Negative stiffness structures for energy efficient MEM switches

Micro-electro-mechanical (MEM) switches show promise for ultra-low-power computing since they can operate with negligible subthreshold leakage current. A principal challenge for MEM switch design is to achieve low pull-in voltage (V
pi
) for low-power device operation. Usually this requires low structural stiffness (k), small as-fabricated actuation gap thickness (g), and large actuation area (A). However, assuming the difference between the actuation gap and contact gap is small, such a design has low spring restoring energy (∼0.5kg
²
) and hence is susceptible to stiction-induced failure. To alleviate this challenge, we propose, simulate and analytically model a new MEM actuator design that incorporates a structure with negative stiffness, that is, a buckling fixed-fixed beam. Prior work has leveraged residual stress (σ
o
) in thin films to create buckled structures for memory devices, pressure sensors, and microactuators [1]-[3]. A compensated spring system that combines a negative stiffness spring with a positive stiffness spring to lower the actuation force has been proposed and demonstrated in large-scale vibration isolators [4]-[6]. However, to the authors' knowledge this method has not yet been applied to MEM switches.