Development and Characterization of Next-Generation Contact Materials for Nanoelectromechanical Switches

Nanoelectromechanical (NEM) switches were identified by the semiconductor industry as a low-power "beyond CMOS" technology. However, the reliability of the contact interface currently limits the commercialization of NEM switches, as the electrical contact has to be able to physically open and close up to a quadrillion (10^15) 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 been demonstrated. Thus, commercially viable NEM switches demand the development of novel contact materials along with efficient methods to evaluate the performance of these materials. To assess contact material candidates under NEM switch-like conditions, we developed a novel, high-throughput electrical contact screening method based on atomic force microscopy (AFM) that enables billions of contact cycles in laboratory timeframes. We compared the performance of self-mated and dissimilar single asperity Pt and PtxSi contacts under forces and environments representative of NEM switch operation and cycled up to 10 million times. The contact resistance increased by up to three decades due to cycling-induced growth of insulating tribopolymer in the case of Pt-Pt contacts whereas PtxSi exhibited reduced tribopolymer formation. We also pursued the development of novel contact material candidates that are highly conductive, minimally adhesive, chemically inert, mechanically robust, and amenable to CMOS fabrication processes. One promising candidate material is platinum silicide (PtxSi). The controlled diffusion of thin films of amorphous silicon and platinum allowed us to tune the chemical composition of PtxSi over a wide range (1