Silicon-based high-mobility wide-band-gap tin-based oxide thin film, preparation method thereof and transistor

Abstract

The invention discloses a silicon-based high-mobility wide-band-gap tin-based oxide film, a preparation method thereof and a transistor, and belongs to the technical field of low-power-consumption electronic devices. The preparation method of the tin-based oxide thin film provided by the invention comprises the following steps: firstly, sequentially preparing a sacrificial layer and a single crystal tin-based oxide thin film on a temporary growth substrate to obtain an oxide heterostructure; then preparing a supporting layer, and adhering the single crystal tin-based oxide thin film by using the supporting layer to realize stripping of the single crystal tin-based oxide thin film from the single crystal substrate; and finally, transferring the single crystal tin-based oxide thin film to the silicon substrate to realize compatible integration of the single crystal tin-based oxide thin film and the silicon substrate. The single crystal tin-based oxide thin film is transferred to the silicon substrate through a substrate-free transfer technology, dependence on a high-cost specific substrate is eliminated, a mature silicon-based process is compatible, and a foundation is laid for large-scale integrated circuit application; and finally, the thin film transistor with low power consumption, high performance and low cost is prepared, the cost advantage is remarkable, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of low-power electronic device technology, specifically relating to a silicon-based high-mobility, wide-bandgap tin-based oxide thin film, its preparation method, and a transistor. Background Technology

[0002] As Moore's Law approaches its physical limits, traditional silicon-based transistors face critical challenges such as excessive power consumption and increasing difficulty in miniaturization. Reducing device power consumption has become a core research and development focus in low-power applications such as portable electronic devices and IoT terminals. Currently, while silicon-based transistors have alleviated some power consumption issues through structural optimizations such as FinFETs and gate-all-around (GAA), the space for further power consumption reduction is gradually shrinking due to the inherent carrier mobility and bandgap characteristics of silicon.

[0003] Oxide semiconductor thin films have become important candidate materials for low-power thin-film transistors due to their advantages such as high carrier mobility, wide bandgap (enabling low leakage current), and low-temperature fabrication. Among them, tin-based oxides show unique potential in the field of low-power electronic devices due to their excellent stability and high mobility at room temperature. For example, SrSnO3 has an electron mobility of 228 cm⁻¹. 2 / V The band gap is 3.29 eV, while the mobility of BaSnO3 can reach 320 cm⁻¹. 2 / V The band gap is 3.1 eV. Doping with rare earth elements such as La can further regulate the carrier concentration of tin-based oxides, optimize their electrical performance, and improve the device's on / off ratio and power consumption characteristics.

[0004] However, the fabrication of existing tin-based oxide thin-film transistors, such as single-crystal La:BaSnO3 thin-film transistors, faces a key technological bottleneck: due to the stringent lattice matching requirements of single-crystal La:BaSnO3 films, their growth relies on high-cost specific single-crystal substrates (such as SrTiO3 or LaAlO3 substrates), making them incompatible with mature silicon-based processes. This "substrate dependence" problem leads to the following drawbacks: (1) Miniaturization is difficult: The size of a specific single crystal substrate is limited, and the thin film in the transistors prepared on the specific substrate is relatively thick, making miniaturization difficult and difficult to meet the requirements of high integration. (2) High process cost: Single crystal substrates such as SrTiO3 and LaAlO3 are expensive (50-100 times that of silicon substrates of the same size), which greatly increases the cost of device fabrication; (3) Performance limitations: The dielectric properties and thermal expansion coefficient of a specific substrate do not match those of silicon devices, which can easily introduce interface defects and limit the improvement of core performance such as switching ratio and stability of thin film transistors.

[0005] To address the aforementioned issues, the industry urgently needs a technical solution that enables compatible integration of single-crystal tin-based oxide thin films with silicon substrates, breaking substrate dependence and fully leveraging the high mobility and wide bandgap advantages of single-crystal tin-based oxides to fabricate low-power, low-cost thin-film transistors. Summary of the Invention

[0006] To overcome the shortcomings of existing tin-based oxide thin-film transistors, represented by single-crystal La:BaSnO3, which rely on specific substrates and cannot be integrated with silicon, this invention aims to provide a silicon-based high-mobility, wide-bandgap tin-based oxide thin film, its fabrication method, and a transistor. This invention introduces a substrate-free thin-film transfer technique to transfer a high-quality single-crystal tin-based oxide thin film from a temporary growth substrate to a silicon substrate, achieving compatible integration of the two. Ultimately, this results in the fabrication of low-power, high-performance, and low-cost thin-film transistors, promoting the industrial application of related electronic devices.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention is to provide a method for preparing a silicon-based high-mobility, wide-bandgap tin-based oxide thin film, comprising the following steps: (1) Preparation of sacrificial layer and single crystal tin-based oxide film Single-crystal SrTiO3(001) or single-crystal LaAlO3 substrates were selected as temporary growth substrates. A sacrificial layer with a thickness of 10–100 nm was epitaxially grown on the surface using pulsed laser deposition (PLD). The sacrificial layer required easy etching by the etching solution and a structure similar to the tin-based oxide film, minimizing lattice mismatch and effectively suppressing dislocation defects during film growth. Ba3Al2O6 was preferred for the sacrificial layer because it shares a similar structure with La:BaSnO3 films, with a lattice mismatch of only 0.21%. A single-crystal tin-based oxide film was then grown on the sacrificial layer surface using PLD: the growth temperature was 780℃, the oxygen atmosphere pressure was 10–50 mTorr, and the laser energy density was 0.3–0.8 J / cm². This resulted in a high-quality single-crystal tin-based oxide film with a thickness of 1–100 nm, forming an oxide heterostructure (single-crystal tin-based oxide film / sacrificial layer / growth substrate). (2) Substrate-free transfer of single-crystal tin-based oxide thin films A support layer is prepared by placing it on a single-crystal tin-based oxide film and then immersing it in an etching solution for the sacrificial layer (at room temperature) to dissolve and remove the sacrificial layer. Stress is released at the film interface, causing the single-crystal tin-based oxide film to detach from the substrate and adhere to the support layer surface. This adhesion of the support layer to the single-crystal tin-based oxide film achieves the separation of the single-crystal tin-based oxide film from the single-crystal substrate. The support layer must possess chemical stability, a certain degree of adhesion, and a certain degree of elasticity or ductility. Sometimes, due to residual stress, wrinkles may appear on the single-crystal oxide film on the support layer. If wrinkles occur, a support layer of a different material is selected, and this step is repeated to eliminate residual stress. Preferably, the etching solution is water; the support layer is made of polydimethylsiloxane and / or polycarbonate.

[0008] (3) Integration of single-crystal tin-based oxide thin films with silicon substrates A silicon substrate is subjected to thermal oxidation to grow a silicon oxide insulating layer with a thickness of 100-300 nm on the substrate surface. Subsequently, the insulating layer is subjected to hydrophilic treatment with oxygen plasma to improve its surface hydrophilicity and adhesion. Since the prepared product is ultimately used in transistors, which are top-gate arrays, the device units need to be independent of each other. Since silicon is conductive, an insulating layer is required. The process of growing silicon oxide on silicon is mature, the material is stable and the cost is low. Therefore, this invention forms a silicon oxide insulating layer on a silicon substrate to facilitate subsequent application research.

[0009] A single-crystal tin-based oxide film adhered to a support layer is placed on a silicon substrate, and the temperature is gradually increased to 75°C-105°C for 10-60 minutes. The purpose of the heat treatment is to soften the support layer, thereby allowing it and the single-crystal tin-based oxide film to adhere more smoothly to the silicon substrate. After cooling to room temperature and removing the support layer, the substrate-free transfer of the single-crystal tin-based oxide film is completed, resulting in an integrated structure of the single-crystal tin-based oxide film and the silicon substrate. Preferably, the heat treatment temperature can be 75°C, 90°C, 100°C, 105°C, etc. Those skilled in the art can select the appropriate temperature as needed, and all of them can achieve the purpose of this invention.

[0010] Finally, since organic residues may exist on the surface of the single-crystal tin-based oxide film, a step to remove these residues is also included. Specifically, the single-crystal tin-based oxide film is placed in an oxygen-containing atmosphere at a temperature of 250°C-400°C for 3 hours to remove surface organic residues and improve the contact between the subsequent channel and the source / drain electrodes. Preferably, the temperature for removing surface organic residues can be 250°C, 300°C, 350°C, 400°C, etc. Those skilled in the art can select the appropriate temperature as needed, and all of these temperatures will achieve the purpose of this invention.

[0011] The second aspect of the present invention is to provide a silicon-based high-mobility, wide-bandgap tin-based oxide thin film, which is prepared by the preparation method described in the first aspect above.

[0012] A third aspect of the present invention is to provide a transistor suitable for use in next-generation low-cost, low-power integrated circuits, flexible electronics, and display driver electronic devices. The transistor comprises a silicon-based high-mobility, wide-bandgap tin-based oxide thin film as described in the second aspect above. The method for fabricating the transistor is as follows: Photolithography was performed on a single-crystal tin-based oxide thin film to define the channel layer, which was then etched. Source / drain (S / D) electrodes were fabricated on the surface of the single-crystal tin-based oxide thin film using electron beam evaporation, with an electrode spacing (channel length) of 10–50 µm and an electrode width of 30–100 µm. Atomic layer deposition was used to fabricate a gate dielectric layer on its surface. Electron beam evaporation was used to fabricate a gate electrode (G) directly above the tin-based oxide / gate dielectric region, with an electrode width of 10–50 µm.

[0013] Compared with the prior art, the present invention has the following significant advantages: Breaking substrate dependence and achieving silicon-compatible integration: This invention uses substrate-free transfer technology to transfer single-crystal tin-based oxide thin films to silicon substrates, eliminating dependence on high-cost specific substrates, and achieving compatibility with mature silicon-based processes, laying the foundation for large-scale integrated circuit applications; Excellent low-power performance: The high mobility and wide bandgap of the single-crystal tin-based oxide thin film enable the transistor to achieve an on / off ratio of 5.5 × 10⁻⁶. 9 The off-state current is 1 fA / µm; Significant cost advantages: Silicon substrates are used instead of expensive substrates such as SrTiO3 and LaAlO3, and the temporary substrates can be recycled and reused (SrTiO3 substrates are recycled after etching the sacrificial layer, with a utilization rate of >80%), significantly reducing device fabrication costs; With broad application prospects, it can be extended to flexible silicon-based devices (achieved through a flexible transfer layer), display driving circuits, low-power sensors for the Internet of Things, and other fields, providing a new technical path for next-generation electronic devices. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the oxide heterostructure and its related characterization.

[0015] Figure 2 This is a light image of the thin film transfer process and the thin film during the transfer.

[0016] Figure 3 This improves the contact characteristics between the channel and the source / drain electrodes on the thin film surface in Example 1, both before and after heat treatment.

[0017] Figure 4 This is a flowchart of the transistor fabrication process in Application Example 1.

[0018] Figure 5 This is a schematic diagram of the structure of the transistor fabricated using Example 1.

[0019] Figure 6 These are the transfer characteristic curves and output characteristic curves of the transistor prepared using Example 1.

[0020] Figure 7 These are the transfer characteristic curves of the transistors prepared in Application Examples 2 and 3. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail. The raw materials used in the embodiments are all commercially available products.

[0022] Example 1: 1. Growth and peeling of single-crystal La:BaSnO3 thin films Temporary growth substrate selection: 5 mm × 5 mm single crystal SrTiO3(001) substrate, treated with BOE for 40 s, rinsed with deionized water and then dried; Sacrificial layer growth: PLD technology was used, with Ba3Al2O6 as the target material, a growth temperature of 780℃, and an oxygen pressure of 1×10⁻⁶. -7 ~1×10 -6 Torr, laser energy density 1.5 J / cm², laser strikes 600 times, laser frequency 1 Hz, relying on in-situ RHEED to optimize thin film growth, RHEED pattern as follows Figure 1 As shown in Figure C; La:BaSnO3 thin film growth: PLD target material is La 0.02 Ba 0.98 SnO3 (La doping concentration of 2%) was grown at a temperature of 780℃, an oxygen pressure of 40 mTorr, a laser energy density of 0.5 J / cm², 1350 laser strikes, and a laser frequency of 1 Hz to obtain a 20 nm thick single-crystal La:BaSnO3 film. In-situ RHEED was used to optimize film growth. The RHEED pattern is shown below. Figure 1 As shown in Figure D; a schematic diagram of the obtained oxide heterostructure (La:BaSnO3 / Ba3Al2O6 / SrTiO3) is shown below. Figure 1 As shown in Figure A, the AFM characterization results are as follows: Figure 1As shown in Figure E, the XRD pattern is as follows: Figure 1 As shown in Figure B, multiple single-crystal diffraction peaks are displayed.

[0023] Preparation of the first support layer: Mix polydimethylsiloxane (PDMS) precursors (Dow Corning Sylgard 184, 10:1), drop them onto a pre-cleaned glass plate, and cure at 70°C for 1 hour to obtain a PDMS support layer (thickness ≈ 1 cm).

[0024] Thin film peeling: The oxide heterostructure (La:BaSnO3 / Ba3Al2O6 / SrTiO3) was gently placed on the PDMS support layer, and the entire structure was immersed in deionized water for 30 min (room temperature). After etching the Ba3Al2O6 sacrificial layer, the La:BaSnO3 film was peeled off from the temporary growth substrate, yielding the PDMS / La:BaSnO3 composite. This process is performed in... Figure 2 It is shown in Figure A.

[0025] Silicon substrate integration Silicon substrate pretreatment: A 300 nm thick SiO2 insulating layer is grown on the silicon surface by thermal oxidation, and then the SiO2 surface is treated with oxygen plasma to improve its surface hydrophilicity and adhesion. Preparation of the second support layer: A 10% polycarbonate (PPC) solution (using anisole as the solvent) is dropped onto a pre-cleaned silicon wafer, and heated at 90°C for 30 minutes to form a PPC support layer (thickness ≈ 5 μm). Place a drop of water on the La:BaSnO3 surface of the PDMS / La:BaSnO3 composite; then place the PPC flat on top; gradually heat to 90°C and maintain for more than 10 minutes; after heating, allow the sample to cool to room temperature, hold the PPC layer with tweezers, and gently lift the PPC at a speed of 1 mm / s to transfer the La:BaSnO3 film onto the PPC support layer, thus obtaining the PPC / La:BaSnO3 composite. (The PPC will harden after cooling, and its adhesion to the oxide film is stronger than that between PDMS and the oxide.)

[0026] Thin film transfer: The PPC / La:BaSnO3 composite was placed on a silicon substrate (Si / SiO2) at room temperature, gradually heated to 90°C and held for 10 minutes. After cooling to room temperature, it was immersed in anisole to dissolve the PPC layer. This process... Figure 2 As shown in Figure A, during this process, the PPC layer is held with tweezers and gently lifted at a speed of 1 mm / s to complete the substrate-free transfer of the single-crystal La:BaSnO3 thin film. Figure 2Figures B through D show the optical imaging of the thin film at each stage. Due to potential organic residues on the surface, a subsequent heat treatment at 300°C for 3 hours in an oxygen atmosphere was performed to remove these residues and improve the contact between the subsequent channel and source / drain electrodes. The effects before and after heat treatment are shown below. Figure 3 As shown.

[0027] Application Example 1 Transistor fabrication: The transistor fabrication flowchart is as follows Figure 4 As shown, the specific steps include: Etching of La:BaSnO3 channel layer: The La:BaSnO3 film is etched with hydroiodic acid (HI), and the channel layer is defined by photolithography. The etching time is about 40 seconds. Source / drain electrode fabrication: Ti / Au (10 nm / 40 nm) was deposited by electron beam evaporation, and the source / drain electrodes were defined by photolithography with a channel length of 20 µm and a width of 80 µm. Gate dielectric layer fabrication: Atomic layer deposition of Al2O3 (20 nm) was used to fabricate the gate dielectric layer; Gate electrode fabrication: Au (50 nm) was deposited by electron beam evaporation, and the gate electrode was defined by photolithography with a width of 13.59 µm to complete the transistor fabrication. The fabricated transistor structure is shown below. Figure 5 As shown, Figure 5 Figure A is the front view of the transistor, and Figure B is the top view of the transistor.

[0028] The transistors fabricated for use case 1 were subjected to electrical performance testing (at room temperature), and the results are as follows: Transfer characteristics: Gate voltage V gs = -2 V ~ 7 V, source-drain voltage V ds = 1 V, the measured switching ratio I on / off = 5×10 9 The off-state current is 1 fA / µm, and the subthreshold swing SS ≈ 90 mV / dec. Figure 6 Figure A shows its transfer characteristic curve; Output characteristics: V gs =-1 V ~ 4 V (0.5 V increments), V ds =0 V ~ 8 V, Figure 6 Figure B shows its output characteristic curve.

[0029] Example 2 The main steps of Example 2 are the same as those of Example 1, except that the number of laser strikes during the growth of the La:BaSnO3 film is adjusted to 1000, resulting in a single-crystal La:BaSnO3 film with a thickness of 15 nm.

[0030] Application Example 2 Transistors were fabricated using the single-crystal La:BaSnO3 thin film obtained in Example 2, following the same method as in Application Example 1. The resulting transistors underwent transfer characteristic testing (room temperature), and the results are as follows: Figure 7 Figure A shows the transfer characteristic curve t of the transistor fabricated using Example 2. channel =15nm, gate voltage V gs = -2 V ~ 4 V, source-drain voltage V ds = 1 V, the measured switching ratio I on / off = 1.5×10 7 The off-state current is 21 fA / µm, and the subthreshold swing SS ≈ 90 mV / dec.

[0031] Example 3 The main steps of Example 3 are the same as those of Example 1, except that the number of laser strikes during the growth of the La:BaSnO3 film is adjusted to 650, resulting in a single-crystal La:BaSnO3 film with a thickness of 10 nm.

[0032] Application Example 3 Transistors were fabricated using the single-crystal La:BaSnO3 thin film obtained in Example 3, following the same method as in Application Example 1. The resulting transistors underwent transfer characteristic testing (room temperature), and the results are as follows: Figure 7 Figure B shows the transfer characteristic curve t of the transistor fabricated using Example 3. channel =10nm, gate voltage V gs = -2 V ~ 8 V, source-drain voltage V ds = 1 V, the measured switching ratio I on / off = 1.5×10 5 The off-state current is 24 fA / µm, and the subthreshold swing SS ≈ 160 mV / dec.

[0033] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-based high-mobility, wide-bandgap tin-based oxide thin film, characterized in that, Includes the following steps: (1) A sacrificial layer and a single-crystal tin-based oxide film are sequentially prepared on a single-crystal substrate to obtain an oxide heterostructure; (2) Prepare a support layer. Place a support layer on a single crystal tin-based oxide film and then immerse it in the etching solution of the sacrificial layer. Use the support layer to adhere the single crystal tin-based oxide film to achieve the peeling of the single crystal tin-based oxide film from the single crystal substrate. If wrinkles appear on the surface of the single crystal tin-based oxide film adhering to the support layer, select a support layer of another material and repeat this step. (3) Perform thermal oxidation on the silicon substrate to grow a silicon oxide insulating layer on the surface of the silicon substrate, and perform hydrophilic treatment on the silicon oxide insulating layer; place the single crystal tin-based oxide film attached to the support layer on the silicon substrate, and after heat treatment, remove the support layer to complete the integration of the single crystal tin-based oxide film and the silicon substrate to obtain the target product.

2. The preparation method according to claim 1, characterized in that, The single-crystal substrate is a single-crystal SrTiO3 substrate or a single-crystal LaAlO3 substrate.

3. The preparation method according to claim 1, characterized in that, The thickness of the sacrificial layer is 10~100 nm, and the material of the sacrificial layer is Ba3Al2O6; the etching solution of the sacrificial layer is water.

4. The preparation method according to claim 1, characterized in that, The thickness of the single-crystal tin-based oxide film is 1~100 nm.

5. The preparation method according to claim 1, characterized in that, The support layer is made of polydimethylsiloxane and / or polycarbonate.

6. The preparation method according to claim 1, characterized in that, The hydrophilic treatment is an oxygen plasma treatment.

7. The preparation method according to claim 1, characterized in that, The heat treatment temperature is 75°C-105°C, and the time is 10-60 minutes.

8. The preparation method according to claim 1, characterized in that, It also includes a step of removing residual organic matter from the surface of the single-crystal tin-based oxide film. The specific steps are: placing the single-crystal tin-based oxide film in an oxygen-containing atmosphere at a temperature of 250℃-400℃ to remove residual organic matter.

9. A silicon-based high-mobility, wide-bandgap tin-based oxide thin film, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 8.

10. A transistor, characterized in that, The transistor comprises a silicon-based high-mobility, wide-bandgap tin-based oxide thin film as described in claim 9.

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