| CPC H03H 9/605 (2013.01) [H03H 9/02086 (2013.01); H03H 9/205 (2013.01)] | 23 Claims |
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1. A ladder filter comprising:
an input port and an output port;
a plurality of series arm bulk acoustic wave resonators electrically connected in series between the input port and the output port; and
a plurality of shunt bulk acoustic wave resonators electrically connected between respective adjacent ones of the plurality of series arm bulk acoustic wave resonators and ground, each of the plurality of series arm bulk acoustic wave resonators and the plurality of shunt bulk acoustic wave resonators including a central active region and a raised frame region outside of the central active region, each of the plurality of series arm bulk acoustic wave resonators and the plurality of shunt bulk acoustic wave resonators including a piezoelectric film and an upper electrode disposed on an upper surface of the piezoelectric film, at least one of the plurality of series arm bulk acoustic wave resonators including a layer of oxide disposed directly on the piezoelectric film in the raised frame region, and a metal layer disposed directly on only a portion of the upper electrode in only a portion of the central active region and disposed on the layer of oxide in the raised frame region, the metal layer having a thickness in the raised frame region that is no greater than the thickness of the metal layer in the only the portion of the central active region to reduce spurious mode signals in the at least one of the plurality of series arm bulk acoustic wave resonators.
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