Patent ID: 7432785

Claim:
A thin film resonator comprising: a membrane layer formed on a substrate; a lower electrode formed on the membrane layer; a piezoelectric layer formed on the lower electrode; an upper electrode formed on the piezoelectric layer, wherein a top and bottom of said lower electrode are surrounded by the membrane layer, wherein said lower electrode is made of a material having a higher modulus of elasticity in tension than the membrane layer; a mass loading layer disposed sandwiched between the lower electrode and the membrane layer and having a predetermined thickness; wherein said mass loading layer is made of a material having a higher modulus of elasticity in tension than the membrane layer and a lower modulus of elasticity in tension than the lower electrode, wherein a resonant frequency variation by a change of a thickness of the mass loading layer is smaller than that by a change of a thickness of the upper electrode and greater than that by a change of a thickness of the membrane layer, when the same level of thickness changes are made to the mass loading layer, the upper electrode and the membrane layer which originally have the same thickness.