Phase shift structures for acoustic resonators

A stacked crystal filter (SCF) comprising:

• a first piezoelectric layer;
• a second piezoelectric layer having a polarity that is opposite a polarity of the first piezoelectric layer to provide a phase shift;
• a shared electrode between the first piezoelectric layer and the second piezoelectric layer;
• a first electrode on the first piezoelectric layer opposite the shared electrode;
• and
• a second electrode on the second piezoelectric layer opposite the shared electrode, wherein the second electrode is thicker than the first electrode.

A filter circuit comprising:

• an input and an output;
• a first acoustic resonator coupled between the input and the output, the first acoustic resonator comprising at least two piezoelectric layers having the same polarity;
• and
• a second acoustic resonator coupled between the input and the output, the second acoustic resonator comprising a first piezoelectric layer having the same polarity of the at least two piezoelectric layers of the first acoustic resonator and a second piezoelectric layer having a polarity that is opposite the polarity of the first piezoelectric layer.

A coupled resonator filter (CRF) comprising:

• a first piezoelectric layer between a first electrode and a second electrode;
• a second piezoelectric layer between a third electrode and a fourth electrode, the second piezoelectric layer having a polarity that is opposite a polarity of the first piezoelectric layer to provide a phase shift, the second piezoelectric layer further having a different thickness than the first piezoelectric layer;
• and a
• coupling structure between the second electrode and the third electrode.