Methods of manufacturing film bulk acoustic wave resonators

A film bulk acoustic wave filter assembly comprising:

• a first film bulk acoustic wave filter coupled to a common node;
• and
• a second film bulk acoustic wave filter coupled to the common node, at least one of the first film bulk acoustic wave filter and the second film bulk acoustic wave filter including a plurality of film bulk acoustic wave resonators to filter a radio frequency signal, at least one of the plurality of film bulk acoustic wave resonators including a substrate having a main surface, a lower electrode disposed on the main surface of the substrate, and a piezoelectric film disposed on the lower electrode, the piezoelectric film having a lower layer with a first non-uniform acoustic velocity profile across the main surface of the substrate and an upper layer with a second non-uniform acoustic velocity profile across the main surface of the substrate that is opposite to the first non-uniform acoustic velocity profile that at least partially compensates for the first non-uniform acoustic velocity profile and provides the piezoelectric film with an acoustic velocity profile that is more uniform across the main surface of the substrate than the first non-uniform acoustic velocity profile.