Significance of the Casimir force and surface roughness for actuation dynamics of MEMS

TL;DR

This study investigates how surface roughness and Casimir forces affect MEMS actuation dynamics, revealing that roughness influences stability and contact behavior even at larger distances than expected, with implications for device design.

Contribution

It provides realistic calculations showing the significant impact of surface roughness on MEMS stability and contact, considering Casimir and electrostatic forces based on measured optical and topographical data.

Findings

Roughness affects MEMS dynamics at distances larger than the RMS roughness.

Surface roughness can facilitate reaching stable equilibria despite potential destabilization.

Findings are crucial for designing stable MEMS devices operating below 100 nm.

Abstract

Using the measured optical response and surface roughness topography as inputs, we perform realistic calculations of the combined effect of Casimir and electrostatic forces on the actuation dynamics of micro-electromechanical systems (MEMS). In contrast with the expectations, roughness can influence MEMS dynamics even at distances between bodies significantly larger than the root-mean-square roughness. This effect is associated with statistically rare high asperities that can be locally close to the point of contact. It is found that, even though surface roughness appears to have a detrimental effect on the availability of stable equilibria, it ensures that those equilibria can be reached more easily than in the case of flat surfaces. Hence our findings play a principal role for the stability of microdevices such as vibration sensors, switches, and other related MEM architectures operating at distances below 100 nm.