High frequency capacitive micromechanical resonators with reduced motional resistance using the HARPSS technology

The paper reports on the implementation and characterization of thick bulk mode VHF capacitive disk resonators with reduced motional resistance. Single crystal silicon (SCS) side-supported disk resonators with thickness of 18 μm and 10 μm and capacitive gaps of 160 nm and 75 nm, respectively (gap aspect-ratio>130), are fabricated on silicon-on-insulator substrates using a 3-mask HARPSS-on-SOI process. Over 20× lower motional resistance and larger signal-to-noise ratio compared to the previous thin VHF SCS resonators is demonstrated, resulting from the new resonator design with increased number of electrodes and larger device thickness. Quality factors in the order of 30,000 to 50,000 at resonant frequencies of 150-230 MHz are demonstrated for the thick disk resonators. The measured data is in excellent agreement with the theoretical values.