Frequency filter and method for manufacturing the same

Abstract

Provided is a frequency filter that operates in a high frequency band. The frequency filter comprises a medium layer, an input comb electrode, and an output comb electrode. The medium layer has flexoelectric characteristics. The input comb electrode is provided on the medium layer. The output comb electrode is provided on the medium layer. The medium layer enables the generation of an elastic wave in the medium layer according to an input electric field in the input comb electrode, and the generation of an output electric field according to the elastic wave in the output comb electrode.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to frequency filters and methods for manufacturing frequency filters. [Background technology]

[0002] A wireless communication system is equipped with a frequency filter, and Patent Document 1 discloses a surface acoustic wave (SAW) filter as a frequency filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-51000 Summary of the Invention [Problem to be solved by the invention]

[0004] In SAW filters, the thinner the piezoelectric element that transmits the elastic waves, the faster the propagation speed and the smaller the energy loss. However, as the frequency band used becomes higher, the improvement in the characteristics of SAW filters is approaching its limit.

[0005] In order to solve the above problems, an object of the present disclosure is to provide a frequency filter that can operate in a high frequency band. [Means for solving the problem]

[0006] A frequency filter according to the present disclosure includes a medium layer, an input comb electrode, and an output comb electrode. The medium layer has flexoelectric characteristics. The input comb electrode is provided on the medium layer. The output comb electrode is provided on the medium layer. The medium layer has: It includes single-layer or multi-layer two-dimensional thin films, and the flexoelectric properties in the medium layer are greater than the piezoelectric properties in the two-dimensional thin film. [Effects of the Invention]

[0007] According to the present disclosure, a frequency filter capable of operating in a high frequency band is provided.

[0008] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a perspective view showing the configuration of a frequency filter according to the first embodiment. [Figure 2] FIG. 10 is a perspective view showing the configuration of a frequency filter according to a second embodiment. [Figure 3] 10 is a plan view showing the configuration of an input comb electrode according to a second embodiment. FIG. [Figure 4] 10 is a plan view showing a configuration of an input comb electrode in a first modification of the second embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] <First Embodiment> 1 is a perspective view showing the configuration of a frequency filter 10 according to Embodiment 1. The frequency filter 10 is a high-frequency surface acoustic wave (SAW) filter.

[0011] The frequency filter 10 includes a medium layer 11 , an input comb electrode 12 , an output comb electrode 13 , an input wiring 14 , and an output wiring 15 .

[0012] The medium layer 11 has flexoelectric properties. In this specification, the flexoelectric effect and the inverse flexoelectric effect are collectively referred to as flexoelectric properties, but the properties may also be simply referred to as flexoelectric effects.

[0013] In a medium layer 11 having flexoelectric properties, an electric field is generated in response to a strain gradient within the medium layer 11. This is called the flexoelectric effect. Also, a strain gradient is generated within the medium layer 11 in response to the electric field. This is called the inverse flexoelectric effect.

[0014] Medium layer 11 generates an acoustic wave corresponding to the input electric field at input comb electrode 12, the acoustic wave being excited by the inverse flexoelectric characteristic of medium layer 11. The acoustic wave propagates through medium layer 11. Medium layer 11 then generates an output electric field corresponding to the acoustic wave at output comb electrode 13, the output electric field being converted from the acoustic wave by the flexoelectric characteristic of medium layer 11. The acoustic wave propagating through medium layer 11 is also called a surface acoustic wave.

[0015] The medium layer 11 in the first embodiment is formed of a single-layer or multi-layer two-dimensional thin film 11A. The two-dimensional thin film 11A has a two-dimensional atomic bonding structure. A multi-layer two-dimensional thin film has a structure in which single-layer two-dimensional thin films are stacked. Van der Waals forces act between the layers, and the multi-layer two-dimensional thin films are bonded to each other by these van der Waals forces. The two-dimensional thin film 11A is formed of, for example, an insulating material or a semiconductor material. The two-dimensional thin film 11A is formed of, for example, hexagonal boron nitride, molybdenum disulfide, molybdenum telluride, or the like. The thickness of the two-dimensional thin film 11A is equal to or less than a single atom or 10 nm. The thickness of the two-dimensional thin film 11A is such that the flexoelectric properties of the two-dimensional thin film 11A are greater than the piezoelectric properties. The medium layer 11 is not limited to the two-dimensional thin film 11A. The medium layer 11 may also be formed of a non-piezoelectric insulating material.

[0016] The input comb electrode 12 is provided on the two-dimensional thin film 11A. The input comb electrode 12 has two comb teeth. The two comb teeth are arranged opposite each other to form a nested structure. The comb teeth of the input comb electrode 12 have one or more sets of parallel portions. The input comb electrode 12 is made of a conductive material. The input comb electrode 12 is made of, for example, copper, gold, aluminum, graphene, or the like. An input signal is input to the input comb electrode 12. An electric field is formed in the comb teeth of the input comb electrode 12 according to the spacing between the comb teeth.

[0017] The output comb electrode 13 is provided on the same two-dimensional thin film 11A. The output comb electrode 13 has two comb teeth. The two comb teeth are arranged opposite each other to form a nested structure. The comb teeth of the output comb electrode 13 are arranged parallel to the comb teeth of the input comb electrode 12. The spacing between the comb teeth of the input comb electrode 12 is equal to the spacing between the comb teeth of the output comb electrode 13. The comb teeth of the output comb electrode 13 have one or more sets of parallel portions. The output comb electrode 13 is made of a conductive material. The output comb electrode 13 is made of, for example, copper, gold, aluminum, graphene, or the like. An acoustic wave generated in the input comb electrode 12 reaches the output comb electrode 13. An electric field corresponding to the acoustic wave is formed in the comb teeth of the output comb electrode 13.

[0018] The input wiring 14 is electrically connected to the input comb electrode 12. An input signal is applied to the input comb electrode 12 via the input wiring 14.

[0019] The output wiring 15 is electrically connected to the output comb electrode 13. An output signal corresponding to the electric field in the output comb electrode 13 is taken out via the output wiring 15 to the outside.

[0020] Next, a method for manufacturing the frequency filter 10 will be described. First, a medium layer 11 is formed. The medium layer 11 has flexoelectric properties. Here, a single-layer or multi-layer two-dimensional thin film 11A is formed. The two-dimensional thin film 11A is fabricated by the Scotch tape method or molecular beam epitaxy. Then, the input comb electrode 12 and the output comb electrode 13 are vapor-deposited on the two-dimensional thin film 11A.

[0021] Next, the operation of the frequency filter 10 will be described. An input signal containing multiple frequency components is input to the input comb electrode 12 from an external circuit via the input wiring 14. The input signal is a high-frequency signal, and includes, for example, random frequency components. An electric field is generated between the teeth of the input comb electrode 12, which corresponds to the tooth spacing. Due to the inverse flexoelectric effect, a strain gradient based on the electric field is generated in the two-dimensional thin film 11A, exciting an elastic wave.

[0022] The elastic wave propagates through the two-dimensional thin film 11A and reaches the output comb electrode 13. At the output comb electrode 13, a strain gradient corresponding to the frequency of the elastic wave is generated within the two-dimensional thin film 11A. Due to the flexoelectric effect, an electric field corresponding to the strain gradient is generated between the comb teeth. An output signal corresponding to the electric field is output to the outside via the output wiring 15.

[0023] As a result, only an output signal of a specific frequency is extracted from an input signal containing multiple frequency components. In other words, only the specific frequency passes through this frequency filter 10.

[0024] The frequency of the signal output to the outside is calculated using the following formula (1).

[0025]

number

[0026] Here, f represents the frequency, v represents the propagation speed of the elastic wave, and λ represents the wavelength of the elastic wave excited in the input comb electrode 12, that is, the comb tooth spacing.

[0027] The propagation velocity v is calculated using the following equation (2).

[0028]

number

[0029] Here, ρ is the density and E is the elastic modulus. The higher the propagation speed v and the smaller the comb tooth spacing λ, the higher the frequency f.

[0030] To summarize the above, frequency filter 10 in Embodiment 1 includes medium layer 11, input comb electrode 12, and output comb electrode 13. Medium layer 11 has flexoelectric characteristics. Input comb electrode 12 is provided on medium layer 11. Output comb electrode 13 is provided on medium layer 11. Medium layer 11 enables the generation of an elastic wave in medium layer 11 in response to an input electric field in input comb electrode 12, and the generation of an output electric field in output comb electrode 13 in response to the elastic wave.

[0031] When the medium layer 11 is a two-dimensional thin film 11A, the device can be thinned down to atomic size. Elastic waves do not propagate in the thickness direction of the two-dimensional thin film 11A. Furthermore, the reduction in the size of the medium layer 11 through which the elastic waves propagate reduces the probability of defects in the medium layer 11. Therefore, the elastic waves are less likely to attenuate. Even when the medium layer 11 is a multilayer two-dimensional thin film 11A, the friction between the layers is small, resulting in little energy dissipation. For these reasons, the elastic waves are less likely to attenuate in the frequency filter 10. The frequency filter 10 can be applied to high-frequency devices. Furthermore, the two-dimensional thin film 11A electrically responds more sensitively to deformation than bulk materials. This is another advantage.

[0032] In frequency filters that use piezoelectric elements, the piezoelectric effect disappears when the dimensions are reduced to a few nanometers or less. This limits the improvement in performance of high-frequency devices that use piezoelectric elements. On the other hand, the frequency filter 10 according to the first embodiment can also be applied to devices that use high frequencies of several GHz or more, and the device size can also be reduced.

[0033] <Embodiment 2> In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals.

[0034] Fig. 2 is a perspective view showing the configuration of a frequency filter 20 according to the second embodiment. The frequency filter 20 includes an input comb electrode 22 and an output comb electrode 23. Fig. 3 is a plan view showing the configuration of the input comb electrode 22 according to the second embodiment.

[0035] The input comb-tooth electrode 22 includes a first input comb-tooth portion 22A, a second input comb-tooth portion 22B, and a bent portion 22C. The second input comb-tooth portion 22B is electrically connected to the first input comb-tooth portion 22A at an angle relative to the first input comb-tooth portion 22A. The first input comb-tooth portion 22A in the second embodiment is connected to the second input comb-tooth portion 22B via the bent portion 22C. The comb teeth of the first input comb-tooth portion 22A are parallel to each other, and the comb teeth of the second input comb-tooth portion 22B are also parallel to each other. The comb-tooth spacing of the second input comb-tooth portion 22B is equal to the comb-tooth spacing of the first input comb-tooth portion 22A.

[0036] The output comb-tooth electrode 23 includes a first output comb-tooth electrode 23A and a second output comb-tooth electrode 23B. The second output comb-tooth electrode 23B is provided separately from the first output comb-tooth electrode 23A. The first output comb-tooth electrode 23A has comb teeth parallel to the first input comb-tooth portion 22A. The second output comb-tooth electrode 23B has comb teeth parallel to the second input comb-tooth portion 22B.

[0037] An input signal containing random frequency components is input to the input comb electrode 22 from an external circuit via the input wiring 14. The input signal is a high-frequency signal. Electric fields corresponding to the tooth spacing are generated between the teeth of the first input comb portion 22A and between the teeth of the second input comb portion 22B. Due to the inverse flexoelectric effect, a strain gradient based on the electric field is generated in the two-dimensional thin film 11A, exciting an elastic wave. In the second embodiment, the tooth spacing of the first input comb portion 22A and the tooth spacing of the second input comb portion 22B are equal. Therefore, the wavelength of the elastic wave excited in the first input comb portion 22A is equal to the wavelength of the elastic wave excited in the second input comb portion 22B. In Equation (1), the wavelength λ of the first input comb portion 22A and the wavelength λ of the second input comb portion 22B are equal to each other.

[0038] The elastic wave generated in the first input comb-tooth portion 22A propagates through the two-dimensional thin film 11A and reaches, for example, the first output comb-tooth electrode 23A. The elastic wave generated in the second input comb-tooth portion 22B propagates through the two-dimensional thin film 11A and reaches, for example, the second output comb-tooth electrode 23B. In each of the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B, a strain gradient corresponding to the frequency of the elastic wave is generated in the two-dimensional thin film 11A. Due to the flexoelectric effect, an electric field corresponding to the strain gradient is generated between the comb teeth of the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B. An output signal corresponding to the electric field is output to the outside via the output wiring 15.

[0039] As a result, only output signals of specific frequencies are extracted from input signals containing random frequency components. In other words, only specific frequencies pass through this frequency filter 20. In the second embodiment, the comb tooth spacing of the first input comb tooth portion 22A is equal to the comb tooth spacing of the second input comb tooth portion 22B, so that two output signals having the same frequency are obtained from two locations for one input signal.

[0040] (Modification 1 of Embodiment 2) FIG. 4 is a plan view showing the configuration of the input comb electrode 32 in the first modification of the second embodiment.

[0041] The input comb-tooth electrode 32 includes a first input comb-tooth portion 32A and a second input comb-tooth portion 32B. The second input comb-tooth portion 32B is electrically connected to the first input comb-tooth portion 32A at an angle relative to the first input comb-tooth portion 32A. The spacing between the teeth of the second input comb-tooth portion 32B is different from the spacing between the teeth of the first input comb-tooth portion 32A.

[0042] In this case, the distribution of the electric field generated between the teeth of the first input-side comb tooth portion 32A is different from the distribution of the electric field generated between the teeth of the second input-side comb tooth portion 32B. Regarding the inverse flexoelectric effect, the strain gradient generated in the first input-side comb tooth portion 32A is different from the strain gradient generated in the second input-side comb tooth portion 32B. Therefore, the wavelength of the elastic wave excited in the first input-side comb tooth portion 32A is different from the wavelength of the elastic wave excited in the second input-side comb tooth portion 32B. In Equation (1), the wavelength λ of the first input-side comb tooth portion 32A is different from the wavelength λ of the second input-side comb tooth portion 32B.

[0043] The elastic wave generated in the first input comb-tooth portion 32A propagates through the two-dimensional thin film 11A and reaches, for example, the first output comb-tooth electrode 23A. The elastic wave generated in the second input comb-tooth portion 32B propagates through the two-dimensional thin film 11A and reaches, for example, the second output comb-tooth electrode 23B. In each of the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B, a strain gradient corresponding to the frequency of the elastic wave is generated in the two-dimensional thin film 11A. Due to the flexoelectric effect, an electric field corresponding to the strain gradient is generated between the comb teeth of the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B. An output signal corresponding to the electric field is output to the outside via the output wiring 15. The frequency of the output signal output from the first output comb-tooth electrode 23A is different from the frequency of the output signal output from the second output comb-tooth electrode 23B.

[0044] In this way, for one input signal, two output signals with different frequencies are obtained.

[0045] (Modification 2 of Embodiment 2) The two-dimensional thin film 11A may have anisotropy in the in-plane elastic modulus of the two-dimensional thin film 11A. In this case, the propagation velocity v of the elastic wave in equation (2) varies depending on the propagation direction. Therefore, the frequency of the elastic wave in equation (1) also varies depending on the propagation direction.

[0046] In such a configuration, even if the interval between the teeth of the second input comb-tooth portion 22B is equal to the interval between the teeth of the first input comb-tooth portion 22A, two output signals having different frequencies are obtained.

[0047] <Third Embodiment> In the third embodiment, the same components as those in the first or second embodiment are denoted by the same reference numerals.

[0048] In the third embodiment, medium layer 11 is formed of an insulating substrate (not shown) made of an insulating material. When medium layer 11 is an insulating substrate made of an insulating material, the flexoelectric effect and the inverse flexoelectric effect are exhibited in the insulating material. Input comb-tooth electrode 22 and output comb-tooth electrode 23 are provided on the insulating substrate.

[0049] As in the second embodiment, referring to FIG. 3, the input comb electrode 22 includes a first input comb portion 22A, a second input comb portion 22B, and a bent portion 22C. The second input comb portion 22B is electrically connected to the first input comb portion 22A at an angle relative to the first input comb portion 22A. The first input comb portion 22A in the third embodiment is connected to the second input comb portion 22B via the bent portion 22C. The comb teeth of the first input comb portion 22A are parallel to each other, and the comb teeth of the second input comb portion 22B are also parallel to each other. The interval between the comb teeth of the second input comb portion 22B may be equal to or different from the interval between the comb teeth of the first input comb portion 22A.

[0050] 2, the output comb-tooth electrode 23 includes a first output comb-tooth electrode 23A and a second output comb-tooth electrode 23B. The second output comb-tooth electrode 23B is provided separately from the first output comb-tooth electrode 23A. The first output comb-tooth electrode 23A has comb teeth parallel to the first input comb-tooth portion 22A. The second output comb-tooth electrode 23B has comb teeth parallel to the second input comb-tooth portion 22B.

[0051] An input signal containing random frequency components is input to the input comb electrode 22 from an external circuit via the input wiring 14. The input signal is a high-frequency signal. Electric fields corresponding to the tooth spacing are generated between the teeth of the first input comb portion 22A and between the teeth of the second input comb portion 22B. Due to the inverse flexoelectric effect, a strain gradient based on the electric field is generated in the insulating material, exciting elastic waves. When the tooth spacing of the first input comb portion 22A and the tooth spacing of the second input comb portion 22B are equal, elastic waves of the same wavelength are excited. In this case, the wavelength λ in Equation (1) has the same value. On the other hand, when the tooth spacing of the first input comb portion 22A and the tooth spacing of the second input comb portion 22B are different, elastic waves of different wavelengths are excited. In this case, the wavelength λ in Equation (1) has different values.

[0052] The elastic waves propagate through the insulating substrate 11B made of an insulating material and reach the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B. A strain gradient corresponding to the frequency of the elastic waves is generated in the insulating material of each of the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B. Due to the flexoelectric effect, an electric field corresponding to the strain gradient is generated between the comb teeth of each of the first output comb-tooth electrode 23A and the second output comb-tooth electrode 23B. An output signal corresponding to the electric field is output to the outside via the output wiring 15.

[0053] As in the second embodiment, two output signals having the same frequency or two output signals having different frequencies are obtained for one input signal containing random frequency components, which reduces the number of components compared to when two output signals are obtained by forming an electrical circuit.

[0054] Although this disclosure has been described in detail, the above description is illustrative in all respects and is not restrictive. It is understood that countless variations not illustrated can be envisioned.

[0055] In the present disclosure, the embodiments can be freely combined, and the embodiments can be modified or omitted as appropriate. [Explanation of symbols]

[0056] 10 frequency filter, 11 medium layer, 11A two-dimensional thin film, 12 input side comb tooth electrode, 13 output side comb tooth electrode, 14 input side wiring, 15 output side wiring, 20 frequency filter, 22 input side comb tooth electrode, 22A first input side comb tooth portion, 22B second input side comb tooth portion, 22C bent portion, 23 output side comb tooth electrode, 23A first output side comb tooth electrode, 23B second output side comb tooth electrode, 32 input side comb tooth electrode, 32A first input side comb tooth portion, 32B second input side comb tooth portion.

Claims

1. a medium layer having flexoelectric properties; an input-side comb electrode provided on the medium layer; an output comb electrode provided on the medium layer, the medium layer includes a single-layer or multi-layer two-dimensional thin film; A frequency filter, wherein the flexoelectric characteristic in the medium layer is greater than the piezoelectric characteristic in the two-dimensional thin film.

2. 2. The frequency filter of claim 1, wherein the thickness of the two-dimensional thin film is less than or equal to a monoatomic thickness or 10 nm.

3. 3. The frequency filter according to claim 1, wherein the two-dimensional thin film is made of any one of hexagonal boron nitride, molybdenum disulfide, and molybdenum telluride.

4. 3. The frequency filter according to claim 1, wherein the two-dimensional thin film has anisotropy in the modulus of elasticity in the plane of the two-dimensional thin film.

5. 2. The frequency filter according to claim 1, wherein the medium layer is formed of a non-piezoelectric insulating material.

6. 3. The frequency filter according to claim 1, wherein the input comb electrode and the output comb electrode are made of any one of copper, gold, aluminum, and graphene.

7. 3. The frequency filter according to claim 1, wherein the comb teeth of the output comb electrode are arranged parallel to the comb teeth of the input comb electrode.

8. 3. The frequency filter according to claim 1, wherein the interval between the teeth of the output comb electrode is equal to the interval between the teeth of the input comb electrode.

9. The input comb electrode is a first input side comb tooth portion; a second input side comb tooth portion that is angled with respect to the first input side comb tooth portion and is electrically connected to the first input side comb tooth portion, The output comb electrode is a first output comb electrode having comb teeth parallel to the first input comb tooth portion; 3. The frequency filter according to claim 1, further comprising: a second output comb-teeth electrode provided separately from the first output comb-teeth electrode and having comb teeth parallel to the second input comb-teeth portion.

10. The frequency filter according to claim 9 , wherein the interval between the teeth of the second input side comb-teeth portion is equal to the interval between the teeth of the first input side comb-teeth portion.

11. The frequency filter according to claim 9 , wherein a tooth interval of the second input side comb-teeth portion is different from a tooth interval of the first input side comb-teeth portion.

12. input wiring electrically connected to the input comb electrode; 3. The frequency filter according to claim 1, further comprising: an output wiring electrically connected to the output comb electrode.

13. 2. The frequency filter according to claim 1, wherein the medium layer includes an insulating substrate made of an insulating material.

14. forming a medium layer having flexoelectric properties; and a step of depositing an input comb electrode and an output comb electrode on the medium layer by vapor deposition, the medium layer includes a single-layer or multi-layer two-dimensional thin film; The method for manufacturing a frequency filter, wherein the flexoelectric characteristic in the medium layer is greater than the piezoelectric characteristic in the two-dimensional thin film.

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