A filter device is provided which is low in power loss, small in size and operates in wide bands. The filter device includes a first signal-side resonator having an input signal electrode, an output signal electrode, a first piezoelectric film, an input electrode film, and a common electrode film being...http://www.google.com/patents/US7212083?utm_source=gb-gplus-sharePatent US7212083 - Filter device utilizing stacked resonators and acoustic coupling and branching filter using same
