Performance and reliability of MEMS coatings in liquids

Abstract

Reliability of MEMS in liquids is an importantconcern for MEMS operating in harsh environments in petrochemical, biomedical, and defense applications. Our previous studies have demonstrated reliability concerns for silicon microcantilevers in liquid environments such as saline. In this paper, the effect of coatings on reliability of MEMS in liquids, such as DI water and saline, is compared to that in air. Silicon microcantilevers coated with Titanium (Ti) and SU-8 were vibrated in liquids for 10 8 -10 9 cycles. The resonant frequency of the microcantilevers was periodically monitored to evaluate performance.Reliability of microcantilevers coated with Ti and SU-8 was compromised as indicated by a gradual decrease in resonant frequency in liquids. These changes in resonant frequency were attributed to factors such as stress-corrosion cracking, water absorption, and intrinsic stresses.

Study of SU-8 reliability in wet thermal ambient for application to polymer micro-optics on VCSELs

“…18) However, Ali et al reported that absorption of water in the material can lead to swelling and to a residual strain in SU-8 cantilevers. 19) This phenomenon was also observed by Feng et al who assumed a reversible mechanism. 20) These authors concluded that the resulting strain can be minimized by applying a drying process.…”