Patent ID: 7522020

Claim:
A boundary acoustic wave device comprising: a substrate having a first surface and a second surface opposed to the first surface; a first IDT electrode disposed on the first surface; a second IDT electrode disposed on the second surface; a first dielectric film extending over the first surface so as to cover the first IDT electrode; and a second dielectric film extending over the second surface so as to cover the second IDT electrode; wherein either the substrate or the first and second dielectric films have piezoelectric characteristics; the velocity of a slow transverse wave propagating in the substrate is greater than at least one of the velocity of a slow transverse wave propagating in the first dielectric film and the velocity of a slow transverse wave propagating in the second dielectric film; and the substrate has a thickness of about 3λ to about 100λ so as to prevent boundary acoustic waves propagating along the first surface from being combined with boundary acoustic waves propagating along the second surface.