Silicon nitride-on-silicon bar resonator using internal electrostatic transduction

This paper demonstrates an electrostatic transducer for lateral-mode bar resonators in which a high dielectric constant (high-K) thin film is sandwiched between polysilicon electrodes and the top surface of the resonator. This internal electrostatic transducer has several advantages over both air-gap electrostatic and piezoelectric transduction, including lower motional impedance (R_x), compatibility with advanced scaled CMOS device technology, and extended dynamic range. The resonators are fabricated on 4 μm thick heavily-doped SOI wafers with 200 nm thick silicon nitride film as the dielectric transducer. Using this configuration, we have demonstrated a 121 MHz silicon nitride-on-silicon lateral-mode bar resonator with a quality factor (Q) of 2,100 in air and motional impedance of 9 kΩ.