Patent ID: 7586390

Claim:
A bulk acoustic wave resonator comprising: a substrate; a first electrode layer formed over one face of said substrate; a first layer formed over said first electrode layer; a piezoelectric layer formed over said first layer; and a second electrode layer formed over said piezoelectric layer; wherein both the first lattice mismatch, which is determined between a short edge of the lattice constituting a closest packed plane of a material consisting of said first layer and a short edge of the lattice constituting a closest packed plane of a material consisting of said piezoelectric layer, and the second lattice mismatch, which is determined between a long edge of the lattice constituting a closest packed plane of a material consisting of said first layer and a long edge of the lattice constituting a closest packed plane of a material consisting of said piezoelectric layer, are 7% or less; wherein a value of the elastic stiffness C 33 of a material constituting said first electrode layer is 300 GN/m 2 or more; wherein a lower surface of said first layer is in contact with an upper surface of said first electrode layer; wherein a lower surface of said piezoelectric layer is in contact with an upper surface of said first layer; wherein a thickness of said first layer is no greater 50 nm; and wherein the thickness of said first layer is thinner than a thickness of said first electrode layer.