Acoustic wave element and method for manufacturing same

Abstract

An acoustic wave element which can be reduced in size and produced relatively easily, practically used without using harmful substances, and can suppress a surface acoustic wave propagation loss, which has an excellent temperature coefficient of frequency and a velocity dispersion characteristic, and with which an increase in the reflection coefficient of interdigital transducers can be suppressed, and a method for manufacturing the acoustic wave element are provided. The acoustic wave element includes a pair of electrodes provided on both surfaces of a piezoelectric substrate, and a dielectric film provided on a first surface of the piezoelectric substrate so as to cover the electrode. The acoustic wave element alternatively includes interdigital transducers provided on a first surface of the piezoelectric substrate, and a dielectric film provided on the interdigital transducers, a gap between the interdigital transducers, and/or a second surface of the piezoelectric substrate.

Claims

1. An acoustic wave element comprising: a piezoelectric substrate; a pair of electrodes respectively provided on both surfaces of the piezoelectric substrate; and a dielectric film provided on at least any one surface of the piezoelectric substrate so as to cover an electrode provided on the surface, wherein the piezoelectric substrate is a 33° to 39° rotated Y-cut X-propagation LiNbO.sub.3 substrate, a 161° to 167° rotated Y-cut X-propagation LiNbO.sub.3 substrate, an LiNbO.sub.3 substrate, a 44° to 50° rotated Y-cut X-propagation LiTaO.sub.3 substrate, a 162° to 168° rotated Y-cut X-propagation LiTaO.sub.3 substrate, an LiTaO.sub.3 substrate, a langasite substrate, a quartz substrate, a ZnO substrate, a piezoelectric ceramics substrate, an AlN thin film substrate, a ZnO thin film substrate, a piezoelectric ceramics thin film substrate, or a ScAlN thin film substrate, in the dielectric film, an acoustic velocity of a propagating transverse wave is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate, and a surface acoustic wave velocity is 1010 m/s or more, and the dielectric film includes a (Bi.sub.2O.sub.3)x(SiO.sub.2 or GeO.sub.2).sub.(1-x) film wherein X is 0.3 to 1.0, a compound film including Bi, a BSO film, a BGO film, an In.sub.2O.sub.3 film, or a compound film including In.

2. The acoustic wave element according to claim 1, wherein an acoustic wave propagates in a direction perpendicular to each surface of the piezoelectric substrate, and a temperature coefficient of frequency is in a range from −20 ppm/° C. to +5 ppm/° C.

3. The acoustic wave element according to claim 1, wherein in each electrode, an acoustic velocity of a propagating transverse wave is ⅔ times or less of the acoustic velocity of the slow transverse wave propagating through the piezoelectric substrate, and the surface acoustic wave velocity is 1010 m/s or more.

4. The acoustic wave element according to claim 1, wherein h/λ.sub.eff =0.005 to 0.3 and H/λ.sub.eff =0.01 to 0.3 are satisfied where λ.sub.eff represents a wavelength of an acoustic wave propagating through the piezoelectric substrate, h represents a thickness of the each electrode or each of the interdigital transducers, and H represents a film thickness of the dielectric film.

5. The acoustic wave element according to claim 1, wherein each electrode or the interdigital transducers include an electrode film made of Au, Au/Cr, Ag, Ag/Cr, Bi, Bi/Cr, In, or an alloy of two or more thereof, or made of Al, Zn, Ru, Cr, Cu, Cu/Cr, Pt, Pt/Ti, or an alloy of two or more thereof, or made of Al, Zn, Ru, Cr, Cu, Cu/Cr, Pt, Pt/Cr, Pt/Ti, or an alloy of two or more thereof on Au, Au/Cr, Ag, Ag/Cr, Bi, Bi/Cr, In, or an alloy of two or more thereof.

6. The acoustic wave element according to claim 1, wherein a SiO.sub.2 film or a dielectric film for temperature compensation is provided between the piezoelectric substrate provided with each electrode or the interdigital transducers and the dielectric film, or a SiO.sub.2 film is provided on the dielectric film.

7. A method for manufacturing an acoustic wave element according to claim 1, the method comprising: vapor-depositing each electrode or the interdigital transducers, and/or the dielectric film at a temperature higher than a central operating temperature of the acoustic wave element by 100° C. or more, or at a temperature lower than the central operating temperature of the acoustic wave element by 100° C. or more.

8. An acoustic wave element comprising: a piezoelectric substrate; interdigital transducers provided on a first surface of the piezoelectric substrate; and a dielectric film provided on the interdigital transducers, wherein the piezoelectric substrate is a −10° to 75° rotated Y-cut X-propagation LiNbO.sub.3 substrate, a 120° to 170° rotated Y-cut X-propagation LiNbO.sub.3 substrate, a Y-Z LiNbO.sub.3 substrate, an X-cut 35° to 45° Y-propagation LiNbO.sub.3 substrate, an X-cut 160° to 175° Y-propagation LiNbO.sub.3 substrate, an LiNbO.sub.3 substrate, a −10° to 60° rotated Y-cut X-propagation LiTaO.sub.3 substrate, an X-cut 35° to 45° Y-propagation LiTaO.sub.3 substrate, an LiTaO.sub.3 substrate, a langasite substrate, a quartz substrate, a ZnO substrate, a piezoelectric ceramics substrate, an AN thin film substrate, a ZnO thin film substrate, a piezoelectric ceramics thin film substrate, or a ScAlN thin film substrate, in the dielectric film, an acoustic velocity of a propagating transverse wave is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate, and a surface acoustic wave velocity is 1010 m/s or more and the dielectric film includes a (Bi.sub.2O.sub.3)x(SiO.sub.2 or GeO.sub.2).sub.(1-x) film wherein X is 0.3 to 1.0, a compound film including Bi, a BSO film, a BGO film, an In.sub.2O.sub.3 film, or a compound film including In.

9. The acoustic wave element according to claim 8, wherein an acoustic wave propagates along each surface of the piezoelectric substrate, and/or in a direction perpendicular to each surface of the piezoelectric substrate, and a temperature coefficient of frequency is in a range from −20 ppm/° C. to +5 ppm/° C.

10. The acoustic wave element according to claim 8, wherein in the interdigital transducers, an acoustic velocity of a propagating transverse wave is ⅔ times or less of the acoustic velocity of the slow transverse wave propagating through the piezoelectric substrate, and the surface acoustic wave velocity is 1010 m/s or more.

11. The acoustic wave element according to claim 8, wherein when a number of electrodes alternately arranged in the interdigital transducers is 2N+1, and when λ.sub.N is an operating center wavelength of the propagating acoustic wave, V.sub.N is a velocity of the acoustic wave at the time, V.sub.n is a velocity of the acoustic wave when the wavelength of the acoustic wave is represented by λn=λ.sub.N[1+{N−(n−1)}δ] where n is 1 to 2N+1, a value of Nδ is 0.005 to 0.3, and a value of a.sub.n is 0.8 to 1.2, a width of an n-th electrode is represented by L.sub.n=X.sub.n/2=a.sub.n(λ.sub.n/4)×(V.sub.n/V.sub.N), and a center-to-center interval of neighboring electrodes is represented by X.sub.n=a.sub.n(λ.sub.n/2)×(V.sub.n/V.sub.N).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a sectional view showing an acoustic wave element in a first embodiment of the present invention.

(2) FIG. 2 is a sectional view showing a modified example of an acoustic wave element including a support substrate in the first embodiment of the present invention.

(3) FIG. 3 is a sectional view showing a modified example of an acoustic wave element including a dielectric film reflector having a multilayer structure in the first embodiment of the present invention.

(4) FIG. 4 shows an acoustic wave element in a second embodiment of the present invention, and (A) is a sectional view thereof, and (B) is a plan view thereof in which a dielectric film is omitted.

(5) FIG. 5 is a sectional view showing a modified example of an acoustic wave element including a dielectric film reflector having a multilayer structure in the second embodiment of the present invention.

(6) FIG. 6 is a sectional view showing a modified example of an acoustic wave element in which a dielectric film is not provided on a piezoelectric substrate surface of an interdigital transducer side, in the second embodiment of the present invention.

(7) FIG. 7 shows an acoustic wave element of a modified example in the second embodiment of the present invention in which a surface acoustic wave or a pseudo surface acoustic wave propagates along a surface of the piezoelectric substrate in the acoustic wave element, and (A) is a sectional view thereof, and (B) is a plan view thereof in which a dielectric film is omitted.

(8) FIG. 8 shows an acoustic wave element of a modified example in the second embodiment of the present invention in which a surface acoustic wave or a pseudo surface acoustic wave propagates along a surface of the piezoelectric substrate including a support substrate, and (A) is a sectional view thereof, and (B) is a plan view thereof in which a dielectric film is omitted.

(9) FIG. 9 shows an acoustic wave element of a modified example in the second embodiment of the present invention in which a pair of reflectors are provided so as to sandwich interdigital transducers, and (A) is a sectional view thereof, and (B) is a plan view thereof in which a dielectric film is omitted.

(10) FIG. 10 is a graph showing a change of a velocity of a longitudinal pseudo-acoustic wave (V.sub.eff) with respect to a film thickness ratio H/λ.sub.eff (where λ.sub.eff represents an operation wavelength) when an Al electrode is provided on a 36° rotated Y-cut X-propagation LiNbO.sub.3 substrate, and a dielectric film (film thickness: H) made of Bi.sub.2O.sub.3 is further provided thereon in the acoustic wave element in the first or second embodiment of the present invention.

(11) FIG. 11 is a graph showing a change of a velocity of a transverse pseudo-acoustic wave (V.sub.eff) with respect to a film thickness ratio H/λ.sub.eff (where λ.sub.eff represents an operation wavelength) when an Al electrode is provided on a 164° rotated Y-cut X-propagation LiTaO.sub.3 substrate, and a dielectric film (film thickness: H) made of Bi.sub.2O.sub.3 is further provided thereon in the acoustic wave element in the first or second embodiment of the present invention.

(12) FIG. 12 is a graph showing a change of a velocity of surface pseudo-acoustic wave (V.sub.eff) with respect to a film thickness ratio H/λ.sub.eff (where λ.sub.eff represents an operation wavelength) when an Al electrode is provided on a 36° rotated Y-cut X-propagation LiTaO.sub.3 substrate, and a dielectric film (film thickness: H) made of Bi.sub.2O.sub.3 is further provided thereon in the acoustic wave element in the first or second embodiment of the present invention.

(13) FIG. 13 is a graph showing a resonance admittance characteristic at (A) 20° C. and (B) 35° C. in an acoustic wave element having Cu/Cr-structured interdigital transducers on a conventional 36° rotated Y-cut X-propagation LiTaO.sub.3 substrate (the abscissa shows frequency).

(14) FIG. 14 is a graph showing a resonance admittance characteristic at (A) 20° C. and (B) 35° C. in an acoustic wave element having Cu/Cr-structured interdigital transducers on a 36° rotated Y-cut X-propagation LiTaO.sub.3 substrate and a dielectric film made of Bi.sub.2O.sub.3 is further provided thereon in the acoustic wave element in the second embodiment of the present invention (the abscissa shows frequency).

(15) FIG. 15 shows an acoustic wave element in a third embodiment of the present invention, and (A) is a sectional view thereof, and (B) is a plan view thereof in which a dielectric film is omitted.

(16) FIG. 16 is a sectional view of a configuration having a pair of electrodes in an acoustic wave element in a fourth embodiment of the present invention.

(17) FIG. 17 shows a configuration having interdigital transducers in the acoustic wave element in the fourth embodiment of the present invention, and (A) is a sectional view thereof, and (B) is a plan view thereof.

(18) FIG. 18 is a graph showing a resonance admittance characteristic at (A) 20° C. and (B) 30° C. in an acoustic wave element having interdigital transducers made of an Au/Cr metal film on a 10° rotated Y-cut X-propagation LiNbO.sub.3 substrate in the acoustic wave element in the fourth embodiment of the present invention (the abscissa shows frequency).

(19) FIG. 19 is a graph showing changes of (A) a propagation velocity of a pseudo surface acoustic wave, (B) propagation attenuation of a pseudo surface acoustic wave, and (C) an electromechanical coupling coefficient k.sup.2 of the piezoelectric substrate with respect to H/λ.sub.eff and h/λ.sub.eff (where λ.sub.eff is an operation wavelength) when an Al film is attached to the surface of a Y-cut X-propagation LiNbO.sub.3 substrate, and a BSO thin film (film thickness: H) or a Bi.sub.2O.sub.3 thin film (film thickness: H) is further attached thereto, and when an Au thin film (film thickness: h) is attached to Y-cut X-propagation LiNbO.sub.3 substrate in the acoustic wave element in the first to fourth embodiments of the present invention.

(20) FIG. 20 is a graph showing changes of (A) a propagation velocity of a pseudo surface acoustic wave, (B) propagation attenuation of a pseudo surface acoustic wave, and (C) an electromechanical coupling coefficient k.sup.2 of the piezoelectric substrate with respect to H/λ.sub.eff and h/λ.sub.eff (where λ.sub.eff is an operation wavelength) when an Al film is attached to a surface of a Y-cut X-propagation LiTaO.sub.3 substrate, a Bi.sub.2O.sub.3 thin film (film thickness: H) or a BSO thin film (film thickness: H) is further attached thereto, and when a Bi film (film thickness: h) is attached to a surface of a Y-cut X-propagation LiTaO.sub.3 substrate and an Al film is further attached thereto, in the acoustic wave element in the first to third embodiments of the present invention.

(21) FIG. 21 is a graph showing changes of (A) a propagation velocity with respect to rotation angle, (B) an electromechanical coupling coefficient k.sup.2 with respect to H/λ.sub.eff and h/λ.sub.eff (where λ.sub.eff is an operation wavelength), and (C) a propagation velocity with respect to H/λ.sub.eff when a rotation angle is 150° C. when an interdigital transducer of an Al film is attached to a surface of a 120° to 170° rotated Y-cut X-propagation LiNbO.sub.3 substrate, and a BSO thin film (film thickness: H) is further attached thereto, in the acoustic wave element in the first to fourth embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(22) Hereinafter, embodiments of the present invention will be described with reference to drawings.

Configuration of Acoustic Wave Element in the First Embodiment of the Present Invention

(23) FIGS. 1 to 3 show an acoustic wave element in the first embodiment of the present invention.

(24) As shown in FIG. 1, an acoustic wave element 10 in the first embodiment of the present invention includes a piezoelectric substrate 11, a pair of electrodes 12, and a dielectric film 13.

(25) The piezoelectric substrate 11 includes a substrate having a flat plate structure or a piezoelectric thin film. The piezoelectric substrate 11 includes a 33° to 39° rotated Y-cut X-propagation LiNbO.sub.3 substrate, a 161° to 167° rotated Y-cut X-propagation LiNbO.sub.3 substrate, an LiNbO.sub.3 substrate, a 44° to 50° rotated Y-cut X-propagation LiTaO.sub.3 substrate, a 162° to 168° rotated Y-cut X-propagation LiTaO.sub.3 substrate, an LiTaO.sub.3 substrate, a langasite substrate, a quartz substrate, a ZnO substrate, a piezoelectric ceramics substrate, an AlN thin film substrate, a ZnO thin film substrate, a piezoelectric ceramics thin film substrate, or a SLAIN thin film substrate.

(26) A pair of positive and negative electrodes 12 are provided to both surfaces 11a and 11b of the piezoelectric substrate 11, respectively. Each electrode 12 includes Au, Au/Cr, Ag, Ag/Cr, Bi, Bi/Cr, In, or an alloy of two or more thereof. At this time, in each electrode 12, acoustic velocity of a propagating transverse wave may be ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate, and the surface acoustic wave velocity may be 1010 m/s or more. Furthermore, each electrode 12 is formed of usual electrodes, and may include Al, Zn, Ru, Cr, Cu, Cu/Cr, Pt, Pt/Cr, Pt/Ti, or an alloy of two or more thereof. Furthermore, a combination of each electrode 12 and usual electrodes may be employed.

(27) The dielectric film 13 is provided so as to cover only electrode 12 provided on the surface of a first surface 11a of piezoelectric substrate 11. Dielectric film 13 includes a (Bi.sub.2O.sub.3).sub.X(SiO.sub.2 or GeO.sub.2).sub.(1-X) film [where X is 0.3 to 1.0], a compound film including Bi, a BSO film, a BGO film, an In.sub.2O.sub.3 film, or a compound film including In.

(28) In the dielectric film 13, the acoustic velocity of the transverse wave is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11, and the surface acoustic wave velocity is 1010 m/s or more. In the acoustic wave element 10, by applying a voltage between the electrodes 12, the acoustic wave propagates in the direction perpendicular to each of the surfaces of the piezoelectric substrate 11. Furthermore, in the acoustic wave element 10, the temperature coefficient of frequency is in a range from −20 ppm/° C. to +5 ppm/° C.

(29) The acoustic wave element 10 satisfies f.sub.0=V.sub.eff/λ.sub.eff, and L=(λ.sub.eff/2)×(2N+1) (N is an integer including 0), where f.sub.0 represents an operating resonance frequency, λ.sub.eff represents a wavelength (operation wavelength) of an acoustic wave propagating through the piezoelectric substrate 11, V.sub.eff represents a velocity of the acoustic wave, and L represents a total film thickness of the piezoelectric substrate 11, the dielectric film 13, and the electrode 12.

(30) Note here that as shown in FIG. 2, the acoustic wave element 10 includes dielectric film 13 on the first surface 11a of piezoelectric substrate 11 so as to cover electrode 12 provided on the surface and a portion on which the electrode 12 is not provided. Furthermore, the acoustic wave element 10 may include a pair of support substrates 21 at both ends of the second surface 11b of the piezoelectric substrate 11. In this case, acoustic wave causes vibration of the piezoelectric substrate 11 between the support substrates 21.

(31) Furthermore, as shown in FIG. 3, the acoustic wave element 10 includes dielectric films 13a and 13b on both surfaces 11a and 11b of piezoelectric substrate 11 so as to cover electrodes 12 provided on both surfaces, respectively. The dielectric film 13b provided on a second surface 11b side of piezoelectric substrate 11 has a multilayer structure including a first reflection film 22a and a second reflection film 22b, which reflect an acoustic wave. Furthermore, the acoustic wave element 10 may include a support substrate 21 provided so as to cover the dielectric film 13b having a multilayer structure.

Configuration of Acoustic Wave Element in the Second Embodiment of the Present Invention

(32) FIGS. 4 to 9 show an acoustic wave element in a second embodiment of the present invention.

(33) As shown in FIG. 4, an acoustic wave element 30 in the second embodiment of the present invention includes a piezoelectric substrate 11, interdigital transducers 31, and a dielectric film 13. Note here that in the following description, the same reference numerals are given to the same configurations as those in the acoustic wave element 10 in the first embodiment of the present invention, and redundant description thereof will be omitted.

(34) The piezoelectric substrate 11 is formed of a substrate having a flat plate structure or a piezoelectric thin film. The piezoelectric substrate 11 includes a −10° to 75° rotated Y-cut X-propagation LiNbO.sub.3 substrate, a 120° to 170° rotated Y-cut X-propagation LiNbO.sub.3 substrate, an LiNbO.sub.3 substrate, a −5° to 60° rotated Y-cut X-propagation LiTaO.sub.3 substrate, an LiTaO.sub.3 substrate, a langasite substrate, a quartz substrate, a ZnO substrate, an AlN thin film substrate, a ZnO thin film substrate, or a ScAlN thin film substrate.

(35) The interdigital transducers 31 is provided on the first surface 11a of the piezoelectric substrate 11. The interdigital transducers 31 is made of Au, Au/Cr, Ag, Ag/Cr, Bi, Bi/Cr, In, or an alloy of two or more thereof. At this time, the acoustic velocity of the transverse wave propagating in each of the interdigital transducers 31 may be ⅔ or less of the acoustic velocity of the slow transverse wave propagating in the piezoelectric substrate 11, and the surface acoustic wave velocity may be 1010 m/s or more. Furthermore, the interdigital transducers 31 may be made of usual electrodes, and may be made of Al, Zn, Ru, Cr, Cu, Cu/Cr, Pt, Pt/Cr, Pt/Ti, or an alloy of two or more thereof. Furthermore, a combination of the interdigital transducers 31 and usual electrodes may be employed.

(36) The interdigital transducer 31 includes a positive electrode side bus bar 41a, a negative electrode side bus bar 42a, a plurality of positive electrodes 41b, and a plurality of negative electrodes 42b. The positive electrode side bus bar 41a and negative electrode side bus bar 42a are arranged in parallel to each other at a predetermined interval. Positive electrodes 41b are provided at intervals along the positive electrode side bus bar 41a so as to vertically extend from the positive electrode side bus bar 41a toward the negative electrode side bus bar 42a. Negative electrodes 42b are provided at intervals along the negative electrode side bus bar 42a so as to vertically extend from the negative electrode side bus bar 42a toward the positive electrode side bus bar 41a. The positive electrodes 41b and negative electrodes 42b are alternately arranged along the positive electrode side bus bar 41a and the negative electrode side bus bar 42a, respectively, with equal or different periods so as not to be brought into contact with each other.

(37) The dielectric film 13 is provided on the interdigital transducers 31, the first surface 11a of piezoelectric substrate 11 in a gap between interdigital transducers 31, and/or a second surface 11b of the piezoelectric substrate 11. In the dielectric film 13, the acoustic velocity of each propagating transverse wave is ⅔ times or less of the acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11, and the surface acoustic wave velocity is 1010 m/s or more. In the acoustic wave element 30, the acoustic wave propagates along each surface of the piezoelectric substrate 11, and in the direction perpendicular to the surface of the piezoelectric substrate 11. Furthermore, in the acoustic wave element 30, the temperature coefficient of frequency is in a range from −20 ppm/° C. to +5 ppm/° C.

(38) Furthermore, as shown in FIG. 5, the acoustic wave element 30 includes the dielectric film 13b having a multilayer structure including the first reflection film 22a and the second reflection film 22b reflecting an acoustic wave also on the second surface 11b of the piezoelectric substrate 11. Furthermore, the acoustic wave element 30 may include a support substrate 21 provided so as to cover the dielectric film 13b having a multilayer structure. In this case, in the acoustic wave element 30, the acoustic wave propagates along each surface of the piezoelectric substrate 11. Furthermore, as shown in FIG. 6, the acoustic wave element 30 may not include a dielectric film 13 at a first surface 11a side of the piezoelectric substrate 11, and may include the dielectric film 13 only at a second surface 11b side of the piezoelectric substrate 11, and may include a reflection film 43 made of a dielectric substance and provided so as to cover the dielectric film 13, and a support substrate 21 so as to cover the reflection film 43. The reflection film 43 has a transverse wave velocity larger than that of the piezoelectric substrate 11, and can reflect an acoustic wave. In this case, in the acoustic wave element 30, an acoustic wave propagates along each surface of the piezoelectric substrate 11.

(39) Furthermore, as shown in FIG. 7, the acoustic wave element 30 may have a configuration in which the dielectric film 13 is made of a thin film, and a surface acoustic wave propagates along the surface of the piezoelectric substrate 11. Furthermore, as shown in FIG. 8, the acoustic wave element 30 may have a configuration in which a support substrate 21 is provided, the dielectric film 13 is formed of a thin film, and a surface acoustic wave or a pseudo surface acoustic wave propagates along the surface of the piezoelectric substrate 11. Furthermore, as shown in FIG. 9, the acoustic wave element 30 may include a resonator including a pair of reflectors 44 having multiple electrode fingers in which the reflectors 44 are provided on the first surface 11a of piezoelectric substrate 11 so as to sandwich the interdigital transducer 31. The dielectric film 13 is provided so as to cover not only the interdigital transducer 31 but also each reflector 44. Also in this case, the surface acoustic wave propagates along the surface of the piezoelectric substrate 11.

Action of Acoustic Wave Element in the First and Second Embodiments of the Present Invention

(40) Next, an action of the acoustic wave elements 10 and 30 in the first and second embodiments of the present invention will be described.

(41) The acoustic wave elements 10 and 30 can constitute, for example, an acoustic wave oscillator, an acoustic wave resonator, a bulk wave resonator, a piezoelectric thin film resonator, a surface acoustic wave oscillator, a surface acoustic wave resonator, an acoustic wave filter element, a surface acoustic wave filter element, a resonator having an excellent temperature characteristic, a delay line, a high sensitive sensor that does not need temperature compensation, and the like. Furthermore, acoustic waves to be used are a Rayleigh wave, a longitudinal wave, a transverse wave, a pseudo longitudinal wave mainly including a longitudinal wave, a pseudo transverse wave mainly including a transverse wave, a surface acoustic wave having propagation velocity slower than that of a slow transverse wave of the piezoelectric substrate, a Love wave, a Lamb wave, a pseudo surface acoustic wave having propagation velocity faster than the slow transverse wave of the piezoelectric substrate, or a pseudo longitudinal surface acoustic wave having propagation velocity faster than the fast transverse wave of the piezoelectric substrate.

(42) In the acoustic wave elements 10 and 30, the acoustic velocity of the transverse wave of at least the dielectric film 13 is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11. Therefore, when the acoustic wave element is constructed as an element for surface acoustic wave, it is possible to obtain a surface acoustic wave whose energy radiation of the acoustic wave leaking into the piezoelectric substrate 11 becomes zero, and to obtain a substrate having a large velocity dispersion characteristic. Furthermore, it is possible to achieve a rotation angle which allows propagation attenuation of the pseudo surface acoustic wave to be zero, and to obtain a substrate having a large velocity dispersion characteristic. Furthermore, the element can be reduced in size. Thus, when the surface acoustic wave is used, the propagation loss can be suppressed, energy of the surface acoustic wave can be concentrated on the surface of the piezoelectric substrate 11, and the Q value and the velocity dispersion characteristic can be increased. Furthermore, since thicknesses of the electrode 12 and the dielectric film 13 can be reduced, fabrication becomes easy and size can be reduced.

(43) Furthermore, when the acoustic wave elements 10 and 30 are provided with a dielectric film 13, adjustment of the center frequency and temperature compensation can be carried out. Thus, for example, when a pair of the interdigital transducers 31 are provided, dielectric film 13 is provided on an interdigital transducer 31 having higher center frequency, the center frequency is adjusted. Thereby, the center frequency of surface acoustic wave excited or received by the interdigital transducers 31 can be made equal. Furthermore, with this method, frequency of the filter can be adjusted.

(44) Furthermore, the acoustic wave elements 10 and 30 invention may include a SiO.sub.2 film or a dielectric film for temperature compensation between the piezoelectric substrate 11 provided with each electrode 12 or the interdigital transducers 31, and the dielectric film 13, or may include a SiO.sub.2 film on the dielectric film 13. In this case, by using a very thin SiO.sub.2 film or dielectric film for temperature compensation, an excellent temperature characteristic can be obtained. The SiO.sub.2 film satisfies, for example, H/λ.sub.eff=0.005 to 0.15 where H represents a film thickness, and λ.sub.eff represents a wavelength of acoustic wave propagating through the piezoelectric substrate. Examples of the dielectric film for temperature compensation include SiOF, a langasite-based thin film, SiO.sub.2 including impurity, and the like.

Temperature Coefficient of Frequency (TCF)

(45) A temperature coefficient of frequency (TCF) of the acoustic wave elements 10 and 30 is given by the following formula:
TCF=TCV−α  (1).
Herein, TCV represents a velocity-temperature coefficient, and a represents a linear expansion coefficient in the propagation direction. TCV is given by the following formula (2),
TCV=[(V.sub.t1−T.sub.t2)/V.sub.t1]/(t.sub.1−t.sub.2)  (2)
wherein the velocity at temperature t.sub.1 is represented by V.sub.t1, and the velocity at temperature t.sub.2 is represented by V.sub.t2.

(46) In general, since many substances expand as temperature rises, α is a positive value. Furthermore, since a substance becomes softer as temperature rises, TCV becomes a negative value. TCF of LiNbO.sub.3 single crystal substrate used in the acoustic wave elements 10 and 30 is in the range from −50 ppm/° C. to −100 ppm/° C., and TCF of LiTaO.sub.3 single crystal substrate is in the range of −25 ppm/° C. to −50 ppm/° C. Thus, conventionally, in order to obtain zero TCF, a SiO.sub.2 thin film having a positive temperature coefficient of frequency is used.

Example 1

(47) When a dielectric film 13 (film thickness: H) made of Bi.sub.2O.sub.3 is provided on a pseudo longitudinal acoustic wave resonator on which Al films (thickness of a film: h) as a pair of electrodes 12 are provided on both surfaces 11a and 11b of a 36° rotated Y-cut X-propagation LiNbO.sub.3 piezoelectric substrate 11 at a film thickness ratio h/λ.sub.eff of 0.01 (herein, λ.sub.eff represents an operation wavelength) in a structure shown in FIG. 1, the velocity of the pseudo longitudinal acoustic wave (V.sub.eff) with respect to a film thickness ratio H/λ.sub.eff is obtained by simulation. The results are shown in FIG. 10. As shown in FIG. 10, it has been shown that as the film thickness ratio H/λ.sub.eff is reduced, the velocity of the longitudinal pseudo-acoustic wave (V.sub.eff) is largely increased, and a large negative velocity dispersion characteristic is shown.

(48) Similarly, when a dielectric film 13 (film thickness: H) made of Bi.sub.2O.sub.3 is provided on a transverse pseudo-acoustic wave resonator on which Al films (thickness of a film: h) as a pair of electrodes 12 are respectively provided on both surfaces 11a and 11b of a 164° rotated Y-cut X-propagation LiTaO.sub.3 piezoelectric substrate 11 at a film thickness ratio h/λ.sub.eff of 0.01, the velocity of the transverse pseudo-acoustic wave (V.sub.eff) with respect to a film thickness ratio H/λ.sub.eff is obtained by simulation. The results are shown in FIG. 11. As shown in FIG. 11, it has been shown that a large negative velocity dispersion characteristic is shown.

(49) Similarly, when a dielectric film 13 (film thickness: H) made of Bi.sub.2O.sub.3 is provided on a pseudo surface acoustic wave resonator on which Al films (thickness of a film: h) as a interdigital transducers 31 are provided on a surface 11a of a semi-infinite plane 36° rotated Y-cut X-propagation LiTaO.sub.3 substrate (piezoelectric substrate 11) at a film thickness ratio h/λ.sub.eff of 0.01, the velocity of the pseudo surface acoustic wave (V.sub.eff) with respect to a film thickness ratio H/λ.sub.eff is obtained by simulation. The results are shown in FIG. 12. As shown in FIG. 12, it has been shown that a large negative velocity dispersion characteristic is shown.

(50) Such a large negative velocity dispersion characteristic is considered to be because the acoustic velocity of the transverse wave propagating through the dielectric film 13 is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11. It has been shown that a large negative velocity dispersion characteristic is similarly shown in each electrode 12 or the interdigital transducer 31 when thickness of each electrode 12 or the interdigital transducer 31 is h.

(51) In a resonator and a transducer corresponding to FIGS. 1 to 9, and FIGS. 15 to 17, TCF of piezoelectric substrate 11, each electrode 12, an interdigital transducers 31, and a dielectric film 13 is, each singly, a positive value for α, and a negative value for TCV. Only negative TCF is obtained as a whole. In a structure of the acoustic wave element, a film thickness of the dielectric film 13, each electrode 12, and the interdigital transducers 31 is much smaller than a thickness of the support substrate 21 of the piezoelectric substrate 11. Therefore, due to values of the linear expansion coefficient in the propagation direction and in-plane direction of the piezoelectric substrate 11 and the support substrate 21, the dielectric film 13, each electrode 12, and the interdigital transducers 31 undergo thermal distortion due to changes in temperature. When the linear expansion coefficient in the propagation direction of the piezoelectric substrate 11 or the support substrate 21 is a positive value, when the temperature rises, λ.sub.eff is increased according to the size of the positive linear expansion coefficient. Therefore, by the increase of λ.sub.eff and thermal distortion of the dielectric film 13, each electrode 12, and the interdigital transducers 31, values H/λ.sub.eff and h/λ.sub.eff are reduced. At this time, from graphs in FIGS. 10 to 12, and 19 to 21, the value of V is increased, TCV by the velocity dispersion becomes a positive value, and TCV represented by the formula (2) is increased and brought near to a positive value. Therefore, when the dielectric film 13, each electrode 12, and the interdigital transducers 31 are provided, even when a film thickness of the dielectric film 13, each electrode 12, or the interdigital transducers 31 is small, the temperature coefficient of frequency is largely improved. In this way, in the acoustic wave elements 10 and 30, even when the temperature coefficient of frequency of the piezoelectric substrate 11, the support substrate 21, each electrode 12 or the interdigital transducers 31, and the dielectric film 13 are a negative value, when the velocity dispersion characteristic and thermal distortion are considered, the temperature coefficient of frequency that is near zero can be obtained.

(52) Note here that it is considered that changing temperature at the time of vapor-depositing each electrode 12, the interdigital transducers 31, and the dielectric film 13 can increase distortion in the dielectric film 13, and that the improvement effect of the temperature coefficient of frequency can be further increased. It is preferable that the vapor deposition temperature at this time is, for example, a temperature higher by 100° C. or more than the central operating temperature of the acoustic wave elements 10 and 30, or a temperature lower by 100° C. or more than the central operating temperature of the acoustic wave elements 10 and 30.

Example 2

(53) A conventional acoustic wave element having Cu/Cr-structured interdigital transducers 31 on a 36° rotated Y-cut X-propagation LiTaO.sub.3 substrate (piezoelectric substrate 11) was produced, and the resonance admittance characteristics at 20° C. and 35° C. were examined. The results are shown in FIGS. 13(A) and 13(B), respectively. Furthermore, an acoustic wave element 30 having Cu/Cr-structured interdigital transducers 31 on a 36° rotated Y-cut X-propagation LiTaO.sub.3 substrate (piezoelectric substrate 11), and further having a dielectric film 13 made of Bi.sub.2O.sub.3 thereon was made, and the resonance admittance characteristic at 20° C. and 35° C. was examined. The results are shown in FIGS. 14(A) and 14(B), respectively.

(54) When a temperature coefficient of frequency TCF is obtained from peak position at each temperature of the resonance admittance characteristic shown in FIG. 13, TCF is −25 ppm/° C. It has been shown that in the acoustic wave element which does not include dielectric film 13, and does not obtain a large dispersion characteristic, only a value that is substantially equal to TCF of the piezoelectric substrate 11 is obtained. On the contrary, when the temperature coefficient of frequency TCF is obtained from FIG. 14, TCF is −5 ppm/° C. It has been shown that by providing the dielectric film 13, the temperature coefficient of frequency is improved by +20 ppm/° C. Note here that the result of the velocity obtained from the acoustic wave element 30 of FIGS. 13 and 14 are shown in FIG. 12 with the mark “x”. As shown in FIG. 12, it has been shown that the values coincide well with theoretical value.

Configuration of Acoustic Wave Element in the Third Embodiment of the Present Invention

(55) FIG. 15 shows an acoustic wave element in a third embodiment of the present invention.

(56) As shown in FIG. 15, an acoustic wave element 50 in the third embodiment of the present invention includes a piezoelectric substrate 11, interdigital transducers 31, and a dielectric film 13. Note here that in the following description, the same reference numerals are given to the same configurations as those in the acoustic wave elements 10 and 30 in the first and second embodiments of the present invention, and redundant description thereof will be omitted.

(57) The interdigital transducer 31 is a distribution type. In the acoustic wave element 50, when a number of positive electrodes 41b and negative electrodes 42b that are alternately arranged in the interdigital transducer 31 is 2N+1, and when λ.sub.N is an operating center wavelength of the propagating acoustic wave, V.sub.N is a velocity of the acoustic wave at the time, V.sub.n is a velocity of the acoustic wave when the wavelength of the acoustic wave is represented by λn=λ.sub.N[1+{N−(n−1)}δ] (where n is 1 to 2N+1), a value of Nδ is 0.005 to 0.3, and a value of a.sub.n may be 0.8 to 1.2, a width of the n-th electrode is represented by L.sub.n=X.sub.n/2=a.sub.n(λ.sub.n/4)×(V.sub.n/V.sub.N), and a center-to-center interval of neighboring electrodes may be represented by X.sub.n=a.sub.n(X.sub.n/2)×(V.sub.n/V.sub.N). In this case, an acoustic wave transducer and a surface acoustic wave transducer in a wide frequency range can be obtained.

Configuration of Acoustic Wave Element in the Fourth Embodiment of the Present Invention

(58) FIGS. 16 and 17 show an acoustic wave element in a fourth embodiment of the present invention.

(59) As shown in FIGS. 16 and 17, an acoustic wave element 70 in the fourth embodiment of the present invention includes a piezoelectric substrate 11, and a pair of electrodes 12 or the interdigital transducers 31. Note here that in the following description, the same reference numerals are given to the same configurations as those in the acoustic wave elements 10 and 30 in the first and second embodiments of the present invention, and redundant description thereof will be omitted.

(60) In the form shown in FIG. 16, a pair of electrodes 12 are made of a metal electrode film, and are provided on both surfaces 11a and 11b of piezoelectric substrate 11, respectively. Each electrode 12 is made of Au, Au/Cr, Ag, Ag/Cr, Bi, Bi/Cr, In, Pb, Pb/Cr, or an alloy of two or more thereof. Furthermore, in each electrode 12, an acoustic velocity of a propagating transverse wave is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11, and the surface acoustic wave velocity is 1010 m/s or more. The acoustic wave element 70 satisfies h/λ.sub.eff=0.005 to 0.3, when a wavelength of the acoustic wave propagating through the piezoelectric substrate 11 is λ.sub.eff, and a thickness of each electrode 12 is h. Note here that each electrode 12 may be an electrode including a composition of a metal electrode film and usual electrode.

(61) Furthermore, in the form shown in FIG. 17, a piezoelectric substrate 11 has a parallel plate structure, and the interdigital transducer 31 is made of a metal electrode film and is formed on the first surface 11a of piezoelectric substrate 11. Alternatively, the piezoelectric substrate 11 has a semi-infinite flat structure, and the interdigital transducer 31 is made of a metal electrode film and is provided on the surface 11a of the piezoelectric substrate 11. The interdigital transducer 31 is made of Au, Au/Cr, Ag, Ag/Cr, Bi, Bi/Cr, In, or an alloy of two or more thereof. Furthermore, in the interdigital transducer 31, an acoustic velocity of a propagating transverse wave is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11, and the surface acoustic wave velocity is 1010 m/s or more. The acoustic wave element 70 satisfies h/λ.sub.eff=0.005 to 0.3, when λ.sub.eff represents a wavelength of the acoustic wave propagating through the piezoelectric substrate 11, and h represents a thickness of the interdigital transducer 31. Note here that the interdigital transducer 31 may be an electrode including a composition of a metal electrode film and usual electrode.

(62) Next, an action is described.

(63) In acoustic wave element 70, the acoustic velocity of a transverse wave of each electrode 12 or the interdigital transducers 31 formed of metal electrode film is ⅔ times or less of an acoustic velocity of a slow transverse wave propagating through the piezoelectric substrate 11. Therefore, when the acoustic wave element is constructed as an element for surface acoustic wave, it is possible to obtain a surface acoustic wave whose energy radiation of acoustic wave leaking into the piezoelectric substrate 11 becomes zero, and to obtain a substrate having a large velocity dispersion characteristic. Furthermore, it is possible to achieve a rotation angle which allows the propagation attenuation of the pseudo surface acoustic wave to be zero, and to obtain a substrate having a large velocity dispersion characteristic. Furthermore, the element can be reduced in size. Thus, when the surface acoustic wave is used, or when a pseudo surface acoustic wave whose propagation attenuation is zero is used, the propagation loss can be suppressed, and energy of the surface acoustic wave can be concentrated on the surface of the piezoelectric substrate 11, and the Q value and the velocity dispersion characteristic can be increased. In this way, without using the dielectric film, the velocity dispersion characteristic can be increased, and an excellent temperature coefficient of frequency can be obtained. Furthermore, it is not necessary to use harmful substances such as TeO.sub.2, so that practical use can be achieved using other highly safe materials.

(64) Note here that the acoustic wave element 70 may include a pair of support substrates respectively provided on both ends of the second surface 11b of the piezoelectric substrate 11. This corresponds to, for example, a structure in which dielectric film 13 is removed from FIG. 2. The structure allows the piezoelectric substrate 11 between the support substrates to vibrate by an acoustic wave. Furthermore, the acoustic wave element 70 may include a dielectric substance provided so as to cover the electrode 12 of the second surface 11b of piezoelectric substrate 11 and having a multilayer structure including the first reflection film and the second reflection film reflecting an acoustic wave, and a support substrate provided so as to cover the dielectric substance having a multilayer structure. This corresponds to, for example, a structure in which dielectric films 13a and 13b are removed from FIG. 3.

(65) Furthermore, the acoustic wave element 70 may include a dielectric substance provided so as to cover the second surface 11b of piezoelectric substrate 11 and having a multilayer structure including the first reflection film and the second reflection film reflecting an acoustic wave, and a support substrate provided so as to cover the dielectric substance having a multilayer structure. This corresponds to, for example, a structure in which dielectric film 13a is removed from FIG. 5, such that the acoustic wave propagates along each surface of the piezoelectric substrate 11. Furthermore, the acoustic wave element 70 may include a reflection film provided so as to cover the second surface 11b of piezoelectric substrate 11 and made of a dielectric substance, and a support substrate provided so as to cover the reflection film. The reflection film has a transverse wave velocity that is higher than that of the piezoelectric substrate 11 and can reflect an acoustic wave. This corresponds to, for example, a structure in which dielectric film 13 is removed from FIG. 6, and the acoustic wave propagates along each surface of the piezoelectric substrate 11. Furthermore, the acoustic wave element 70 may include a pair of reflectors made of multiple electrode fingers, and each reflector may include a resonator provided so as to sandwich interdigital transducers 31 with respect to the first surface 11a of piezoelectric substrate 11. This corresponds to, for example, a structure in which dielectric film 13 is removed from FIG. 9, such that the surface acoustic wave or the pseudo surface acoustic wave propagate along the surface of the piezoelectric substrate 11.

Example 3

(66) An acoustic wave element 70 having interdigital transducers 31 having an Au/Cr-structure on a 10° rotated Y-cut X-propagation LiNbO.sub.3 substrate (piezoelectric substrate 11) was produced, and the resonance admittance characteristic at 20° C. and 30° C. were examined. The results are shown in FIGS. 18(A) and 18(B), respectively. When a temperature coefficient of frequency TCF is obtained from peak position at each temperature of the resonance admittance characteristic shown in FIG. 18, TCF is −15 ppm/° C. When this result is compared with the results of that of acoustic wave elements having a conventional structure shown in FIG. 13, it has been shown that use of the interdigital transducer film as the interdigital transducer 31 improves the temperature coefficient of frequency by +30 ppm/° C. even without using a dielectric film.

Example 4

(67) Simulation was carried out with respect to a surface of the piezoelectric substrate 11 including a Y-cut X-propagation LiNbO.sub.3 substrate to which an Al film (film thickness: h.sub.Al) satisfying h.sub.Al/λ.sub.eff=0.01 was attached, and a BSO thin film (film thickness: H) or a Bi.sub.2O.sub.3 thin film (film thickness: H) as a dielectric film 13 was further attached thereon, and a surface of the piezoelectric substrate 11 including a Y-cut X-propagation LiNbO.sub.3 substrate to which an Au thin film (film thickness: h) of a metal film as an interdigital transducer 31 was attached. In the simulation, changes of the propagation velocity of the pseudo-acoustic surface relative to the H/λ.sub.eff and h/λ.sub.eff (herein, λ.sub.eff represents an operation wavelength), the propagation attenuation, and an electromechanical coupling coefficient k.sup.2 of the piezoelectric substrate 11 are obtained, respectively. The results are shown in FIGS. 19(A) to 19(C).

(68) As shown in FIG. 19(A), it has been shown that when h/λ.sub.eff is 0.01, in the Au thin film, the propagation velocity is reduced by about 350 m/s from 4100 m/s to 3700 m/s. Similarly, in the BSO thin film and the Bi.sub.2O.sub.3 thin film, it has been shown that the propagation velocity is reduced by about 150 m/s. It has been shown that by using BSO, Au, Bi.sub.2O.sub.3 thin films, when H/λ.sub.eff and h/λ.sub.eff are 0.01, a large velocity dispersion characteristic of 0.033≤(v.sub.o−v.sub.H)/v.sub.o≤0.09 obtained, where v.sub.o is a velocity of the surface acoustic wave when a film thickness of the thin film is zero, and v.sub.H is a velocity of the surface acoustic wave when a film thickness of the thin film is H and h.

(69) Furthermore, as shown in FIG. 19(B), it has been shown that, in the Au thin film, the propagation attenuation becomes zero when h/λ.sub.eff is 0.005 is more, and that in the BSO thin film and the Bi.sub.2O.sub.3 thin film, since an Al film satisfying h.sub.Al/λ.sub.eff=0.01 is attached, a surface acoustic wave whose propagation attenuation is zero can be obtained. Furthermore, as shown in FIG. 19(C), it has been shown that all thin films have the electromechanical coupling coefficient k.sup.2 larger than any conventional thin films.

(70) Next, simulation was carried out with respect to a surface of the piezoelectric substrate 11 including a Y-cut X-propagation LiTaO.sub.3 substrate to which an Al film as an electrode material (film thickness: h.sub.Al) satisfying h.sub.Al/λ.sub.eff=0.01 was attached, and a Bi.sub.2O.sub.3 thin film (film thickness: H) or a BSO thin film (film thickness: H) as a dielectric film 13 was further attached thereto, and a surface of the piezoelectric substrate 11 including a Y-cut X-propagation LiTaO.sub.3 substrate to which a Bi thin film of a conductor (film thickness: h) was attached, and an Al film (film thickness: h.sub.Al) satisfying h.sub.Al/λ.sub.eff=0.01 was further attached thereon. In the simulation, changes of the propagation velocity of the pseudo-acoustic surface relative to the H/λ.sub.eff and h/λ.sub.eff, the propagation attenuation, and an electromechanical coupling coefficient k.sup.2 of the piezoelectric substrate 11 are obtained, respectively. The results are shown in FIGS. 20(A) to 20 (C).

(71) As shown in FIG. 20(A), it has been shown that a larger velocity dispersion characteristic is obtained by using Bi, Bi.sub.2O.sub.3, and BSO thin films. Furthermore, as shown in FIG. 20(B), the Bi.sub.2O.sub.3 thin film and the BGO thin film, the propagation attenuation becomes zero, respectively, when H/λ.sub.eff is 0.06 or more, and in the Bi thin film, the propagation attenuation becomes zero when H/λ.sub.eff is 0.04 or more, and a surface acoustic wave with energy confined to the surface of the piezoelectric substrate 11 was obtained. Furthermore, as shown in FIG. 20(C), it has been shown that all thin films have the electromechanical coupling coefficient k.sup.2 larger than any conventional thin films. In this way, it has been shown that even when an Al film as an electrode material is sandwiched or loaded, by using a Bi thin film of a conductor, a Bi.sub.2O.sub.3 thin film or a BGO thin film of the dielectric film 13, a surface acoustic wave without propagation attenuation is obtained. Note here that since Bi is a conductor, it needs to be attached to the lower surface of an Al electrode.

(72) Next, simulation was carried out with respect to a surface of the piezoelectric substrate 11 including a Y-cut X-propagation LiNbO.sub.3 substrate (the acoustic velocity of propagating transverse wave is 4080 m/s) having a rotation angle of 120° to 170°, as the interdigital transducer 31, an Al thin film (film thickness: h) satisfying h/λ.sub.eff=0.01 was attached, and a BSO film (film thickness: H) was further attached thereon. In the simulation, changes of the propagation velocity with respect to the rotation angle, the electromechanical coupling coefficient k.sup.2 with respect to the rotation angle when H/λ.sub.eff is 0.02, and the propagation velocity with respect to H/λ.sub.eff when the rotation angle of 150° are obtained respectively. The results are shown in FIGS. 21(A) to 21(C).

(73) As shown in FIG. 21(A), it has been shown that when the rotation angle is in the range from 130° to 150°, the propagation velocity of the Rayleigh wave and that of the transverse surface wave are the same and are degenerated, and a substrate without spurious characteristic can be obtained. Furthermore, as shown in FIG. 21(B), it has been shown that a large electromechanical coupling coefficient k.sup.2 is obtained. Furthermore, as shown in FIG. 21(C), it has been shown that the velocity difference with respect to H/λ.sub.eff=0.01 is as large as 130 m/s, and a substrate whose temperature coefficient of frequency is largely improved is obtained.

REFERENCE SIGNS LIST

(74) 10: Acoustic wave element (First Embodiment) 11: Piezoelectric substrate 11a: First surface 11b: Second surface 12: Electrode 13: Dielectric film 21: Support substrate 22a: First reflection film 22b: Second reflection film 30: Acoustic wave element (Second Embodiment) 31: Interdigital transducer 41a: Positive electrode side bus bar 41b: Positive electrode 42a: Negative electrode side bus bar 42b: Negative electrode 43: Reflection film 44: Reflector 50: Acoustic wave element (Third Embodiment) 70: Acoustic wave element (Fourth Embodiment)