Acoustic wave device including scandium-containing aluminum mitride film

Abstract

An acoustic wave device includes a ScAlN film including a first and second principal surfaces opposed to each other, and a first excitation electrode on the first principal surface and a second excitation electrode on the second principal surface. The ScAlN film includes a first electrode vicinity region at a vicinity of the first electrode, a second electrode vicinity region at a vicinity of the second electrode, and a central region. Assuming that, among a longer diameter and a shorter diameter of a crystal grain in the ScAlN film when ellipse approximation is applied to the crystal grain, the shorter diameter is a crystal grain size, and an average value of the crystal grain size in each region is an average grain size R, the Rof the first electrode vicinity region is smaller than the Rof the central region.