ACOUSTIC WAVE ELEMENTS, AND DUPLEXERS AND ELECTRONIC DEVICES USING SAME
An acoustic wave element that includes a piezoelectric body, an aluminum oxide layer disposed on the piezoelectric body, an electrode disposed on the aluminum oxide layer, and a protection film disposed on the aluminum oxide layer to cover the electrode. The piezoelectric body is formed of a piezoelectric material based on lithium niobate having Euler angles (φ, θ, ψ). The aluminum oxide layer is formed of Al 2 O 3 . The electrode is configured to excite a main acoustic wave having a wavelength λ. The protection film has a film thickness greater than 0.27λ. The Euler angles satisfy either ψ≦−2φ−3° or −2φ+3°≦ψ and both of −100°≦θ≦−60° and 2φ−2°≦ψ≦2φ+2°.
1 . An acoustic wave element comprising:
a piezoelectric body formed from a piezoelectric material based on lithium niobate, the piezoelectric body having Euler angles (φ, θ, ψ) satisfying either ψ≦−2φ−3° or −2φ+3°≦ψ and both of −100°≦θ≦−60° and 2φ−2°≦ψ≦2φ+2°;
an aluminum oxide layer formed from Al 2 O 3 disposed on the piezoelectric body;
an electrode disposed on the aluminum oxide layer, the electrode being configured to excite a main acoustic wave having a wavelength λ; and
a protection film disposed on the aluminum oxide layer to cover the electrode, the protection film having a film thickness greater than 0.27λ.
2 . The acoustic wave element of claim 1 wherein the protection film is formed from a silicon oxide film.
3 . A duplexer comprising:
a first filter including the acoustic wave element of claim 1 ; and
a second filter having a passband higher than that of the first filter.
4 . An electronic device comprising:
the acoustic wave element of claim 1 ; and
a circuit element connected to the acoustic wave element.
5 . The acoustic wave element of claim 2 wherein the protection film has a reverse temperature characteristic to that of the piezoelectric body.
6 . The acoustic wave element of claim 1 wherein the aluminum oxide layer is formed from sapphire and has a thickness greater than or equal to 0.001λ and less than or equal to 0.02λ.
7 . The acoustic wave element of claim 1 wherein the electrode is formed from elemental metals including aluminum, copper, silver, gold, titanium, tungsten, molybdenum, platinum, and chromium, an alloy including at least two of the elemental metals, or a laminated structure including at least two of the elemental metals.
8 . The acoustic wave element of claim 7 wherein the electrode has a thickness greater than or equal to 0.01λ and less than or equal to 0.15λ.
9 . The acoustic wave element of claim 8 wherein the electrode is a comb-shaped Inter-Digital Transducer electrode having electrode fingers and the wavelength λ is twice an average pitch of the electrode fingers.
10 . The acoustic wave element of claim 1 wherein the piezoelectric body has Euler angles (φ, θ, ψ) of (−3°, −90°, −3°).
11 . The acoustic wave element of claim 10 wherein the aluminum oxide layer is formed from sapphire and has a thickness of 0.006λ.
12 . The acoustic wave element of claim 11 wherein the electrode is formed from copper and has a thickness of 0.062λ.
13 . The acoustic wave element of claim 12 wherein the protection film has a thickness of 0.35λ.
14 . The acoustic wave element of claim 1 wherein the acoustic wave element has a resonant frequency and the Euler angles of the piezoelectric body suppress spurious signals at a frequency of approximately 1.3 times the resonant frequency.
15 . A method of forming an acoustic wave element comprising:
forming an aluminum oxide layer on a piezoelectric body, the piezoelectric body being formed from a piezoelectric material based on lithium niobate and having has Euler angles (φ, θ, ψ) satisfying either ψ≦−2φ−3° or −2®+3°≦ψ and both of −100°≦θ≦−60° and 2φ−2°≦ψ≦2φ−2°;
forming an Inter-Digital Transducer (IDT) electrode on the aluminum oxide layer, the IDT electrode being configured to excite a main acoustic wave having a wavelength k; and
forming a protection film on the aluminum oxide layer to cover the electrode, the protection film having a film thickness greater than 0.27λ.
16 . The method of claim 15 wherein forming the aluminum oxide layer includes forming an aluminum oxide layer having a thickness that is greater than or equal to 0.001λ and less than or equal to 0.02λ.
17 . The method of claim 16 wherein forming the IDT electrode on the aluminum oxide layer includes forming an IDT electrode having a thickness greater than or equal to 0.01λ and less than or equal to 0.15λ on the aluminum oxide layer.
18 . The method of claim 17 wherein the piezoelectric body has Euler angles (φ, θ, ψ) of (−3°, −90°, −3°).
19 . The method of claim 18 wherein forming the IDT electrode on the aluminum oxide layer includes forming a copper IDT electrode on the aluminum oxide layer having a thickness of 0.062λ.
20 . The method of claim 16 wherein forming the IDT electrode on the aluminum oxide layer includes forming an IDT electrode having a plurality of electrode fingers on the aluminum oxide layer, the plurality of electrode fingers having an average pitch that is one half λ.