Patent ID: 7358831

Claim:
An encapsulated film bulk acoustic resonator (FBAR) device, comprising: a substrate; an FBAR stack over the substrate, the FBAR stack comprising an FBAR and having a top surface remote from the substrate, the FBAR comprising opposed planar electrodes and a piezoelectric element between the electrodes; means 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 acoustic Bragg reflector comprising a metal Bragg layer and a plastic Bragg layer juxtaposed with the metal Bragg layer, wherein: the FBAR device has a band-pass characteristic having a center frequency; at least one of the Bragg layers has a nominal thickness equal to one quarter of the wavelength in the material of the respective Bragg layer of an acoustic signal equal in frequency to the center frequency; and the metal Bragg layer is thinner than the nominal thickness.