Patent ID: 7898145

Claim:
A boundary acoustic wave device comprising: a piezoelectric substance made of LiNbO 3 having a surface obtained by rotating a Y axis by about 15°±10° as a primary surface; a dielectric substance made of a silicon oxide laminated to the piezoelectric substance; and an electrode structure disposed at a boundary between the piezoelectric substance and the dielectric substance and including an IDT arranged to utilize a boundary acoustic wave propagating along the boundary; wherein when a density of the IDT, a thickness thereof, a wavelength determined by a period of electrode fingers of the IDT, and a duty ratio thereof are represented by p (kg/m 3 ), H (μm), λ (μm), and x, respectively, x and a product of H/λ and ρ are set in a range that satisfies the following formula (1): ( H /λ) xρ> 70.7924( x+ 0.055) (−2.0884) +797.09 Formula (1); and the IDT includes an Au-based metal layer made of Au or an alloy primarily including Au and is made of a laminate metal film including a frequency adjusting film/Ti/Pt/the Au-based metal layer/Pt/Ti.