Surface acoustic wave device

Abstract

A surface acoustic wave device (e.g., filter or convolver) is designed to increase an electromechanical coupling factor K and is basically configured by a substrate, a buffer layer, a piezoelectric layer and an electrode layer. Herein, the substrate is made of a bulk material (e.g., SrTiO ), which allows growth of a perovskite compound crystal being expressed by a general chemical formula of SrZO (where Z denotes an element such as Zr and Sn whose valence is 4). The buffer layer is formed on the substrate and is made of the perovskite compound crystal (e.g., SrZrO , SrSnO ), which has good lattice matching with KNbO . The piezoelectric layer is made of a KNbO single crystal and is formed on the buffer layer with a thickness of 500 nm or so. The electrode layer is formed on or below the piezoelectric layer. An interdigital transducer consisting of input and output electrodes is formed by patterning using photolithography technique being effected on the electrode layer, which is made of a metal material (e.g., Al). In addition, it is possible to form a temperature stabilization layer between the piezoelectric layer and electrode layer. The temperature stabilization layer is made of a material (SiO ) having a temperature coefficient reverse to a temperature coefficient of the piezoelectric layer so as to ease distortion being caused to occur due to differences in thermal expansion between the piezoelectric layer and electrode layer. Incidentally, the temperature stabilization layer has a prescribed thickness, which is approximately 1000 nm.