Patent ID: 7612636

Claim:
A bulk acoustic wave (BAW) device comprising: a stacked bulk acoustic wave resonator (SBAR) comprising an acoustic decoupler between first and second film bulk acoustic resonators (FBARs), the first FBAR being resonant at a resonant frequency and comprising first and second planar electrodes abutting opposite sides of a first resonator volume free of intervening electrodes and containing piezoelectric material disposed for acoustic vibrations parallel to a propagation axis normal to the first and second electrodes, the first FBAR having a first electrical impedance parallel to the propagation axis, the second FBAR being resonant at the resonant frequency and comprising third and fourth planar electrodes abutting opposite sides of a second resonator volume free of intervening electrodes and containing piezoelectric material disposed for acoustic vibrations parallel to the propagation axis, the second FBAR having a second electrical impedance parallel to the propagation axis and different from the first electrical impedance, wherein the first resonator volume has a first thickness dimension between the first and second planar electrodes parallel to the propagation axis and the second resonator volume has a second thickness dimension between the third and fourth planar electrodes parallel to the propagation axis, the second thickness dimension being different from the first thickness dimension, and wherein each of the first and second planar electrodes has a thickness parallel to the propagation axis that is different from a thickness of each of the third and fourth planar electrodes parallel to the propagation axis, compensating for the difference between the first and second thickness dimensions, such that the first and second FBARs have substantially the same overall acoustic thickness.