Patent ID: 8125123

Claim:
A piezoelectric thin film resonant element comprising a resonant portion and a non-resonant portion adjacent to the resonant portion, the resonant portion having a laminate structure including: a piezoelectric film having a predetermined plan-view shape; a lower electrode formed on a lower surface of the piezoelectric film and having an edge formed with an inclined portion which is inclined with respect to a surface of the film at a predetermined angle; an upper electrode formed on an upper surface of the piezoelectric film; and an additional film formed on the upper electrode at a position corresponding to the inclined portion of the lower electrode; the piezoelectric thin film resonant element also comprising a substrate supporting the resonant portion, wherein a cavity is provided under the lower electrode, the cavity extending through the resonant portion and into the non-resonant portion, and at least part of the additional film is disposed at a position offset from an end of the cavity toward a center of the cavity, wherein the resonant portion has a greater acoustic impedance at a part of the laminate structure corresponding to the inclined portion of the lower electrode than a part of the laminate structure inner than the inclined portion of the lower electrode.