Time-dependent analysis of low VDD program operation in double-gate SONOS memories by full-band Monte Carlo simulation

Abstract

In this paper, we investigate warm electron injection (WEI) as a mechanism for NOR programming of double-gate SONOS memories through two dimensional (2D) full-band Monte Carlo simulations. WEI is characterized by an applied VDS smaller than 3.15 V, so that electrons cannot easily accumulate a kinetic energy larger than the height of the Si/SiO2 barrier. We perform a time-dependent simulation of the program operation where the local gate current density is computed with a continuum-based method and is adiabatically separated from the 2D full Monte Carlo simulation used to obtain the electron distribution in the phase space. Trapping and detrapping from the nitride layer is taken into account by using a simplified Shockley–Read–Hall model. In this way, we are able to compute the time evolution of the charge stored in the nitride layer and of the threshold voltages corresponding to forward and reverse biases. We show that WEI is a viable option for NOR programming in order to reduce power supply and preserve reliability and complementary metal-oxide-semiconductor logic level compatibility. With the limitations of our adopted physical model, our results confirm the experimental observation showing that WEI provides a well localized trapped charge and offers interesting perspectives for multilevel and dual bit operation, even in devices with negligible short channel effects.