PIEZOELECTRIC THIN FILM RESONATOR

摘要

In a piezoelectric resonator, a portion of a thin film unit is supported by a substrate. A portion of the thin film unit acoustically isolated from the substrate includes a) a vibration unit and b) an additional film. The vibration unit includes a piezoelectric film sandwiched between a pair of electrodes. The piezoelectric film is overlapped with the pair of electrodes in plan view. The additional film is disposed on one of the piezoelectric film and the electrodes so as to extend along at least a portion of the periphery of the vibration unit. When x (MN·second/m 3 ) denotes an acoustic impedance of the additional film defined by the square root of the product of the density and Young's modulus, A denotes the product of the density and the thickness of the additional film, B denotes the product of the densities and the thicknesses of the electrodes, and y = A/B, the following conditional expressions are satisfied:
In the range of 9.0 ‰ x < 44.0, 0.0092 ‹ x + 0.88 ‰ y < 0.067 ‹ x + 0.60
In the range of 44.0 ‰ x < 79.0, - 0.0035 ‹ x + 1.45 ‰ y < 0.015 ‹ x + 2.9