Novel Materials Solutions and Simulations for Nanoelectromechanical Switches

Nanoelectromechanical (NEM) switches are a candidate to replace solid-state transistors due to their low power consumption. However, the reliability of the contact interface limits the commercialization of NEM switches, since for practical purposes, the electrical contact should be able to physically open and close up to a quadrillion (10¹⁵) times without failing due to adhesion (by sticking shut) or contamination (reducing switch conductivity). These failure mechanisms are not well understood, and materials that exhibit the needed performance have not yet been demonstrated. This study presents the development of platinum silicide (Pt_xSi) as a promising NEM switch contact material. Using controlled solid-state diffusion of thin films of amorphous silicon and platinum, Pt_xSi was formed over a range of stoichiometries (1≤x≤3). The platinum-rich silicide phase (Pt₃Si) may be a particularly ideal contact material for NEM switches due to its combination of mechanical robustness with metal-like conductivity. We then present a novel, high-throughput contact material screening method for NEM contact materials based on atomic force microscopy (AFM) that enables billions of contact cycles in laboratory timeframes for arbitrary material pairs. Self-mated Pt contacts showed more than three orders-of-magnitude increase in contact resistance after 2·10⁹ cycles due to the growth of insulating tribopolymer. Finally, we present density functional theory (DFT) and molecular dynamics (MD) based studies to understand tribopolymer formation and growth. These calculations show that irreversible stress-induced polymerization processes are strongly affected by the ability of the molecule to displace laterally. Additionally, lower interaction energies between the model organic molecules and the Pt_xSi surface compared to Pt are found. This combination of experimental and theoretical methods in the framework of a materials genome effort aims to ultimately lead to accelerated discovery of suitable contact materials for NEM switches and to their commercialization.