Patent ID: 8710713

Claim:
A boundary acoustic wave device comprising: a multilayer structure including a first medium having piezoelectric characteristics, a non-electroconductive second medium, and a third medium through which slow transverse waves propagate at a lower acoustic velocity than slow transverse waves propagating through the first and second media, the first medium, the third medium and the second medium being stacked in that order; and an IDT disposed between the first medium and the third medium; wherein the IDT includes a metal layer made of a metal having a density ρ in the range of about 3000 kg/m 3 to about 21500 kg/m 3 ; and the IDT has electrode fingers arranged at a pitch of λ and has a thickness H 1 satisfying the relationship of approximately 0.006λ≦H 1 ≦0.2λ, and the third medium has a thickness H 2 satisfying the relationship of approximately H 1 <H 2 ≦0.7λ; and the thickness H 1 of the IDT is set such that an acoustic velocity of boundary acoustic waves is less than or equal to the lowest value of the acoustic velocities of longitudinal waves, fast transverse waves and slow transverse waves.