Patent ID: 7176510

Claim:
A thin film capacitor comprising: a pair of electrodes; and a dielectric layer sandwiched between the electrodes, wherein a phase characteristic of an impedance resulting from voltage application to the pair of electrodes peaks periodically according to a frequency of a signal to be inputted or outputted and the frequency of the signal (usable frequency) is adjusted to fall in between values representing adjacent peaks and, wherein a resonant frequency fn is given by: fn=nV/2t (n=1, 3, 5 . . . ), in which t is an entire film thickness, defined as the sum of the thicknesses of the dielectric layer and the pair of electrodes for constituting a piezoelectricity-influenced oscillatory portion, and V is an effective sonic velocity of a sonic wave propagating through the oscillatory portion, and the resonant frequency is so adjusted as not to fall within the range of the signal frequencies.