Low cost packaging for thin-film resonators and thin-film resonator-based filters

摘要

An acoustic reflector (48) is applied over a thin-film piezoelectric resonator (41, 61) which is supported on a semiconductor or semiconductor- compatible substrate (42, 62) of a microelectronic device (40, 60), enabling an encapsulant (49) to be applied over the reflector- covered resonator without acoustically damping the resonator. In one embodiment, alternating high and low acoustic impedance layers (51, 53 . . . 55) of one-quarter wavelength thicknesses constructively reflect the resonating wavelength to make an encapsulant in the form of an inexpensive plastic molding compound appear as a "clamping" surface to a resonator (41) peripherally supported over an opening (43) on a silicon substrate (42). In another embodiment, an encapsulant- and reflector- covered resonator (61) is mechanically supported above a second reflector (68) which eliminates the need for peripheral support, making substrate (68) also appear as a clamping surface. The invention enables low cost plastic packaging of resonators and associated circuitry on a single monolithic structure. A radio frequency transceiver front-end application is given as an exemplary implementation.