Patent ID: 7196596

Claim:
A Film Bulk Acoustic Resonator (FBAR) filter having an unbalanced-balanced input/output structure for receiving an unbalanced input signal, filtering the unbalanced input signal in a predetermined frequency band and outputting a filtered signal as a balanced output signal, the FBAR filter comprising: a wafer; a filter circuit unit including a plurality of FBAR resonators formed on a predetermined region on a top of the wafer; and a balun circuit unit including a plurality of metal layers electrically connected to each other to implement a balun circuit and a plurality of dielectric layers each placed between the plurality of metal layers, the balun circuit unit being electrically connected to the filter circuit unit on a predetermined region of the wafer; wherein the filter circuit unit is hermetically sealed by a cap structure including sidewalls with a certain height and an upper cover coupled to top of the sidewalls.