Patent ID: 8305163

Claim:
A tunable filter, comprising: a surface acoustic wave resonator including: a piezoelectric substrate including a recess in an upper surface thereof; an IDT electrode defined by an electrode material provided in the recess in the upper surface of the piezoelectric substrate; a ZnO film arranged to cover the upper surface of the piezoelectric substrate; and a variable capacitor connected with the surface acoustic wave resonator; wherein the piezoelectric substrate is a LiNbO 3 substrate with Euler angles of (0°, 100°+20°, 0°), and the electrode material defining the IDT electrode is one of Al, Ag, Pt, Au, Ta, W, Mo, Ni, or Cu; and the IDT electrode of the surface acoustic wave resonator is primarily made of an electrode layer made of Al, and when h is a thickness of the ZnO film and λ is a wavelength determined by a pitch of electrode fingers of the IDT electrode of the surface acoustic wave resonator, a normalized film thickness h/λ of the ZnO film is in a range from about 0.0007 to about 0.006.