Semiconductor device and method of forming a semiconductor device

A method of forming a semiconductor device, the method comprising:

• at least partially covering a front surface of a substrate wafer with a bonding layer;
• providing a second wafer comprising a single-crystal piezoelectric film having a first surface and an opposing second surface, a plurality of silicon pillars arranged over the second surface of the single-crystal piezoelectric film, and a bottom electrode arranged on the second surface of the single-crystal piezoelectric film;
• bonding the second wafer to the substrate wafer such that the plurality of silicon pillars are bonded to the front surface of the substrate wafer with the bonding layer and a cavity is enclosed between the second surface of the piezoelectric film and the front surface of the substrate wafer;
• and
• providing a top electrode adjacent to the first surface of the single-crystal piezoelectric film, wherein the bonding layer is disposed between each of the plurality of silicon pillars and the substrate wafer and sandwiched by the plurality of silicon pillars and the substrate wafer
• providing a via extending through the single-crystal piezoelectric film to expose the bottom electrode, wherein the top electrode, the bottom electrode and the via are disposed above and over the cavity, the cavity is between two adjacent pillars of the plurality silicon pillars.