Bulk acoustic wave (BAW) device with oppositely polarized piezoelectric layers for higher order resonance and method of manufacture

A bulk acoustic wave (BAW) device, comprising:

• a layer stack, comprising:
• a first electrode;
• a second electrode;
• a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystalline structure having a first polarization;
• a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer comprising a second crystalline structure having a second polarization opposite to the first polarization;
• and
• at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer,
• wherein:
• a distance between the first piezoelectric layer and the second piezoelectric layer is less than four percent (4%) of a total thickness of the layer stack;
• and
• the at least one intermediate layer comprises:
• a first amorphous layer of a first amorphous material;
• and
• a seed layer configured to determine the second polarization of the second piezoelectric layer.

A method of fabricating a two-terminal bulk acoustic wave (BAW) device, the method comprising:

• forming a layer stack comprising:
• forming a first electrode configured to couple to a first terminal;
• forming a second electrode configured to couple to a second terminal;
• forming a first piezoelectric layer between the first electrode and the second electrode, the first piezoelectric layer comprising a first crystalline structure having a first polarization;
• forming a second piezoelectric layer between the first piezoelectric layer and the second electrode, the second piezoelectric layer comprising a second crystalline structure having a second polarization opposite to the first polarization;
• and
• forming at least one intermediate layer between the first piezoelectric layer and the second piezoelectric layer, wherein the at least one intermediate layer comprises:
• a first amorphous layer of a first amorphous material;
• and
• a seed layer configured to determine the second polarization of the second piezoelectric layer.