Ultimate sensing with an ultrathin single crystalline silicon resonator

Miniaturization of resonating sensors is a promising method to reduce the thermo-mechanical noise and raise the mass and force sensitivity. Fabrication technique based on SOI (silicon on insulator) wafer was developed for making ultrathin single-crystalline structures down to 20 nm thick. Mechanical quality factor (Q-factor) of the cantilever decreases with decreasing thickness due to the energy dissipation on the surface; however heating in ultra-high vacuum (UHV) cleans the surface at the atomic scale, resulting in dramatic increase of the Q-factor. All measurements were performed in an UHV chamber equipped with a laser Doppler vibrometer. Leaving the cleaned cantilever in UHV, small quantities of molecule are adsorbed on the cantilever and lower the Q-factor. These behaviors are measured on both 170 nm thick Si[100] and 50 nm thick Si[111] cantilevers. Using these ultra-thin resonators, mass change below a picogram and external force loaded on the cantilever are demonstrated.