Patent ID: 7230367

Claim:
A piezoelectric resonator comprising: a substrate; a lower electrode provided on or above the substrate; a piezoelectric member provided on or above the lower electrode; an upper electrode provided on or above the piezoelectric member; and a cavity provided below a vibration member including the lower electrode, the piezoelectric member, and the upper electrode, wherein where a resonance frequency of vibration with a thickness of the vibration member being a half of a wavelength is taken as fr 1 , an average of ultrasonic velocity in a material forming the cavity is taken as Vc 2 , and a value determined based on the resonance frequency fr 1 and the average of ultrasonic velocity Vc 2 is λc (=Vc 2 /fr 1 ), a depth t 2 of the cavity is set as shown below, ( 2 ⁢ n - 1 ) × λ ⁢ ⁢ c 4 - λ ⁢ ⁢ c 8 ≦ t2 ≦ ( 2 ⁢ n - 1 ) × λ ⁢ ⁢ c 4 + λ ⁢ ⁢ c 8 , where n is an arbitrary natural number.