Acoustic resonator including composite polarity piezoelectric layer having opposite polarities

A bulk acoustic wave (BAW) resonator device, comprising:

• a bottom electrode disposed over a substrate and an acoustic reflector;
• a monolithic piezoelectric layer disposed over the bottom electrode, the piezoelectric layer comprising a first portion having a negative polarity and a second portion having a positive polarity that is substantially opposite to the negative polarity of the first portion with no discernible interface between the first and second portions;
• and
• a top electrode disposed over the second portion of the monolithic piezoelectric layer,
• wherein the first portion of the monolithic piezoelectric layer has a first thickness and the second portion of the monolithic piezoelectric layer has a second thickness that is not equal to the first thickness, thereby lowering a coupling coefficient kt2 of the BAW resonator device while maintaining a combined thickness of the bottom electrode, the monolithic piezoelectric layer and the top electrode.