Patent ID: 7439824

Claim:
A bulk acoustic wave filter comprising a substrate, carrying: a set of piezoelectric series resonator means having a thin film resonator structure comprising: a piezolayer; and bottom electrodes and top electrodes; a set of piezoelectric shunt resonator means having a thin film resonator structure, similar to said set of series resonator means, wherein the fundamental resonance frequency is shifted to lower frequencies by applying at least one differential detuning layer at a position above a piezo median plane, determining the bandwidth of said bulk acoustic wave filter, positioned side by side with said set of series resonator means; acoustic mirror layers positioned between said substrate and said piezoelectric resonator means comprising stacked layers of alternating low acoustic impedance and high acoustic impedance; and wherein the thin film bulk acoustic wave resonator filter has an overmode-detuning component in which at least one additional differential layer is applied at a position below the piezo median plane for at least one of the series or shunt resonators, and wherein the frequency of the overmode of the series resonators is lowered with respect to the frequency of the overmode of the shunt resonators to provide overmode detuning.