Thin-film piezoelectric resonator and thin-film piezoelectric filter using the same

Abstract

A thin-film piezoelectric resonator including a substrate (); a piezoelectric layer (), a piezoelectric resonator stack () with a top electrode () and bottom electrode (), and a cavity (). The piezoelectric resonator stack () has a vibration region () where the top electrode and bottom electrode overlap in the thickness direction, and the vibration region comprises a first vibration region, second vibration region, and third vibration region. When seen from the thickness direction, the first vibration region is present at the outermost side, the third vibration region is present at the innermost side and does not contact the first vibration region, and the second vibration region is interposed between the first vibration region and third vibration region. The resonance frequency of the primary thickness-longitudinal vibration of the vibration region () is fat the first vibration region, is fat the third vibration region, wherein fand fsatisfy a relationship of f<f, and is a value between fand fat the second vibration region, said value increasing from the outer portion contacting the first vibration region to the inner portion contacting the third vibration region.