Flexible surface acoustic wave device based on wet transfer of aluminum nitride film and preparation method of flexible surface acoustic wave device

Abstract

The invention relates to the technical field of surface acoustic wave devices, in particular to a flexible surface acoustic wave device based on a wet transfer aluminum nitride film and a preparation method thereof, which specifically adopts a wet transfer technology to transfer a high-quality aluminum nitride (AlN) piezoelectric film from a growth substrate to a flexible mica substrate, and solves the interface stress problem by introducing a buffer layer (such as SrTiO3). And a transferred AlN thin film is integrated on the buffer layer. According to the method, the problem of lattice mismatch during direct growth of the AlN film is avoided, and meanwhile, the excellent piezoelectric property of the AlN film is reserved. In addition, the device prepared by the invention has the advantages of flexibility, high temperature resistance, high performance and the like, and is suitable for application scenes of wearable equipment, high-temperature sensors and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of surface acoustic wave devices, and in particular to a flexible surface acoustic wave device based on wet-transferred aluminum nitride film and a preparation method thereof. Background Art

[0002] Surface acoustic wave (SAW) devices utilize the surface acoustic wave effect of piezoelectric materials to achieve signal processing and are widely used in communications, sensors, filters, and other fields. Traditional SAW devices typically use rigid substrates (such as quartz and silicon). Although they have good performance, they are prone to failure in high-temperature environments and lack flexibility, which limits their application in flexible electronic devices. With the rapid development of flexible electronic devices, especially the rise of wearable devices and high-temperature sensors, traditional rigid SAW devices can no longer meet the demand.

[0003] Furthermore, conventional SAW devices typically utilize rigid substrates (such as quartz and silicon) to directly grow piezoelectric thin films, a method that has limitations in flexible applications. While flexible substrates (such as mica) offer excellent high-temperature resistance and flexibility, growing high-quality AlN thin films directly on them faces challenges such as lattice mismatch and thermal expansion coefficient mismatch, resulting in poor film quality. Summary of the Invention

[0004] The purpose of the present invention is to provide a flexible surface acoustic wave device based on wet transfer of aluminum nitride film and a preparation method. The high-quality AlN film is integrated onto a flexible mica substrate through wet transfer technology, solving the lattice mismatch problem faced by direct growth while retaining the excellent piezoelectric properties of the AlN film.

[0005] To achieve the above objectives, the present invention provides a flexible surface acoustic wave device based on wet-transferred aluminum nitride film, which comprises, from bottom to top, a flexible mica base layer, a buffer layer, an AlN piezoelectric film layer, and a metal electrode layer, wherein the thickness of the mica base layer is 50 to 100 μm, the thickness of the buffer layer is 50 to 200 nm, the thickness of the AlN piezoelectric film layer is 500 to 2000 nm, and the thickness of the metal electrode layer is 100 to 200 nm.

[0006] An adhesion layer is further provided between the buffer layer and the AlN piezoelectric film layer. The material of the adhesion layer is Cr and the thickness is 5 to 20 nm.

[0007] Wherein, the buffer layer material is SrTiO3 or other materials with good lattice matching.

[0008] The electrode material of the metal electrode layer is Al, Pt or other metals with good conductivity.

[0009] The AlN piezoelectric film is completely transferred from the growth substrate to the flexible mica substrate through a wet transfer technology.

[0010] Furthermore, the present invention also proposes a method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride film, which is used to prepare the flexible surface acoustic wave device based on wet transfer of aluminum nitride film, comprising the following steps:

[0011] Step 1: epitaxially growing an AlN thin film on a growth substrate;

[0012] Step 2: Spin-coat a transfer dielectric layer on the surface of the AlN film;

[0013] Step 3: Bonding the growth substrate to the flexible mica substrate through a transfer medium layer;

[0014] Step 4: Remove the growth substrate by chemical etching to complete the transfer of the AlN film;

[0015] Step 5: Prepare a metal electrode on the transferred AlN film;

[0016] Step 6: Package the device.

[0017] Optionally, in step 1, the growth temperature of the AlN film is 800-1100° C., using magnetron sputtering technology.

[0018] Optionally, in step 2, the transfer medium layer is PMMA with a thickness of 200 to 500 nm.

[0019] Optionally, a buffer layer has been deposited on the flexible mica substrate in step 3 .

[0020] Optionally, in step 4, a hot phosphoric acid H 3 PO 4 solution is used to etch the sapphire growth substrate.

[0021] The present invention provides a flexible surface acoustic wave device based on wet transfer of aluminum nitride film and a preparation method. Specifically, a wet transfer technique is used to transfer a high-quality aluminum nitride (AlN) piezoelectric film from a growth substrate to a flexible mica substrate. The interfacial stress problem is solved by introducing a buffer layer (such as SrTiO3), and the transferred AlN film is integrated on the buffer layer. The present invention avoids the lattice mismatch problem encountered when directly growing AlN film, while retaining the excellent piezoelectric properties of the AlN film. In addition, the device prepared by the present invention has the advantages of flexibility, high temperature resistance, and high performance, and is suitable for application scenarios such as wearable devices and high-temperature sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 It is a structural schematic diagram of a flexible surface acoustic wave device based on wet-transferred aluminum nitride film of the present invention.

[0024] Figure 2 It is a schematic diagram of the process flow of wet-transferring AlN thin films of the present invention. DETAILED DESCRIPTION

[0025] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0026] See also Figure 1 The present invention provides a flexible surface acoustic wave device based on wet-transferred aluminum nitride film, which comprises a flexible mica substrate layer, a buffer layer, an AlN piezoelectric film layer, and a metal electrode layer, arranged in sequence from bottom to top. The thickness of the mica substrate layer is 50 to 100 μm, the thickness of the buffer layer is 50 to 200 nm, the thickness of the AlN piezoelectric film layer is 500 to 2000 nm, and the thickness of the metal electrode layer is 100 to 200 nm.

[0027] An adhesion layer is further provided between the buffer layer and the AlN piezoelectric film layer. The material of the adhesion layer is Cr and the thickness is 5 to 20 nm.

[0028] The buffer layer material is SrTiO3 or other materials with good lattice matching.

[0029] The electrode material of the metal electrode layer is Al, Pt or other metals with good conductivity.

[0030] The AlN piezoelectric film is completely transferred from the growth substrate to the flexible mica substrate through a wet transfer technology.

[0031] Furthermore, the present invention also proposes a method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride film, which is used to prepare the flexible surface acoustic wave device based on wet transfer of aluminum nitride film, comprising the following steps:

[0032] Step 1: epitaxially growing an AlN thin film on a growth substrate;

[0033] Step 2: Spin-coat a transfer dielectric layer on the surface of the AlN film;

[0034] Step 3: Bonding the growth substrate to the flexible mica substrate through a transfer medium layer;

[0035] Step 4: Remove the growth substrate by chemical etching to complete the transfer of the AlN film;

[0036] Step 5: Prepare a metal electrode on the transferred AlN film;

[0037] Step 6: Package the device.

[0038] In step 1, the growth temperature of the AlN film is 800-1100° C., and magnetron sputtering technology is used.

[0039] In step 2, the transfer medium layer is PMMA with a thickness of 200 to 500 nm.

[0040] In step 3, a buffer layer has been deposited on the flexible mica substrate.

[0041] In step 4, a hot phosphoric acid H3PO4 solution is used to etch the sapphire growth substrate.

[0042] In this embodiment, the buffer layer is used to relieve interface stress, and the adhesion layer (Cr) can enhance film adhesion.

[0043] The preparation method has the following key steps:

[0044] Epitaxial growth of high-quality AlN films on sapphire or silicon substrates;

[0045] Spin-coat PMMA as the transfer medium;

[0046] Bonding the AlN film to a mica substrate with a pre-deposited buffer layer;

[0047] removing the growth substrate by chemical etching and stripping;

[0048] Fabricating interdigital electrodes on the transferred AlN film;

[0049] Carry out device packaging.

[0050] The process flow of wet transfer AlN film is shown as follows Figure 2 shown.

[0051] Specifically, the following is further explained in conjunction with the embodiments and the production process:

[0052] 1. Ultrasonic cleaning of the sapphire substrate with acetone, ethanol, and deionized water in sequence to remove surface impurities, then drying with nitrogen. A 2 μm thick c-axis oriented AlN film was grown on the sapphire substrate using a magnetron sputtering instrument. The AlN piezoelectric film was grown at a growth temperature of 1000°C to a thickness of 2000 nm, with an atmospheric pressure of 2×10-4 Pa, a nitrogen pressure of 0.5 to 1 Pa, a sputtering power of 2.5 kW, and a sputtering time of 2 h.

[0053] 2. Ultrasonic cleaning of the AlN film with acetone, ethanol, and deionized water to remove surface contaminants. Spin-coat a 300nm thick layer of PMMA (polymethyl methacrylate) on the AlN film as a transfer medium. Spin coating speed: 3000–4000 rpm (thickness ~300–500nm). Bake at 180°C for 2 minutes (to cure the PMMA).

[0054] 3. Mica Substrate Pretreatment: The mica substrate was ultrasonically cleaned with acetone, ethanol, and deionized water for 10 minutes to remove surface impurities, then dried with nitrogen. A SrTiO3 buffer layer was deposited on the mica substrate using PLD at 750°C, a pressure of 2×10⁻4 Pa, and 10Pa of oxygen for 30 minutes to a thickness of 200nm. Cr was then magnetron sputtered using 20sccm of Ar gas at a pressure of 5×10⁻3 Torr. The sputtering power was turned on (100W) for 15 minutes to a thickness of 10nm. Annealing was then performed in a N₂ atmosphere at 300–400°C for 30 minutes to promote diffusion between the Cr and AlN interfaces.

[0055] 4. Hot-press bond the AlN / PMMA film to the mica / SrTiO3 substrate at 150°C. Precisely align the PMMA / AlN film and the mica / SrTiO3 substrate and hot-press bond them. Use a temperature of 150–200°C to soften the PMMA and enhance adhesion. Use a pressure of 0.5–1 MPa for 10–30 minutes.

[0056] 5. Remove the sapphire substrate using hydrochloric acid etching; etching solution: hot phosphoric acid H3PO4, 85°C. Time: 1–3 hours (depending on the AlN thickness). Observe that the substrate is completely dissolved, leaving only the PMMA / AlN film.

[0057] 6. Dissolve PMMA with acetone to complete the AlN film transfer. Soak in acetone for 1–2 hours and remove the residue with ultrasound assistance.

[0058] 7. Fabricate interdigital electrodes on the AlN film using photolithography. A double-layer interdigital electrode is prepared: the lower electrode has a narrow period (1 μm) for high-frequency response (5 GHz). The upper electrode has a wide period (2 μm) for low-frequency response (1 GHz). The intermediate insulating layer is SiO2 (50 nm) to prevent short circuits. Electrode patterning is achieved using photolithography, with an electrode spacing of 10 to 50 μm.

[0059] 8. Deposit an Al2O3 protective layer and encapsulate it. Prepare a double-layer protective layer of Al2O3 / SiO2. The inner layer of SiO2 is deposited with 50-100nm chemical vapor deposition (PECVD); the outer layer of Al2O3 is deposited with 100-200nm using magnetron sputtering.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. Wet transfer avoids the lattice mismatch problem during direct growth and obtains high-quality AlN films;

[0062] 2. Flexible mica substrate makes the device bendable;

[0063] 3. The buffer layer design effectively alleviates the interfacial stress during the transfer process;

[0064] 4. The preparation process is compatible with large-scale production.

[0065] The above disclosure is merely one or more preferred embodiments of the present invention, and certainly cannot be used to limit the scope of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made in accordance with the claims of the present invention still fall within the scope of the invention.

Claims

1. A flexible surface acoustic wave device based on wet-transferred aluminum nitride film, characterized in that: A flexible mica base layer, a buffer layer, an AlN piezoelectric film layer and a metal electrode layer are sequentially arranged from bottom to top, wherein the thickness of the mica base layer is 50 to 100 μm, the thickness of the buffer layer is 50 to 200 nm, the thickness of the AlN piezoelectric film layer is 500 to 2000 nm, and the thickness of the metal electrode layer is 100 to 200 nm; An adhesion layer is further provided between the buffer layer and the AlN piezoelectric film layer. The material of the adhesion layer is Cr and the thickness is 5 to 20 nm.

2. The flexible surface acoustic wave device based on wet transfer aluminum nitride film according to claim 1, characterized in that: The buffer layer material is SrTiO3 or other materials with good lattice matching.

3. The flexible surface acoustic wave device based on wet transfer of aluminum nitride film according to claim 2, characterized in that: The electrode material of the metal electrode layer is Al, Pt or other metals with good conductivity.

4. The flexible surface acoustic wave device based on wet transfer of aluminum nitride film according to claim 3, characterized in that: The AlN piezoelectric film is completely transferred from the growth substrate to the flexible mica substrate through a wet transfer technology.

5. A method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride thin film, for preparing the flexible surface acoustic wave device based on wet transfer of aluminum nitride thin film according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: epitaxially growing an AlN thin film on a growth substrate; Step 2: Spin-coat a transfer dielectric layer on the surface of the AlN film; Step 3: Bonding the growth substrate to the flexible mica substrate through a transfer medium layer; Step 4: Remove the growth substrate by chemical etching to complete the transfer of the AlN film; Step 5: Prepare a metal electrode on the transferred AlN film; Step 6: Package the device.

6. The method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride film according to claim 5, characterized in that: In step 1, the growth temperature of the AlN film is 800-1100° C., and magnetron sputtering technology is used.

7. The method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride film according to claim 6, characterized in that: In step 2, the transfer medium layer is PMMA with a thickness of 200 to 500 nm.

8. The method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride film according to claim 7, characterized in that: In step 3, a buffer layer has been deposited on the flexible mica substrate.

9. The method for preparing a flexible surface acoustic wave device based on wet transfer of aluminum nitride thin film according to claim 7, characterized in that: In step 4, a hot phosphoric acid H3PO4 solution is used to etch the sapphire growth substrate.

Images