A scalable physical model for Nano-Electro-Mechanical relays

Nano-Electro-Mechanical (NEM) relay is a promising device overcoming the energy-efficiency limitations of CMOS transistors operating at or near the sub-threshold voltage. Many exploratory research projects are currently under way investigating the mechanical, electrical and logical characteristics of NEM relays. One particular issue that this paper addresses is the need for a scalable and accurate physical model of the NEM switch that can be plugged into the standard EDA software. The existing models are accurate and detailed but they suffer from the convergence problem. This problem requires finding ad-hoc workarounds and significantly impacts the designer´s productivity. In this paper we propose a new simplified Verilog-A mode. To test scalability of the proposed model we cross-checked it against our analysis of a range of benchmark circuits. Results show that, compared to standard model, the proposed model is sufficiently accurate with an average of 6% error and can handle larger designs without divergence. In particular the largest circuit we could handle with the standard model in our experiments contained only 22 NEM relays, while the proposed approach could handle circuits comprised of 192 NEM relays.