Patent ID: 7808344

Claim:
A boundary acoustic wave filter device comprising: a piezoelectric substrate made of LiNbO 3 having a principal plane obtained by rotating the Y-axis through about 15 degrees +−10 degrees; a dielectric substrate made of silicon oxide and laminated on the piezoelectric substrate; and an electrode structure arranged at a boundary between the piezoelectric substrate and the dielectric substrate; wherein the boundary acoustic wave filter device utilizes a boundary acoustic wave that propagates along the boundary; the electrode structure defines a longitudinally coupled resonator boundary acoustic wave filter portion that includes a plurality of IDTs arranged in a boundary acoustic wave propagating direction in which the boundary acoustic wave propagates, and a pair of reflectors arranged respectively on both sides of a region in which the plurality of IDTs are provided in the boundary acoustic wave propagating direction; in each of the plurality of IDTs, the overlap width of electrode fingers is W and the interval of electrode fingers is P, and a ratio of W/P is in a range of about 20 to about 45; and each IDT is defined by a metal thin film, a metallization ratio of each IDT is about 0.45 or less, and where the density of the metal thin film is ρ (g/cm 3 ), the thickness of an electrode is h (μm) and the interval of electrode fingers is P (μm), ρ×h/P is greater than or equal to about 1.2 (g/cm 3 ).