Identifying spurious modes in RF-MEMS resonators using photoelastic imaging

This paper reports the first use of dynamic photoelastic imaging for identifying in-plane vibration modes in high-frequency MEMS resonators. In a set of width-extensional mode resonators (WE-BARs), we map fundamental width-extensional modes ω
₍₀₁₎
and unwanted higher-order spurious length-extensional modes ω
_{(i, 0)}
. In addition, we detect unexpected spurious modes `ω
_χ
' for all designs that are potentially detrimental due to their proximity to w
_(0,1)
. We show the dependence of both intended modes and spurious modes on aspect ratio and discuss methods of mitigation for the latter. It is shown that the photoelastic technique is broadly applicable to high-resolution mapping and identification of vibration modes in MEMS resonators.