Stable Deflection in Ferroelectric Negative-Capacitance Hybrid MEMS Actuator with Cubic Non-Linear Spring

Electrostatic 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 non-linear spring with a ferroelectric negative-capacitance hybrid MEMS actuator. We use a physics-based framework based on the energy landscape to illustrate the stability improvement. This framework uses energy-displacement and voltage-displacement plots for analysis. We predict that the actuator can operate in three distinct modes: (a) monostable, (b) bistable and (c) 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 design of the cubic spring constant, we predict pull-in free, low-voltage operation of the hybrid actuator, as 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.