Thickness shear vibration type double mode filter having a passively damped coupling capacitor

摘要

A thickness shear vibration type double mode filter includes two or more vibrating elements disposed in parallel on a piezoelectric substrate and a coupling capacitor formed on the piezoelectric substrate at a position intermediate two of the vibrating elements. The coupling capacity includes a capacitor electrode formed on one main surface of the piezoelectric substrate and an opposing ground electrode formed on a second main surface of the substrate. Input/output electrodes of the vibrating elements are formed on the same surface of the piezoelectric substrate as the capacitor electrode. A damper formed of a resin material on which no solder adheres is formed on top of the capacitor electrode and has sufficient mass to suppress undesired vibration in the area of the coupling capacitor.