Physics-based modelling of vertical strained impact ionization MOSFET (VESIMOS)

Abstract

CMOS device scaling faces several fundamental limits as it scaled beyond the sub-30nm regime. Non-scalability of the subthreshold slope (S) and adverse short channel effects degrading the current drivability and electron mobility of a MOSFET. An innovative device structure with appropriate device physics understanding is vitally needed for scaling the silicon MOSFET into nanometer regime. Underlying this problem is the subthreshold slope concept, which is a measure of switching abruptness in transistor. S is fundamentally limited at 60mV/decade by the drift-diffusion based transport in current CMOS technology. Impact ionization MOSFET (IMOS) that works on the principle of avalanche breakdown mechanism has become promising candidate to overcome this S value constraint. In this paper, we report for the first time an analytical modelling of vertical strained Impact Ionization MOSFET (VESIMOS). We derive the equations and their range of validity and compare the characteristic with TCAD simulations to give truthful interpretation and profound effects in evaluating the device operation for circuit application.