US Patent 7772742 Boundary acoustic wave device

A boundary acoustic wave device includes a first medium, a second medium, a third medium, and a fourth medium that are laminated in that order and, an electrode including an IDT electrode disposed at an interface between the first medium and the second medium, the temperature coefficient of delay time TCD of a boundary acoustic wave has a positive value, the fourth medium or the second medium has a positive temperature coefficient of sound velocity TCV, the first medium has a negative temperature coefficient of sound velocity TCV, and the sound velocity of transverse wave of the third medium is set to be less than the sound velocity of transverse wave of the fourth medium and/or the second medium.