Surface acoustic wave (SAW) resonator having trap-rich region

A surface acoustic wave (SAW) resonator device includes a semiconductor substrate having a first surface and a second surface. The semiconductor substrate comprises a bulk region, and a surface region. The surface region has a high trap density, and a reduced carrier mobility, compared to the bulk region. A piezoelectric layer, having a first surface and a second surface, is disposed over the semiconductor substrate. A plurality of electrodes are disposed over the first surface of the piezoelectric layer, and the plurality of electrodes are configured to generate surface acoustic waves in the piezoelectric layer. The SAW resonator device also comprises a layer disposed between the first surface of the semiconductor substrate and the second surface of the piezoelectric layer.