Lamb wave device
A Lamb wave device includes a base substrate, a piezoelectric thin film which is provided on the base substrate and which has a floating portion floating above the base substrate, the floating portion having a first surface facing the base substrate and a second surface opposite to the first surface, and an IDT electrode disposed on at least one of the first and the second surfaces of the piezoelectric thin film. The piezoelectric thin film is made of LiTaO 3 or LiNbO 3 , and the c-axis of the piezoelectric thin film is set in approximately the same direction as that of a line substantially perpendicular to the first and the second surfaces of the piezoelectric thin film, and the crystal structure of the piezoelectric thin film is a rotation twin crystal having the c-axis functioning as the rotation axis.
1. A Lamb wave device comprising:
a base substrate;
a piezoelectric thin film provided on the base substrate and including a floating portion floating above the base substrate, the floating portion having a first surface facing the base substrate and a second surface opposite to the first surface; and
an IDT electrode disposed on at least one of the first and the second surfaces of the piezoelectric thin film; wherein
the piezoelectric thin film is made of one of LiTaO 3 and LiNbO 3 ; and
a c-axis of the piezoelectric thin film is set in approximately the same direction as that of a substantially perpendicular line to the first and the second surfaces of the piezoelectric thin film, and the crystal structure of the piezoelectric thin film is a rotation twin crystal having the c-axis functioning as the rotation axis.
2. The Lamb wave device according to claim 1 , wherein
the piezoelectric thin film is made of LiNbO 3 ;
the IDT electrode is made of one of Al and an alloy including Al as a primary component; and
when the thickness of the IDT electrode is represented by h, the thickness of the piezoelectric thin film is represented by d, and the wavelength of a usage mode of the Lamb wave is represented by λ, h and d satisfy one of the following conditions I to III:
0.01 ≦h/d≦ 0.24 and 0.090 ≦d/λ≦ 0.107 I
0.01 ≦h/d≦ 0 24 and 0.133 ≦d/λ≦ 0233 II
0.01 ≦h/d≦ 0.24 and 0.257 ≦d/λ≦ 0.300. III
3. The Lamb wave device according to claim 1 , wherein
the piezoelectric thin film is made of LiTaO 3 ;
the IDT electrode is made of one of Al and an alloy including Al as a primary component; and
when the thickness of the IDT electrode is represented by h, the thickness of the piezoelectric thin film is represented by d, and the wavelength of a usage mode of the Lamb wave is represented by λ, h and d satisfy one of the following conditions IV to VI:
0.01 ≦h/d≦ 0.26 and 0.093 ≦d/λ≦ 0.125 IV
0.01 ≦h/d≦ 0.26 and 0.141 ≦d/λ≦ 0.240 V
0.01 ≦h/d≦ 0.26 and 0.260 ≦d/λ≦ 0.300. VI
4. The Lamb wave device according to claim 1 , wherein the IDT electrode is disposed on the second surface of the piezoelectric thin film.
5. The Lamb wave device according to claim 1 , wherein the IDT electrode is disposed on the first surface of the piezoelectric thin film.