Local Vₜₕ Variability and Scalability in Silicon-on-Thin-BOX (SOTB) CMOS With Small Random-Dopant Fluctuation

The silicon on thin buried oxide (SOTB) has the smallestVthvariation among planar CMOS due to a low-dose channel. This study focuses on evaluating local variability components and searching for the dominant factor after reducing random-dopant fluctuation (RDF) by decreasing impurities in the channel. Improving short-channel-effect immunity is important to reduce both the global and local variations. The localVthvariationAVtwas very small, ~ 1.0 and 0.7 mV·¿m for NMOS and PMOS, respectively; however, additional unknown factors other than RDF still exist. Silicon-on-insulator thickness variation does not play a major role in ¿Vth, and the SOTB is scalable to less than 25 nm while maintaining small variability and, hence, low power consumption. The larger variability in NMOS compared to that in PMOS cannot be explained by conventional RDF but seems to be strongly related to channel doping.