Patent ID: 8525385

Claim:
A boundary acoustic wave device comprising: a piezoelectric substrate made of LiTaO 3 and including a groove in an upper surface thereof; an IDT electrode arranged such that at least a portion of the IDT electrode is buried in the groove of the piezoelectric substrate; a silicon oxide layer stacked on the piezoelectric substrate; and a dielectric layer made of a dielectric exhibiting a higher acoustic velocity than the silicon oxide layer; wherein the IDT electrode includes a main electrode layer made of a metal having a density of about 16 g/cm 3 or higher, and an auxiliary electrode layer made of a metal having a density of about 4 g/cm 3 or higher, but lower than 16 g/cm 3 ; and where a wavelength of a boundary acoustic wave excited by the IDT electrode is λ, a depth A of the groove corresponding to a partial length of the IDT electrode buried in the groove is within a range of about 0.1% to about 10% of λ, a film thickness B of the silicon oxide layer is within a range of about 20% to about 140% of λ, the density of the main electrode is denoted by C (g/cm 3 ), a thickness D of the main electrode layer is within a range of about 1% to about 10% of λ, the density of the auxiliary electrode is denoted by E (g/cm 3 ), a thickness F of the auxiliary electrode positioned above the main electrode layer is within a range of about 0% to about 10% of λ, and a duty ratio G of the IDT electrode is within a range of about 0.4 to about 0.7, θ of Euler angles (0°, θ, 0°) of the piezoelectric substrate made of LiTaO 3 is within a range of about (θ 0 −20°) or more to about (θ 0 +20°) or less with respect to θ 0 expressed by: θ 0 =65.53 G+ 0.7568 F+ 0.8454 E+ 7.091 D+ 1.609 C− 0.03789 B− 3.535 A+ 60.85.