Patent ID: 8310321

Claim:
A tunable filter, comprising: a surface acoustic wave resonator including: a piezoelectric substrate made of LiNbO 3 with Euler angles of (0°, 80° to 130°, 0°) and including a recess provided in an upper surface thereof; and an IDT electrode including a metal material that is primarily made of at least a material selected from a group consisting of Au, Pt, W, Ta, Ag, Cu, Mo, and Ni and embedded in the recess; wherein when λ is a wavelength of a surface acoustic wave, a relationship among the metal from which the IDT electrode is primarily made, a lower limit of a film thickness of the electrode, and a duty is a relationship shown in Table 1, an upper limit of the film thickness of the electrode is a value shown in Table 1, and the duty is in a range from about 0.15 to about 0.85; and a variable capacitor connected with the surface acoustic wave resonator: TABLE 1 (X: Duty) Upper limit Electrode Lower limit of film thickness (λ) of film thickness (λ) Au 0.0381 − 0.0211X − 0.0222X 2 0.25 Pt 0.0501 − 0.0445X − 0.0031X 2 0.25 W 0.0748 − 0.0978X + 0.0444X 2 0.25 Ta 0.0739 − 0.0789X + 0.0222X 2 0.25 Ag 0.1287 − 0.1767X + 0.0667X 2 0.25 Cu 0.1883 − 0.23X + 0.0667X 2 0.25 Mo 0.1497 − 0.0990X 0.25 Ni 0.22112 − 0.13613X + 0.0439X 2 0.25.