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Abstract

The encapsulated film bulk acoustic resonator (FBAR) device comprises a substrate, an FBAR stack over the substrate, an element for acoustically isolating the FBAR stack from the substrate, encapsulant covering the FBAR stack, and an acoustic Bragg reflector between the top surface of the FBAR stack and the encapsulant. The FBAR stack comprises an FBAR and has a top surface remote from the substrate. The FBAR comprises opposed planar electrodes and a piezoelectric element between the electrodes. The acoustic Bragg reflector comprises a metal Bragg layer and a plastic Bragg layer juxtaposed with the metal Bragg layer. The large ratio between the acoustic impedances of the metal of the metal Bragg layer and the plastic material of the plastic Bragg layer enables the acoustic Bragg reflector to provide sufficient acoustic isolation between the FBAR and the encapsulant for the frequency response of the FBAR device to exhibit minor, if any, spurious artifacts arising from undesirable acoustic coupling between the FBAR and the encapsulant.

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First Claim