A Novel Capacitive Sensing Principle for Microdevices

Abstract

Conventional capacitive sensing places significant limitations on the sensor design due to the pull-in instability caused by the electrostatic force. The main purpose of this study is to examine a low-cost novel capacitive sensing principle based on electrostatic balance which promises to avoid these design limitations. The approach uses an asymmetric electric field on a structure with fingers that can generate a repulsive force while the gap is low and create an attractive force while the gap is large. The size and thickness of the fingers are also responsible for creating repulsive or attractive forces on the structure. This approach has recently been applied successfully in the design of capacitive actuators to provide a repulsive driving force. A new design principle for capacitive sensing is described that avoids pull-in instability by designing the fingers such that the structure is at the equilibrium.

A MEMS Microphone Using Repulsive Force Sensors

“…However, it has been used for only actuation mechanisms. In 2015, Zhou et al [39] proposed that this method is also a promising alternative to avoid pull-in instabilities for capacitive sensing mechanisms. In this paper we will investigate the application of the electrostatic repulsive force for a microphone design.…”

“…This configuration was introduced by He et al [13,35] to produce a repulsive force (outof-plane) on the moving finger for actuation. In a prior study, the authors presented the feasibility of using the repulsive force concept as a sensing mechanism for micro devices [39]. In a unit cell of the sensor, a net repulsive force is generated on the moving finger by the electrostatic attractive forces of the fixed electrodes on both sides of the moving finger.…”