Perovskite-based X-ray direct imaging detector with low leakage current

Abstract

The invention provides a low-leakage-current perovskite-based X-ray direct imaging detector structure, and relates to the field of radiation detection. According to the invention, the metal oxide film is added between the pixel electrode and the PI adhesion layer, so that the electron injection efficiency can be improved, and the current of a drain device can be reduced; in addition, the PI adhesion layer is doped with the metal oxide, so that the work function of the oxide and the PI adhesion layer is improved, and the performance of the TFT-based perovskite X-ray detector is improved.

Description

Technical Field

[0001] The present invention relates to the field of radiation detection, and particularly to a low leakage current perovskite-based X-ray direct imaging detector. Background Art

[0002] Due to high X-ray absorption rate and high sensitivity, metal halide perovskite has become the core technology of the next-generation direct imaging detector digital photography system. Its low-temperature deposition process is conducive to the large-area deposition of perovskite on the TFT substrate (thin film transistor), forming large area and flexibility, which can cope with more free medical application scenarios.

[0003] However, the high dark current of perovskite photodetectors has greatly hindered the application of X-ray imaging devices. Firstly, the high dark current will quickly fill the TFT storage capacitor, causing the actual detected information to be submerged by noise. In addition, the large dark current will significantly increase the instantaneous noise, resulting in a poor signal-to-noise ratio (SNR). Recently, many literatures have studied methods to reduce the dark current, including doping, heterojunction and other schemes.

[0004] In addition, many tiny defect states are likely to appear during the preparation of perovskite, and these defect states will form conduction paths when an electric field is applied. From the electrical characteristics, single-layer perovskite devices will generate a large leakage current. In order to reduce the leakage current, the film quality of the thick film will be improved and the denseness of the thick film will be improved during the process, but it cannot be completely improved in the end. In order to overcome the technical problem of leakage current, the industry needs to explore new processes and schemes for improvement. Summary of the Invention

[0005] In view of the above problems or deficiencies, the present invention provides a low leakage current perovskite-based X-ray direct imaging detector. The technical solution adopted by the present invention is as follows:

[0006] Compared with a conventional X-ray direct imaging detector, the present invention adds a metal layer, such as Figure 2 , 3 , as shown in FIG. 4.

[0007] A low leakage current perovskite-based X-ray direct imaging detector provided by the present invention includes a pixel unit, and the structure of the pixel unit includes a substrate, a TFT substrate, a pixel layer, a metal layer, a perovskite material, a top electrode, and a packaging layer.

[0008] The substrate is a PI substrate, and the upper surface of the PI substrate is a buffer layer. The buffer layer is a multi-layer inorganic layer structure (SiN, SiO, Si), which is used to prevent the conductive ions of the substrate from diffusing into the TFT device and affecting the performance of the TFT device;

[0009] The upper surface of the buffer layer is a TFT substrate, and the upper surface of the TFT substrate is a pixel electrode and a pixel definition layer. The pixel definition layer is used to define the size of the pixel electrode;

[0010] The pixel electrode is generally an ITO transparent electrode or a metal electrode (such as Al, Cu, Ni, etc.);

[0011] The pixel layer includes a pixel definition layer and a pixel electrode; the pixel definition layer includes a first pixel definition layer and a second pixel definition layer. The first pixel definition layer has the same thickness as the pixel electrode and is located in the same planar layer; the lower surface of the second pixel definition layer coincides with all of the upper surface of the first pixel definition layer and part of the upper surface of the pixel electrode.

[0012] The upper surface of the pixel electrode and the pixel definition layer is a metal layer;

[0013] The perovskite material is prepared on the metal layer by spin coating or spraying. Specifically, the perovskite material is 50μm MAPbI 3 .

[0014] The top electrode is located on the upper surface of the perovskite material and uses 1μm Ag electrode material;

[0015] The perovskite material usually absorbs water and oxygen. A packaging layer is prepared above the top electrode to block water and oxygen. The packaging layer is 1μm SiN material.

[0016] The packaging layer is located above the electrode and is used to block the erosion of water and oxygen on the perovskite device.

[0017] As an implementation method, as Figure 2 shown, the metal layer includes a metal oxide thin film and a PI adhesion layer; the upper surface of the pixel electrode and the pixel definition layer forms a metal oxide thin film by magnetron sputtering or solution method. The metal oxide is generally materials such as zinc oxide, titanium oxide, and aluminum oxide. The metal oxide material is a whole-surface thin film material. The upper surface of the metal oxide is a PI adhesion layer, specifically PI-δ-ABX 3 thin film.

[0018] As an implementation method, as Figure 3 shown, the upper surface of the pixel electrode and the pixel definition layer forms a metal oxide thin film by magnetron sputtering or solution method. Generally, the metal oxide is materials such as zinc oxide, titanium oxide, and aluminum oxide. The metal oxide thin film forms a pixel pattern by dry etching, covers the pixel electrode, and is parallel to the upper surface of the pixel definition layer. The upper surface of the metal oxide thin film and the pixel definition layer is a PI adhesion layer, specifically PI-δ-ABX 3 thin film.

[0019] As an implementation method, as Figure 4 shown, the PI adhesion layer is specifically a PI thin film doped with metal oxides (such as PI-ZnO, PI-NiO, etc.) or PI-δ-ABX 3, the slit coating process is commonly used. Among them, the PI-ZnO adhesion layer helps to match the work functions of the metal oxide and the PI adhesion layer.

[0020] A low leakage current perovskite-based X-ray direct imaging detector provided by the present invention has the following advantages: by adding a metal oxide between the pixel electrode and the PI adhesion layer, the electron injection efficiency can be improved and the leakage device current can be reduced. Description of the Drawings

[0021] Figure 1 is a structural diagram of a typical TFT-based perovskite detector.

[0022] Figure 2 is a structural diagram of a TFT perovskite detector with a whole-surface metal oxide added.

[0023] Figure 3 is a structural diagram of a typical TFT perovskite detector with a pixel-level metal oxide added.

[0024] Figure 4 is a structural diagram of a typical TFT perovskite detector with a pixel-level metal oxide added and metal oxide nanoparticles doped in the PI adhesion layer in total.

[0025] Figure 5 is a comparison diagram of the electrical characteristics of a TFT perovskite detector with a whole-surface metal oxide added. Detailed Embodiments

[0026] To make the structure and process of the present invention easy to understand, the present invention will be specifically described below in conjunction with the drawings and specific embodiments. The following embodiments are only used to further illustrate the present invention and do not make any limitation to the content of the invention itself. Those skilled in the art can make some non-essential improvements and adjustments according to the present invention.

[0027] Embodiment 1

[0028] A low leakage current perovskite-based X-ray direct imaging detector according to this embodiment, the detector includes pixel units, and the basic structure of each pixel unit is as Figure 1 shown, including a substrate, a TFT substrate, a pixel layer, a PI adhesion layer, a perovskite material, a top electrode, and a packaging layer.

[0029] The substrate includes a PI substrate and a buffer layer. The upper surface of the PI substrate is the buffer layer, and the buffer layer is a multi-layer inorganic layer structure (SiN, SiO, Si), which is used to prevent the conductive ions of the substrate from diffusing into the TFT device and affecting the performance of the TFT device;

[0030] The upper surface of the substrate (i.e., the upper surface of the buffer layer) is the TFT substrate; specifically as Figure 2As shown, the TFT substrate uses the ILD insulating layer as the base, the active layer is embedded in the ILD insulating layer, and there are source electrodes, gate electrodes, and drain electrodes above the active layer. The gate electrode and the active layer are isolated by the GI layer to form a capacitive structure. The source electrode and the drain electrode are located on the left and right sides of the gate electrode; the gate electrode, the source electrode, and the drain electrode protrude from the upper surface of the ILD insulating layer; the upper surface of the TFT substrate is leveled with the parts of the source electrode and the drain electrode that protrude from the ILD insulating layer by coating and leveling a photosensitive PI material.

[0031] The upper surface of the TFT substrate is the pixel layer, which includes a pixel definition layer and a pixel electrode; among them, the pixel definition layer is used to define the size of the pixel electrode. The pixel definition layer includes a first pixel definition layer and a second pixel definition layer. The first pixel definition layer has the same thickness as the pixel electrode and is located in the same planar layer; the lower surface of the second pixel definition layer coincides with the entire upper surface of the first pixel definition layer and coincides with a part of the upper surface of the pixel electrode.

[0032] The pixel electrode is a 100nm ITO transparent electrode;

[0033] The upper surface of the pixel layer is a PI adhesion layer, specifically a PI-δ-ABX3 thin film.

[0034] The perovskite material is prepared on the PI-δ-ABX 3 thin film by spin coating or spraying, where the perovskite material is specifically 100μm MAPbI 3 .

[0035] The top electrode is located on the upper surface of the perovskite material and uses a 1μm Ag electrode material;

[0036] The perovskite material usually absorbs water and oxygen, and a packaging layer is prepared above the top electrode to block water and oxygen. The packaging layer is a 1μm SiN material.

[0037] In this embodiment, by replacing the PI adhesion layer with a metal layer, the leakage current of the X-ray detection device is significantly reduced;

[0038] Specifically, the metal layer includes a metal oxide thin film and a PI adhesion layer; the metal oxide thin film is located on the upper surfaces of the pixel electrode and the pixel definition layer, specifically a 50nm zinc oxide thin film prepared by magnetron sputtering. The upper surface of the metal oxide is a PI thin film doped with perovskite material (PI-δ-ABX 3 ), and the slit coating process is used, with a thickness of 1μm.

[0039] As Figure 5 shown, after preparing a 50nm zinc oxide thin film by magnetron sputtering, the leakage current of the X-ray detection device decreases from 10nAcm 2 to 1nAcm 2, the device leakage current is reduced by one order of magnitude (-5V to +5V scanning voltage).

[0040] Example 2

[0041] The structure of a low-leakage-current perovskite-based X-ray direct imaging detector in this example is as Figure 3 shown. The difference from Example 1 is that a 50nm titanium oxide thin film is prepared on the upper surface of the pixel electrode and the pixel definition layer by magnetron sputtering. As Figure 3 shown, the titanium oxide thin film forms a pixel pattern by dry etching, covers the pixel electrode, is parallel to the upper surface of the pixel definition layer, and the upper surfaces of the metal oxide and the pixel definition layer are PI films doped with perovskite materials (PI-δ-ABX 3 ).

[0042] Example 3

[0043] The structure of a pixel-level packaged perovskite-based direct X-ray imaging detector in this example is as Figure 4 shown. The difference from Example 1 is that ZnO nanoparticles with a diameter of 20nm to 500nm are doped in the PI film used, and the slit coating or spin coating process is used, with a thickness of 1μm.

[0044] Doping nanoparticles in the PI improves the adhesion effect between the perovskite layer and the metal oxide layer, and at the same time increases the conduction path from the perovskite to the metal oxide. While reducing the leakage current in the ZnO layer, it improves the effective photocurrent path and increases the photoelectric response characteristics of the perovskite device.

[0045] Example 4

[0046] The structure of a low-leakage-current perovskite-based X-ray direct imaging detector in this example is different from that of Example 2 in that ZnO nanoparticles with a diameter of 20nm to 500nm are doped in the PI film used, and the slit coating or spin coating process is used, with a thickness of 1μm. At the same time, the PI film layer is locally patterned, which ensures the adhesion between the perovskite layer and the metal oxide layer and provides direct contact between the perovskite layer and the metal oxide layer. The metal oxide layer reduces the leakage current and increases the conduction path between the perovskite layer and the metal oxide layer, improving the photoelectric response characteristics of the perovskite device.

[0047] It is understood that the present invention is described by way of some embodiments, and those skilled in the art will be aware that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application belong to the scope protected by the present invention.

Claims

1. A low leakage current perovskite-based X-ray direct imaging detector, characterized in that: The detector includes a pixel unit, and the pixel unit includes a substrate, a thin film transistor TFT substrate, a pixel layer, a metal layer, a perovskite material, a top electrode, and an encapsulation layer; Specifically, the upper surface of the substrate is a TFT substrate, and the upper surface of the TFT substrate is a pixel layer; the pixel layer includes a pixel definition layer and a pixel electrode, wherein the pixel definition layer is located outside the pixel electrode and is used to define the size of the pixel electrode, and the pixel definition layer includes a first pixel definition layer and a second pixel definition layer, and the first pixel definition layer has the same thickness as the pixel electrode and is located in the same plane layer; the lower surface of the second pixel definition layer overlaps with the entire upper surface of the first pixel definition layer and overlaps with a portion of the upper surface of the pixel electrode; The upper surface of the pixel layer is a metal layer, which specifically includes a metal oxide film and a PI adhesion layer; the metal oxide film is located on the upper surface of the pixel electrode, and the PI adhesion layer is located above the pixel layer; The upper surface of the metal layer is a perovskite material, the upper surface of the perovskite material is a top electrode, and the upper surface of the top electrode is encapsulated using an encapsulation layer.

2. A low leakage current perovskite-based X-ray direct imaging detector according to claim 1, characterized in that: The material of the metal oxide film is specifically zinc oxide, titanium oxide or aluminum oxide, and the PI adhesion layer is specifically a PI-δ-ABX3 film doped with a perovskite material or a PI film doped with a metal oxide.

3. A low leakage current perovskite-based X-ray direct imaging detector according to claim 2, characterized in that: The metal oxide doped in the metal oxide doped PI film is specifically nanoparticles of zinc oxide and nickel oxide with a diameter of 20nm to 500nm.

4. The low leakage current perovskite-based X-ray direct imaging detector according to claim 3, characterized in that: The metal oxide film is prepared on the upper surface of the pixel layer by magnetron sputtering.

5. The low leakage current perovskite-based X-ray direct imaging detector according to claim 4, characterized in that: The PI adhesion layer is prepared by slit coating or spin coating process.

6. A low leakage current perovskite-based X-ray direct imaging detector according to claim 5, characterized in that: The metal oxide film is located on the upper surfaces of the pixel electrode and the pixel definition layer, and the upper surface of the metal oxide film is a PI adhesion layer.

7. The low leakage current perovskite-based X-ray direct imaging detector according to claim 5, characterized in that: The metal oxide film is located on the upper surface of the pixel electrode, and the metal oxide film and the upper surface of the pixel definition layer are PI adhesion layers.

8. The low leakage current perovskite-based X-ray direct imaging detector according to claim 7, characterized in that: The metal oxide film is located on the upper surface of the pixel electrode. The upper surface of the metal oxide film and the pixel definition layer is a PI adhesion layer. The PI adhesion layer is patterned to provide a channel for direct contact between the perovskite material layer and the metal oxide film.

9. The low leakage current perovskite-based X-ray direct imaging detector according to claim 8, characterized in that: The perovskite material is specifically MAPbI3.

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