Layers, structures, acoustic wave resonators, devices and systems

An electrical oscillator comprising:

• electrical oscillator circuitry;
• and
• a bulk acoustic wave resonator coupled with the electrical oscillator circuitry to excite electrical oscillation in the bulk acoustic wave resonator, in which the bulk acoustic wave resonator includes at least:
• an acoustic reflector electrode, in which the acoustic reflector electrode includes at least a first pair of metal electrode layers and a second pair of metal electrode layers;
• a first piezoelectric layer having a first piezoelectric axis orientation and a first thickness;
• a second piezoelectric layer having a second piezoelectric axis orientation;
• a third piezoelectric layer having a third piezoelectric axis orientation that opposes the second piezoelectric axis orientation, and having a third thickness acoustically and electrically coupled with the acoustic reflector electrode to facilitate a main resonant frequency of the bulk acoustic wave resonator;
• and
• an integrated capacitive layer electrically coupled with the acoustic reflector electrode to facilitate limiting of an electromechanical coupling of the bulk acoustic wave resonator.

An electrical filter comprising:

• a plurality of bulk acoustic wave resonators over a substrate, in which a first bulk acoustic wave resonator of the plurality of bulk acoustic wave resonators includes at least:
• an acoustic reflector electrode, in which the acoustic reflector electrode includes at least a first pair of metal electrode layers and a second pair of metal electrode layers;
• a first piezoelectric layer having a first piezoelectric axis orientation and a first thickness;
• a second piezoelectric layer having a second piezoelectric axis orientation;
• a third piezoelectric layer having a third piezoelectric axis orientation that opposes the second piezoelectric axis orientation, and having a third thickness acoustically and electrically coupled with the acoustic reflector electrode to facilitate a main resonant frequency of the first bulk acoustic wave resonator;
• and
• an integrated capacitive layer electrically coupled with the acoustic reflector electrode to facilitate limiting of an electromechanical coupling of the first bulk acoustic wave resonator.