VHF single crystal silicon capacitive elliptic bulk-mode disk resonators-part II: implementation and characterization

This work, the second of two parts, reports on the implementation and characterization of high-quality factor (Q) side-supported single crystal silicon (SCS) disk resonators. The resonators are fabricated on SOI substrates using a HARPSS-based fabrication process and are 3 to 18 μm thick. They consist of a single crystal silicon resonant disk structure and trench-refilled polysilicon drive and sense electrodes. The fabricated resonators have self-aligned, ultra-narrow capacitive gaps in the order of 100 nm. Quality factors of up to 46 000 in 100 mTorr vacuum and 26000 at atmospheric pressure are exhibited by 18 μm thick SCS disk resonators of 30 μm in diameter, operating in their elliptical bulk-mode at ∼150 MHz. Motional resistance as low as 43.3 kΩ was measured for an 18-μm-thick resonator with 160 nm capacitive gaps at 149.3 MHz. The measured electrostatic frequency tuning of a 3-μm-thick device with 120 nm capacitive gaps shows a tuning slope of -2.6 ppm/V. The temperature coefficient of frequency for this resonator is also measured to be -26 ppm/°C in the temperature range from 20 to 150°C. The measurement results coincide with the electromechanical modeling presented in Part I.