A range adjustable all-metal oxide sensor pixel

Abstract

The application discloses a full metal oxide sensor pixel with adjustable range, which comprises a metal oxide diode, a pre-storage capacitor CO and a read TFT transistor, wherein the gate and the drain of the metal oxide diode are connected to a VSS power supply, the source of the metal oxide diode is connected to the drain of the read TFT transistor, the pre-storage capacitor CO is arranged in parallel across the gate and the source of the metal oxide diode, the source of the read TFT transistor is connected to data, and the source of the read TFT transistor is connected to a driving control signal Gn. The application has the advantages that a new metal oxide diode is adopted to realize the sensing of a photosensitive signal, and the defects existing in the PIN diode scheme in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of optical signal detection, and in particular to an ultra-low leakage current sensor based on a metal oxide diode. Background Technology

[0002] Optical detection imaging has numerous applications, such as X-ray imaging in medicine. X-rays are used to irradiate the human body, and sensors detect the resulting X-ray signals. These signals are converted into electrical signals of varying magnitudes, and then processed to create image signals with different grayscale levels, thus forming an X-ray image and providing assistance in the medical field. In optical detection imaging, the optical signal must first be converted into an electrical signal, which then corresponds to the optical signal. The image is obtained through the acquisition and processing of this electrical signal. Therefore, the final step is to acquire the optical signal and convert it into an electrical signal to form data representing the optical signal.

[0003] like Figure 1 The diagram shows a commonly used technical solution in the prior art: a PIN diode sensor circuit scheme. This scheme uses a PIN diode to sense optical signals and convert them into electrical signals. The circuit structure includes a PIN diode and a TFT transistor. The anode of the PIN diode receives a bias voltage signal to drive and control the current flow. The cathode of the PIN diode is connected to the source of the TFT transistor, and the source of the TFT transistor is connected to the data line. The data line is used to output electrical signal data representing the optical signal. The gate of the TFT transistor receives a driving voltage Vgate to control the TFT transistor's on / off state.

[0004] Its working principle includes: when a light signal is detected, the Pin diode converts the light signal into an electrical signal, in which the current flows to the TFT and the data line; then, by controlling the conduction state of the TFT transistor gate voltage Vgate, the electrical signal is transmitted to the data line, thereby realizing the sensing acquisition. Subsequent imaging can be performed by processing the data line signal.

[0005] The advantages of using PIN diodes are low cost and simple sensing circuitry. However, their disadvantages are also obvious. Using PIN diodes for photosensitive sensing is difficult to debug due to the extremely low leakage current of PIN diodes. At the same time, using PIN diodes will cause lag and image retention that cannot be avoided, resulting in poor subsequent imaging effects. In addition, the large leakage current of the TFT used for switching control in the off state will interfere with the signal reading process of other rows. That is, the leakage current of aSi TFT is the same as that of PIN diodes. When reading row n+1, other rows should theoretically be in the off state. However, because the off-state effect of aSi TFT is not as good as that of IGZO TFT, the difference between 100fA and 0.1fA, if the array is large and the reading time is long, the integrated signal is the leakage current signal of other rows of TFTs, rather than the effective signal of the current row, which will interfere with small signal application scenarios. Therefore, existing sensor solutions using PIN diodes for photosensitive sensing have drawbacks, such as the difficulty in debugging due to the reduction of leakage current from the -13th power level to the -15th power level in PIN and aSi TFT; data anomalies in small signal segments and the inability to correspond between multiple lines caused by unstable and high leakage current; large lag preventing the implementation of high-frequency + large signal application scenarios; and the simple pixel structure that cannot meet higher measurement ranges. All of these limitations restrict current sensor pixels from further meeting the requirements for photosensitive sensing. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an ultra-low leakage current sensor based on a metal oxide diode. This new metal oxide diode is used to realize the sensing of photosensitive signals, thus solving the defects of the PIN diode solution in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: an ultra-low leakage current sensor based on a metal oxide diode, comprising a metal oxide diode, a pre-stored capacitor C0, and a read TFT transistor, wherein the gate and drain of the metal oxide diode are connected to a VSS power supply, and its source is connected to the drain of the read TFT transistor; a pre-stored capacitor C0 is connected in parallel across the gate and source terminals of the metal oxide diode; the source of the read TFT transistor is connected to the data; and the source of the read TFT transistor is connected to a drive control signal Gn.

[0008] The sensor also includes a storage capacitor Cst, one end of which is connected to a reset power supply Vreset, and the other end is connected to the source of a metal oxide diode.

[0009] The sensor also includes an RST TFT transistor, the source of which is connected to the drain of the read TFT, and the drain of the RST TFT transistor is connected to the reset power supply Vreset; the gate of the RST TFT transistor receives a reset drive control signal.

[0010] The sensor also includes an AMP TFT transistor, which is connected in series between the drain of the read TFT transistor and the source of the metal oxide diode. Its gate is connected to the source of the metal oxide diode, its source is connected to the drain of the read TFT transistor, and its drain is connected to the power supply VSS.

[0011] The gate of the read TFT is connected to the scan control circuit, which outputs a scan signal Gn to drive the read TFT to switch on and off.

[0012] The gate of the RST TFT transistor is connected to the output of the scan control circuit, and the scan signal Gn+1 output by the scan control circuit controls the on / off state of the RST TFT.

[0013] The scanning signal Gn+1 is the scanning signal at the next moment of the scanning signal Gn.

[0014] The gate-source-drain voltage of the photosensitive device is adjusted by regulating the voltage difference between VSS and Vreset. This dynamic adjustment is adapted to different light intensities and application scenarios. Weak photoelectric signals are amplified proportionally, while stronger photoelectric signals are reduced. The IC has a built-in proportional coefficient correction function to read the signal in the back end, which is used to adapt to different light intensities and has a built-in range adjustment mechanism.

[0015] The metal oxide diode is used to convert optical signals into electrical signals, wherein the optical signals are visible light or high-energy rays, or high-energy particles converted by a scintillator.

[0016] The scintillator includes GoS material and Csl material.

[0017] The advantages of this invention are: it utilizes the inherently low Ioff of metal oxides, effectively reducing the difficulty of process debugging; since PIN is an amorphous silicon doped structure, the carrier transport mechanism of the material itself cannot avoid a high leakage current of 100fA or more, with a target of 10fA or less, resulting in limited process coverage; the transport mechanism of metal oxides is completely different from that of PIN, and as long as basic material debugging is completed, an ultra-low leakage current effect of 0.1fA or less can be achieved.

[0018] An external charge pre-storage circuit scheme was implemented using Cst capacitor and pre-stored capacitor C0, eliminating the risk of residual charge lag inherent in semiconductor materials. By adjusting the VSS voltage to change the pre-stored amount and photoelectric signal multiplication ratio, the range of the sensor circuit was adjusted to correspond to different dosage application scenarios, thus expanding the application field. An RST TFT transistor was added to the circuit design, which can reset the electrical signal to zero after the signal is read, further promoting residual charge elimination to adapt to the high-frequency application scenario of this case. An AMP TFT transistor was added to the circuit design to further amplify the output electrical signal, avoid signal interference, increase anti-interference capability, and make the amplified signal easier for control devices on the data signal line to read. Attached Figure Description

[0019] The following is a brief explanation of the contents of each of the accompanying drawings and the markings in the drawings:

[0020] Figure 1 This is a schematic diagram of a detection circuit for an existing optical signal sensor.

[0021] Figure 2 This is a schematic diagram of Embodiment 1 of the optical signal detection sensor of the present invention;

[0022] Figure 3 This is a schematic diagram of embodiment 3 of the optical signal detection sensor of the present invention;

[0023] Figure 4 This is a schematic diagram illustrating the regulation and control mechanism of the present invention.

[0024] The Chinese and English labels in the above figure are as follows:

[0025] PIN: Depletion-mode amorphous silicon diode;

[0026] Diode: a diode;

[0027] aSi: Amorphous silicon;

[0028] SiO: Silicon oxide;

[0029] lag: afterimage;

[0030] VSS: Low-voltage source;

[0031] PGA3: Reads three levels;

[0032] Vgs: Gate-source voltage;

[0033] Cst: Storage capacitor;

[0034] Gn: The nth row gate control signal, which is directly input by the IC;

[0035] Gn-1: The (n-1)th row gate control signal, transferred from the previous row signal;

[0036] Gn+1: The gate control signal for the (n+1)th row, which is transferred from the signal of the next row;

[0037] Gn+m: The gate control signal for the (n+m)th row, which is transferred in when the next m rows of signals are received;

[0038] TFT: Thin Film Transistor;

[0039] Vreset: Reset voltage, maintain constant potential;

[0040] Ioff: Leakage current. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and the description of the preferred embodiments.

[0042] Example 1:

[0043] This application's sensor circuit, applied to optical signal sensing and imaging fields such as X-ray imaging, falls within the core detection domain. The sensor circuit converts X-ray and other optical signals into electrical signals, which are then converted into corresponding grayscale images by the imaging control equipment based on the magnitude of the electrical signals, thus achieving X-ray and other optical signal imaging detection. As the most fundamental component, the optical signal imaging detection sensor's core function is to convert optical signals into electrical signals and transmit them via data lines for subsequent detection and conversion by the imaging device. This application addresses the shortcomings of existing PIN diode technology by providing a novel detection sensor circuit based on a metal-oxide-semiconductor diode (MODS), achieving accurate and reliable detection of optical signals while reducing lag. It improves the detection capabilities for small signals, expands the pixel range, and broadens the application scope.

[0044] like Figure 2 As shown, an ultra-low leakage current sensor based on a metal oxide diode includes a metal oxide diode, a pre-stored capacitor CO, a read TFT transistor, a storage capacitor Cst, and an RST TFT transistor.

[0045] The gate and drain of the metal-oxide-semiconductor diode (IGZO) are connected to the VSS power supply, and its source is connected to the drain of the read TFT transistor. A pre-stored capacitor C0 is connected in parallel across the gate and source of the IGZO. The source of the read TFT transistor is connected to the data input, and the source of the read TFT transistor is connected to the drive control signal Gn. One end of the storage capacitor Cst is connected to the reset power supply Vreset, and the other end is connected to the source of the IGZO.

[0046] The source of the RST TFT transistor is connected to the drain of the read TFT, and the drain of the RST TFT transistor is connected to the reset power supply Vreset. The gate of the RST TFT transistor receives the reset drive control signal Gn. The gate of the RST TFT transistor is connected to the output of the scan control circuit, and the scan signal Gn+1 output by the scan control circuit controls the on / off state of the RST TFT; where the scan signal Gn+1 is the scan signal for the next moment after the scan signal Gn.

[0047] Its working principle is as follows:

[0048] When using the sensor circuit of this application for optical signal detection, the gate of the read TFT is connected to the scan control circuit. The scan control circuit outputs a scan control signal according to a set scan cycle, which is used to output a scan signal Gn to drive the read TFT to turn on and off. Each scan cycle is the signal reading cycle. According to the actual application scenario, the VSS and Vreset voltages and the capacitance values ​​of C0 and Cst are set. When the optical signal shines on the metal oxide diode, due to its photoelectric characteristics, the optical signal is converted into a corresponding electrical signal and the charge flows towards the data signal line. During the flow, the voltage is modulated by the Cst capacitor to prevent it from exceeding the TFT's tolerance range and to reduce the coupling interference of surrounding signals to the photoelectric signal, thereby improving stability. Then, in the corresponding reading cycle, the scan control signal Gn of the current row of the scan line controls the conduction of the read TFT transistor. Whether it is on or off indicates whether the data line terminal can be read, so that the charge can flow in a direction and be output to the data line side through the read TFT. Of course, after reading, the control signal Gn+1 of the next reading cycle is used to drive and control the RST TFT to achieve zeroing of the electrical signal, so that the electrical signal through the readTFT transistor is zeroed, avoiding the defect of lag caused by the presence of charge between the next scan reading cycle and the previous scan reading cycle.

[0049] In this application, the circuit design described above has wider adaptability and can be used in different scenarios. It employs a maximum linear dose control (VSS) mechanism, dynamically adjusting the VSS voltage to adapt to different photosensitive scenarios. For example... Figure 4As shown, the TFT Drain is always N, the Source is always M, and the gate is always O; Vreset is fixed at 4V, and adjusting VSS can control the current value of the metal oxide diode; when VSS is 0V, the current flowing through MN is in the 1pA range. After photosensitive, the current fluctuates, and the brightness information can be obtained by collecting the current fluctuation value and integrating it, which is used for high-range scenarios with large signals; when VSS is 5V, the current flowing through MN is in the 1uA range. After photosensitive, the current fluctuates, and the brightness information of small signals can be multiplied by increasing the current value, which is used for low-range scenarios with small signals. Here, the large and small signal ranges refer to X-ray metrology and X-ray dose. The conventional upper limit is 4 to 6000 nGy, and a wider range can be adapted by self-adjusting the range.

[0050] The sensor circuit in this application is used to sense optical signals, specifically visible light. To enable it to collect high-energy rays such as X-rays, a scintillator material can be used to convert the corresponding X-rays into visible light, which is then converted by a metal-oxide diode. The metal-oxide diode is used to convert the optical signal into an electrical signal, where the optical signal is visible light or high-energy rays / particles converted by the scintillator. Scintillators include GoS materials and Csl materials.

[0051] The advantages of this application include:

[0052] 1. By introducing a metal oxide diode structure, the sensing of different gray levels is achieved through the charge sharing mechanism of the Cgd off+C0 capacitor and the charge redistribution interference generated by the metal oxide photosensitive element; different distribution ratios and amplitudes can be designed in the initial circuit design, and redistribution is carried out in actual use.

[0053] 2. Utilizing the inherently extremely low leakage current characteristics of metal oxides to achieve ultra-low grayscale sensing effect;

[0054] 3. Utilizing the material properties of metal oxides that cannot undergo transitions under visible light to achieve extremely low lag sensing effects;

[0055] 4. The maximum linear dose can be adjusted by adjusting VSS, and the ROIC can be maximized. ROIC is a read-out IC with different built-in read levels, which can be used for different scenarios. If the maximum level is exceeded, the ROIC model needs to be replaced. This solution can extend the usage limit of ROIC.

[0056] 5. For dynamic high-frequency scenarios, the higher the frequency, the better the effect; the X-ray source is always on, and the high frequency refers to the speed of the object being measured and the detection and refresh speed of the detector itself. If the object is stationary, 1Hz is sufficient. If the object being measured is moving, it is recommended to be >60Hz.

[0057] PIN photodiodes are fabricated using aSi material. Under conventional processes, the leakage current is 1pA, requiring process optimization to reach 10fA or less before they can be used. Metal oxide materials, due to their high bandgap (3.4eV), can achieve a current of <10fA with conventional processes, effectively reducing the difficulty of process debugging. In this case, charge storage uses a standard capacitor Cst with a high-temperature SiO film, completely avoiding the lag problem caused by charge capture and recombination by the PIN reverse bias capacitor.

[0058] In this case, the charge is pre-stored in C0, and the pre-stored amount can be changed by adjusting the VSS voltage to correspond to different dose application scenarios. The different dose application scenarios are: low dose requirements for radiation sources in medical scenarios, higher dose requirements for pet medical applications, and the highest dose requirements for industrial applications.

[0059] Current products must be designed to work with different detectors for different scenarios.

[0060] Taking the medical PGA3 application scenario as an example, for the 30Hz application scenario: a) The average current density of charge transfer within one frame is ≈36pA; the Vgs of the metal oxide diode needs to be designed between 0 and 2.0V; b) Cst adopts the conventional 140um pixel Cdiode 1pF capacitor design, and the voltage difference change across Cst is ≈1.0V; a separate pre-stored capacitor C0 is added to reduce power consumption as an auxiliary requirement, designed according to C0≈Cst=1.0pF, and the VSS voltage requirement is 2.0V; c) After the current row of Gn is read, the next row performs N-point reset, and the remaining n-2 rows are used for signal transfer for the next read; d) The charge of C0 is transferred through the leakage current of the metal oxide diode, and the average current density is the same as the design value in a) to achieve charge rearrangement between Vreset and VSS; d) Gn is turned on, and the N-point charge is output through the read TFT;

[0061] The sensor circuit in this application embodiment is applied to the detection of non-static light signals, at least low-frequency light signals. It cannot be applied to the detection of static light signals because static light signals are detected while the light signal is in a certain state. After trying to maintain a certain state, the voltage across C0 becomes 0 after infinite equilibrium, resulting in no grayscale effect and the data cannot be read. Therefore, the sensor pixel circuit of this application is suitable for dynamic scenes, especially high-frequency scenes, and the higher the frequency, the better the effect.

[0062] Example 2:

[0063] This application improves upon Embodiment 1 by adding an AMP TFT transistor to the circuit of Embodiment 1. The AMP TFT transistor is connected in series between the drain of the read TFT transistor and the source of the metal-oxide-semiconductor diode (MOS diode). Its gate is connected to the source of the MOS diode, its source is connected to the drain of the read TFT transistor, and its drain is connected to the power supply VSS. The function of the AMP TFT is to amplify the electrical signal, avoiding the defects of easy interference and difficulty in detection when the electrical signal output by the MOS diode is small. By adding the AMP TFT, it is controlled by the electrical signal output by the MOS diode, thereby converting its output into a high-level signal output to the data line, increasing its anti-interference capability, and making the data easier to read, thus meeting the requirements of the reading range.

[0064] This application uses a metal oxide short-circuited TFT as a photodiode, taking advantage of the low Ioff inherent in the metal oxide itself, which effectively reduces the difficulty of process debugging. It also uses a Cst charge pre-store circuit scheme to eliminate the lag risk caused by the PIN diode, and achieves the purpose of reducing lag through Cst+C0 circuit pre-store.

[0065] Obviously, the specific implementation of this invention is not limited to the above-described methods. Any non-substantial improvements made using the inventive concept and technical solution of this invention are within the protection scope of this invention.

Claims

1. A range adjustable all-metal oxide sensor pixel, characterized by: The sensor comprises a metal oxide diode, a pre-storage capacitor CO, and a read TFT transistor, wherein the gate and the drain of the metal oxide diode are connected to a VSS power supply, the source of the metal oxide diode is connected to the drain of the read TFT transistor, the pre-storage capacitor CO is connected in parallel between the gate and the source of the metal oxide diode; the source of the read TFT transistor is connected to data; and the source of the read TFT transistor is connected to a driving control signal Gn.

2. A range adjustable all-metal oxide sensor pixel as claimed in claim 1, characterized in that: The sensor further comprises a storage capacitor Cst, one end of which is connected to a reset power supply Vreset, and the other end of which is connected to the source of the metal oxide diode.

3. A range adjustable all-metal oxide sensor pixel as claimed in claim 1 or 2, characterized in that: The sensor further comprises an RST TFT transistor, the source of which is connected to the drain of the read TFT, the drain of which is connected to the reset power supply Vreset; and the gate of the RST TFT transistor is connected to a reset driving control signal.

4. A metal oxide diode based ultra-low leakage current sensor as claimed in claim 1 or 2, wherein: The sensor further comprises an AMP TFT transistor, which is connected in series between the drain of the read TFT transistor and the source of the metal oxide diode, the gate of which is connected to the source of the metal oxide diode, the source of which is connected to the drain of the read TFT transistor, and the drain of which is connected to the power supply VSS.

5. A range adjustable all-metal oxide sensor pixel as claimed in claim 1 or 2, characterized in that: The gate of the read TFT is connected to a scan control circuit, which is used to output a scan signal Gn to drive the on-off of the read TFT, wherein Gn is a scan signal at a time point of the nth row in the sensor pixel array.

6. A range adjustable all-metal oxide sensor pixel as in claim 3, wherein: The gate of the RST TFT transistor is connected to an output end of the scan control circuit, and a scan signal Gn+1 output by the scan control circuit is used to control the on-off of the RST TFT. The scan signal Gn+1 is a scan signal at a time point of the next row or multiple next rows of the scan signal Gn.

7. A range adjustable all-metal oxide sensor pixel as claimed in any one of claims 1-6, characterized in that: The VSS / Vreset voltage is adjusted dynamically, which is suitable for different detection scenarios under different light intensities, and the pixel itself can realize the function of range adjustment.

8. The range adjustable all-metal oxide sensor pixel of claim 1, wherein: The metal oxide diode is used to convert a light signal into an electric signal, wherein the light signal is a visible light signal or a light signal converted by a scintillator from a high-energy ray or a high-energy particle.

9. The range adjustable all-metal oxide sensor pixel of claim 8, wherein: The scintillator comprises a GoS material or a Csl material.

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