Scaling Fully Depleted SOI CMOS

Quasi-two-dimensional (2-D) device analyses, 2-D numerical device simulations, and circuit simulations of nanoscale conventional, single-gate fully depleted (FD) silicon-on-insulator (SOI) CMOS are done to examine the scalability and performance potential of the technology. The quasi-2-D analyses, which can apply to double-gate devices as well, also provide a simple expression to estimate the effective channel length (Leff) of FD/SOI MOSFETs. The insightful results show that threshold-voltage control via channel doping and polysilicon gates is not a viable option for extremely scaled FD/SOI CMOS, and hence that undoped channels and metal gate(s) with tuned work function(s) must be employed. Quantitative as well as qualitative insights gained on the short-channel effects reveal the need for ultrathin films (t(Si) < 10 nm) for Leff < 50 nm. However, the implied manufacturing burden, compounded by effects of carrier-energy quantization for ultrathin t(Si) forces a pragmatic limit on t(Si) of about 5 nm, which in turn limits the scalability to Leff = 25-30 nm. Unloaded CMOS-inverter ring-oscillator simulations, done with our process/physics-based compact model (UFDG) in SPICE3, show very good performance for Leff = 35 nm, and suggest viable technology designs for low-power as well as high-performance applications. These simulations also reveal that moderate variations in t(Si) can be tolerated, and that the energy quantization significantly influences the scaled-technology performance and hence must be properly accounted for in optimal FD/SOI MOSFET design.