Film bulk acoustic resonator structure and method of making

A filtering device comprising:

• a substrate including;
• a first horizontal major surface;
• and
• a second horizontal major surface;
• a first stack further including;
• a first layer of piezoelectric material;
• a first conductive layer deposited on a first surface of the first layer of piezoelectric material;
• and
• a second conductive layer deposited on a second surface of the first layer of piezoelectric material;
• and
• a second stack further including;
• a second layer of piezoelectric material;
• a third conductive layer deposited on a first surface of the second layer of piezoelectric material;
• and
• a fourth conductive layer deposited on a second surface of the second layer of piezoelectric material, the first stack and the second stack positioned vertically with respect to the first and second horizontal surface.

A method for forming a device in a substrate comprising:

• forming a plurality of trenches within the substrate, each of the plurality of trenches having sidewalls;
• growing a piezoelectric layer on at least one of the sidewalls of at least two of the plurality of trenches;
• removing the substrate material between the at least two of the plurality of trenches to produce at least one freestanding piezoelectric layer having a first free end and a second attached end;
• and
• placing a conductive layer over the freestanding piezoelectric layer.

A method for forming a device in a substrate comprising:

• forming a trench within the substrate, the trench having a sidewall;
• growing a piezoelectric layer on the sidewall of the trench;
• removing the substrate material of the sidewall of the trench to produce a freestanding piezoelectric layer having a first free end and a second attached end;
• and
• placing a conductive layer on each side of the freestanding piezoelectric layer.