A method for low-temperature growth of aluminum nitride scandium thin films based on van der Waals buffer layers and heterostructures

Abstract

This invention discloses a low-temperature growth method and heterostructure of aluminum scandium nitride thin films based on a van der Waals buffer layer. The heterostructure, from bottom to top, comprises: a substrate; a transition metal chalcogenide (TMDC) buffer layer formed on the substrate; and an aluminum scandium nitride ferroelectric layer formed on the buffer layer. This invention utilizes a transition metal chalcogenide (TMDC) as a van der Waals buffer layer to prepare high-quality aluminum scandium nitride thin films at low temperatures via magnetron sputtering, solving the long-standing technical challenge of low-temperature, high-quality growth of aluminum scandium nitride (AlScN) thin films and integration with heterostructure substrates.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device and thin film material technology, specifically relating to a method for low-temperature integration of high-quality aluminum scandium nitride (AlScN) ferroelectric thin films on various substrates (including silicon substrates) and the heterostructure formed therefrom. Background Technology

[0002] Wurtzite-structured aluminum nitride thin films have been widely used in radio frequency front-end devices such as high-frequency surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) resonators due to their stable piezoelectric coefficient, high acoustic wave propagation velocity, and good acoustic impedance characteristics. In 2009, Akiyama et al. first reported the modification of aluminum nitride by doping with scandium (Sc). Studies have shown that the resulting aluminum scandium nitride (AlScN) exhibits a significantly improved piezoelectric coefficient (d33) compared to pure AlN, demonstrating its great application potential in next-generation high-performance microelectromechanical systems (MEMS) piezoelectric devices. More notably, in 2019, Fichtner et al. discovered that AlScN can exhibit distinct ferroelectricity at specific Sc ​​doping concentrations. This discovery expands the application fields of AlScN from traditional piezoelectric devices to cutting-edge fields such as non-volatile memories, neuromorphic computing, high electron mobility transistors, and photodetectors. Ferroelectric AlScN materials possess a combination of advantages, including compatibility with semiconductor back-end processes, the ability to maintain ferroelectricity at ultra-thin scales, high remanent polarization intensity, and high Curie temperature. They are considered to be one of the most promising functional thin film materials in the post-Moore era.

[0003] Despite the promising prospects of aluminum scandium nitride (AlScN) materials, the fabrication and integration of high-quality thin films still face significant challenges. On one hand, traditional buffer layers, such as metals (Pt, Mo) or nitrides (TiN), used to achieve c-axis orientation growth on heterogeneous substrates like silicon, suffer from poor lattice matching, resulting in AlScN films with small grains and numerous grain boundaries. This leads to insufficient ferroelectric polarization reversal and high leakage current, among other performance defects. On the other hand, techniques such as molecular beam epitaxy and metal-organic chemical vapor deposition (MOCVD) for obtaining high-quality films rely on excessively high growth temperatures (>400°C), which are severely incompatible with the low-temperature and flexible integration processes required for semiconductor back-end fabrication. Therefore, developing a universal strategy for achieving high-quality AlScN thin film integration on any substrate at low temperatures using ultrathin buffer layers has become a key bottleneck driving its practical application. Summary of the Invention

[0004] To address the core contradiction in existing technologies—namely, the excessively high growth temperature of high-quality AlScN thin films and the poor film quality induced by traditional buffer layers—this invention aims to provide a low-temperature integration method and heterostructure for aluminum nitride scandium ferroelectric thin films based on a van der Waals two-dimensional material buffer layer. This approach aims to achieve high-quality, high c-axis orientation growth of aluminum nitride scandium ferroelectric thin films on any substrate (including silicon substrates) at low temperatures (≤150°C) through an ultrathin (up to a single-atom-layer thickness) buffer layer, resulting in films with excellent ferroelectric properties (high remanent polarization, low leakage current) and excellent process compatibility.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a heterogeneous structure based on a van der Waals buffer layer.

[0006] The heterostructure based on a van der Waals buffer layer provided by the present invention comprises, from bottom to top: a substrate; a transition metal chalcogenide (TMDC) buffer layer formed on the substrate; and an aluminum nitride scandium ferroelectric layer formed on the buffer layer.

[0007] The core of this invention lies in using transition metal chalcogenides (TMDC) as a van der Waals buffer layer to prepare high-quality aluminum scandium nitride (AlScN) thin films via magnetron sputtering at low temperatures. This solves the long-standing technical challenge of low-temperature, high-quality growth of AlScN thin films and their integration with heterogeneous substrates.

[0008] As a key technical feature of this invention, the transition metal chalcogenide buffer layer is selected from at least one of the following materials: molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide. The number of layers can be single to multiple (e.g., 1, 2, 3, 4, or 8 layers), with a corresponding thickness of 0.5 nm or more. The core function of this buffer layer lies in its smooth van der Waals surface and in-plane lattice constant (e.g., in the range of 3.18 Å to 3.29 Å) close to that of aluminum scandium nitride (AlScN), providing an ideal template for the low-temperature epitaxial growth of AlScN while effectively shielding stress and defects caused by substrate lattice mismatch.

[0009] As another key technical feature of this invention, the Sc doping content in the aluminum nitride scandium ferroelectric layer is 20%-40% (e.g., 25%, 35%), and its thickness is 7 nm to 200 nm (e.g., 7 nm, 22 nm, 50 nm, 90 nm, 200 nm). Under these preferred parameters, the film can exhibit significantly high c-axis orientation and high remanent polarization (>100 μC / cm). -2 Ferroelectric properties with high coercivity and high breakdown field strength.

[0010] In some embodiments of the present invention, the substrate includes, but is not limited to: single-crystal alumina, silicon substrate, silicon dioxide / silicon substrate, platinum metal thin film / silicon substrate, gold metal thin film / silicon substrate, highly doped silicon substrate, indium tin oxide / glass substrate, etc. The core requirement is that it can maintain structural and chemical stability in a high vacuum environment below 400°C and does not chemically react with transition metal chalcogenides and nitrides.

[0011] In some embodiments of the present invention, the heterostructure further includes an optional top electrode formed on the ferroelectric layer.

[0012] In some embodiments of the present invention, the top electrode is made of a conductive material selected from at least one of the following: platinum, copper, gold, titanium, aluminum, and titanium nitride. The top electrode needs to be patterned using a mask, a lift-off process, or a patterned etching process to form a circular structure or other desired pattern with a diameter of 20 μm to 50 μm, to facilitate subsequent electrical performance testing.

[0013] According to a specific embodiment of the present invention, the heterostructure comprises, from bottom to top: a silicon dioxide / silicon substrate, a four-layer continuous molybdenum disulfide thin film buffer layer, and a 50 nm aluminum scandium nitride (Al) substrate. 0.75 Sc 0.25 N, where the subscript represents the relative atomic abundance of the metallic element.

[0014] According to a specific embodiment of the present invention, the heterostructure comprises, from bottom to top: a highly doped silicon substrate, a monolayer molybdenum disulfide continuous thin film buffer layer, and a 50 nm aluminum scandium nitride (Al) substrate. 0.75 Sc 0.25 N, where the subscript represents the relative atomic abundance of the metallic element.

[0015] According to a specific embodiment of the present invention, the heterostructure comprises, from bottom to top: a silicon substrate, a monolayer molybdenum disulfide continuous thin film buffer layer, and a 200 nm aluminum scandium nitride (Al) layer. 0.75 Sc 0.25 N).

[0016] According to a specific embodiment of the present invention, the heterostructure comprises, from bottom to top: an alumina single-crystal substrate, four layers (2 nm thick) of continuous molybdenum disulfide thin film buffer layer, and a 50 nm aluminum scandium nitride (Al) layer. 0.75 Sc 0.25 N).

[0017] Secondly, the present invention provides a method for preparing the heterostructure based on the van der Waals buffer layer described in the first aspect.

[0018] The method for preparing a heterostructure based on a van der Waals buffer layer provided by this invention includes the following steps: S1. A transition metal chalcogenide buffer layer was prepared on a growth substrate using chemical vapor deposition. S2. Place the growth substrate with the buffer layer in the magnetron sputtering cavity and perform high-temperature pretreatment (i.e., vacuum annealing) to remove gas in a high-vacuum environment. S3. On the pretreated sample, an aluminum nitride scandium ferroelectric layer is grown in situ by magnetron sputtering at a growth temperature ≤150℃.

[0019] In some embodiments of the present invention, in step S1, the growth substrate is a c-plane alumina single-crystal substrate (i.e., (0001) oriented single-crystal alumina). A high-quality continuous thin film of transition metal chalcogenide is prepared by chemical vapor deposition to obtain a buffer layer attached to the growth substrate.

[0020] In some embodiments of the present invention, in step S2, the high-temperature pretreatment is performed at a temperature of 200°C to 400°C for 20 to 60 minutes. This step aims to further remove any organic residues and adsorbed gases that may be present on the surface of the buffer layer, providing a clean surface environment for high-quality film growth.

[0021] In some embodiments of the present invention, the magnetron sputtering process conditions in step S3 are as follows: using one or more of the following materials as the target source: aluminum, scandium, aluminum-scandium alloy, aluminum nitride, and aluminum-scandium nitride; using argon as the working gas; using nitrogen as the reaction gas; and controlling the growth gas pressure within the range of 1-20 mTorr. The power supply used for the magnetron sputtering includes, but is not limited to, a DC power supply, an RF power supply, and a pulsed DC power supply; and controlling the growth power (or the total power of multiple targets) between 150 W and 600 W.

[0022] In some embodiments of the present invention, the method further includes: S4, fabricating a patterned top electrode structure on an aluminum scandium nitride ferroelectric layer.

[0023] In some embodiments of the present invention, the method for preparing a patterned top electrode structure includes the following steps: preparing a top electrode on a grown aluminum nitride scandium ferroelectric layer using standard micro-nano fabrication processes: spin-coating photoresist (positive photoresist, negative photoresist, or PMMA, etc.); obtaining a photoresist mask with a preset pattern through photolithography and development; depositing the top electrode metal using physical vapor deposition (magnetron sputtering, electron beam evaporation, DC sputtering); and finally stripping the photoresist and its redundant metal using an organic solvent (such as acetone, N-methylpyrrolidone) to ultimately form a patterned top electrode (e.g., circular, with a diameter of 5-100 μm and a thickness of 20-100 nm).

[0024] Optionally, in some embodiments of the present invention, the method further includes the following step after S1 and before S2: transferring the transition metal chalcogenide buffer layer to the target substrate using a polymer-assisted wet transfer method.

[0025] In some embodiments of the present invention, the polymer-assisted wet transfer method specifically includes the following steps: spin-coating a layer of polymethyl methacrylate (PMMA) anisole solution as a support layer onto the surface of a sample with a grown buffer layer; immersing the sample in an alkaline solution to separate the PMMA / buffer layer stack structure from the growth substrate by etching the interface between the growth substrate and the buffer layer; cleaning with deionized water and then using a target substrate to receive the PMMA / buffer layer stack structure; after low-temperature annealing to enhance adhesion, dissolving and removing the PMMA support layer with an organic solvent, finally obtaining a clean and flat transition metal chalcogenide buffer layer on the target substrate. The mass concentration of the polymethyl methacrylate (PMMA) anisole solution can be 2%-10%; the alkaline solution can be a potassium hydroxide solution with a concentration of 0.5-5 mol / L; the low-temperature annealing temperature can be 60-100℃; and the organic solvent can be acetone, etc.

[0026] Optionally, in some embodiments of the present invention, the method further includes the following steps after S3 and before S4: transferring the aluminum nitride scandium ferroelectric layer / transition metal chalcogenide buffer layer to the target substrate using a PMMA / PDMS-assisted transfer method.

[0027] In some embodiments of the present invention, the method specifically includes the following steps: spin-coating a layer of polymethyl methacrylate (PMMA) anisole solution as a support layer onto the surface of the aluminum scandium nitride ferroelectric layer, followed by adhering polydimethylsiloxane (PDMS) as a mechanical release layer; immersing the sample in an aqueous solution to weaken the adhesion between the transition metal chalcogenide and the substrate; then using mechanical force to peel the PDMS and the substrate, at which point the aluminum scandium nitride film is completely retained on the PMMA / PDMS layer; transferring the PDMS / PMMA structure to a Pt / Si substrate, performing low-temperature annealing to enhance adhesion, and then using an organic solvent to dissolve and remove the PMMA support layer, finally obtaining a clean and flat aluminum scandium nitride structure on the target substrate. The mass concentration of the polymethyl methacrylate (PMMA) anisole solution can be 2%-10%; the low-temperature annealing temperature can be 60-100°C; and the organic solvent can be acetone, etc.

[0028] Thirdly, the present invention provides an application of the heterogeneous structure based on the van der Waals buffer layer described in the first aspect.

[0029] The application is the use of heterostructures based on van der Waals buffer layers in the fabrication of electronic devices.

[0030] In some embodiments of the present invention, the electronic device is a ferroelectric capacitor incorporating the heterostructure. Due to the strong inductive effect of transition metal chalcogenides, the influence of the substrate on growth is shielded, while also possessing transferability. This strategy is applicable to a wide range of substrate structures and different aluminum scandium nitride thicknesses, and is widely applicable to the design of aluminum scandium nitride ferroelectric and piezoelectric devices.

[0031] In some embodiments of the present invention, the electronic device is an integrated chip or flexible electronic device that includes the ferroelectric capacitor, and its compatibility with CMOS back-end processes is clearly defined.

[0032] Compared with existing technologies, the low-temperature growth strategy and heterostructure of aluminum nitride scandium thin films based on van der Waals buffer layers provided by this invention produce the following significant beneficial effects: 1. High-quality low-temperature growth was achieved, and the crystal quality was significantly improved. This invention utilizes the atomically flat van der Waals surface of transition metal chalcogenides (such as MoS2) and its in-plane lattice constant, which is close to that of AlScN, to provide an ideal "soft template" for the nucleation and growth of AlScN. Crucially, this template effect remains effective even at low temperatures (≤150°C). As shown in Example 1, the AlScN film grown on four layers of MoS2 exhibits a half-width at half-maximum (FWHM) of only 0.83° on its (002) X-ray diffraction rocking curve, significantly lower than that of Comparative Example 1 (3.23°) grown on a conventionally textured Pt buffer layer. This data directly demonstrates that the AlScN film grown in this invention possesses extremely high c-axis orientation consistency and a large grain size, effectively reducing the density of defects such as grain boundaries, thus laying a structural foundation for obtaining excellent electrical properties. By changing the number of transition metal chalcogenides and their lattice constants, it can be further adapted to different types of wurtzite materials, resulting in high-performance aluminum scandium nitride with excellent growth quality under low heat loss.

[0033] 2. It breaks through substrate limitations and achieves heterogeneous integration and process compatibility. Since the TMDC buffer layer can be attached to any substrate using mature transfer technology, this invention eliminates the stringent requirements on substrate lattice type, symmetry, and thermal stability. As shown in Example 2, even on a single-crystal silicon substrate, high-quality AlScN low-temperature integration can be achieved through an ultrathin (~0.5 nm) monolayer MoS2 buffer layer. The low-temperature process is fully compatible with the temperature limitations of semiconductor front-end processes, enabling AlScN ferroelectric devices to be three-dimensionally integrated with CMOS logic circuits. This method is applicable to various substrates such as silicon, glass, and flexible polymers, paving the way for the integration of high-performance ferroelectric functional layers in emerging fields such as flexible electronics and transparent electronics. The ultrathin buffer layer greatly saves vertical space in the device structure, which is beneficial for device miniaturization and high-density integration.

[0034] 3. A ferroelectric thin film with excellent comprehensive performance was obtained, exhibiting stable electrical properties. Thanks to its high-quality crystal structure, the aluminum scandium nitride thin film grown in this invention exhibits stable ferroelectricity. In Example 1, the remanent polarization (Pr) of the film reaches as high as 129.2 μC / cm. 2 The concentration was significantly higher than that of control example 1 (95.0 μC / cm). 2 The leakage current density decreased by nearly an order of magnitude, indicating a stronger non-volatile storage potential. For example... Figure 4 As shown, both the films grown directly on MoS2 / Si (Example 2) and those transferred (Example 1) exhibit saturated and stable hysteresis loops, demonstrating the robustness of the strategy and the intrinsic ferroelectricity of the prepared films. Attached Figure Description

[0035] Figure 1 This is a cross-sectional schematic diagram of the aluminum nitride scandium / TMDC heterostructure ferroelectric capacitor provided in an embodiment of the present invention.

[0036] Figure 2 The flowchart illustrates the fabrication process of growing scandium aluminum nitride on various target substrates based on the TMDC buffer layer, as provided in this embodiment of the invention.

[0037] Figure 3 The XRD structural characterization results are for the aluminum scandium nitride thin films prepared in Examples 3, 4, 5, 6, and 7 of this invention. Figure 4 The XRD structural characterization results are for the aluminum scandium nitride thin films prepared in Examples 5, 8, 9, and 10 of this invention. Figure 5 The image shows a comparison of the (002) rocking curves of the aluminum scandium nitride thin film grown using the method of this invention and the aluminum scandium nitride thin film obtained by the conventional method. Example 1 shows aluminum scandium nitride grown on an alumina single crystal substrate with 4 layers of MoS2 induced growth, while Comparative Example 1 shows an aluminum scandium nitride thin film of the same thickness grown on a Pt / Si substrate.

[0038] Figure 6 The graph shows a comparison of the ferroelectric properties of the aluminum scandium nitride ferroelectric capacitor prepared by the method of this invention with those of the comparative example, specifically the hysteresis loop of the remanent polarization intensity (Pr) as a function of the applied electric field (E) (after deducting the contributions of leakage current and dielectric polarization response). Example 2 shows a 50 nm aluminum scandium nitride transferred onto a Pt / Si substrate, while Comparative Example 2 shows an aluminum scandium nitride thin film of the same thickness grown directly on a Pt / Si substrate. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0040] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0041] Example 1 A 50 nm AlScN thin film was grown on a 4-layer MoS2 / sapphire substrate and transferred to Pt / Si. A (0001) oriented single-crystal alumina (sapphire) with a thickness of 500 μm was used as the growth substrate. A silicon wafer (Pt / Si) with a 300 nm thermally oxidized SiO2 layer and a 100 nm Pt electrode at the bottom was used as the target substrate / bottom electrode. Four layers (2 nm thick) of MoS2 were grown as a buffer layer using in-situ metal-organic chemical vapor deposition. The sample was then vacuum annealed and degassed in a magnetron sputtering chamber at 300 °C for 40 minutes. After annealing, the sample was then subjected to in-situ magnetron sputtering at 150 °C to grow a 50 nm thick layer of scandium aluminum nitride (Al). 0.75 Sc 0.25 N) thin film. The magnetron sputtering process conditions used are as follows: using Al and Al 0.57 Sc 0.43The alloy was used as the target source, argon as the working gas, and nitrogen as the reactant gas, with the growth pressure controlled at 2 mTorr. The magnetron sputtering power supply was an RF power supply, with the total growth power controlled at 300 W. X-ray diffraction was performed on the obtained film to characterize its crystal structure. Subsequently, a layer of polymethyl methacrylate (PMMA) anisole solution (4% mass concentration) was spin-coated onto the sample surface as a support layer, followed by the adhesion of polydimethylsiloxane (PDMS) as a mechanical release layer. The sample was immersed in an aqueous solution to reduce the adhesion between the transition metal chalcogenide and the substrate. Then, mechanical force was used to peel the PDMS and substrate, at which point the aluminum scandium nitride film remained intact on the PMMA / PDMS layer. The PDMS / PMMA structure was transferred to a Pt / Si substrate, and after low-temperature annealing to enhance adhesion, the PMMA support layer was removed using an organic solvent, finally obtaining a clean and flat aluminum scandium nitride structure on the target substrate. Subsequently, a layer of PMMA electron paste was spin-coated onto the transferred ferroelectric layer, and a patterned photomask was obtained by electron beam exposure and development. After depositing a Pt top electrode with a thickness of 50 nm, the photomask was removed by immersion in acetone, and finally a patterned top electrode was obtained.

[0042] Example 2 Direct growth of AlScN thin films on monolayer MoS2 / highly doped Si substrates A (0001) oriented single-crystal alumina (sapphire) with a thickness of 500 μm was used as the growth substrate. A 0.5 nm thick MoS2 buffer layer was grown using in-situ metal-organic chemical vapor deposition. The buffer layer was then transferred to a highly doped Si substrate using a PMMA-assisted transfer process. The transfer process included the following steps: spin-coating a PMMA support layer onto the sample surface with the buffer layer; immersing the sample in an alkaline solution to separate the PMMA / MoS2 stack from the growth substrate through the interface between MoS2 and alumina; rinsing with deionized water and then using a target substrate to support the PMMA / MoS2 stack; annealing at a low temperature to enhance adhesion; and then removing the PMMA support layer using an organic solvent to finally obtain a clean, flat, single-layer MoS2 buffer layer on highly doped Si. The PMMA anisole solution had a mass concentration of 4%; the alkaline solution was a 2 mol / L potassium hydroxide solution; and the low-temperature annealing temperature was 100 °C.

[0043] Vacuum annealing and degassing were performed in the magnetron sputtering chamber at 300°C for 40 minutes. The annealed sample was then subjected to in-situ magnetron sputtering at 150°C to grow a 50 nm thick layer of scandium aluminum nitride (Al). 0.75 Sc 0.25N) Thin film. The growth parameters of AlScN were completely consistent with those in Example 1, and the structure was characterized by XRD after growth. Subsequently, a layer of photoresist was spin-coated on the ferroelectric layer, and a patterned photomask was obtained by photolithography and development. After depositing a Pt top electrode with a thickness of 50 nm, the photoresist was removed by immersion in acetone, and finally the patterned top electrode was obtained.

[0044] Example 3 7nm AlScN thin film grown on monolayer MoS2 / sapphire substrate and transferred to Pt / Si A 500 μm thick single-crystal alumina (sapphire) with (0001) orientation was used as the growth substrate. A 0.5 nm thick MoS2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition. The sample was then vacuum annealed at 300 °C for 40 minutes in a magnetron sputtering chamber. After annealing, the sample was then subjected to in-situ magnetron sputtering at 150 °C to grow a 7 nm thick layer of scandium aluminum nitride (Al). 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0045] Example 4 A 22 nm AlScN thin film was directly grown on a monolayer MoS2 / sapphire substrate. A (0001) oriented single-crystal alumina (sapphire) with a thickness of 500 μm was used as the growth substrate. A 0.5 nm thick MoS2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition (MOCVD). The sample was then vacuum annealed at 300 °C for 40 minutes in a magnetron sputtering chamber. Following the annealing, a 22 nm thick aluminum scandium nitride (Al2N2) layer was grown by in-situ magnetron sputtering at a growth temperature of 150 °C. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0046] Example 5 A 50 nm AlScN thin film was directly grown on a monolayer MoS2 / sapphire substrate. A 500 μm thick single-crystal alumina (sapphire) with (0001) orientation was used as the growth substrate. A 0.5 nm thick MoS2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition. The sample was then vacuum annealed at 300 °C for 40 minutes in a magnetron sputtering chamber. After annealing, a 50 nm thick layer of scandium aluminum nitride (Al2N2) was grown by in-situ magnetron sputtering at 150 °C. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0047] Example 6 A 90 nm AlScN thin film was directly grown on a monolayer MoS2 / sapphire substrate. A 500 μm thick single-crystal alumina (sapphire) with (0001) orientation was used as the growth substrate. A 0.5 nm thick MoS2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition (MOCVD). The sample was then vacuum annealed at 300 °C for 40 minutes in a magnetron sputtering chamber. Following the annealing, a 90 nm thick aluminum scandium nitride (Al2N2) layer was grown by in-situ magnetron sputtering at 150 °C. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0048] Example 7 200 nm AlScN thin film directly grown on monolayer MoS2 / sapphire substrate A 500 μm thick single-crystal alumina (sapphire) with (0001) orientation was used as the growth substrate. A 0.5 nm thick MoS2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition. Vacuum annealing and degassing were performed in a magnetron sputtering chamber at 300 °C for 40 minutes. The annealed sample was then subjected to in-situ magnetron sputtering at 150 °C to grow a 200 nm thick aluminum scandium nitride (Al2N2) layer. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0049] Example 8 A 50 nm AlScN thin film was directly grown on a monolayer WS2 / sapphire substrate. A (0001) oriented single-crystal alumina (sapphire) with a thickness of 500 μm was used as the growth substrate. A 0.5 nm thick WS2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition (MOCVD). The sample was then vacuum annealed and degassed in a magnetron sputtering chamber at 300 °C for 40 minutes. Following the annealing, a 50 nm thick layer of aluminum scandium nitride (Al) was grown by in-situ magnetron sputtering at a growth temperature of 150 °C. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0050] Example 9 A 50 nm AlScN thin film was directly grown on a monolayer MoSe2 / sapphire substrate. A 500 μm thick single-crystal alumina (sapphire) with (0001) orientation was used as the growth substrate. A 0.5 nm thick MoSe2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition. The sample was then vacuum annealed at 300 °C for 40 minutes in a magnetron sputtering chamber. After annealing, a 50 nm thick aluminum scandium nitride (Al2N2) layer was grown by in-situ magnetron sputtering at a growth temperature of 150 °C. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0051] Example 10 A 50 nm AlScN thin film was directly grown on a monolayer WSe2 / sapphire substrate. A (0001) oriented single-crystal alumina (sapphire) with a thickness of 500 μm was used as the growth substrate. A 0.5 nm thick WSe2 layer was grown as a buffer layer using in-situ metal-organic chemical vapor deposition (MOCVD). The sample was then vacuum annealed and degassed in a magnetron sputtering chamber at 300 °C for 40 minutes. After annealing, the sample was then subjected to in-situ magnetron sputtering at 150 °C to grow a 50 nm thick aluminum scandium nitride (Al2N2) layer. 0.75 Sc 0.25 (N) thin film. The growth parameters of AlScN were completely consistent with those of Example 1, and the structure was characterized by XRD after growth.

[0052] Comparative Example 1 AlScN thin films grown on textured Pt / Si substrates Using an insulating silicon (001) single crystal substrate with a thickness of 500 μm, a 50 nm thick Pt thin film with strong (111) orientation was grown by magnetron sputtering at a growth temperature of 440°C. Subsequently, a 50 nm thick aluminum nitride scandium (Al) film was grown at 150°C. 0.75 Sc 0.25 N) Thin film. The growth parameters of the AlScN ferroelectric layer were completely consistent with those of Example 1 to ensure that the performance difference was solely due to the difference in the buffer layer. Subsequently, a layer of photoresist was spin-coated onto the ferroelectric layer, and a patterned photomask was obtained through photolithography and development. After depositing a Pt top electrode with a thickness of 50 nm, the photoresist was removed by immersion in acetone to finally obtain the patterned top electrode.

[0053] Performance testing: 1. The crystal quality (FWHM) of the AlScN ferroelectric layer in the above embodiments and comparative examples was measured and evaluated using a high-resolution X-ray diffractometer.

[0054] 2. Using a 4200 semiconductor analyzer, the leakage current, saturation polarization, and coercive field of the AlScN ferroelectric capacitors in the above embodiments and comparative examples were measured and evaluated.

[0055] Table 1 shows the ferroelectric layer performance test results obtained in Example 1, Example 2, and Comparative Example 2.

[0056] Results analysis: Depend on Figure 3 , Figure 4 , Figure 5 , Figure 6 As can be seen from the test results in Table 1: (1) Crystallization quality: such as Figure 5 As shown, the AlScN(0002) plane X-ray diffraction rocking curve of Example 1 has the narrowest half-width at half-maximum (FWHM) (0.83°), indicating that it has the highest c-axis orientation and crystal quality. Example 2 is also superior to Comparative Example 1, which proves that the template-inducing effect of the MoS2 buffer layer on AlScN is significantly better than that of the traditional Pt buffer layer, effectively reducing the defect density caused by lattice mismatch.

[0057] (2) Strategy scalability: such as Figure 3 As shown, out-of-plane diffraction results of the AlScN (0002) plane can be observed in Examples 3, 4, 5, 6, and 7. No diffraction peaks other than AlScN (0002) and Al2O3 (0006) are found within the test range, indicating that AlScN has a strong out-of-plane texture. This demonstrates that this strategy is applicable to AlScN of different thicknesses. Figure 4As shown, out-of-plane diffraction results of AlScN(0002) can be observed in Examples 5, 8, 9 and 10, and there are no diffraction peaks other than AlScN(0002) and Al2O3(0006), indicating that different transition metal chalcogenides have an effect on the texture induction of AlScN.

[0058] (3) Ferroelectric properties: such as Figure 6 As shown, the AlScN films prepared in Examples 1 and 2 both exhibit saturated hysteresis loops, and the remanent polarization intensity (P) is high. r The P value was significantly higher than that of Comparative Example 1. In particular, Example 1 showed a significantly higher P value. r The value reached 129.2 μC / cm. 2 This is significantly higher than the 95.0 μC / cm of Comparative Example 1. 2 This demonstrates that the buffer layer strategy of the present invention can effectively promote the flipping of ferroelectric domains and obtain superior ferroelectric performance.

[0059] (4) Insulation performance: Under the same electric field, the leakage current density of Examples 1 and 2 is nearly an order of magnitude lower than that of Comparative Example 1. This is attributed to the fact that the AlScN thin film induced by MoS2 has a larger grain size and fewer grain boundaries, thereby effectively suppressing leakage current channels.

[0060] In summary, by introducing a van der Waals buffer layer, this invention successfully solves the core challenge of low-temperature, high-quality integration of AlScN thin films. It significantly surpasses existing technologies in terms of crystal quality, process compatibility, and final device performance, providing a key technical path for the large-scale application of AlScN ferroelectric materials in next-generation integrated circuits and multifunctional electronic systems.

[0061] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.

Claims

1. A heterostructure based on a van der Waals buffer layer, comprising, from bottom to top: Substrate; A transition metal chalcogenide buffer layer is formed on the substrate; An aluminum nitride scandium ferroelectric layer is formed on the buffer layer.

2. The heterostructure based on a van der Waals buffer layer according to claim 1, characterized in that: The transition metal chalcogenide buffer layer is selected from at least one of the following materials: molybdenum disulfide, tungsten disulfide, molybdenum diselenide, and tungsten diselenide; And / or, the transition metal chalcogenide buffer layer has one to multiple layers, with a corresponding thickness of 0.5 nm or more.

3. The heterostructure based on a van der Waals buffer layer according to claim 1 or 2, characterized in that: In this context, the doping content of Sc is 20%-40%; And / or, the thickness of the aluminum nitride scandium ferroelectric layer is from 7 nm to 200 nm.

4. The heterostructure based on a van der Waals buffer layer according to any one of claims 1-3, characterized in that: The substrate material is selected from materials that maintain structural and chemical stability in a high vacuum environment below 400°C and do not chemically react with transition metal chalcogenides and nitrides. Furthermore, the substrate includes, but is not limited to: single-crystal alumina, silicon substrate, silicon dioxide / silicon substrate, platinum metal thin film / silicon substrate, gold metal thin film / silicon substrate, highly doped silicon substrate, and indium tin oxide / glass substrate.

5. The heterostructure based on a van der Waals buffer layer according to any one of claims 1-4, characterized in that: The heterostructure also includes a top electrode, which is formed on the ferroelectric layer; Furthermore, the material of the top electrode is a conductive material selected from at least one of the following: platinum, copper, gold, titanium, aluminum, and titanium nitride.

6. The method for preparing a heterostructure based on a van der Waals buffer layer according to any one of claims 1-5, comprising the following steps: S1. A transition metal chalcogenide buffer layer was prepared on a growth substrate using chemical vapor deposition. S2. Place the growth substrate with the buffer layer in the magnetron sputtering cavity and perform high-temperature pretreatment and degassing in a high-vacuum environment. S3. On the pretreated sample, an aluminum nitride scandium ferroelectric layer is grown in situ by magnetron sputtering at a growth temperature ≤150℃.

7. The method according to claim 6 or 7, characterized in that: In step S2, the temperature of the high-temperature pretreatment is 200 ℃ to 400 ℃, and the time is 20 to 60 minutes; And / or, in step S3, the magnetron sputtering process conditions are as follows: using one or more of the following materials as the target source: aluminum, scandium, aluminum-scandium alloy, aluminum nitride, and aluminum-scandium nitride; using argon as the working gas; using nitrogen as the reaction gas; and controlling the growth gas pressure within the range of 1-20 mTorr. The power supply used for the magnetron sputtering includes, but is not limited to, DC power supply, RF power supply, and pulsed DC power supply, and the growth power is controlled between 150 W and 600 W.

8. The method according to claim 6 or 7, characterized in that: The method further includes: S4, fabricating a patterned top electrode structure on the aluminum scandium nitride ferroelectric layer.

9. The method according to any one of claims 6-8, characterized in that: The method further includes the following steps after S1 and before S2: transferring the transition metal chalcogenide buffer layer to the target substrate using a polymer-assisted wet transfer method; Alternatively, the method may further include the following steps after S3 and before S4: transferring the aluminum nitride scandium ferroelectric layer / transition metal chalcogenide buffer layer to the target substrate using a PMMA / PDMS-assisted transfer method.

10. The application of the heterostructure based on a van der Waals buffer layer according to any one of claims 1-5 or the heterostructure based on a van der Waals buffer layer prepared by the method according to any one of claims 6-9 in the fabrication of electronic devices; Furthermore, the electronic device includes: Ferroelectric capacitors containing the heterostructure or integrated chips or flexible electronic devices containing the ferroelectric capacitors.

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