An air-gap type film bulk acoustic resonator (FBAR) is created by securing two substrate parts, one providing a resonance structure and the other providing a separation structure, i.e., a cavity. When the two substrate parts are secured, the resonance structure is over the cavity, forming an air gap isolating the resonant structure from the support substrate. The FBAR may be used to form a duplexer, which includes a plurality of resonance structures, a corresponding plurality of cavities, and an isolation part formed between the cavities. The separate creation of the resonance structures and the cavities both simplifies processing and allows additional elements to be readily integrated in the cavities.