A semiconductor process for cointegration of BAW thin-film piezoelectrics with microwave BJTs

A compatible process for the monolithic integration of the BAW (bulk acoustic wave) piezoelectric thin-film resonator with silicon BJTs (bipolar junction transistors) is presented. The process uses RIE (reactive ion etching) trench-isolated BJTs cointegrated with high-Q AlN resonators which do not use the p⁺ etch stop. Dielectrically assisted liftoff is used for AlN definition. The process is used for the design of a semicustom ASIC (application-specific integrated circuit) palette consisting of resonators, BJTs, resistors, and digitally weighted MOS capacitors. This ASIC palette is then used for the design of 1-GHz oscillators. To facilitate the use of SPICE and S-parameter techniques, resonator equivalent circuit elements are obtained using TOUCHSTONE optimization routines.