High-Order Modes of Thin Film Amorphous Silicon Coupled Disk Resonator Arrays

High-order resonance modes of disk resonators are promising due to their high quality factors in dissipative media. In this work, thin film hydrogenated amorphous silicon disk resonators actuated by lateral electrodes were mechanically coupled in arrays ranging from one (single resonator) up to four elements. The resonators were moderately to weakly coupled, which can allow further enhancement of sensitivity for mass sensing. The devices were fabricated by an easily scalable surface micromachining process on
$5\times 5$
cm glass substrates with process temperatures not exceeding 175 °C. Modes of different orders were measured at frequencies ranging from 0.2 up to 10 MHz, exhibiting maximum quality factors of 3115 in vacuum and 427 in air. Experimental mode shapes obtained from laser Doppler vibrometry were consistent with those obtained from finite element method simulations. Measurements of quality factor showed a significantly sharper increase with frequency in air than in vacuum, which was attributed to lessened extrinsic energy dissipation to the fluidic medium of the high-order flexural modes. Vibrometry measurements suggest that this could be explained by reduced flexural motion of the high-order modes. The results also showed that the addition of a mechanical coupling beam was not detrimental to the quality factor, ultimately demonstrating that the proposed devices are potential candidates for mode-localized sensing purposes in dissipative media and large-area applications. [2023-0124]