N- and P-Well Optimization for High Speed N-Epitaxy CMOS Circuits

The speed of MOS circuits is essentially determined by channel length and parasitic capacitances such as Miller and S/D-junction capacitances. To realize fast transistors in CMOS, dopant concentrations in the p- and n-well are required which are low enough to guarantee small S/D-junction capacitances, but which are high enough to avoid early field oxide transistor turn-on and parasitic bipolar effects like latch-up. Therefore, aside from short channels doping profiles of p- and n-wells play a key role in high speed CMOS circuits.