image sensor according to an embodiment of the present application; and

FIG. 9 illustrates an image sensing method according to an embodiment of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The transistors in this application may be bipolar transistors or field effect transistors. The transistor comprises a control electrode, a first electrode and a second electrode, wherein the control electrode is coupled to a control metal layer, the first electrode and the second electrode are coupled to an active layer with an optical memory function, and a dielectric layer is arranged between the control metal layer and a semiconductor layer. The conductivity characteristics of the active layer of the phototransistor having a memory function are changed by modulation of input light. When the transistor is a bipolar transistor, the control electrode refers to a base electrode of the bipolar transistor, the first electrode refers to a collector electrode or an emitter electrode of the bipolar transistor, and the corresponding second electrode refers to the emitter electrode or the collector electrode of the bipolar transistor; when the transistor is a field effect transistor, the control electrode refers to a gate electrode of the field effect transistor, the first electrode may be a drain electrode or a source electrode of the field effect transistor, and the corresponding second electrode may be a source electrode or a drain electrode of the field effect transistor. 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 the drain will vary with the bias state of the transistor. Since a transistor used in a display is generally a Thin Film Transistor (TFT), the embodiment of the present application does not take the thin film transistor as an example for description, and a drain and a source of the transistor in the embodiment of the present application may vary according to a bias state of the transistor.

The application provides a photoelectric sensor, a pixel circuit and an image sensor, which are based on a photosensitive unit with an optical memory function to improve the imaging quality under the condition of transient and low-dose light input. The optical memory function of the photosensitive unit means that at the end of exposure, the photosensitive unit receives input light and generates a photo-generated current; after the exposure is finished, the photosensitive unit still keeps the photo-generated current for a preset time period even if the incident light is removed.

Studies have shown that materials having an optical memory function and being capable of serving as an active layer or a photosensitive functional layer include metal oxide semiconductors among inorganic semiconductors (for example, indium zinc oxide IZO has a high photoelectric response intensity and a good optical memory function due to a narrow forbidden band width and a high oxygen vacancy concentration), and some organic semiconductors and the like. Specifically, under the action of external light, the photosensitive unit with the optical memory function can generate photo-generated carriers like other types of photosensitive units, and further has the conductance or current modulated by input light. But in contrast, photosensitive cells based on such materials have significant optical memory due to lattice relaxation processes. For example, it takes an extremely long time for recombination of photogenerated carriers in a metal oxide semiconductor phototransistor to disappear, and thus the light generation current can be maintained for a long time in such a photoconductive unit. For another example, in a reverse biased mos photodiode, the photo current can last for more than several hours, which is far longer than the time required for photo readout detection. Under the action of light, the resistance of the metal oxide semiconductor photosensitive resistor changes and the metal oxide semiconductor photosensitive resistor has the capability of continuously keeping the resistance state.

In the scheme in the application, the optical memory characteristics of metal oxide semiconductors and organic semiconductor materials are utilized to enhance the photoelectric conversion capability of the photosensitive unit and improve the signal-to-noise ratio and sensitivity of a photoelectric sensor or an image sensor. In the application that the incident photoelectric signal is weak or the irradiation time is short, for example, in the X-ray medical imaging equipment, the optical memory characteristic of the metal oxide semiconductor photosensitive unit is utilized, so that the X-ray exposure time is reduced, the damage to the human body is avoided, and meanwhile, a clear image can be ensured to be obtained.

Fig. 1 is a schematic diagram illustrating an operation mode of a phototransistor with an optical memory function according to an embodiment of the present application. Of course, besides the phototransistor, there may be other forms of light sensing units with optical memory function, such as photodiode or photoresistor, etc. The characteristics of the light-sensitive cell with optical memory function will be further described here only by taking a photo transistor as an example. In a dark state, the output current of the phototransistor is Idk; in the exposure period, the output current of the phototransistor rises to Iph0 due to the input of incident light. In the subsequent time period after the stop of the incident light, the output current of the phototransistor is Iph1, which is reduced compared with Iph0, but the reduction range is limited, and basically, the photo-generated current is considered to be kept unchanged before and after the exposure period. Thus, in the following description the current in the light sensitive cell during the exposure phase and the integration phase or the photo signal accumulation phase is the photo generated current.

FIG. 2(a) is a modular schematic diagram of a photosensor and image sensor pixel according to one embodiment of the present application.

As shown in fig. 2(a), the photosensor 102 may include a photosensitive unit 1022 having an optical memory function, and a storage unit 1024 coupled to the photosensitive unit 1022. The photoelectric sensor can be applied to different devices, for example, the sensed photoelectric signal can be used for image capture, photoelectric switch, light intensity detection, touch identification, Time of flight (Time of flight), and the like.

According to one embodiment, as shown in fig. 2(a), when a photosensor is used for image capture, the image sensor pixel circuit 104 may include the photosensor 102 and a scanning unit 1042 coupled thereto. According to other embodiments, an image sensor including such pixel circuits may include column/row readout amplification circuits. According to one embodiment, a positive phase input terminal of the sense amplifying circuit may be coupled to a reference voltage, and a negative phase input terminal may be coupled to the output terminal through the charge-amplifiable capacitor and the reset switch. According to other embodiments, the pixel may also include a signal amplification unit, and/or a reset unit, etc. functional units inside the pixel before the readout signal is output to the pixel.

Fig. 2(b) is a timing chart showing the operation of the photosensor and the image sensor shown in fig. 2 (a).

There is an exposure phase and an integration phase/photo-generated signal accumulation phase for either the photosensor or the image sensor.

During the exposure period t1, the light-sensitive unit 1022 with optical memory function can detect the incident light and generate a corresponding photocurrent.

During the integration phase/photo-generated signal accumulation phase t2, the incident light stops illuminating, but due to the optical memory effect, photo-generated current is still continuously present in the photosensitive cells. According to one embodiment, the photo-generated current duration (which may be on the order of milliseconds) is much greater than the incident light duration (which may be on the order of microseconds). At this stage, the photo-generated current may be converted to a photo-generated voltage or charge and retained in memory cell 1024 after being refreshed. According to other embodiments, the integration phase t2 may also already start when the exposure phase t1 has not yet ended. The term "integration" means the operation of accumulating the photo-generated signals, and is not limited to any particular operation or circuit configuration.

For the image sensor, as shown in fig. 2(b), a readout stage is also included, in which the scan cells can be turned on row by row, so that the charges/voltages held by the memory cells can be transferred row by row to a readout amplifier circuit and further filtered, noise reduced, digitized, etc. Naturally, the conversion of the readout mode and the position where the readout amplification circuit is provided is well known, and any change is within the scope of the present application.

In the conventional photoelectric sensor or image sensor, the integration time is equal to or shorter than the exposure time, or the integration operation is performed in synchronization with the exposure. This is because the photo-generated current of a conventional phototransistor exists only during the exposure period, and thus the integration operation must also be performed during the exposure period. It is noted that in the present application, whether the integration operation is started within the exposure time period or at a certain point in time after the exposure time period, the integration operation is continued after the exposure is finished. The integration time in this application may be much longer than the exposure time, for example, the integration time length is in the order of milliseconds, and the exposure time may be in the order of microseconds. This is precisely because, for light-sensitive cells with an optical memory function, the photo-generated current can still be maintained or memorized after the removal of the incident light. Therefore, the pixel circuit can obtain a longer time for the integration operation, which will significantly increase the effective photoelectric signal intensity, suppress the influence of dark current and other noise amount, and obtain clear image data.

FIG. 3(a) is a schematic diagram of a photosensor and image sensor pixel circuit according to one embodiment of the present application. Among them, the photosensor 302 may include a photosensitive unit 3022 connected in series between a power supply and a node P; also included is a memory cell, which according to one embodiment may include a storage capacitor C_pxThe upper plate of which is coupled to node P and the lower plate of which receives a reference potential or is coupled to another node. According to one embodiment, the image sensor 304 may include the photosensor 302, and may further include a scan unit 3042 coupled between the node P and the readout line. The operation principle of the photo sensor and the pixel circuit in fig. 3(a) is similar to that shown in fig. 2(a), and is not described herein again.

In this embodiment, the capacitance C_pxTwo functions are achieved: (1) in an integration time period, converting photo-generated current into internal node voltage by using the optical memory effect of the photosensitive unit; (2) in the subsequent reading process, the photogenerated voltage is kept, and the influence of leakage current, voltage feed-through effect and the like on the reading voltage is restrained.

Fig. 3(b) is a schematic diagram of a photosensor and image sensor pixel circuit according to another embodiment of the present application. Wherein the storage unit in the photosensor 302 can include a storage capacitor C_pxAnd an amplifying transistor M1. Where the photo-generated current still passes through C_pxIs converted to a voltage and controls the transconductance of the amplifying transistor M1. Thus, the photo-generated current passes through C_pxAnd M1 is converted to a drain-source current of M1. Photo-generationThe larger the value of the current, the larger the value of the drain-source current that translates to M1, correspondingly. And the photo-generated current continuously acts on C due to the optical memory effect_pxIs much longer than the exposure period, thus passing through C_pxAnd the drain-source current of M1 converted by M1 is obviously increased, so that the amplification of the photo-generated current is realized.

According to one embodiment, the image sensor 304 may include a photosensor 302, and a scanning unit 3042. When the scan unit 3042 (e.g., scan transistor) is in an off state, C_pxOnly the transconductance of M1 is modulated, and the drain-source current of M1 is almost 0; after the scanning unit 3042 is turned on, it is turned on_pxThe controlled M1 output current is output to an external amplifier circuit via the scanning unit 3042.

Fig. 3(c) is a schematic diagram of a photosensor and image sensor pixel circuit according to yet another embodiment of the present application. In this embodiment, the amplifying transistor M2 included in the memory cell of the photosensor 302 is of the P type. According to one embodiment, the image sensor 304 may include the photosensor 302 and may further include a scanning unit 3042.

In the integration phase, the photogenerated current passes through C_pxIs converted to a voltage on node P and thus modulates the transconductance of P-type transistor M2. When the scan cell 306 is turned on, the transistor M2 outputs a signal current to an external amplification circuit. In the structure shown in FIG. 3(C), the capacitor C_pxThe upper plate of which is coupled to the internal node P and the lower plate of which receives the reference potential 1; the gate of the transistor M2 is coupled to the internal node P, its source receives the reference potential 2, and its drain is coupled to the scan cell 306. In order that the transistor M2 can 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.

According to various embodiments, other types of internal amplification units may be included in addition to the transistors M1 and M2 shown in fig. 3(b) and 3 (c). However, any means or method of amplifying a signal corresponding to a photo-generated charge or voltage is within the scope of the present application.

Fig. 4 is a schematic diagram of a photosensor and image sensor pixel circuit according to another embodiment of the present application. The photosensitive cells of the photosensor 402 may comprise at least a phototransistor T with an optical memory function_phThe memory cell may comprise an integral control transistor T_intAnd a storage capacitor C_px. According to one embodiment, image sensor pixel circuit 404 may include photosensor 402 and may also include a scanning element such as scanning transistor T_s。

Specifically, the phototransistor T_phIs coupled to a power supply, and has a gate configured to receive a control signal V_BWith its source coupled to an integral control transistor T_intOf the substrate.

As shown in fig. 4, the transistor T is controlled by integration_intIs configured to receive the integration control signal Int, T_intIs coupled to the internal node P. Storage capacitor C_pxIs also coupled to the internal node P, C_pxReceives a reference potential or is coupled to another node.

As shown in fig. 4, the scan transistor T in the image sensor pixel circuit 404_sIs configured to receive the Scan signal Scan, has its drain coupled to the internal node P and its source coupled to the sense line.

In the photosensor or image sensing pixel circuit illustrated in FIG. 4, the memory cell is not limited to use with C_pxAnd (5) realizing. Various circuit variations can be implemented with reference to the different memory cell structures illustrated in fig. 3(a) - (c). And will not be described in detail herein. In addition, fig. 4 illustrates the implementation method of the image sensing pixel by using only the N-type transistor technology as an example, but the pixel circuit may be implemented by using all P-type transistors, or by including both N-type and P-type transistors. Since these different circuit variations do not require inventive effort for a person skilled in the art, they also fall within the scope of protection of the present application.

Fig. 5 is a timing diagram illustrating the operation of a photosensor and an image sensor including the pixel circuit of fig. 4. During an exposure period T1, the phototransistor T_phDue to incident lightIrradiation of light to generate photogenerated carriers, photogenerated current I_phThe value of (c) increases. When the Int signal is high, corresponding to the integration period T2, the integration control transistor T_intIs turned on, and the phototransistor T is_phBy passing a photo-generated current through T_intTo the storage capacitor C_pxAnd (6) charging. After that, the Int signal becomes low level, integrating and controlling the transistor T_intIs turned off. The voltage converted by the photo-generated current is stored in the capacitor C_pxAnd (4) maintaining. During the read-out phase, the voltage value corresponding to the photo-generated current is always controlled by C_pxHold until the Scan signals Scan1, Scan2, Scan3, etc. transition to high level row by row, the storage capacitor C_pxIs transferred out of the pixel circuit.

As can be seen from fig. 5, there may be a time interval between the integration time t2 and the exposure time t 1. In practical applications, the rising of the photo-generated current in the light-sensing unit requires a certain time, so that the integration can be started after a certain time interval after the exposure time, which is also to allow the photo-generated current to rise to a more stable value after a sufficient response time, thereby improving the accuracy of the integration operation. For the image sensor, the integral control signal Int in fig. 5 is common to the whole panel, and when the integral control signal Int jumps to a high level, the integral control transistors T of all the pixel circuits of the image sensor_intAre all in an open state. The global integration time is relatively short compared to the row-by-row readout process.

According to one embodiment, the scan transistor T of each pixel of the image sensor_sThe integration period is switched off, so that the integration of each pixel and the readout process are performed in a time-sharing manner. The reading process can effectively expand the application range of the image sensor. For example, in consumer electronics, image sensors such as touch, fingerprint recognition, palm print recognition and the like are often supported on a flat panel display platform, and the integration level of an actual finished product is high and the functions are rich. However, as the integration degree is improved and the physical distance is smaller, signal crosstalk inevitably exists between different functional modules such as display and sensing modules. To suppress display driving signals and image transmissionCrosstalk between sensors typically requires that the display and image sensing readout processes be performed in a time-shared manner. Thus, in the integration stage of the image sensor, display driving can be performed; and the readout stage of the image sensor can stop the display drive. Therefore, the driving time sequence of the image sensor is not only beneficial to picking up images under weak and transient input light, but also can be flexibly cooperated with other photoelectric devices such as the driving of a flat panel display.

The photoelectric sensor and the image sensing pixel circuit have high reliability. Capacitor C_pxThe amount of charge accumulated is proportional to the phototransistor T_phThe amount of photo-generated current and the integration time, and the length of the integration time is controlled by the integration control transistor T_intIs uniquely determined. For an image sensor pixel, the amount of charge drawn by the external amplification circuit is also exclusively by the storage capacitor C_pxAccumulated charge amount on the capacitor C_pxAnd the capacitance value of the external amplifying circuit. Therefore, the photoelectric conversion relationship of the photosensor and the pixel circuit in the present application is almost independent of the electrical properties of the transistor. Even if the transistor T_intAnd T_sThe output voltage value of the pixel circuit remains constant in the case of non-uniform or drifting electrical properties.

In addition, the output signal intensity of the photoelectric sensor and the image sensing pixel circuit is high, and the photoelectric sensor and the image sensing pixel circuit can respond to weak input optical signals well. Due to light-sensitive cells, e.g. phototransistors T_phEven if the duration of the incident light is short and the intensity of the input photoelectric signal is weak, the photosensitive unit can still constantly provide light-emitting current after the incident light is removed. The actual integrated intensity of the photo-generated current can be greatly improved by adjusting the pulse length of the integrated control signal Int.

Moreover, the photoelectric sensor and the image sensing pixel circuit provided by the application are less influenced by dark-state current. During the integration phase, stored in the capacitor C_pxMay be affected by leakage current, and the path that may be affected includes T_intBranch circuit、T_sBranch and C_pxLeakage itself. Taking into account T_intThe number of branch series transistors is large, and the leakage current value is small; for the pixel circuit, T_sThe branch circuit can inhibit the leakage thereof by adjusting the low level value (namely the value of the turn-off voltage) of the Scan signal; c_pxThe pixel circuit in the embodiment of the application has low dark state noise and is beneficial to detecting weak light signals.

According to various embodiments, the photo-sensor and the photo-sensitive cells of the image sensor pixels comprise photo-transistors which are not limited to having a photo-memory function. Other devices such as photodiodes, photoresistors, etc. with optical memory may also be used to construct the light sensing units of the present application. Several other embodiments of image sensing pixel circuits are described below.

FIG. 6 is a schematic diagram of a photosensor and image sensor pixel circuit according to another embodiment of the present application. Wherein the light sensitive unit of the photosensor 602 may comprise, for example, a photodiode D with an optical memory function_phA cathode receiving a supply voltage and an anode coupled to an integral control transistor T_intOf the substrate. Other circuit connection modes are similar to the pixel circuit shown in fig. 4, and are not described again here. According to one embodiment, image sensor pixel circuit 604 may include a photo 602 and may also include a scanning unit.

The circuit is mainly used for a photodiode D_phSubject to the effects of incident light modulation. In order to enhance the optical memory effect of the photodiode, the anode or cathode metal material thereof may be appropriately selected such that a schottky junction diode is formed between the anode metal thereof and, for example, the metal oxide/organic semiconductor layer active layer or the metal oxide/organic semiconductor layer active layer and the cathode metal layer.

According to another embodiment, the photodiode D_phAnd integral control tube T_intOther configurations of (a) are possible (not shown). For example, integral control tube T_intCan receive Int signal, and its drain can receive power supplyA voltage, the source of which can be coupled to the photodiode D_phA cathode of (D)_phCoupled to the internal node P, other connections may be similar to the embodiment shown in fig. 6.

FIG. 7 is a schematic diagram of a photosensor and image sensor pixel circuit according to yet another embodiment of the present application. Wherein, the photosensitive unit of the photosensor 702 can include a photosensitive resistor R with optical memory function_ph. According to one embodiment, image sensor pixel circuit 604 may include a photo 602 and may also include a scanning unit. Photoresistor R_phMay receive a supply voltage, R_phIs coupled to the integral control transistor T_intOf the substrate. In addition, a photoresistor R_phAnd integral control transistor T_intOther variations of (2) connection means are possible (not shown in the figures). For example, the transistor T is controlled by integration_intReceives an integration control signal Int at its gate, receives a supply voltage at its drain, and is coupled at its source to a photoresistor R_phThe first terminal of (1), the photoresistor R_phIs coupled to the pixel circuit internal node P. Other circuit connection modes are similar to the pixel circuit shown in fig. 4, and are not described again here.

Fig. 8 is a schematic diagram of an image sensor according to an embodiment of the present application. The image sensor may include a pixel array, a scan control circuit, and a readout circuit. The scanning circuit may be used to provide corresponding progressive scanning control signals, integration control signals, bias voltages required by the light sensitive cells, and the like. The readout circuit may include not only the operational amplifier circuit, the reset transistor, the coupling capacitor, and the like illustrated in the foregoing embodiments, but also an analog-to-digital conversion module, a filter module, and the like.

According to one embodiment, part or all of the scan control circuit and the readout circuit may also be implemented by a metal oxide semiconductor transistor or an organic semiconductor device. In other words, the peripheral driving circuit and the pixel array can be manufactured by the same process as the photosensitive unit, so as to reduce the number of connecting wires around the image sensor module and improve the integration level and reliability of the image sensor.

For a conventional image sensor including, for example, an N-row by M-column pixel array, when the scanning unit of the ith row of pixels is turned on, image sensing data in the M pixels of the ith row may be picked up by the readout amplifying circuits of the corresponding columns and converted into output voltage signals, respectively. Wherein i is an integer of 1 or more and N or less. For the jth 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 thereon_PThis is because the j-th readout line is coupled to the scan cells of the N pixel circuits, and the transistor parasitic capacitances of these scan cells are opposite to the parasitic capacitance C of the j-th readout line_PMake a contribution; and there may be overlap between the jth readout line and N scan lines, the overlap capacitance being opposite to the parasitic capacitance C_PAlso contributes. Parasitic capacitance C_PThe value of the readout voltage of the pixel circuit of the conventional image sensor is reduced.

However, when the image sensor with the optical memory function or the electronic device including the image sensor provided by the present application is used, the light output current can be continuously and stably provided under the conditions of weak light irradiation/short light input, so that the storage unit is programmed and stores stronger photogenerated charge/photogenerated voltage signal, and the parasitic capacitance C can be reduced_PInfluence on the image sensor.

FIG. 9 illustrates a photo sensing method according to an embodiment of the present application.

At 902, incident light is sensed by a photosensitive cell having a memory function during an exposure phase and a photo-generated current is generated. According to one embodiment, the photosensitive cell having the optical memory function may include a metal oxide semiconductor or organic semiconductor photosensitive cell having the optical memory function.

At 904, the photo-generated current is converted into a photo-generated charge or voltage in an integration phase, and the photo-generated charge or voltage is stored or maintained, wherein the integration phase at least comprises a preset time period after the exposure phase is finished. According to one embodiment, the photo-generated charge or voltage may also be amplified using a memory cell. According to one embodiment, the integration phase may also include a time period that overlaps with the exposure phase.

Wherein the integration phase is longer in time than the exposure phase. In particular, the integration phase also comprises a time period coinciding with the exposure phase.

By utilizing the photoelectric sensor, the image sensor and the corresponding method, clear images can be reliably obtained in application scenes with short exposure time and weak incident light intensity, and the influence of negative factors such as dark current and parasitic capacitance on the quality of captured photoelectric signals is reduced.

The above-described embodiments are provided for illustrative purposes only and are not intended to be limiting, and various changes and modifications may be made by those skilled in the art without departing from the scope of the present disclosure, and therefore, all equivalent technical solutions should fall within the scope of the present disclosure.

Claims

1. A photosensor, comprising:

the photosensitive unit is configured to receive incident light and generate photo-generated current in an exposure stage, and has a light memory function, namely the photo-generated current is still kept in the photosensitive unit after the incident light is removed; and

and the storage unit is coupled to the photosensitive unit and is configured to convert the photo-generated current into photo-generated charge or photo-generated voltage and store or maintain the photo-generated charge or the photo-generated voltage in an integration phase, wherein the integration phase at least comprises a preset time period after the exposure phase is finished.

2. The photosensor according to claim 1, wherein the photosensor unit having a light memory function comprises a metal oxide semiconductor device or an organic semiconductor device having a light memory function.

3. The photosensor circuit of claim 2, wherein the photosensitive cells include at least a phototransistor, a photodiode, or a photoresistor.

4. The photosensor circuit of claim 1, wherein the storage cell comprises a storage capacitor coupled to the photosensitive cell, the storage capacitor configured to perform an integration operation that converts the photo-generated current to the photo-generated charge or photo-generated voltage.

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

6. The photosensor circuit of claim 5, wherein the integration control unit comprises an integration transistor having a first pole and a second pole coupled to the storage capacitor and the photosensitive cell, respectively, or to the photosensitive cell and a power source, respectively, and a control pole configured to receive an integration control signal.

7. The photosensor circuit of claim 4, wherein the storage unit further comprises an amplification unit coupled to the storage capacitor configured to amplify the photo-generated charge or voltage.

8. The photosensor of any of claims 1-7, where the integration phase is longer in time than 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 photosensor according to any of claims 1-9 and a scanning unit coupled to the storage unit of the photosensor and configured to output the photo-generated current signal or voltage signal or corresponding electrical signal out of the pixel circuit under control of a scanning signal.

11. A pixel circuit as claimed in claim 10, wherein in case the photosensor comprises an amplifying cell, the amplifying cell comprises an N-type amplifying transistor having a first pole coupled to the scanning cell and a control pole and a second pole coupled to a first plate and a second plate of the storage capacitor, respectively.

12. A pixel circuit as claimed in claim 10, wherein in case the photosensor comprises an amplifying cell, the amplifying cell comprises a P-type amplifying transistor having a control electrode coupled to a first plate of the storage capacitor, a second plate of the capacitor being coupled to a first reference potential, a first plate thereof being coupled to a second reference potential, a second plate thereof being coupled to the scanning cell, wherein the second reference potential is higher than the first reference potential and a supply voltage.

13. An image sensor includes a pixel array, and a scan 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 1-12.

14. The image sensor of claim 13, wherein the devices in the scan control circuit and the readout circuit are made from metal oxide semiconductor or organic semiconductor processes.

15. An electronic device comprising a photosensor according to any of claims 1-12 or an image sensor according to any of claims 13-14.

16. A photoelectric sensing method comprises

Sensing incident light by a photosensitive unit with a light memory function in an exposure phase and generating a photo-generated current; and

and converting the photo-generated current into photo-generated charge or voltage in an integration phase, and storing or maintaining the photo-generated charge or voltage, wherein the integration phase at least comprises a preset time period after the exposure phase is ended.

17. The method of claim 16, wherein the integration phase is longer in time than the exposure phase.

18. The method of claim 17, wherein the integration phase further comprises a time period coinciding with the exposure phase.