Patent ID: 7868519

Claim:
A piezoelectric resonator comprising: a substrate; a vibration portion including a piezoelectric thin film sandwiched between a pair of electrodes; and an acoustic reflector portion disposed between the substrate and the vibration portion, the acoustic reflector portion including: a plurality of low acoustic impedance layers made of a material having relatively low acoustic impedance and a plurality of high acoustic impedance layers made of a material having relatively high acoustic impedance, the low and high acoustic impedance layers being disposed alternately between the substrate and the vibration portion; and at least one adjustment layer disposed between one of the high acoustic impedance layers and one of the low acoustic impedance layers, the at least one adjustment layer having an acoustic impedance value between the acoustic impedance of the high acoustic impedance layers and the acoustic impedance of the low acoustic impedance layers; wherein the low acoustic impedance layers and the high acoustic impedance layers have compressive stresses, and the at least one adjustment layer has a tensile stress.