Patent ID: 9041486
Filing Date: 2015-05-26
Classification: H03H

Abstract:
1. A ladder-type elastic wave filter comprising: a piezoelectric substrate formed of a material with a negative temperature coefficient; a first series elastic-wave resonator formed on the piezoelectric substrate and connected in series between an input terminal and an output terminal, the first series elastic-wave resonator having a first capacitance; a second series elastic-wave resonator connected in series between the input terminal and the output terminal and having a second capacitance, the first capacitance of the first series elastic-wave resonator being higher than the second capacitance of the second series elastic-wave resonator; a parallel elastic-wave resonator formed on the piezoelectric substrate and connected in parallel between the first series elastic-wave resonator and a ground terminal; and a dielectric film formed on the piezoelectric substrate the dielectric film covering the first series elastic-wave resonator and the second series elastic-wave resonator, the dielectric film formed of a material with a positive temperature coefficient, a thickness of the dielectric film being thicker than a film thickness with which a frequency-temperature coefficient of a passing characteristic of the first series elastic-wave resonator becomes 0.