Variation-aware global placement for improving timing-yield of carbon-nanotube field effect transistor circuit

Abstract

As the conventional silicon-based CMOS technology marches toward the sub-10nm region, the problem of high power density becomes increasingly serious. Under this circumstance, the carbon-nanotube field effect transistors (CNFETs) emerge as a promising alternative to the conventional silicon-based CMOS devices. However, they experience a much larger variation than the silicon-based CMOS devices, which results in a large circuit delay variation and hence, a significant timing yield loss. One of the main variation sources is the carbon-nanotube (CNT) density variation. However, it shows a special property not existing for silicon-based CMOS devices, namely the asymmetric spatial correlation. In this work, we propose novel global placement algorithms to reduce the timing yield loss caused by the CNT density variation. To effectively reduce the statistical circuit delay, we first develop a statistical delay measure for a segment of gates. Based on this measure, we further develop a segment-based strategy and a path-based placement strategy to reduce the delays of the statistically critical paths. Experimental results demonstrated that both of our approaches effectively improve the timing yield.