Patent ID: 7986198
Filing Date: 2011-07-26
Classification: H03H

Abstract:
1. A frequency-variable acoustic thin film resonator, comprising: a first piezoelectric thin film; a pair of primary electrodes for applying an electric signal, which are formed on the first piezoelectric thin film; a second piezoelectric thin film that is disposed so that an oscillation generated in the first piezoelectric thin film propagates to the second piezoelectric thin film; a pair of secondary electrodes for outputting an electric signal, which are formed on the second piezoelectric thin film; a load that is connected between the secondary electrodes; and a control portion that controls a value of the load, whereby an acoustic thin film resonator element is formed so that an electric signal inputted from the primary electrodes is outputted from the secondary electrodes by a piezoelectric effect, and a resonant frequency and an antiresonant frequency are made variable through the control of the value of the load, wherein the first piezoelectric thin film and the second piezoelectric thin film are disposed in a laminated state, between the first piezoelectric thin film and the second piezoelectric thin film, a second electrode is provided so as to be shared by both of the piezoelectric thin films, a first electrode is provided on a surface of the first piezoelectric thin film on a side opposite the second electrode, a third electrode is provided on a surface of the second piezoelectric thin film on a side opposite the second electrode, the first and second electrodes function as the primary electrodes, the second and third electrodes function as the secondary electrodes, and where a total of film thicknesses of the first and second electrodes and the first piezoelectric thin film is defined as a film thickness P, and a sum of the film thickness P and thicknesses of the second piezoelectric thin film and the third electrode is defined as an entire film thickness T, a film thickness ratio P/T is set to be in a range of values larger than a value at which a resonator element constituted of the first and second electrodes and the first piezoelectric film has a maximum effective coupling coefficient and smaller than a value at which a resonator element constituted of the second and third electrodes and the second piezoelectric film has a maximum effective coupling coefficient.