Patent ID: 7737603

Claim:
A boundary acoustic wave device using a non-leaky propagation type boundary acoustic wave, comprising: a plurality of boundary acoustic wave elements, each boundary acoustic wave element including a single crystal substrate, a solid layer provided on the single crystal substrate, and interdigital electrodes arranged at a boundary between the single crystal substrate and the solid layer; wherein the single crystal substrates have a same cut angle; a propagation direction of a boundary acoustic wave of at least one of the boundary acoustic wave elements is different from that of at least one of the other boundary acoustic wave elements; a thickness of the solid layer is set such that energy of the boundary acoustic wave is not present on an outer surface of the single crystal substrate and is not present on an outer surface of the solid layer, the outer surface of the single crystal substrate and the outer surface of the solid layer are defined by respective surfaces of the single crystal substrate and the solid layer opposite to abutting surfaces of the single crystal substrate and the solid layer; a thickness of the electrodes is set so that the acoustic velocity of an SH type boundary acoustic wave is lower than the acoustic velocity of a slow transverse wave propagating through the solid layer and the acoustic velocity of a slow transverse wave propagating through the piezoelectric single crystal substrate; H/λ>8261.744ρ −1376 , when ρ (kg/m 3 ) represents the density of the electrodes, H represents the thickness of the electrodes, and λ represents the wavelength of a boundary wave which is defined by a placement period of electrode fingers of the interdigital electrodes; and ρ>3,745 kg/m 3 .