Patent ID: 7760049

Claim:
A film bulk acoustic resonator comprising: a substrate; an acoustic reflector portion formed on the substrate; an acoustic resonator portion including a lower electrode, a piezoelectric film, and an upper electrode which are sequentially stacked on the acoustic reflector portion; and a smoothing layer formed between the acoustic reflector portion and the acoustic resonator portion, wherein: the acoustic reflector portion includes low acoustic impedance layers and high acoustic impedance layers which are alternately stacked on the substrate; the high acoustic impedance layers have higher acoustic impedance than the low acoustic impedance layers; the smoothing layer is an insulating layer, is in contact with the lower electrode and an uppermost part of the acoustic reflector portion, said smoothing layer is formed by spin coating, and has lower acoustic impedance than the low acoustic impedance layers; and the uppermost part of the acoustic reflector portion is one of the high acoustic impedance layer.