Loss mechanisms of multi-frequency whispering gallery mode RF-MEMS resonators

Abstract

This work investigates the dominant loss mechanisms of the multi-frequency whispering gallery mode (WGM) resonators theoretically and experimentally, which provides a deep understanding about the working principles of the devices and guidance on their high-end applications. For the first time, the distinct Akhiezer damping (AKE) effects on various order WGMs were comprehensively clarified. At atmosphere, the air damping, which is conventionally expected to be negligible in high-order bulk acoustic wave (BAW) modes, is nonnegligible for all the WGMs. In vacuum, substantial Q enhancements more than two times were obtained. The high-order WGMs benefit more f × Q improvement from the high vacuum than the low-order ones, achieving a promising f × Q product of 1.16 × 1013. What’s more, the Q dynamics over a wide temperature range were characterized, which matched well with the theoretical analysis. The AKE is comparable with anchor loss in low-order modes, while it becomes dominated in the high-order ones. Therefore, the high-order WGMs exhibit higher Q enhancements at cryogenic temperatures. An excellent f × Q product up to 5.91 × 1013 was implemented at 7 K.