Stable Deflection in Ferroelectric Negative-Capacitance Hybrid MEMS Actuator With Cubic Nonlinear Spring

Abstract

Electrostaticmicroelectromechanicalsystems (MEMS) actuators suffer from an instability called pull-in, wherein the movable electrode snaps onto the fixed electrode beyond a certain applied voltage. Thus, the entire allowed range is not utilized for stable operation. We propose pull-in free, low-voltage operation by using a cubic nonlinear spring with a ferroelectric negative-capacitance hybrid MEMS actuator. We use a physics-based framework based on the energy landscape to illustrate stability improvement. This framework uses energy–displacement and voltage–displacement plots for analysis. We predict that the actuator can operate in three distinct modes: 1) monostable; 2) bistable; and 3) always-stable, based on the value of the cubic spring constant. We also estimate the threshold values of the cubic spring constant that demarcate the three modes of operation. By proper choice of the cubic spring constant, we predict pull-in free, low-voltage operation of the hybrid actuator, when compared to the standalone MEMS actuator. The results obtained are in agreement with the numerical simulations. This work will aid in the design of electrostatic MEMS actuators for low-voltage applications without pull-in instability.