Thick High Frequency Capacitive Harpss Resonators with Reduced Motional Resistance

This paper reports on implementation and high-Q operation of thick bulk mode VHF capacitive disk resonators with reduced motional resistance. Single crystal silicon (SCS) disk resonators as thick as 18 m with capacitive gap size of 160nm (aspect ratio>110) are fabricated on SOI substrates using a three-mask version of the HARPSS on SOI process. The new resonator design with increased number of electrodes as well as larger device thickness results in over 20X lower motional resistance and larger signal to noise ratio comparing to the previously demonstrated thin VHF HARPSS resonators. Quality factor as high as 25,900 is measured for an 18 m thick side-supported disk resonator in air at the frequency of 149.3MHz. The same resonator exhibits a quality factor of 45,700 in vacuum.