Two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor and manufacturing method thereof
By using a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, combined with built-in electric field and bias voltage control, the problem of existing X-ray detectors relying on external power sources has been solved, realizing the integration of self-powered detection and synaptic functions, which is suitable for medical diagnosis, security screening and radiation monitoring.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-10
- Publication Date
- 2026-05-15
AI Technical Summary
Existing X-ray detectors rely on external power sources, have limited detection height and sensitivity, and lack integrated synaptic functions, making it difficult to meet the needs of portable and intelligent application scenarios.
A two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor was developed. The bottom layer, ferroelectric functional layer and top layer were fabricated on the substrate by mechanical stripping and PDMS dry transfer technology. Self-powered detection was achieved by using the built-in electric field, and the synaptic function was simulated by bias voltage control.
It achieves self-powered X-ray detection under zero bias voltage, simulates short-term or long-term synaptic plasticity, improves the practicality and intelligence of the device, and is suitable for medical diagnosis, security screening and radiation monitoring.
Smart Images
Figure CN122054713A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor and its fabrication method, belonging to the field of X-ray synaptic transistors. Background Technology
[0002] X-rays, high-energy electromagnetic waves with wavelengths of 0.01 nm to 10 nm and energies of 124 eV to 1.24 MeV, are indispensable in fields such as medical diagnosis, security screening, radiation monitoring, and industrial non-destructive testing due to their strong penetrating power. The core of their detection lies in capturing X-ray photons of varying intensities and reconstructing the internal information of the object under test through photoelectric conversion and imaging systems. Current bottlenecks in detection technology have shifted from "whether detection is possible" to "how to achieve efficient, low-power, and intelligent detection," directly driving research into self-powered X-ray detection and X-ray visual synaptic devices. Existing X-ray detectors are divided into indirect and direct detection types. Indirect detection requires a two-step conversion: "high-energy radiation → visible light → electrical signal," and scattering effects easily lead to a decrease in resolution. While direct detection can achieve direct conversion from X-rays to electrical signals using semiconductor materials, it suffers from dependence on external power supplies and limited functionality, making it difficult to meet the practical needs of portable and intelligent applications. In the field of direct detection, traditional semiconductor materials (such as cadmium telluride (CdTe), amorphous selenium (α-Se), and silicon (Si) have been commercialized, but they suffer from problems such as insufficient carrier mobility-lifetime product, weak X-ray absorption, and high manufacturing costs. More importantly, these devices generally rely on external bias voltages, which cannot meet the low-power requirements of scenarios such as portable medical devices and field radiation monitoring. Meanwhile, the penetration of artificial intelligence and image recognition technologies requires X-ray detectors to not only "sense" signals but also perform "preliminary processing," i.e., combining detection and synaptic simulation functions, which poses new challenges to existing devices. Summary of the Invention
[0003] To address the shortcomings of existing technologies, this invention provides a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor and its fabrication method, achieving ultra-low limit self-powered X-ray detection and synaptic function integration.
[0004] The technical solution adopted by this invention to solve its technical problem is: In a first aspect, this application provides a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, comprising a substrate, wherein a bottom layer, a ferroelectric functional layer, and a top layer are disposed thereon in sequence, the bottom layer is connected to a first electrode, the top layer is connected to a second electrode, the bottom layer and the top layer are independently composed of a two-dimensional semi-metallic material, the ferroelectric functional layer comprises a two-dimensional ferroelectric material, the bottom layer is not in contact with the top layer, and the work function of the bottom layer is not equal to the work function of the top layer.
[0005] The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor provided in this application has excellent stability and can be widely used in medical diagnosis, security screening, radiation monitoring and intelligent sensing, providing core support for "detection-synapse" integrated devices.
[0006] Furthermore, in the bottom layer and the top layer, the thickness difference between the thicker and thinner layers is greater than 0 and less than or equal to 63 nm.
[0007] Furthermore, in the group of contacts where the work function difference between two-dimensional ferroelectric materials and two-dimensional semi-metallic materials is greater (the contact between the bottom layer and the ferroelectric functional layer is one group of contacts, and the contact between the top layer and the ferroelectric functional layer is another group of contacts), the contact area is larger.
[0008] Furthermore, the work function difference between the bottom layer and the ferroelectric functional layer is greater than the work function difference between the top layer and the ferroelectric functional layer.
[0009] Furthermore, the contact area of the one with a larger contact area is 1.09 to 3.4 times that of the one with a smaller contact area.
[0010] Furthermore, the bandgap of the two-dimensional ferroelectric material is 0.7 eV to 3.0 eV.
[0011] Furthermore, the ferroelectric functional layer includes a ferroelectric layer (composed of a two-dimensional ferroelectric material) and a hexagonal boron nitride layer located on the bottom, top, or both (bottom and top) surfaces of the ferroelectric layer.
[0012] Furthermore, the two-dimensional ferroelectric material is selected from two-dimensional semiconductor materials with spontaneous polarization, such as halide salts, metal thiophosphates, and metal selenophosphates.
[0013] Furthermore, the two-dimensional semi-metallic material is graphene.
[0014] Secondly, this application provides a method for fabricating a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, which is carried out according to one of the following two sets of steps; The first set of steps includes: fabricating a first electrode and a second electrode on a substrate; mechanically peeling off a first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material, transferring it to the substrate, contacting the first electrode but not the second electrode, to form a bottom layer; mechanically peeling off a two-dimensional ferroelectric material film from a crystal of a two-dimensional ferroelectric material, transferring it to the substrate, contacting the bottom layer but not the second electrode, to form a ferroelectric functional layer; and mechanically peeling off a second two-dimensional semi-metallic film with a work function different from the first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material, transferring it to the substrate, contacting the ferroelectric functional layer and the second electrode, but not the bottom layer, to form a top layer. The second set of steps includes: mechanically peeling a first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material and transferring it to a substrate to form a bottom layer; mechanically peeling a two-dimensional ferroelectric material film from a crystal of a two-dimensional ferroelectric material and transferring it to the substrate, where it contacts the bottom layer to form a ferroelectric functional layer; mechanically peeling a second two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material with a work function different from that of the first two-dimensional semi-metallic film, transferring it to the substrate, where it contacts the ferroelectric functional layer but not the bottom layer to form a top layer; and fabricating a first electrode that contacts the bottom layer and a second electrode that contacts the top layer on the substrate.
[0015] The beneficial effects of this invention are as follows: This invention combines the built-in electric field induced by ferroelectric polarization to achieve self-powered X-ray detection under zero bias. If an X-ray pulse is used as the stimulation signal, synaptic enhancement or inhibition can be achieved through bias voltage modulation, simulating short-term or long-term synaptic plasticity. The device fabrication process of this invention is simple, and its stability is excellent. It can be widely applied in medical diagnostics, security screening, radiation monitoring, and intelligent sensing fields, providing core technical support for integrated "detection-synapse" devices.
[0016] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description
[0017] Figure 1 This is a schematic diagram of the structure of the two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor of the present invention.
[0018] Figure 2 The experiment compares the X-ray response current density diagrams corresponding to different contact area differences.
[0019] Figure 3 The experiment compares the curves of X-ray response current as a function of the thickness of a two-dimensional semi-metallic material on one side.
[0020] Figure 4 The figure shows a comparison of the X-ray response current density performance of the three two-dimensional ferroelectric vertical heterojunctions with that of the comparative example.
[0021] Figure 5 The figure shows the verification results of synaptic behavior achieved by X-ray pulse stimulation under the condition of an applied bias voltage in a two-dimensional ferroelectric vertical heterojunction, which is the fourth experimental comparison.
[0022] Figure 6 The graph shows the variation of heterojunction response current density with X-ray dose rate in one of the improved embodiments.
[0023] Reference numerals: 1. Top layer; 2. Ferroelectric functional layer; 3. Bottom layer; 4. Oxide layer; 5. Substrate; 61. Second electrode; 63. First electrode. Detailed Implementation
[0024] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.
[0025] The following disclosure provides many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.
[0026] To address the issues of existing X-ray detectors, such as reliance on external power supplies, detection height limitations, insufficient sensitivity, and lack of integrated synaptic functionality, this paper refers to... Figure 1 This application provides a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, including a substrate 5. The substrate 5 has a bottom layer 3, a ferroelectric functional layer 2, and a top layer 1 stacked sequentially. The bottom layer 3 is connected to a first electrode 63, and the top layer 1 is connected to a second electrode 61. The bottom layer 3 and the top layer 1 are independently made of two-dimensional semi-metallic materials (both the bottom layer and the top layer are two-dimensional semi-metallic materials, and the materials of the bottom layer and the top layer can be the same or different). The ferroelectric functional layer 2 has a two-dimensional ferroelectric material, and the bottom layer 3 is not in contact with the top layer 1.
[0027] The substrate is specifically a substrate with an oxide layer 4. For example, a silicon substrate with a silicon oxide layer. The two-dimensional ferroelectric material is selected from two-dimensional semiconductor materials with spontaneous polarization, such as halide salts, metal thiophosphates, and metal selenophosphates. Two-dimensional semi-metallic materials include graphene, etc.
[0028] Accordingly, embodiments of this application provide a method for fabricating a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, which is performed according to one of the following two sets of steps.
[0029] The first set of steps includes: fabricating a first electrode and a second electrode on a substrate; mechanically peeling a first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material, transferring it to the substrate, contacting the first electrode but not the second electrode, to form a bottom layer; mechanically peeling a two-dimensional ferroelectric material film from a crystal of a two-dimensional ferroelectric material, transferring it to the substrate, contacting the bottom layer but not the second electrode, to form a ferroelectric functional layer; and mechanically peeling a second two-dimensional semi-metallic film (the work function of the second two-dimensional semi-metallic film is different from that of the first two-dimensional semi-metallic film) from a crystal of a two-dimensional semi-metallic material, transferring it to the substrate, contacting the ferroelectric functional layer and the second electrode, but not the bottom layer, to form a top layer. The resulting structure is as follows. Figure 1 As shown at point b in the middle.
[0030] The second set of steps includes: mechanically peeling a first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material and transferring it to a substrate to form a bottom layer; mechanically peeling a two-dimensional ferroelectric material film from a crystal of a two-dimensional ferroelectric material and transferring it to the substrate, where it contacts the bottom layer to form a ferroelectric functional layer; mechanically peeling a second two-dimensional semi-metallic film (the work function of the second two-dimensional semi-metallic film is different from that of the first two-dimensional semi-metallic film) from a crystal of a two-dimensional semi-metallic material and transferring it to the substrate, where it contacts the ferroelectric functional layer but not the bottom layer to form a top layer; and fabricating a first electrode in contact with the bottom layer and a second electrode in contact with the top layer on the substrate. The resulting structure is as follows. Figure 1 As shown at point a in the middle.
[0031] Specifically, the bottom layer, ferroelectric functional layer, and top layer can all be obtained by mechanical exfoliation using adhesive tape, and then transferred to the desired location using PDMS (polydimethylsiloxane) dry transfer technology. Obtaining the desired two-dimensional material directly through mechanical exfoliation is beneficial for obtaining two-dimensional materials with higher crystal quality; preparing two-dimensional vertical heterostructures using PDMS dry transfer technology is beneficial for precise transfer.
[0032] Two-dimensional wide-bandgap semiconductors have become a research hotspot due to their excellent optoelectronic properties, high breakdown electric field, and radiation resistance. Among them, ferroelectric layered materials stand out, with tunable bandgap, high carrier mobility, and built-in electric fields induced by in-plane / out-plane polarization that can achieve photogenerated carrier separation without external bias voltage. This provides an electric field drive for self-powered detection and lays the foundation for building "detector-synapse" integrated devices. They are core candidate materials for breaking through traditional technological bottlenecks and upgrading X-ray detection to "low power consumption + intelligence." In this application, the built-in electric field formed by the two-dimensional ferroelectric material can promote the separation of electron-hole pairs. The built-in electric field generated by the spontaneous polarization of the two-dimensional ferroelectric material itself can independently drive the separation of electron-hole pairs, increasing the carrier concentration in the two-dimensional ferroelectric vertical heterojunction, thereby improving the self-powered detection performance of the two-dimensional ferroelectric vertical heterojunction.
[0033] Two-dimensional ferroelectric materials are brought into contact with two-dimensional semi-metallic materials of different thicknesses, forming two built-in electric fields at the corresponding interfaces. When there are different work function differences between the bottom and top layers and the ferroelectric functional layer, two built-in electric fields with opposite directions and different magnitudes are formed, constituting a two-dimensional ferroelectric vertical heterojunction with an asymmetric Schottky barrier, enabling self-powered detection. For example, two different two-dimensional semi-metallic materials can be used, one as the bottom layer and the other as the top layer. Furthermore, the work function of graphene is significantly correlated with its thickness; even if both the top and bottom layers are graphene, having different thicknesses can result in different work functions for the top and bottom layers.
[0034] Specifically, in the bottom and top layers, the thickness difference between the thicker and thinner layers is greater than 0 and less than or equal to 63 nm. Further, the thickness difference between the bottom and top layers ranges from 9 nm to 32 nm; within this range, the current variation is more significant with changes in thickness difference.
[0035] In the contact between the bottom layer and the ferroelectric functional layer, and in the contact between the top layer and the ferroelectric functional layer, the contact area of the one with the larger contact area is 1.09 to 3.4 times that of the one with the smaller contact area.
[0036] Preferably, the contact area of the larger contact area is 1.25 to 3.26 times that of the smaller contact area.
[0037] More preferably, the contact area of the one with a larger contact area is 1.38 to 2.6 times that of the one with a smaller contact area.
[0038] The size of the contact area is directly related to the number of carriers migrating. Under the same built-in electric field, the side with a larger contact area will have more carriers migrating. However, as the contact area ratio increases, the total contact area of the two-dimensional semi-metallic material and the two-dimensional ferroelectric material decreases within the same effective area, and the separation of photogenerated electron-hole pairs by the built-in electric field decreases. Under the combined effect of these two mechanisms, the self-powered detection performance is superior within the same unit effective area when the area ratio is between 1.38 and 2.6.
[0039] When the side with a larger work function difference between the two-dimensional ferroelectric material and the two-dimensional semi-metallic material has a larger contact area, the synergistic effect of the contact area difference and the electrode thickness difference leads to a double-asymmetric Schottky barrier two-dimensional ferroelectric vertical heterojunction. In this heterojunction, the built-in electric field formed by the side with a larger work function difference between the two-dimensional ferroelectric material and the two-dimensional semi-metallic material dominates, and charge carriers primarily move under the influence of this built-in electric field. The side with a larger contact area between the two-dimensional ferroelectric material and the two-dimensional semi-metallic material experiences greater carrier migration, resulting in better self-powered detection performance.
[0040] The band gap of two-dimensional ferroelectric materials is directly related to the wavelength of light they can absorb; photon energy must be no less than the band gap to be absorbed by the two-dimensional material. A suitable band gap is closely related to the realization of self-powered X-ray detection and synaptic functions in two-dimensional ferroelectric vertical heterojunctions.
[0041] Specifically, the bandgap of the two-dimensional ferroelectric material is 0.7 eV to 3.0 eV. Preferably, it is 0.7-1.63 eV, which enables effective absorption of visible, infrared, and ultraviolet light. More preferably, it is 1.63-3.0 eV, which enables effective X-ray absorption.
[0042] The implementation of Comparison 1 includes the following steps: 1) Cut the silicon substrate with silicon oxide layer into 1 cm × 1 cm pieces, place the obtained substrate in ultrapure water for ultrasonic cleaning, wipe it with a lint-free cotton soaked in anhydrous ethanol, and then dry the surface with nitrogen.
[0043] 2) Place a mesh-like mask with 50 μm channel spacing in the center of the substrate and secure it to the substrate surface using insulating tape. Place the substrate with the mask in a small ion sputtering apparatus. First, perform a vacuum treatment, then turn on the power and perform ion sputtering (bombarding a metallic target) at a current of 5 mA for 60 s. Repeat this sputtering process three times. After sputtering, remove the substrate and use tweezers to remove the insulating tape and mask.
[0044] 3) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the blue film tape, and repeatedly mechanically peel it off to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe the color of the graphene material under a microscope, select graphene material of suitable and uniform thickness, and transfer the graphene to the electrode channel prepared in step 2) using a two-dimensional transfer platform. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the graphene to a specific location on the substrate.
[0045] 4) Cut a 10 cm section of blue film tape, place a small amount of NbOCl2 (niobium oxychloride) crystals inside the blue film tape, and obtain two-dimensional NbOCl2 material through repeated mechanical peeling. Adhere the NbOCl2 material from the blue film tape using PDMS, and transfer the NbOCl2 material to the substrate using a two-dimensional transfer platform. Place the NbOCl2 material on the graphene material, and heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the NbOCl2 material to the appropriate position.
[0046] 5) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the tape, and repeatedly mechanically peel it off to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe its color under a microscope, select graphene material of the same thickness and uniformity as the graphene material obtained in step 3), and transfer it to a substrate using a two-dimensional transfer platform. The graphene is placed on top of the NbOCl2 material, without contacting the underlying graphene. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS; the graphene will transfer to a specific location on the substrate.
[0047] Multiple two-dimensional ferroelectric vertical heterojunctions with different contact areas between two graphene and NbOCl2 materials were prepared using the same steps 1), 2), 3), 4), and 5). Real-time currents of the heterojunctions under X-ray irradiation (with and without) were obtained using a semiconductor analyzer. Different radiation doses (μGy·s⁻¹) were calculated. -1 The ratio of the real-time response current to the effective area of the heterojunction under X-ray irradiation was used to calculate the response current density (J / cm²). 2 )).like Figure 2 As shown, under the same built-in electric field, the side with a larger contact area will have more carrier migration. However, as the contact area ratio (A1 / A2) increases, the total contact area of the two-dimensional semi-metallic material and the two-dimensional ferroelectric material decreases within the same effective area, and the separation of photogenerated electron-hole pairs by the built-in electric field decreases. Under the combined effect of these two mechanisms, when the area ratio is between 1.38 and 2.6, the self-powered detection performance is superior within the same unit effective area.
[0048] Experimental Comparison 2 includes the following steps: 1) Cut the silicon substrate with silicon oxide layer into 1 cm × 1 cm pieces, place the obtained substrate in ultrapure water for ultrasonic cleaning, wipe it with a lint-free cotton soaked in anhydrous ethanol, and then dry the surface with nitrogen.
[0049] 2) Place a mesh-like mask with 50 μm channel spacing in the middle region of the substrate and secure it to the substrate surface using insulating tape. Place the substrate with the mask in a small ion sputtering apparatus. First, perform a vacuum treatment, then turn on the power and perform ion sputtering (bombarding a metallic target) at a current of 5 mA for 60 s, for a total of 3 sputtering cycles. After sputtering, remove the substrate and use tweezers to remove the insulating tape and mask.
[0050] 3) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the blue film tape, and repeatedly mechanically peel it off to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe the color of the graphene material under a microscope, select graphene material of suitable and uniform thickness, and transfer the graphene to the electrode channel prepared in step 2) using a two-dimensional transfer platform. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the graphene to a specific location on the substrate.
[0051] 4) Cut a 10 cm section of blue film tape, place a small amount of NbOCl2 crystals inside the tape, and obtain two-dimensional NbOCl2 material through repeated mechanical peeling. Use PDMS to pick up the NbOCl2 material from the blue film tape, and transfer it to a substrate using a two-dimensional transfer platform. Place the NbOCl2 material on the graphene material, and heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the NbOCl2 material to the appropriate position.
[0052] 5) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the tape, and repeatedly mechanically peel it off to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe its color under a microscope, select graphene material of suitable and uniform thickness, and transfer it to a substrate using a two-dimensional transfer platform. Place one side of the graphene on top of the NbOCl2 material, without contacting the underlying graphene. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS; the graphene will transfer to a specific location on the substrate.
[0053] 6) The response current of the heterojunction is measured under X-rays using a semiconductor analyzer. The same procedure as in step 5) is used to transfer a suitable thickness of graphene material onto the top layer of graphene material again, and the response current is measured under the same X-rays.
[0054] Using the same step 6), the response current (Current (pA) of the two-dimensional ferroelectric vertical heterojunction based on the asymmetric Schottky barrier under X-rays is obtained, as shown in step 6). Figure 3As shown, the contact area between the bottom graphene material and the NbOCl2 material is much larger than that between the top graphene material and the NbOCl2 material. Therefore, in the two-dimensional ferroelectric vertical heterojunction shown, the interface between the bottom graphene material and the NbOCl2 material is dominant. As the thickness (nm) of the top graphene material increases, the influence of the interface between the top graphene material and the NbOCl2 material gradually increases, leading to a decrease in the response current of the heterojunction. Furthermore, when the thickness difference is 9–32 nm, the change in current with the thickness difference is more significant. It can be seen that the structure and performance of the vertical heterojunction are optimized under the synergistic effect of the two asymmetric Schottky barriers.
[0055] Experimental Comparison 3 includes the following steps: 1) Cut the silicon substrate with silicon oxide layer into 1 cm × 1 cm pieces, place the obtained substrate in ultrapure water for ultrasonic cleaning, wipe it with a lint-free cotton soaked in anhydrous ethanol, and then dry the surface with nitrogen.
[0056] 2) Place a mesh-like mask with 50 μm channel spacing in the center of the substrate and secure it to the substrate surface using insulating tape. Place the substrate with the mask in a small ion sputtering apparatus. First, perform a vacuum treatment, then turn on the power and perform three ion sputtering cycles at a current of 5 mA, each lasting 60 s. After sputtering, remove the substrate and use tweezers to remove the insulating tape and mask.
[0057] 3) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the tape, and repeatedly peel it off mechanically to obtain two-dimensional graphene material. Adhere the graphene material from the blue film tape using polydimethylsiloxane (PDMS), observe the color of the graphene material under a microscope, select graphene material of suitable and uniform thickness, and transfer it to the electrode channel prepared in step 2) using a two-dimensional transfer platform. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the graphene to a specific location on the substrate.
[0058] 4) Cut a 10 cm section of blue film tape, place a small amount of NbOCl2 crystals inside the tape, and obtain two-dimensional NbOCl2 material through repeated mechanical peeling. Use PDMS to pick up the NbOCl2 material from the blue film tape, and transfer it to a substrate using a two-dimensional transfer platform. Place the NbOCl2 material on the graphene material, and heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the NbOCl2 material to the appropriate position.
[0059] 5) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the tape, and repeatedly mechanically peel it off to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe its color under a microscope, select a thinner and more uniform graphene material, and transfer it to a substrate using a two-dimensional transfer platform. Place one side of the graphene on top of the NbOCl2 material, without contacting the underlying graphene. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS; the graphene will transfer to a specific location on the substrate. This is denoted as Gr / NbOCl2 / Gr.
[0060] In step 4), the NbOCl2 crystal was replaced with boron nitride (h-BN) crystal (boron nitride is not a two-dimensional ferroelectric material), and the same steps 1), 2), 3), and 5) were used to prepare a two-dimensional vertical heterojunction based on a double asymmetric Schottky barrier. A self-powered X-ray detector was then used as a comparative example. This is denoted as Gr / h-BN / Gr.
[0061] Real-time currents of the heterojunction with and without X-ray irradiation were obtained using a semiconductor analyzer. Different radiation doses (μGy·s⁻¹) were calculated. -1 The response current density (J (μA / cm2)) is calculated by the ratio of the real-time response current to the effective area of the heterojunction under X-ray irradiation. Figure 4 As shown, under the same dose rate of X-rays, the response current of the two-dimensional ferroelectric vertical heterojunction is significantly larger. It can be seen that the structure and performance of the vertical heterojunction are optimized under the synergistic effect of the built-in electric field induced by ferroelectric polarization.
[0062] Experimental Comparison 4: Using Gr / NbOCl2 / Gr as the experimental device, the real-time current was measured after X-ray irradiation for different times under a constant bias voltage of 0.2 V across the heterojunction using a semiconductor analyzer. Figure 5 As shown, the response current (pA) and relaxation time (time (s)) of the two-dimensional ferroelectric vertical heterojunction increase with the increase of the pulse width, exhibiting excellent artificial synaptic function.
[0063] One of the improved embodiments The preparation method includes the following steps: 1) Cut the silicon substrate with silicon oxide layer into 1 cm × 1 cm pieces, place the obtained substrate in ultrapure water for ultrasonic cleaning, wipe it with a lint-free cotton soaked in anhydrous ethanol, and then dry the surface with nitrogen.
[0064] 2) Place a mesh-like mask with 50 μm channel spacing in the middle region of the substrate and secure it to the substrate surface using insulating tape. Place the substrate with the mask in a small ion sputtering apparatus. First, perform a vacuum treatment, then turn on the power and perform ion sputtering (bombarding a metallic target) at a current of 5 mA for 60 s, for a total of 3 sputtering cycles. After sputtering, remove the substrate and use tweezers to remove the insulating tape and mask.
[0065] 3) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the blue film tape, and repeatedly mechanically peel it off to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe the color of the graphene material under a microscope, select graphene material of suitable and uniform thickness, and transfer the graphene to the electrode channel prepared in step 2) using a two-dimensional transfer platform. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the graphene to a specific location on the substrate.
[0066] 4) Cut a 10 cm section of blue film tape, place a small amount of h-BN crystals inside the tape, and obtain two-dimensional h-BN material through repeated mechanical peeling. Adhere the h-BN material from the blue film tape using PDMS, and transfer it to a substrate using a two-dimensional transfer platform. Place the h-BN material on the graphene material, and heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the h-BN material to the appropriate position.
[0067] 5) Cut a 10 cm section of blue film tape, place a small amount of NbOCl2 crystals inside the tape, and obtain two-dimensional NbOCl2 material through repeated mechanical peeling. Use PDMS to pick up the NbOCl2 material from the blue film tape, and transfer it to the substrate using a two-dimensional transfer platform. Place the NbOCl2 material on the h-BN material, and heat the PDMS at 80°C for 10 minutes. Then, move the PDMS to transfer the NbOCl2 material to the appropriate position.
[0068] 6) Cut a 10 cm section of blue film tape, place a small amount of graphite crystals inside the tape, and repeatedly peel it mechanically to obtain two-dimensional graphene material. Use PDMS to pick up the graphene material from the blue film tape, observe its color under a microscope, select graphene material of suitable and uniform thickness, and transfer it to the substrate using a two-dimensional transfer platform. Place one side of the graphene on top of the NbOCl2 material, without contacting the underlying graphene. Heat the PDMS at 80°C for 10 minutes. Then, move the PDMS; the graphene will transfer to a specific position on the substrate. The heterojunction preparation is complete.
[0069] Real-time currents of the heterojunction with and without X-ray irradiation were obtained using a semiconductor analyzer. Different radiation doses (μGy·s⁻¹) were calculated. -1 The response current density (J (μA / cm²)) is calculated by the ratio of the real-time response current to the effective area of the heterojunction under X-ray irradiation. The response current density of the Gr / h-BN / NbOCl₂ / Gr heterojunction under X-ray irradiation at different dose rates is shown below. Figure 6 As shown, the measured response current density of the heterojunction gradually increases with increasing dose rate, where the wide-bandgap h-BN material reduces the influence of visible light in the environment.
[0070] Improved Implementation Example 2 The embodiment of this invention is a Gr / NbOCl2 / h-BN / NbOCl2 / Gr vertical heterojunction. The preparation method and steps are the same as those in Experimental Comparison II. A mechanical peeling method is inserted between steps 3) and 4) to transfer a layer of NbOCl2. The Gr / NbOCl2 / h-BN / NbOCl2 / Gr vertical heterojunction achieves a stable self-powered response under X-rays.
[0071] Other embodiments The embodiment of this invention is a Gr / AgCrP2S6 / Gr vertical heterojunction. The preparation method and steps are described in Experiment Comparison 1. The Gr / AgCrP2S6 / Gr vertical heterojunction achieved a stable self-powered response under X-rays.
[0072] This invention utilizes a two-dimensional ferroelectric vertical heterojunction to synergistically modulate a double-asymmetric Schottky barrier, achieving ultra-low-limit self-powered X-ray detection and synaptic functionality integration, thus enhancing the practicality and intelligence of the device. Specifically, by synergistically controlling the differences in electrode thickness and contact area, a double-asymmetric Schottky barrier is formed at both ends of the heterojunction. Combined with the built-in electric field induced by ferroelectric polarization, self-powered X-ray detection under zero bias voltage is achieved. Simultaneously, using X-ray pulses as stimulation signals, synaptic enhancement / inhibition is achieved through bias voltage modulation, simulating short-term / long-term synaptic plasticity.
[0073] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0074] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.
Claims
1. A two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, comprising a substrate, characterized in that, The substrate has a bottom layer, a ferroelectric functional layer, and a top layer stacked sequentially. The bottom layer is connected to a first electrode, and the top layer is connected to a second electrode. The bottom layer and the top layer are independently composed of two-dimensional semi-metallic materials. The ferroelectric functional layer includes two-dimensional ferroelectric materials. The bottom layer is not in contact with the top layer, and the work function of the bottom layer is not equal to that of the top layer.
2. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 1, characterized in that, In the bottom layer and the top layer, the thickness difference between the thicker and thinner layers is greater than 0 and less than or equal to 63 nm.
3. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 1, characterized in that, In the group of contacts where the work function difference between two-dimensional ferroelectric materials and two-dimensional semi-metallic materials is greater, the contact area is larger.
4. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 3, characterized in that, The difference in work function between the bottom layer and the ferroelectric functional layer is greater than the difference in work function between the top layer and the ferroelectric functional layer.
5. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 3, characterized in that, The contact area of the one with a larger contact area is 1.09 to 3.4 times that of the one with a smaller contact area.
6. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 1, characterized in that, The bandgap of the two-dimensional ferroelectric material is 0.7 eV to 3.0 eV.
7. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 1, characterized in that, The ferroelectric functional layer includes a ferroelectric layer and a hexagonal boron nitride layer located on the bottom, top, or both sides of the ferroelectric layer.
8. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 1, characterized in that, Two-dimensional ferroelectric materials are selected from two-dimensional semiconductor materials with spontaneous polarization, such as halide salts, metal thiophosphates, and metal selenophosphates.
9. The two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor according to claim 1, characterized in that, The two-dimensional semi-metallic material is graphene.
10. A method for fabricating a two-dimensional ferroelectric vertical heterojunction self-powered X-ray synaptic transistor, characterized in that, Follow one of the following two sets of steps; The first set of steps includes: fabricating a first electrode and a second electrode on a substrate; mechanically peeling off a first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material, transferring it to the substrate, contacting the first electrode but not the second electrode, to form a bottom layer; mechanically peeling off a two-dimensional ferroelectric material film from a crystal of a two-dimensional ferroelectric material, transferring it to the substrate, contacting the bottom layer but not the second electrode, to form a ferroelectric functional layer; and mechanically peeling off a second two-dimensional semi-metallic film with a work function different from the first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material, transferring it to the substrate, contacting the ferroelectric functional layer and the second electrode, but not the bottom layer, to form a top layer. The second set of steps includes: mechanically peeling a first two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material and transferring it to a substrate to form a bottom layer; mechanically peeling a two-dimensional ferroelectric material film from a crystal of a two-dimensional ferroelectric material and transferring it to the substrate, where it contacts the bottom layer to form a ferroelectric functional layer; mechanically peeling a second two-dimensional semi-metallic film from a crystal of a two-dimensional semi-metallic material with a work function different from that of the first two-dimensional semi-metallic film, transferring it to the substrate, where it contacts the ferroelectric functional layer but not the bottom layer to form a top layer; and fabricating a first electrode that contacts the bottom layer and a second electrode that contacts the top layer on the substrate.