CN112272015B - Acoustic wave resonator - Google Patents
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- CN112272015B CN112272015B CN202011240566.3A CN202011240566A CN112272015B CN 112272015 B CN112272015 B CN 112272015B CN 202011240566 A CN202011240566 A CN 202011240566A CN 112272015 B CN112272015 B CN 112272015B
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- 239000000463 material Substances 0.000 claims description 41
- 239000013078 crystal Substances 0.000 claims description 29
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims description 15
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 claims description 7
- UKDIAJWKFXFVFG-UHFFFAOYSA-N potassium;oxido(dioxo)niobium Chemical compound [K+].[O-][Nb](=O)=O UKDIAJWKFXFVFG-UHFFFAOYSA-N 0.000 claims description 7
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- PIGFYZPCRLYGLF-UHFFFAOYSA-N Aluminum nitride Chemical compound [Al]#N PIGFYZPCRLYGLF-UHFFFAOYSA-N 0.000 description 6
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 description 6
- 230000001629 suppression Effects 0.000 description 5
- HMUNWXXNJPVALC-UHFFFAOYSA-N 1-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperazin-1-yl]-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)N1CCN(CC1)C(CN1CC2=C(CC1)NN=N2)=O HMUNWXXNJPVALC-UHFFFAOYSA-N 0.000 description 4
- LDXJRKWFNNFDSA-UHFFFAOYSA-N 2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-1-[4-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]piperazin-1-yl]ethanone Chemical compound C1CN(CC2=NNN=C21)CC(=O)N3CCN(CC3)C4=CN=C(N=C4)NCC5=CC(=CC=C5)OC(F)(F)F LDXJRKWFNNFDSA-UHFFFAOYSA-N 0.000 description 4
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
- H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
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- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Piezo-Electric Or Mechanical Vibrators, Or Delay Or Filter Circuits (AREA)
Abstract
The present invention provides an acoustic wave resonator comprising: a bottom electrode, a piezoelectric film structure, and a top electrode; the piezoelectric film structure comprises at least two layers of superposed piezoelectric films, wherein different Euler angles are formed between every two adjacent piezoelectric films; when a thickness shear wave is excited in the piezoelectric film structure, the piezoelectric vector of each piezoelectric film at the Euler angle
All satisfy the die length
And the piezoelectric vectors of two adjacent piezoelectric films
Located in different quadrants; when a thickness extensional wave is excited in the piezoelectric film structure, the piezoelectric coefficient e of each piezoelectric film at the respective Euler angle33Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films33The sign is opposite. The acoustic wave resonator provided by the invention solves the problem of poor stability of a device mechanical structure caused by increasing the working frequency of the acoustic wave resonator by reducing the thickness of the piezoelectric film in the prior art.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to an acoustic wave resonator.
Background
The acoustic wave resonator is widely applied to band-pass filters and duplexers and is an important component of a radio frequency front-end system. The rapid development of communication technology, especially 5G communication technology, makes the industry have higher requirements for acoustic wave resonators: high electromechanical coupling coefficient, high frequency, and high power capacity.
However, since the operating frequency of the higher-order acoustic wave resonator is completely dependent on the thickness of the piezoelectric film under the quasi-static condition, increasing the operating frequency necessarily means a reduction in the thickness of the piezoelectric film, thereby resulting in a decrease in the mechanical structural stability of the device.
It is seen that increasing the thickness of the piezoelectric film is particularly important to solve the above-mentioned problems, on the premise that the operating frequency remains at the original level.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention is directed to an acoustic wave resonator, which solves the problem of poor mechanical structure stability of the device caused by increasing the operating frequency of the acoustic wave resonator by reducing the thickness of the piezoelectric film in the prior art.
To achieve the above and other related objects, the present invention provides an acoustic wave resonator comprising:
a bottom electrode;
the piezoelectric film structure is formed above the bottom electrode;
a top electrode formed over the piezoelectric film structure;
wherein the piezoelectric film structure comprises at least two stacked piezoelectric films, different Euler angles are formed between two adjacent piezoelectric films, and the piezoelectric coefficients of the piezoelectric films at the respective Euler angles are expressed as
When a thickness shear wave is excited in the piezoelectric film structure, the piezoelectric vectors of the piezoelectric films at respective Euler angles
All satisfy the die length
And the piezoelectric vectors of two adjacent piezoelectric films
Located in different quadrants;
when a thickness extensional wave is excited in the piezoelectric film structure, the piezoelectric coefficient e of each piezoelectric film at each Euler angle3Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films33The sign is opposite.
Optionally, the piezoelectric film has a piezoelectric coefficient at an euler angle (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
optionally, the acoustic wave resonator further includes: and at least one intermediate medium layer is formed between any two adjacent piezoelectric films.
Optionally, the thickness of each piezoelectric film is less than 20 μm, and the thickness ratio of two adjacent piezoelectric films is between 0.5 and 2.
Optionally, the piezoelectric films are made of the same material and include: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
Optionally, the bottom electrode comprises: one of a face electrode, an interdigitated electrode, or a polygonal electrode, the top electrode comprising: one of a planar electrode, an interdigital electrode, or a polygonal electrode.
Optionally, when the top electrode is an interdigital electrode, the acoustic wave resonator further includes: and the top dielectric layer is formed above the piezoelectric film structure at the gap of the interdigital electrode.
Optionally, when the top electrode is an interdigital electrode, the acoustic wave resonator further includes: and the groove structure is formed in the piezoelectric film structure at the gap of the interdigital electrode.
The present invention also provides an acoustic wave resonator, including:
a piezoelectric film structure comprising at least two stacked piezoelectric films, adjacent two piezoelectric films having different Euler angles therebetween, the piezoelectric coefficients of the piezoelectric films at the respective Euler angles being expressed as
The interdigital electrode is formed above the piezoelectric film structure or between any two adjacent piezoelectric films;
when an electric field is applied in the horizontal direction of the piezoelectric film structure and a thickness shear wave is excited, the piezoelectric coefficient e of each piezoelectric film at each Euler angle15Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films15The sign is opposite.
Optionally, the piezoelectric film has a piezoelectric coefficient at an euler angle (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
optionally, the acoustic wave resonator further includes: and at least one intermediate medium layer is formed between any two adjacent piezoelectric films.
Optionally, the thickness of each piezoelectric film is less than 20 μm, and the thickness ratio of two adjacent piezoelectric films is between 0.5 and 2.
Optionally, the piezoelectric films are made of the same material and include: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
Optionally, when the wavelength of an acoustic wave excited by the interdigital electrode is λ, the total thickness of the piezoelectric film structure is less than 0.25 λ, and the finger width of the interdigital electrode is less than or equal to 0.25 λ.
Optionally, the acoustic wave resonator further includes: a top dielectric layer; when the interdigital electrode is formed above the piezoelectric film structure, the top dielectric layer is formed above the piezoelectric film structure at the gap of the interdigital electrode; when the interdigital electrode is formed between any two adjacent piezoelectric films, the top dielectric layer is formed above the piezoelectric films at the gap of the interdigital electrode.
As described above, according to the acoustic wave resonator of the present invention, by setting the piezoelectric vectors/piezoelectric coefficients of the multiple piezoelectric films and the piezoelectric films, the total thickness of the piezoelectric film structure is not changed, the operating frequency of the device is greatly improved, and the mechanical structure stability and the power capacity of the device are ensured to be basically unchanged; under the condition that the working frequency of the device is basically unchanged, the whole thickness of the piezoelectric film structure can be increased, so that the mechanical structure stability and the power capacity of the device are greatly enhanced. The invention also realizes the suppression of stray waves introduced by the stacking of the multilayer piezoelectric films through the design of the middle dielectric layer.
Drawings
Fig. 1 is a schematic structural diagram of an acoustic wave resonator according to a first embodiment of the present invention.
Fig. 2 is a schematic structural diagram of another acoustic wave resonator according to a first embodiment of the present invention.
Fig. 3 is a schematic structural diagram of an acoustic wave resonator according to a comparison between the first embodiment and the second embodiment of the present invention.
Fig. 4 is a schematic diagram of admittance curves of finite element simulations of the acoustic wave resonator described in example 1 and comparative example 1 in the first embodiment of the present invention.
Fig. 5 is a schematic diagram showing admittance curves of finite element simulations of the acoustic wave resonators according to example 2-1, example 2-2 and comparative example 2 in the second embodiment of the present invention.
Fig. 6 is a schematic structural diagram of an acoustic wave resonator in a third embodiment of the present invention.
Fig. 7 is a schematic structural diagram of another acoustic wave resonator according to a third embodiment of the present invention.
Fig. 8 is a schematic structural diagram of an acoustic wave resonator according to a third embodiment of the present invention.
Fig. 9 shows schematic admittance curves of finite element simulations of the acoustic wave resonators described in example 3, comparative example 3-1, and comparative example 3-2 in the third embodiment of the present invention.
Description of the element reference numerals
100 bottom electrode
200 piezoelectric film structure
201-20n piezoelectric film
300 top electrode
300a interdigital electrode
400 middle dielectric layer
500 top dielectric layer
600 groove structure
700 support substrate
800 energy reflecting structure
801 low acoustic impedance layer
802 high acoustic impedance layer
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 9. It should be noted that the drawings provided in the present embodiment are only schematic and illustrate the basic idea of the present invention, and although the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation, the form, quantity and proportion of the components in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.
Example one
As shown in fig. 1 to 3, the present embodiment provides an acoustic wave resonator including:
a bottom electrode 100;
a piezoelectric film structure 200 formed above the bottom electrode 100;
a top electrode 300 formed above the piezoelectric film structure 200;
wherein the piezoelectric film structure 200 comprises at least two stacked piezoelectric films (201-20n), two adjacent piezoelectric films have different Euler angles, and the piezoelectric coefficients of the piezoelectric films at the Euler angles are expressed as
When a thickness shear wave is excited in the piezoelectric film structure 200, the piezoelectric vector of each of the piezoelectric films at the respective Euler angles
All satisfy the die length
And the piezoelectric vectors of two adjacent piezoelectric films
Located in different quadrants.
As an example, the piezoelectric film has a piezoelectric coefficient at euler angles (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
in this example, the piezoelectric vector of each piezoelectric film was adjusted by setting euler angles of the piezoelectric films
All satisfy the die length
And the piezoelectric vectors of two adjacent piezoelectric films
The acoustic wave resonator is positioned in different quadrants, so that the working frequency of the device is greatly improved under the condition that the total thickness of the piezoelectric film structure is basically unchanged, and the mechanical structure stability and the power capacity of the device are basically unchanged; in other words, the acoustic wave resonator according to this embodiment can increase the overall thickness of the piezoelectric film structure under the condition that the operating frequency is substantially unchanged, thereby greatly enhancing the mechanical structural stability and power capacity of the device.
As an example, each of the piezoelectric films has a thickness of less than 20 μm; further, each of the piezoelectric films has a thickness of less than 2 μm.
As an example, the thickness ratio of two adjacent piezoelectric films is between 0.5 and 2 (both inclusive); further, the thickness ratio of two adjacent piezoelectric films is 1, that is, the thicknesses of the piezoelectric films are equal.
As an example, the materials of the piezoelectric films are the same, including: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
As an example, as shown in fig. 1 and 2, the acoustic wave resonator further includes: and at least one middle dielectric layer 400 formed between any two adjacent piezoelectric films for inhibiting stray waves with the maximum stress value at the junction of the two piezoelectric films, and simultaneously reducing the preparation difficulty of the acoustic wave resonator, improving the mechanical strength and improving the power capacity. Specifically, the material of the middle dielectric layer 400 is preferably a material that is easily obtained by deposition, such as silicon dioxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), and the like. It should be noted that the arrangement of the middle dielectric layer may result in the increase of the overall thickness of the acoustic wave resonator, so that the operating frequency of the acoustic wave resonator is slightly reduced; therefore, in practical application, the number and thickness of the intermediate dielectric layers need to be set by comprehensively considering the stray wave suppression effect and the working frequency.
As an example, the bottom electrode 100 includes: one of a planar electrode, an interdigitated electrode, or a polygonal electrode, the top electrode 300 comprising: one of a planar electrode, an interdigital electrode, or a polygonal electrode.
Specifically, in an example, as shown in fig. 1, when the top electrode is an interdigital electrode 300a, the acoustic wave resonator further includes: and a top dielectric layer 500 formed above the piezoelectric film structure 200 at the gap of the interdigital electrode 300a, for suppressing noise introduced by non-uniform device thickness due to the disposition of the interdigital electrode 300 a. The top dielectric layer 500 is preferably made of a material having an acoustic impedance close to that of the material of the interdigital electrode 300a, so that the top dielectric layer 500 and the interdigital electrode 300a form impedance matching, thereby maximally suppressing noise introduced by uneven device thickness. It should be noted that "the top dielectric layer 500 is formed on the piezoelectric film structure 200 at the gap of the interdigital electrode 300 a" means that "the top dielectric layer 500 is formed on the piezoelectric film structure at the uncovered region of the interdigital electrode".
Specifically, in another example, as shown in fig. 2, when the top electrode is an interdigital electrode 300a, the acoustic wave resonator further includes: a trench structure 600 formed in the piezoelectric film structure 200 at the gap of the interdigital electrode 300a for suppressing noise caused by a lateral electric field. The depth of the groove structure 600 may be less than the total thickness of the piezoelectric film structure 200, may be equal to the total thickness of the piezoelectric film structure 200, and may be greater than the total thickness of the piezoelectric film structure 200, which is not limited in this example. It should be noted that "the groove structure 600 is formed in the piezoelectric film structure 200 at the gap of the interdigital electrode 300 a" means that "the groove structure 600 is formed in the piezoelectric film structure at the uncovered region of the interdigital electrode 300 a".
Specifically, when the top electrode is the interdigital electrode 300a, the metallization ratio of the interdigital electrode can be set to suppress higher harmonics of a low order mode in a partial plane; of course, it is also possible to suppress higher harmonics of lower order modes in the partial plane by periodically or non-periodically changing the metallization ratio in the length direction of the interdigital electrode. In practice, the best metallization value can be obtained through a limited number of simulations, and of course, other methods of obtaining metallization values are also applicable to the present example.
As an example, the acoustic wave resonator further includes:
a support substrate 700 formed under the bottom electrode 100;
an energy reflecting structure 800 formed in the supporting substrate 700 or formed between the supporting substrate 700 and the bottom electrode 100 (see fig. 1-3, 6-8).
Specifically, in an example, the energy reflection structure 800 is a cavity formed in the support substrate 700 or formed between the support substrate 700 and the bottom electrode 100, and is configured to reflect energy of the acoustic wave propagating in the piezoelectric film structure 200 and prevent the acoustic wave from leaking to the support substrate 700. Optionally, when the energy reflecting structure 800 is a cavity, the acoustic wave resonator further includes: and a support layer (not shown) formed between the bottom electrode and the cavity for supporting the upper layer (i.e., the bottom electrode, the piezoelectric film structure, and the top electrode) and preventing the core area of the upper layer from being suspended to cause unstable or fragile structure. In a specific application, the thickness of the supporting layer may be set according to actual requirements, such as several micrometers to several hundred micrometers. It should be noted that, when a specific device is manufactured, a cavity penetrating through the supporting substrate may be formed by performing local back etching on the supporting substrate, a cavity may also be formed by performing front opening on an upper layer structure of the supporting substrate, and a cavity may further be formed by etching a sacrificial layer, which is not limited in this example.
Specifically, in another example, the energy reflection structure 800 is a bragg reflection layer (see fig. 8) formed between the support substrate 700 and the bottom electrode 100, and is used for reflecting energy of the acoustic wave propagating in the piezoelectric film structure 200 and preventing the acoustic wave from leaking to the support substrate 700. The Bragg reflection layer comprises at least one low acoustic impedance layer 801 and a high acoustic impedance layer 802; the total number of layers of the low acoustic impedance layer 801 and the high acoustic impedance layer 802 is greater than or equal to 3 and less than or equal to 10, so that the problem of process complexity increase caused by excessive number of layers is avoided while energy reflection is effectively realized. It is noted that the low acoustic impedance layer is typically placed in contact with the bottom electrode for a particular application. Alternatively, the low acoustic impedance layer is preferably a material with a low density and a small stiffness coefficient (i.e., Young's modulus), such as silicon dioxide (SiO)2) Quartz (Quartz), Glass (Glass), polymeric materials, and the like; the high acoustic impedance layer is preferably made of a material having a high density and a large stiffness coefficient (i.e., young's modulus), such as tungsten (W), gold (Au), platinum (Pt), Diamond (Diamond), aluminum nitride (AlN), molybdenum (Mo), or the like. In practical applications, the thickness setting of the low acoustic impedance layer and the thickness setting of the high acoustic impedance layer are both related to the propagation wavelength of the acoustic wave in the piezoelectric film structure in the corresponding high acoustic impedance layer or the corresponding low acoustic impedance layer, for example, the thickness of the low acoustic impedance layer is one fourth of the propagation wavelength of the acoustic wave in the piezoelectric film structure in the low acoustic impedance material, and the thickness of the high acoustic impedance layer is one fourth of the propagation wavelength of the acoustic wave in the piezoelectric film structure in the high acoustic impedance material.
Specifically, the material of the supporting substrate includes, but is not limited to, monocrystalline silicon, and the material of the bottom electrode and the top electrode includes, but is not limited to, aluminum (Al).
Referring to fig. 3 and 4, the performance of the acoustic resonator of the present embodiment is illustrated by taking the structure of the acoustic resonator of the single-crystal silicon supporting substrate/cavity/bottom electrode/piezoelectric film structure/top electrode, and taking the bottom electrode and the top electrode as the surface electrodes for comparison; of these, example 1 and comparative example 1 differ only in the structure of the piezoelectric film, and the other structures are the same.
Example 1: the piezoelectric film structure is a two-layer film structure; the bottom piezoelectric film and the top piezoelectric film are both made of single-crystal lithium niobate, the thicknesses of the bottom piezoelectric film and the top piezoelectric film are both 500nm, the Euler angles of the bottom piezoelectric film are (180 degrees, 90 degrees and 90 degrees), and the piezoelectric vectors of the bottom piezoelectric film and the top piezoelectric film are
The Euler angle of the top layer piezoelectric film is (0 deg., 90 deg., 0 deg.) and the piezoelectric vector
(the piezoelectric vector of the bottom piezoelectric film is positioned in the fourth quadrant, and the piezoelectric vector of the top piezoelectric film is positioned on the + Y axis, that is, the piezoelectric vectors of two adjacent piezoelectric films
Located in different quadrants).
Comparative example 1: the piezoelectric film structure is a single-layer film structure; wherein the piezoelectric film is made of single crystal lithium niobate, has a thickness of 1 μm, and has an Euler angle of (0 deg., 90 deg., 0 deg.) and a piezoelectric vector
Fig. 4 is admittance curves of finite element simulations obtained after performance tests of the acoustic wave resonators described in example 1 and comparative example 1, from which it can be seen that: neglecting the mass loading effect of the bottom electrode and the top electrode, on the premise of the same total thickness of the acoustic wave resonator, the piezoelectric film is stacked and the piezoelectric vector is measured
The working frequency of the acoustic wave resonator is greatly improved, and the electromechanical coupling coefficient is kept at a high level.
Example two
As shown in fig. 1 to 3, the present embodiment provides an acoustic wave resonator including:
a bottom electrode 100;
a piezoelectric film structure 200 formed above the bottom electrode 100;
a top electrode 300 formed above the piezoelectric film structure 200;
wherein the piezoelectric film structure 200 comprises at least two stacked piezoelectric films, two adjacent piezoelectric films have different euler angles therebetween, and the piezoelectric coefficients of the piezoelectric films at the respective euler angles are expressed as
When a thickness extensional wave is excited in the piezoelectric film structure 200, the piezoelectric coefficient e of each of the piezoelectric films at the respective Euler angles33Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films33The sign is opposite.
As an example, the piezoelectric film has a piezoelectric coefficient at euler angles (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
in this example, the piezoelectric coefficient e of each piezoelectric film was set by the multilayer piezoelectric film and the euler angle of each piezoelectric film33Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films33The signs are opposite, so that the total thickness of the piezoelectric film structure of the acoustic wave resonator in the embodiment is basically unchangedUnder the condition, the working frequency of the device is greatly improved, and the stability of the mechanical structure and the power capacity of the device are ensured to be basically unchanged; in other words, the acoustic wave resonator according to this embodiment can increase the overall thickness of the piezoelectric film structure under the condition that the operating frequency is substantially unchanged, thereby greatly enhancing the mechanical structural stability and power capacity of the device.
As an example, each of the piezoelectric films has a thickness of less than 20 μm; further, each of the piezoelectric films has a thickness of less than 2 μm.
As an example, the thickness ratio of two adjacent piezoelectric films is between 0.5 and 2 (both inclusive); further, the thickness ratio of two adjacent piezoelectric films is 1, that is, the thicknesses of the piezoelectric films are equal.
As an example, the materials of the piezoelectric films are the same, including: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
As an example, as shown in fig. 1 and 2, the acoustic wave resonator further includes: and at least one middle dielectric layer 400 formed between any two adjacent piezoelectric films for inhibiting stray waves with the maximum stress value at the junction of the two piezoelectric films, and simultaneously reducing the preparation difficulty of the acoustic wave resonator, improving the mechanical strength and improving the power capacity. Specifically, the material of the middle dielectric layer 400 is preferably a material that is easily obtained by deposition, such as silicon dioxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), and the like. It should be noted that the arrangement of the middle dielectric layer may result in the increase of the overall thickness of the acoustic wave resonator, so that the operating frequency of the acoustic wave resonator is slightly reduced; therefore, in practical application, the number and thickness of the intermediate dielectric layers need to be set by comprehensively considering the stray wave suppression effect and the working frequency.
As an example, the bottom electrode 100 includes: one of a planar electrode, an interdigitated electrode, or a polygonal electrode, the top electrode 300 comprising: one of a planar electrode, an interdigital electrode, or a polygonal electrode.
Specifically, in an example, as shown in fig. 1, when the top electrode is an interdigital electrode 300a, the acoustic wave resonator further includes: and a top dielectric layer 500 formed above the piezoelectric film structure 200 at the gap of the interdigital electrode 300a, for suppressing noise introduced by non-uniform device thickness due to the disposition of the interdigital electrode 300 a. The top dielectric layer 500 is preferably made of a material having an acoustic impedance close to that of the material of the interdigital electrode 300a, so that the top dielectric layer 500 and the interdigital electrode 300a form impedance matching, thereby maximally suppressing noise introduced by uneven device thickness. It should be noted that "the top dielectric layer 500 is formed on the piezoelectric film structure 200 at the gap of the interdigital electrode 300 a" means that "the top dielectric layer 500 is formed on the piezoelectric film structure 200 at the uncovered region of the interdigital electrode 300 a".
Specifically, in another example, as shown in fig. 2, when the top electrode is an interdigital electrode 300a, the acoustic wave resonator further includes: a trench structure 600 formed in the piezoelectric film structure 200 at the gap of the interdigital electrode 300a for suppressing noise caused by a lateral electric field. The depth of the groove structure 600 may be less than the total thickness of the piezoelectric film structure 200, may be equal to the total thickness of the piezoelectric film structure 200, and may be greater than the total thickness of the piezoelectric film structure 200, which is not limited in this example. It should be noted that "the groove structure 600 is formed in the piezoelectric film structure 200 at the inter-digital electrode gap" here means "the groove structure 600 is formed in the piezoelectric film structure 200 at the uncovered region of the inter-digital electrode 300 a".
Specifically, when the top electrode is the interdigital electrode 300a, the metallization ratio of the interdigital electrode can be set to suppress higher harmonics of a low order mode in a partial plane; of course, it is also possible to suppress higher harmonics of lower order modes in the partial plane by periodically or non-periodically changing the metallization ratio in the length direction of the interdigital electrode. In practice, the best metallization value can be obtained through a limited number of simulations, and of course, other methods of obtaining metallization values are also applicable to the present example.
As an example, the acoustic wave resonator further includes:
a support substrate 700 formed under the bottom electrode 100;
an energy reflecting structure 800 formed in the supporting substrate 700 or formed between the supporting substrate 700 and the bottom electrode 100 (see fig. 1-3, 6-8).
Specifically, in an example, the energy reflection structure 800 is a cavity formed in the support substrate 700 or formed between the support substrate 700 and the bottom electrode 100, and is configured to reflect energy of the acoustic wave propagating in the piezoelectric film structure 200 and prevent the acoustic wave from leaking to the support substrate 700. Optionally, when the energy reflecting structure 800 is a cavity, the acoustic wave resonator further includes: and a support layer (not shown) formed between the bottom electrode and the cavity for supporting the upper layer (i.e., the bottom electrode, the piezoelectric film structure, and the top electrode) and preventing the core area of the upper layer from being suspended to cause unstable or fragile structure. In a specific application, the thickness of the supporting layer may be set according to actual requirements, such as several micrometers to several hundred micrometers. It should be noted that, when a specific device is manufactured, a cavity penetrating through the supporting substrate may be formed by performing local back etching on the supporting substrate, a cavity may also be formed by performing front opening on an upper layer structure of the supporting substrate, and a cavity may further be formed by etching a sacrificial layer, which is not limited in this example.
Specifically, in another example, the energy reflection structure 800 is a bragg reflection layer (see fig. 8) formed between the support substrate 700 and the bottom electrode 100, and is used for reflecting energy of the acoustic wave propagating in the piezoelectric film structure 200 and preventing the acoustic wave from leaking to the support substrate 700. The Bragg reflection layer comprises at least one low acoustic impedance layer 801 and a high acoustic impedance layer 802; the total number of layers of the low acoustic impedance layer 801 and the high acoustic impedance layer 802 is greater than or equal to 3 and less than or equal to 10, so that the problem of process complexity increase caused by excessive number of layers is avoided while energy reflection is effectively realized. It is noted that the low acoustic impedance layer is typically placed in contact with the bottom electrode for a particular application. Optionally, the low acoustic impedance layer is preferablySelecting materials with low density and small stiffness coefficient (i.e. Young's modulus), such as silicon dioxide (SiO)2) Quartz (Quartz), Glass (Glass), polymeric materials, and the like; the high acoustic impedance layer is preferably made of a material having a high density and a large stiffness coefficient (i.e., young's modulus), such as tungsten (W), gold (Au), platinum (Pt), Diamond (Diamond), aluminum nitride (AlN), molybdenum (Mo), or the like. In practical applications, the thickness setting of the low acoustic impedance layer and the thickness setting of the high acoustic impedance layer are both related to the propagation wavelength of the acoustic wave in the piezoelectric film structure in the corresponding high acoustic impedance layer or the corresponding low acoustic impedance layer, for example, the thickness of the low acoustic impedance layer is one fourth of the propagation wavelength of the acoustic wave in the piezoelectric film structure in the low acoustic impedance material, and the thickness of the high acoustic impedance layer is one fourth of the propagation wavelength of the acoustic wave in the piezoelectric film structure in the high acoustic impedance material.
Specifically, the material of the supporting substrate includes, but is not limited to, monocrystalline silicon, and the material of the bottom electrode and the top electrode includes, but is not limited to, aluminum (Al).
Referring to fig. 3 and 5, the performance of the acoustic resonator of this embodiment is illustrated by taking the structure of the acoustic resonator of the single-crystal silicon supporting substrate/cavity/bottom electrode/piezoelectric film structure/top electrode, and taking the bottom electrode and the top electrode as the planar electrodes for example; of these, example 2-1, example 2-2, and comparative example 2 differ only in the structure of the piezoelectric film, and the other structures are the same.
Example 2-1: the piezoelectric film structure is a two-layer film structure; the bottom piezoelectric film and the top piezoelectric film are both made of single-crystal lithium niobate, the thicknesses of the bottom piezoelectric film and the top piezoelectric film are both 500nm, the Euler angle of the bottom piezoelectric film is (0 degrees, 54 degrees and 0 degrees), and the piezoelectric coefficient e is33Is 4.5C/m2The Euler angle of the top layer piezoelectric film is (0 DEG, 180 DEG, 0 DEG) and the piezoelectric coefficient e33is-1.3C/m2。
Example 2-2: the piezoelectric film structure is a three-layer film structure; wherein the materials of the bottom piezoelectric film, the middle piezoelectric film and the top piezoelectric film are all single-crystal lithium niobate, the thicknesses of the bottom piezoelectric film, the middle piezoelectric film and the top piezoelectric film are all 333nm, and the Euler angles of the bottom piezoelectric film are (0 degree, 54 degree and 0 degree)DEG) and piezoelectric coefficient e33Is 4.5C/m2The Euler angle of the interlayer piezoelectric film is (0 DEG, 180 DEG, 0 DEG) and the piezoelectric coefficient e33is-1.3C/m2The Euler angle of the top layer piezoelectric film is (0 DEG, 54 DEG, 0 DEG) and the piezoelectric coefficient e33Is 4.5C/m2。
Comparative example 2: the piezoelectric film structure is a single-layer film structure; wherein the piezoelectric film is made of single crystal lithium niobate, has a thickness of 1 μm, an Euler angle of (0 deg., 54 deg., 0 deg.) and a piezoelectric coefficient e33Is 4.5C/m2。
Fig. 5 is admittance curves of finite element simulations obtained after performance tests of the acoustic resonators described in example 2-1, example 2-2 and comparative example 2, from which it can be seen that: neglecting the mass loading effect of the bottom electrode and the top electrode, on the premise that the total thickness of the acoustic wave resonator is basically the same, the piezoelectric film is stacked and the piezoelectric coefficient e is obtained33The operating frequency of the acoustic wave resonator is greatly improved, and the more the number of layers of the piezoelectric film is, the higher the operating frequency of the acoustic wave resonator is. Therefore, on the premise that the total thickness of the piezoelectric film structure is not changed, the acoustic wave resonator realizes the great improvement of the working frequency, and ensures that the mechanical structure stability and the power capacity of the acoustic wave resonator are basically unchanged; in other words, under the condition that the working frequency of the acoustic wave resonator is basically unchanged, the overall thickness of the piezoelectric film structure can be increased through the design of the multilayer piezoelectric film, and the mechanical structure stability and the power capacity of the acoustic wave resonator are greatly enhanced on the premise that the electromechanical coupling coefficient is not seriously influenced.
EXAMPLE III
As shown in fig. 6 to 8, the present embodiment provides an acoustic wave resonator including:
the piezoelectric film structure 200 comprises at least two stacked piezoelectric films, wherein two adjacent piezoelectric films have different Euler angles, and the piezoelectric coefficients of the piezoelectric films at the Euler angles are expressed as
The interdigital electrode 300a is formed above the piezoelectric film structure 200 or between any two adjacent piezoelectric films;
when an electric field is applied in the horizontal direction of the piezoelectric film structure 200 and a thickness shear wave is excited, the piezoelectric coefficient e of each of the piezoelectric films at the respective Euler angles15Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films15The sign is opposite.
As an example, the piezoelectric film has a piezoelectric coefficient at euler angles (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
in this example, the piezoelectric coefficient e of each piezoelectric film was set by the multilayer piezoelectric film and the euler angle of each piezoelectric film15Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films15The signs are opposite, so that the working frequency of the device is greatly improved under the condition that the total thickness of the piezoelectric film structure of the acoustic wave resonator is basically unchanged, and the mechanical structure stability and the power capacity of the device are basically unchanged; in other words, the acoustic wave resonator according to this embodiment can increase the overall thickness of the piezoelectric film structure under the condition that the operating frequency is substantially unchanged, thereby greatly enhancing the mechanical structural stability and power capacity of the device.
As an example, each of the piezoelectric films has a thickness of less than 20 μm; further, each of the piezoelectric films has a thickness of less than 2 μm.
As an example, the thickness ratio of two adjacent piezoelectric films is between 0.5 and 2 (both inclusive); further, the thickness ratio of two adjacent piezoelectric films is 1, that is, the thicknesses of the piezoelectric films are equal.
As an example, the materials of the piezoelectric films are the same, including: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
As an example, when the wavelength of the acoustic wave excited by the interdigital electrode 300a is λ, the total thickness of the piezoelectric film structure 200 is less than 0.25 λ; further, the total thickness of the piezoelectric film structure 200 is less than 0.05 λ.
As an example, when the wavelength of the acoustic wave excited by the interdigital electrode 300a is λ, the finger width of the interdigital electrode 300a is less than or equal to 0.25 λ.
As an example, as shown in fig. 6 and 7, the acoustic wave resonator further includes: and at least one middle dielectric layer 400 formed between any two adjacent piezoelectric films for inhibiting stray waves with the maximum stress value at the junction of the two piezoelectric films, and simultaneously reducing the preparation difficulty of the acoustic wave resonator, improving the mechanical strength and improving the power capacity. Specifically, the material of the middle dielectric layer 400 is preferably a material that is easily obtained by deposition, such as silicon dioxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), aluminum oxide (Al2O3), and the like. It should be noted that the arrangement of the middle dielectric layer may result in the increase of the overall thickness of the acoustic wave resonator, so that the operating frequency of the acoustic wave resonator is slightly reduced; therefore, in practical application, the number and thickness of the intermediate dielectric layers need to be set by comprehensively considering the stray wave suppression effect and the working frequency.
As an example, the acoustic wave resonator further includes: a top dielectric layer 500 for suppressing noise introduced by uneven device thickness due to the disposition of the interdigital electrode 300 a; when the interdigital electrode 300a is formed above the piezoelectric film structure 200, the top dielectric layer 500 is formed above the piezoelectric film structure 200 at the gap of the interdigital electrode 300 a; when the interdigital electrode 300a is formed between any two adjacent piezoelectric films, the top dielectric layer 500 is formed above the piezoelectric films at the gap of the interdigital electrode 300 a. The top dielectric layer 500 is preferably made of a material having an acoustic impedance close to that of the material of the interdigital electrode 300a, so that the top dielectric layer 500 and the interdigital electrode 300a form impedance matching, thereby maximally suppressing noise introduced by uneven device thickness. It should be noted that "the top dielectric layer 500 is formed above the piezoelectric film structure 200 at the gap of the interdigital electrode 300 a" means "the top dielectric layer 500 is formed above the piezoelectric film structure 200 at the uncovered area of the interdigital electrode 300 a", and "the top dielectric layer 500 is formed above the piezoelectric film at the gap of the interdigital electrode 300 a" means "the top dielectric layer 500 is formed above the piezoelectric film at the uncovered area of the interdigital electrode 300 a".
As an example, higher harmonics of a low order mode in a partial plane can be suppressed by setting the metallization ratio of the interdigital electrode 300 a; of course, it is also possible to suppress higher harmonics of lower order modes in the partial plane by periodically or non-periodically changing the metallization ratio in the length direction of the interdigital electrode. In practice, the best metallization value can be obtained through a limited number of simulations, and of course, other methods of obtaining metallization values are also applicable to the present example.
As an example, the acoustic wave resonator further includes:
a support substrate 700 formed under the bottom electrode 100;
an energy reflecting structure 800 formed in the supporting substrate 700 or formed between the supporting substrate 700 and the bottom electrode 100 (see fig. 1-3, 6-8).
Specifically, in an example, the energy reflection structure 800 is a cavity formed in the support substrate 700 or formed between the support substrate 700 and the bottom electrode 100, and is configured to reflect energy of the acoustic wave propagating in the piezoelectric film structure 200 and prevent the acoustic wave from leaking to the support substrate 700. Optionally, when the energy reflecting structure 800 is a cavity, the acoustic wave resonator further includes: and a support layer (not shown) formed between the bottom electrode and the cavity for supporting the upper layer (i.e., the bottom electrode, the piezoelectric film structure, and the top electrode) and preventing the core area of the upper layer from being suspended to cause unstable or fragile structure. In a specific application, the thickness of the supporting layer may be set according to actual requirements, such as several micrometers to several hundred micrometers. It should be noted that, when a specific device is manufactured, a cavity penetrating through the supporting substrate may be formed by performing local back etching on the supporting substrate, a cavity may also be formed by performing front opening on an upper layer structure of the supporting substrate, and a cavity may further be formed by etching a sacrificial layer, which is not limited in this example.
Specifically, in another example, the energy reflection structure 800 is a bragg reflection layer (see fig. 8) formed between the support substrate 700 and the bottom electrode 100, and is used for reflecting energy of the acoustic wave propagating in the piezoelectric film structure 200 and preventing the acoustic wave from leaking to the support substrate 700. The Bragg reflection layer comprises at least one low acoustic impedance layer 801 and a high acoustic impedance layer 802; the total number of layers of the low acoustic impedance layer 801 and the high acoustic impedance layer 802 is greater than or equal to 3 and less than or equal to 10, so that the problem of process complexity increase caused by excessive number of layers is avoided while energy reflection is effectively realized. It is noted that the low acoustic impedance layer is typically placed in contact with the bottom electrode for a particular application. Alternatively, the low acoustic impedance layer is preferably a material with a low density and a small stiffness coefficient (i.e., Young's modulus), such as silicon dioxide (SiO)2) Quartz (Quartz), Glass (Glass), polymeric materials, and the like; the high acoustic impedance layer is preferably made of a material having a high density and a large stiffness coefficient (i.e., young's modulus), such as tungsten (W), gold (Au), platinum (Pt), Diamond (Diamond), aluminum nitride (AlN), molybdenum (Mo), or the like. In practical applications, the thickness setting of the low acoustic impedance layer and the thickness setting of the high acoustic impedance layer are both related to the propagation wavelength of the acoustic wave in the piezoelectric film structure in the corresponding high acoustic impedance layer or the corresponding low acoustic impedance layer, for example, the thickness of the low acoustic impedance layer is one fourth of the propagation wavelength of the acoustic wave in the piezoelectric film structure in the low acoustic impedance material, and the thickness of the high acoustic impedance layer is one fourth of the propagation wavelength of the acoustic wave in the piezoelectric film structure in the high acoustic impedance material.
Specifically, the material of the supporting substrate includes, but is not limited to, monocrystalline silicon, and the material of the bottom electrode and the top electrode includes, but is not limited to, aluminum (Al).
Referring to fig. 8 and fig. 9, the performance of the acoustic wave resonator described in this embodiment is illustrated by taking an acoustic wave resonator structure of a single crystal silicon supporting substrate/bragg reflector/piezoelectric film structure/aluminum metal interdigital electrode (interdigital electrode thickness is 100nm, metallization rate is 10%) as an example; the example 3 and the comparative example 3-1 are different only in the structure of the piezoelectric film and the other structures are the same, and the comparative example 3-2 is the same as the example 3 in that only an intermediate medium layer is additionally arranged and the other structures are the same.
Example 3: the piezoelectric film structure is a two-layer film structure; the bottom piezoelectric film and the top piezoelectric film are both made of single-crystal lithium niobate, the thicknesses of the bottom piezoelectric film and the top piezoelectric film are both 500nm, the Euler angle of the bottom piezoelectric film is (0 degrees, 142 degrees and 0 degrees), and the piezoelectric coefficient e is15is-4.48C/m2The Euler angle of the top layer piezoelectric film is (90 DEG, 0 DEG) and the piezoelectric coefficient e15Is 3.7C/m2。
Comparative example 3-1: the piezoelectric film structure is a single-layer film structure; wherein the piezoelectric film is made of single crystal lithium niobate, has a thickness of 1 μm, an Euler angle of (90 °, 0 °, 0 °), and a piezoelectric coefficient e15Is 3.7C/m2。
Comparative example 3-2: the piezoelectric film structure is a two-layer film structure, and an intermediate medium layer is additionally arranged between the two piezoelectric films; the bottom piezoelectric film and the top piezoelectric film are both made of single-crystal lithium niobate, the thicknesses of the bottom piezoelectric film and the top piezoelectric film are both 500nm, the Euler angle of the bottom piezoelectric film is (0 degrees, 142 degrees and 0 degrees), and the piezoelectric coefficient e is15is-4.48C/m2The Euler angle of the top layer piezoelectric film is (90 DEG, 0 DEG) and the piezoelectric coefficient e15Is 3.7C/m2The intermediate dielectric layer is 150nm SiO2And (3) a layer.
Fig. 9 is admittance curves of finite element simulations obtained after performance tests of the acoustic resonators described in example 3, comparative example 3-1 and comparative example 3-2, from which it can be seen that: neglecting the mass loading effect of the interdigital electrodeOn the premise of the same total thickness of the resonator, by stacking the piezoelectric films and the piezoelectric coefficient e15The working frequency of the acoustic wave resonator is greatly improved, and the electromechanical coupling coefficient keeps the original level; however, since the stack of the two-layer film structure introduces more stray waves (see fig. 9, continuous 3 small clutter appears on the left side of the resonance point), the stray waves can be effectively suppressed by additionally arranging an intermediate medium layer between the bottom-layer piezoelectric film and the top-layer piezoelectric film, which can be seen from the fact that the stray waves on the left side of the resonance point in fig. 9 are completely suppressed.
In summary, according to the acoustic wave resonator of the present invention, through the multiple piezoelectric films and the setting of the piezoelectric vector/piezoelectric coefficient of each piezoelectric film, under the condition that the total thickness of the piezoelectric film structure is not changed, the working frequency of the device is greatly improved, and the mechanical structure stability and the power capacity of the device are ensured to be basically unchanged; under the condition that the working frequency of the device is basically unchanged, the whole thickness of the piezoelectric film structure can be increased, so that the mechanical structure stability and the power capacity of the device are greatly enhanced. The invention also realizes the suppression of stray waves introduced by the stacking of the multilayer piezoelectric films through the design of the middle dielectric layer. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value. The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (15)
1. An acoustic wave resonator, comprising:
a bottom electrode;
the piezoelectric film structure is formed above the bottom electrode;
a top electrode formed over the piezoelectric film structure;
wherein the piezoelectric film structure comprises at least two stacked piezoelectric films, different Euler angles are formed between two adjacent piezoelectric films, and the piezoelectric coefficients of the piezoelectric films at the respective Euler angles are expressed as
When a thickness shear wave is excited in the piezoelectric film structure, the piezoelectric vectors of the piezoelectric films at respective Euler angles
All satisfy the die length
And the piezoelectric vectors of two adjacent piezoelectric films
Located in different quadrants;
when a thickness extensional wave is excited in the piezoelectric film structure, the piezoelectric coefficient e of each piezoelectric film at each Euler angle33Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films33The sign is opposite.
2. The acoustic resonator according to claim 1, wherein the piezoelectric film has a piezoelectric coefficient at an euler angle (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
3. the acoustic resonator according to claim 1, further comprising: and at least one intermediate medium layer is formed between any two adjacent piezoelectric films.
4. The acoustic resonator according to claim 1, wherein each of the piezoelectric films has a thickness of less than 20 μm, and a thickness ratio of the adjacent two piezoelectric films is in a range of 0.5 to 2.
5. The acoustic resonator according to claim 1, wherein the materials of the piezoelectric films are the same, and comprising: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
6. The acoustic resonator according to claim 1, wherein the bottom electrode comprises: one of a face electrode, an interdigitated electrode, or a polygonal electrode, the top electrode comprising: one of a planar electrode, an interdigital electrode, or a polygonal electrode.
7. The acoustic resonator according to claim 6, wherein when the top electrode is an interdigital electrode, the acoustic resonator further comprises: and the top dielectric layer is formed above the piezoelectric film structure at the gap of the interdigital electrode.
8. The acoustic resonator according to claim 6, wherein when the top electrode is an interdigital electrode, the acoustic resonator further comprises: and the groove structure is formed in the piezoelectric film structure at the gap of the interdigital electrode.
9. An acoustic wave resonator, comprising:
a piezoelectric film structure comprising at least two stacked piezoelectric films, adjacent two piezoelectric films having different Euler angles therebetween, the piezoelectric coefficients of the piezoelectric films at the respective Euler angles being expressed as
The interdigital electrode is formed above the piezoelectric film structure or between any two adjacent piezoelectric films;
when an electric field is applied in the horizontal direction of the piezoelectric film structure and a thickness shear wave is excited, the piezoelectric coefficient e of each piezoelectric film at each Euler angle15Are all greater than 0.5C/m2And the piezoelectric coefficients e of two adjacent piezoelectric films15The sign is opposite.
10. The acoustic resonator according to claim 9, wherein the piezoelectric film has a piezoelectric coefficient at an euler angle (α, β, γ)
Wherein e is0Is the piezoelectric coefficient of the piezoelectric film under Euler angle (0, 0, 0),
11. the acoustic resonator according to claim 9, further comprising: and at least one intermediate medium layer is formed between any two adjacent piezoelectric films.
12. The acoustic resonator according to claim 9, wherein each of the piezoelectric films has a thickness of less than 20 μm, and a thickness ratio of the adjacent two piezoelectric films is between 0.5 and 2.
13. The acoustic resonator according to claim 9, wherein the materials of the piezoelectric films are the same, and comprising: one of single crystal lithium niobate, single crystal lithium tantalate, or single crystal potassium niobate.
14. The acoustic resonator according to claim 9, wherein the total thickness of the piezoelectric film structure is less than 0.25 λ and the finger width of the interdigital electrode is 0.25 λ or less at an acoustic wave excited by the interdigital electrode.
15. The acoustic resonator according to claim 9, further comprising: a top dielectric layer; when the interdigital electrode is formed above the piezoelectric film structure, the top dielectric layer is formed above the piezoelectric film structure at the gap of the interdigital electrode; when the interdigital electrode is formed between any two adjacent piezoelectric films, the top dielectric layer is formed above the piezoelectric films at the gap of the interdigital electrode.
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