Partitioning Electrostatic and Mechanical Domains in Nanoelectromechanical Relays

This paper describes the improvement of pull-in stability, contact properties, and reliability of laterally actuated nanoelectromechanical relays by partitioning the mechanical and electrostatic domains in the relay structure. Separation of the two physics allows us to individually optimize the structural stiffness and the actuation voltage to increase the contact pressure and reduce the ON-state resistance without applying excessive drain voltage. The devices can tolerate more than 200% overdrive gate voltage, resulting in near 100% increase in contact force, and reducing the contact resistance from ~10 GQ to ~23 KΩ. For a given overall device dimension, tailoring the mechanical and electrostatic elements independently also enables us to control the pull-in and pull-out voltages, which have different design requirements for different applications. The measurement results show that the pull-in/pull-out hysteresis could vary between 30% and 60% of the actuation (pull-in) voltage. Increasing the mechanical force without affecting the device actuation voltage improves the relay reliability by reducing the possibility of failure due to source-drain stiction when the relay is switched ON. As a proof of concept, mechanical relays are fabricated using polycrystalline silicon coated by a titanium nitride layer deposited via plasma enhanced atomic layer deposition.