| 摘要 |
An object of the present invention is to improve the passing characteristic at high temperature in a ladder-type elastic wave filter and a duplexer including the filter. The ladder-type elastic wave filter of the present invention includes a piezoelectric substrate, a first series elastic-wave resonator formed on the piezoelectric substrate and connected in series between the input and output terminals of the filter, a parallel elastic-wave resonator formed on the piezoelectric substrate and connected in parallel between the series elastic-wave resonator and the ground terminal, and a dielectric film formed on the piezoelectric substrate so as to cover the first series elastic-wave resonator. The piezoelectric substrate is formed of a material with a negative temperature coefficient. The dielectric film is formed of a material with a positive temperature coefficient and its film thickness is formed thicker than that with which the frequency-temperature coefficient of the first series elastic-wave resonator becomes 0. |
