The Design of Dual Work Function CMOS Transistors and Circuits Using Silicon Nanowire Technology

This exploratory study on vertical, undoped silicon nanowire transistors shows less power dissipation with respect to the bulk and SOI MOS transistors while yielding comparable performance. The design cycle starts with determining individual metal gate work functions for each nMOS and pMOS transistor as a function of wire radius to produce a 300 mV threshold voltage. Wire radius and effective channel length are both varied until a common body geometry is determined for both nMOS and pMOS transistors to limit off currents under 1 pA while producing highest on currents. DC characteristics of the optimum n and p-channel transistors such as threshold voltage roll-off, DIBL and subthreshold slope are measured; simple CMOS gates including an inverter, 2- and 3-input nand, nor, and xor gates, and full adder are built to measure the transient performance, power dissipation and layout area. Postlayout simulation results indicate that the worst case delay for a full adder circuit is 8.5 ps at no load and increases by 0.15 ps/aF; worst case power dissipation of the same circuit is 23.6 nW at no load and increases by 4.04 nW/aF at 1 GHz. The full adder layout area occupies approximately 0.11 mum²