A surface acoustic wave resonator, its fabrication method, and a filter

Abstract

This invention discloses a surface acoustic wave (SAW) resonator, its fabrication method, and a filter. The SAW resonator includes: a substrate; a high-velocity acoustic layer on the substrate, the high-velocity acoustic layer being made of boron arsenide; and a piezoelectric layer on the high-velocity acoustic layer located on the side away from the substrate. The technical solution of this invention can enhance the power handling capability of the filter and improve its frequency and performance.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging technology, and in particular to a surface acoustic wave resonator, its fabrication method, and a filter. Background Technology

[0002] Surface acoustic wave (SAW) filters are made from materials with piezoelectric effects, such as piezoelectric ceramics, lithium tantalate crystals, lithium niobate, and quartz. They are passive bandpass filters that utilize the piezoelectric effect of piezoelectric crystal oscillator materials and the physical properties of surface acoustic wave propagation. When a crystal is subjected to mechanical forces, it generates an electric field proportional to the pressure. Crystals with piezoelectric effects also undergo elastic deformation when subjected to electrical signals, emitting mechanical sound waves, thus converting electrical signals into acoustic signals. These sound waves propagate only on the crystal surface, hence the name surface acoustic wave.

[0003] Once the piezoelectric substrate is selected, the operating frequency of the surface acoustic wave (SAW) filter is determined by the width of the IDT electrode strips; the narrower the IDT strips, the higher the frequency. Using semiconductor precision fabrication processes at the 0.35–0.42 μm level and existing piezoelectric materials, SAW filters of 2–3 GHz can be fabricated. To fabricate higher-frequency SAW filters without changing the materials, the only option is to make the strips even finer. However, finer strips lead to a sharp increase in impedance, resulting in a significant decrease in power handling capability.

[0004] With societal progress, mobile phones and other communication tools have entered the 5G era and are continuously advancing towards 6G. This necessitates higher frequency filters. To keep pace with the times, there is an urgent need for a new material in the filter industry that can provide higher sound speeds and is suitable for mass production to significantly improve the performance of surface acoustic wave filters. Summary of the Invention

[0005] This invention provides a surface acoustic wave resonator, its manufacturing method, and a filter, which can enhance the power handling capability of the filter and improve its frequency and performance.

[0006] According to one aspect of the present invention, a surface acoustic wave resonator is provided, characterized in that it comprises:

[0007] Substrate;

[0008] A high-velocity layer located on the substrate, wherein the material of the high-velocity layer includes boron arsenide;

[0009] A piezoelectric layer located on the side of the hypersonic layer away from the substrate.

[0010] Optionally, the thickness of the substrate includes 675 nm; the thickness of the hypersonic layer includes 1000 nm; and the thickness of the piezoelectric layer includes 800 nm.

[0011] Optionally, the substrate material includes at least one of silicon, silicon carbide, silicon oxide, diamond, and sapphire; the piezoelectric layer material includes at least one of ALN, ZnO, lithium tantalate, and lithium niobate.

[0012] Optionally, the surface acoustic wave resonator further includes a temperature compensation layer and an electrode layer, wherein the electrode layer is located on the side of the piezoelectric layer away from the substrate, and the temperature compensation layer is located on the side of the electrode layer away from the piezoelectric layer.

[0013] Optionally, the electrode layer includes at least one interdigital transducer.

[0014] According to another aspect of the present invention, a method for manufacturing a surface acoustic wave resonator is provided, the method comprising:

[0015] Provide a substrate;

[0016] A high-velocity layer is formed by depositing boron arsenide on one side of the substrate;

[0017] A piezoelectric layer is formed on one side of the hypersonic layer formed after the growth of boron arsenide.

[0018] Optionally, depositing boron arsenide on one side of the substrate to form a high-sonic-velocity layer includes:

[0019] Set the process temperature using the specified equipment, with a background vacuum below 0.01 torr and a power setting of 150W.

[0020] Trimethylboron is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylboron gas; arsine is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual arsine gas; the above actions are repeated until the hypersonic layer is formed according to the preset number of cycles.

[0021] Alternatively, trimethylarsenic is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylarsenic gas; then hydrogen boride is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual hydrogen boride gas; the above actions are repeated until the hypersonic layer is formed according to the preset number of cycles.

[0022] Optionally, forming a piezoelectric layer on one side of the hypersonic layer after the growth of boron arsenide includes:

[0023] The background vacuum reached 1.0 × 10⁻⁶. -3 Below Pa, 20 sccm of Ar and 10 sccm of N2 are introduced and stabilized for 10 to 20 seconds; wherein, the purity of both Ar and N2 is required to be above 99.999%;

[0024] Adjust the process parameters, with the gas pressure <0.2Pa, the substrate temperature 300℃, and the target power 1000W, and start sputtering the film using the sputtering equipment, depositing the piezoelectric layer according to the preset time.

[0025] Optionally, the designated equipment includes a PE-ALD device or a Thermal-ALD device; the set process temperature of the PE-ALD device is 150°C, and the set process temperature of the Thermal-ALD device is 500°C.

[0026] According to another aspect of the present invention, a filter is also provided, the filter comprising at least two surface acoustic wave resonators as described in any embodiment of the present invention.

[0027] The technical solution of this embodiment solves the problems of poor power handling capability and insufficient performance of filters in the prior art by using highly synthesized boron arsenide material to replace the original high-sound-velocity and high-thermal-conductivity material to form a high-sound-velocity layer, thereby greatly enhancing the power handling capability of the filter and improving the frequency and performance of the filter.

[0028] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of a surface acoustic wave resonator according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the structure of another surface acoustic wave resonator provided according to an embodiment of the present invention;

[0032] Figure 3 This is a flowchart of a method for manufacturing a surface acoustic wave resonator according to an embodiment of the present invention;

[0033] Figure 4 This is a flowchart of another method for manufacturing a surface acoustic wave resonator according to an embodiment of the present invention;

[0034] Figure 5 This is a flowchart of another method for manufacturing a surface acoustic wave resonator according to an embodiment of the present invention;

[0035] Figure 6 This is a flowchart of another method for manufacturing a surface acoustic wave resonator according to an embodiment of the present invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0038] Figure 1 This is a schematic diagram of a surface acoustic wave resonator according to an embodiment of the present invention. (Refer to...) Figure 1 The present invention provides a surface acoustic wave resonator, comprising: a substrate 110; a high-velocity acoustic layer 120 located on the substrate 110, the high-velocity acoustic layer 120 being made of boron arsenide; and a piezoelectric layer 130 located on the side of the high-velocity acoustic layer 120 away from the substrate 110.

[0039] Specifically, the substrate 110 can be made of a high-resistivity material. A high-velocity acoustic layer 120 is formed by depositing boron arsenide on the surface of the substrate 110, and a piezoelectric layer 130 is formed by sputtering on the surface of the high-velocity acoustic layer 120. Boron arsenide possesses excellent thermal properties and can effectively dissipate the heat generated by the surface acoustic wave resonator. Utilizing the high velocity and high thermal conductivity of boron arsenide, the high-velocity acoustic layer 120 can be formed without reducing the interdigitation size. Combined with existing piezoelectric layer materials such as AlN, ZnO, lithium tantalate, and lithium niobate, high-performance, high-frequency surface acoustic wave resonators and filters can be fabricated on the substrate 110, and can be used in filters for 5G and above. Boron arsenide has ultra-high thermal conductivity comparable to diamond, which can greatly enhance the power handling capacity of the filter. Compared to diamond, a high-velocity, high-thermal-conductivity material, diamond films are difficult to fabricate and mass-produce, while boron arsenide is fully capable of mass production, bringing broader prospects to the surface acoustic wave filter industry.

[0040] The substrate 110 and the high-velocity acoustic layer 120 can form a composite multilayer substrate. In the embodiments of the present invention, the composite multilayer substrate can enable surface acoustic wave resonators and radio frequency filters to achieve characteristics such as low insertion loss, smooth passband, high Q value and excellent low frequency temperature.

[0041] The technical solution of this embodiment solves the problems of poor power handling capability and insufficient performance of filters in the prior art by using highly synthesized boron arsenide material to replace the original high-sound-velocity and high-thermal-conductivity material to form a high-sound-velocity layer, thereby greatly enhancing the power handling capability of the filter and improving the frequency and performance of the filter.

[0042] Optionally, the substrate 110 has a thickness of 675 nm; the hypersonic layer 120 has a thickness of 1000 nm; and the piezoelectric layer 130 has a thickness of 800 nm.

[0043] The presence of substrate 110 provides better support for the hypersonic layer 120. If the thickness of substrate 110 is less than 675 nm, it is too thin and cannot provide adequate support. If the thickness of substrate 110 is greater than 675 nm, the excessive thickness increases cost and can also lead to poor heat dissipation. Therefore, the thickness of substrate 110 can be 675 nm, which provides good support without increasing cost or causing poor heat dissipation.

[0044] The thickness of the hypersonic layer 120 determines the power handling capability of the filter. When the thickness of the hypersonic layer 120 is less than 1000 nm, the improvement in the power handling capability of the filter is limited; when the thickness of the hypersonic layer 120 is greater than 1000 nm, it increases the manufacturing difficulty and results in a low yield. Therefore, the thickness of the hypersonic layer 120 can be 1000 nm, which can improve the power handling capability of the filter without increasing the manufacturing difficulty, and also achieves a high yield.

[0045] The thickness of the piezoelectric layer 130 determines the resonant frequency of the surface acoustic wave resonator. A thickness of less than 800 nm increases manufacturing difficulty and cost. A thickness greater than 800 nm results in excessive loss due to the high frequency. Therefore, a thickness of 800 nm for the piezoelectric layer 130 avoids increasing manufacturing difficulty, cost, and loss.

[0046] Optionally, the substrate 110 is made of at least one of silicon, silicon carbide, silicon oxide, diamond, and sapphire; the piezoelectric layer 130 is made of at least one of ALN, ZnO, lithium tantalate, and lithium niobate.

[0047] Specifically, the substrate 110 can be made of one or a combination of silicon, silicon carbide, silicon oxide, diamond, and sapphire, depending on the requirements. The substrate 110 also serves a temperature compensation function. The substrate 110 can also be a composite multilayer substrate, enabling the surface acoustic wave resonator to achieve low insertion loss, smooth passband, high Q value, and excellent low-frequency temperature characteristics. The piezoelectric layer 130 can be made of ALN, ZnO, lithium tantalate, or lithium niobate, and is used to generate the piezoelectric effect. ALN is a high-velocity acoustic material with a sound velocity of 11000-12000 m / s, which can significantly increase the center frequency of the device, meeting the requirements of 5G communication.

[0048] Figure 2 This is a schematic diagram of another surface acoustic wave resonator according to an embodiment of the present invention, with reference to... Figure 2 Optionally, the surface acoustic wave resonator further includes a temperature compensation layer 150 and an electrode layer 140, wherein the electrode layer 140 is located on the side of the piezoelectric layer 130 away from the substrate 110, and the temperature compensation layer 150 is located on the side of the electrode layer 140 away from the piezoelectric layer 130.

[0049] Specifically, the temperature compensation layer 140 can be made of silicon dioxide or silicon nitride, and can be formed by physical vapor deposition sputtering or chemical vapor deposition. The temperature compensation layer 140 can prevent temperature changes from affecting the resonant frequency of the surface acoustic wave resonator. An electrode layer 140 is formed on the surface of the piezoelectric layer 130 by depositing a metal film using methods such as electron beam evaporation, plasma, or magnetron sputtering. The material for the deposited metal film can be titanium, chromium, copper, silver, aluminum, or a combination thereof.

[0050] Continue to refer to Figure 2 Optionally, the electrode layer 140 includes at least one interdigital transducer 141.

[0051] The transducer 141 has a thickness of 50-800 nm and is composed of metals or alloys such as Ti, Al, Cu, Au, Pt, Mo, and Ni, or a stack of these metals or alloys. The transducer 141 is used to generate surface acoustic waves on the piezoelectric layer 130. The number of interdigital transducers 141 in the electrode layer 140 can be one or more, and the specific number can be set as needed. This embodiment of the invention does not limit this.

[0052] Figure 3 This is a flowchart illustrating a method for fabricating a surface acoustic wave resonator according to an embodiment of the present invention. (Refer to...) Figure 3 This invention provides a method for fabricating a surface acoustic wave resonator, the method comprising:

[0053] S210, Provide a substrate.

[0054] Specifically, the substrate can be formed by physical vapor deposition sputtering or chemical vapor deposition. The substrate material can be one or a combination of silicon, silicon carbide, silicon oxide, diamond, and sapphire, which can be set as needed. The substrate thickness can be 675nm.

[0055] S220, deposit boron arsenide on one side of the substrate to form a high-velocity layer.

[0056] Specifically, a layer of boron arsenide is deposited on a substrate using designated equipment according to a preset process to form a hypersonic layer, the thickness of which can be 1000 nm.

[0057] S230, a piezoelectric layer is formed on one side of the hypersonic layer formed after the growth of boron arsenide.

[0058] Specifically, a piezoelectric layer is formed by sputtering a thin film onto the hypersonic layer formed after the growth of boron arsenide using a sputtering device. The material of the piezoelectric layer can be ALN, ZnO, lithium tantalate, or lithium niobate, and the thickness of the piezoelectric layer 130 can be 800 nm.

[0059] The method for fabricating a surface acoustic wave resonator provided in this embodiment of the invention is used to fabricate the surface acoustic wave resonator provided in any embodiment of the invention. Therefore, the method for fabricating a surface acoustic wave resonator provided in this embodiment of the invention also has the beneficial effects described in the above embodiments, and will not be repeated here.

[0060] Figure 4 This is a flowchart illustrating another method for fabricating a surface acoustic wave resonator according to an embodiment of the present invention, see reference. Figure 4 Optionally, depositing boron arsenide on one side of the substrate to form a high-velocity layer includes the following steps:

[0061] S2211. Use the specified equipment to set the process temperature, with a background vacuum below 0.01 torr and a power setting of 150W.

[0062] S2212, introduce trimethylboron for 0.05s, then purge with N2 for 10s to remove residual trimethylboron gas.

[0063] S2213. Introduce arsine for 0.1s, then purge with N2 for 10s to remove residual arsine gas.

[0064] S2214. Repeat the above actions repeatedly until a hypersonic layer is formed according to the preset number of cycles.

[0065] or, Figure 5 This is a flowchart illustrating another method for fabricating a surface acoustic wave resonator according to an embodiment of the present invention, see reference. Figure 5 Optionally, depositing boron arsenide on one side of the substrate to form a high-velocity layer includes the following steps:

[0066] S2221. Use the specified equipment to set the process temperature, with a base vacuum below 0.01 torr and a power setting of 150W.

[0067] S2222: Introduce trimethylarsenic for 0.05 s, then purge with N2 for 10 s to remove residual trimethylarsenic gas.

[0068] S2223. Introduce hydrogen boride for 0.1s, then purge with N2 for 10s to remove residual hydrogen boride gas.

[0069] S2224. Repeat the above actions repeatedly until a hypersonic layer is formed according to the preset number of cycles.

[0070] Specifically, the specified equipment includes PE-ALD equipment or Thermal-ALD equipment. For example, the deposition of boron arsenide on a substrate using a PE-ALD equipment with a film thickness of 1000 nm will be described. Pre-process preparation includes a process temperature of 150°C, a base vacuum below 0.01 torr, and an RF power supply set to 150W.

[0071] Trimethylboron (purity ≥ 99.999%) is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylboron gas; arsine (purity ≥ 99.999%) is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual arsine gas; the above steps are repeated until 1000 nm boron arsenide is formed according to the preset number of cycles.

[0072] Alternatively, trimethylarsenic (purity ≥ 99.999%) is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylarsenic gas; then hydrogen boride (purity ≥ 99.999%) is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual hydrogen boride gas; the above steps are repeated until boron arsenide of 1000 nm is formed according to the preset number of cycles.

[0073] For example, the deposition of boron arsenide on a substrate using a Thermal-ALD device with a film thickness of 1000 nm will be used as an example. Pre-process preparation includes a process temperature of 500°C, a base vacuum below 0.01 torr, and an RF power supply set to 150W.

[0074] In the ALD process chamber, trimethylarsenic (purity ≥ 99.999%) is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylarsenic gas; then hydrogen boride (purity ≥ 99.999%) is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual hydrogen boride gas; the above steps are repeated until boron arsenide of 1000 nm is formed according to the preset number of cycles.

[0075] Alternatively, in the ALD process chamber, trimethylboron (purity ≥ 99.999%) is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylboron gas; then arsine (purity ≥ 99.999%) is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual arsine gas; the above steps are repeated until 1000 nm of boron arsenide is formed according to the preset number of cycles.

[0076] Figure 6 This is a flowchart illustrating another method for fabricating a surface acoustic wave resonator according to an embodiment of the present invention, see reference. Figure 6 Optionally, forming a piezoelectric layer on one side of the grown boron arsenide hypersonic layer includes the following steps:

[0077] S2301, background vacuum reaches 1.0×10 -3 Below Pa, 20 sccm of Ar and 10 sccm of N2 are introduced, and the mixture is stabilized for 10 to 20 seconds; the purity of both Ar and N2 is required to be above 99.999%.

[0078] S2302. Adjust the process parameters: gas pressure < 0.2 Pa, substrate temperature 300 °C, target power 1000 W, and start sputtering the film using the sputtering equipment. Deposit the piezoelectric layer according to the preset time.

[0079] For example, the piezoelectric layer is formed by using AlN as the material. The process of forming a piezoelectric layer by sputtering an 800 nm thick AlN film onto a hypersonic boron arsenide layer using sputtering equipment includes: achieving a base vacuum of 1.0 × 10⁻⁶. -3 Below Pa, 20 sccm of Ar and 10 sccm of N2 are introduced and stabilized for 10-20 seconds; the purity of both Ar and N2 is required to be above 99.999%. Process parameters are adjusted: gas pressure < 0.2 Pa, substrate temperature 300℃, target power 1000W, and sputtering deposition begins; 800 nm of AlN is deposited according to the preset time. Finally, according to different designs, the surface acoustic wave filter pattern is fabricated on the above substrate using existing conventional processes.

[0080] Optionally, the specified equipment includes a PE-ALD device or a Thermal-ALD device; the set process temperature of the PE-ALD device is 150°C, and the set process temperature of the Thermal-ALD device is 500°C.

[0081] Specifically, the PE-ALD equipment utilizes a plasma-enhanced ALD (PE-ALD) process, which combines plasma-assisted deposition with ALD technology. This process is set at a temperature of 150°C. The Thermal-ALD equipment utilizes thermally treated atomic layer deposition (T-ALD), a traditional and still widely used ALD method. Compared to Thermal-ALD equipment, PE-ALD equipment offers the following advantages: faster deposition rates and shorter deposition times, lower temperatures required for film growth, greater monomer selectivity, and the ability to grow excellent metal films and metal nitrides.

[0082] This invention also provides a filter comprising at least two surface acoustic wave resonators according to any one of the above embodiments.

[0083] The filter can be formed by connecting two or more surface acoustic wave resonators in series and / or in parallel as described in the above embodiments.

[0084] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A surface acoustic wave resonator, characterized in that, include: Substrate; A high-velocity layer located on the substrate, wherein the material of the high-velocity layer includes boron arsenide; A piezoelectric layer located on the side of the hypersonic layer away from the substrate.

2. The surface acoustic wave resonator according to claim 1, characterized in that, The substrate has a thickness of 675 nm; the hypersonic layer has a thickness of 1000 nm; and the piezoelectric layer has a thickness of 800 nm.

3. The surface acoustic wave resonator according to claim 1, characterized in that, The substrate is made of at least one of silicon, silicon carbide, silicon oxide, diamond, and sapphire; the piezoelectric layer is made of at least one of ALN, ZnO, lithium tantalate, and lithium niobate.

4. The surface acoustic wave resonator according to claim 1, characterized in that, The surface acoustic wave resonator further includes a temperature compensation layer and an electrode layer. The electrode layer is located on the side of the piezoelectric layer away from the substrate, and the temperature compensation layer is located on the side of the electrode layer away from the piezoelectric layer.

5. The surface acoustic wave resonator according to claim 4, characterized in that, The electrode layer includes at least one interdigital transducer.

6. A method for fabricating a surface acoustic wave resonator, characterized in that, include: Provide a substrate; A high-velocity layer is formed by depositing boron arsenide on one side of the substrate. A piezoelectric layer is formed on one side of the hypersonic layer formed after the growth of boron arsenide.

7. The manufacturing method according to claim 6, characterized in that, Depositing boron arsenide on one side of the substrate to form a high-velocity layer includes: Use the specified equipment to set the process temperature, with a background vacuum below 0.01 torr and a power setting of 150W; Trimethylboron is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylboron gas; arsine is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual arsine gas; the above steps are repeated until the hypersonic layer is formed according to the preset number of cycles. Alternatively, trimethylarsenic is introduced for 0.05 s, followed by purging with N2 for 10 s to remove residual trimethylarsenic gas; then hydrogen boride is introduced for 0.1 s, followed by purging with N2 for 10 s to remove residual hydrogen boride gas; the above actions are repeated until the hypersonic layer is formed according to the preset number of cycles.

8. The manufacturing method according to claim 6, characterized in that, Forming a piezoelectric layer on one side of the hypersonic layer after the growth of boron arsenide includes: The background vacuum reached 1.0 × 10⁻⁶. -3 Below Pa, 20 sccm of Ar and 10 sccm of N2 are introduced and stabilized for 10 to 20 seconds; wherein, the purity of both Ar and N2 is required to be above 99.999%; Adjust the process parameters, with the gas pressure <0.2Pa, the substrate temperature 300℃, and the target power 1000W, and start sputtering the film using the sputtering equipment, depositing the piezoelectric layer according to the preset time.

9. The manufacturing method according to claim 7, characterized in that, The designated equipment includes a PE-ALD device or a Thermal-ALD device; the set process temperature of the PE-ALD device is 150°C, and the set process temperature of the Thermal-ALD device is 500°C.

10. A filter, characterized in that, It includes at least two surface acoustic wave resonators as described in any one of claims 1-5.

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