Electrostatic Actuators Operating in Liquid Environment : Suppression of Pull-in Instability and Dynamic Response

TL;DR

This paper investigates electrostatic actuators in liquids, demonstrating suppression of pull-in instability and analyzing dynamic response for applications like microfluidics and AFM, with experimental and theoretical validation.

Contribution

It introduces methods to suppress pull-in instability in liquid environments and provides an analytical model for dynamic response of micro-cantilevers in liquids.

Findings

Pull-in effect can be eliminated in liquids.

Validated analytical model for cantilever resonance in liquids.

AC-voltages mitigate electrochemical issues.

Abstract

This paper presents results about fabrication and operation of electrostatic actuators in liquids with various permittivities. In the static mode, we provide experimental and theoretical demonstration that the pull-in effect can be shifted beyond one third of the initial gap and even be eliminated when electrostatic actuators are operated in liquids. This should benefit to applications in microfluidics requiring either binary state actuation (e.g. pumps, valves) or continuous displacements over the whole gap (e.g. microtweezers). In dynamic mode, actuators like micro-cantilevers present a great interest for Atomic Force Microscopy (AFM) in liquids. As this application requires a good understanding of the cantilever resonance frequency and Q-factor, an analytical modeling in liquid environment has been established. The theoretically derived curves are validated by experimental results using a nitride encapsulated cantilever with integrated electrostatic actuation. Electrode potential screening and undesirable electrochemistry in dielectric liquids are counteracted using AC-voltages. Both experimental and theoretical results should prove useful in micro-cantilever design for AFM in liquids.