| AVS 62nd International Symposium & Exhibition | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM-WeM |
| Session: | Beyond CMOS: Resistive Switching Devices |
| Presenter: | Frank Streller, University of Pennsylvania |
| Authors: | F. Streller, University of Pennsylvania G. Wabiszewski, University of Pennsylvania D. Durham, University of Pennsylvania R.W. Carpick, University of Pennsylvania |
| Correspondent: | Click to Email |
Nanoelectromechanical (NEM) switches were identified by the roadmap of 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 times without failing, which typically occurs due to adhesion (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 scientific development and characterization of novel contact materials, along with efficient methods to evaluate the interfacial performance of these materials.
We have developed novel contact material candidates that are highly conductive, minimally adhesive, chemically inert, mechanically robust, and amenable to CMOS fabrication processes.[1,2] One promising candidate is platinum silicide (PtxSi). The controlled diffusion of sequentially-deposited thin films of amorphous silicon and Pt allowed us to tune the chemical composition of PtxSi over a wide range (1<x<3). We measured the mechanical and electrical contact properties of PtxSi of multiple stoichiometries in comparison with pure Pt. These experiments showed that the Pt-rich silicide phase (Pt3Si) may be an ideal contact material for NEM switches due to its desirable combination of mechanical robustness with metal-like conductivity. We also demonstrate that PtxSi can be used to release NEM switches with a self-formed gap caused by interfacial separation driven by shrinkage-induced tensile stress.
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 that enables billions of contact cycles to be tested 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 them up to two billion times. The contact resistance increased by up to six decades due to cycling-induced growth of insulating tribopolymer in the case of Pt-Pt contacts, while PtxSi exhibited better stability. Additionally, we found that the original conductivity can be largely recovered by sliding of the contact, which essentially leads to the displacement of the tribopolymer. This suggests a route for mitigating contamination-induced failure.
[1] Streller et al., Adv. Mater. Interfaces, 1 (2014).
[2] Streller et al., IEEE Nanotech. Mag., 1 (2015).