Compact non-local modeling of impact ionization in SOI MOSFETs for optimal CMOS device/circuit design

Abstract

A comprehensive but compact non-local model for impact ionization current in scaled SOI MOSFETs is developed. The model, applicable to both fully depleted and non-fully depleted SOI CMOS, is intended for device/circuit simulation and has been implemented as post-processing in a circuit simulator SOISPICE [J. G. Fossum, SOI-SPICE-4 ( FD/SOI and NFD/SOI MOSFET Models). University of Florida, Gainesville, FL (March 1995)]. The model is based on transforming the empirical field-dependent impact ionization rate into a carrier temperature-dependent one via a quasi-steady-state approximation of the energy balance equation. The model is valid for weak as well as strong inversion. It is verified via predictions of structure-dependent drain-source breakdown and current kinks in a variety of floating-body SOI MOSFETs. SOISPICE simulations reveal insight into the design optimization of scaled SOI CMOS devices and circuits in which the breakdown, due to the parasitic BJT driven by impact ionization, must be controlled.