Patent ID: 7884527

Claim:
A piezoelectric thin-film resonator comprising: a substrate; a lower electrode that is formed on the substrate; a piezoelectric film that is formed on the lower electrode and the substrate; and an upper electrode that is formed on the piezoelectric film, with the piezoelectric film being partially interposed between the lower electrode and the upper electrode, at least a part of an outer periphery of the piezoelectric film interposed between the lower electrode and the upper electrode overlapping substantially all of an outer periphery of a resonator portion formed by the upper electrode and the lower electrode facing each other across the piezoelectric film in a region from which the lower electrode extends outside the resonator portion, the at least part of the outer periphery of the piezoelectric film overlapping an outer periphery of the upper electrode, the lower electrode and the upper electrodes extending in opposite direction from the resonator portion, the lower electrode being exposed to a cavity below the resonator portion, wherein a portion, in which said at least part of the outer periphery of the piezoelectric film overlaps the outer periphery of the resonator portion and of the upper electrode, has an end that is located inside the cavity or that overlaps an end of the cavity, the piezoelectric film being exposed to air at the end of the portion, and the resonator portion being supported by the substrate via the lower electrode formed on the substrate in a region in which the lower electrode extends from the cavity and being supported by the substrate via the piezoelectric film formed on the substrate in a region in which the upper electrode extends from the cavity.