Simulation and Modeling of SONOS Non-Volatile Memory

Rani, Asha
Master of Science in Electrical Engineering
Defense Date: 
Monday, April 26, 2010

Silicon-Oxide-Nitride-Oxide-Silicon (SONOS) memory is one of the best non-volatile, FLASH-like memories for the next-generation electronic devices which require highlevel portability, stand-alone capability and low-power consumption for extremely long battery life. As the dimensional CMOS scaling for better performance, the application of high-k dielectric (e.g., oxide-nitride layer) to replace current floating polysilicon gate is the most attractive strategy to meet the challenges of conventional floating-gate FLASH memory: reliability issue and lateral interaction.

In this work, SONOS memory cells with varying dielectric thickness have been systematically and analytically studied by using a SYNOPSIS Technology CAD simulation and modeling tool. The mechanisms of carrier tunneling and memory retention of the memory cells have been tested by simulation and studied in detail. In addition, Hafnium oxide (HfO2) as charge trapping layer has also been analyzed by using TCAD simulation.

From the simulation results we have the following conclusions: (i) as the thickness of charge-storage dielectrics (e.g., Si3N4 and HfO2) increases, the threshold voltage shift increases due to the higher capture probability of electrons; (ii) as the thickness of tunneling oxide decreases, the programming speed increases due to the higher electric field across the tunneling oxide; (iii) as the channel length decreases from 210 nm to 70 nm, threshold voltage shift increases with increasing program time; (iv) as the temperature increases, threshold voltage shift decreases. In summary, the SONOS-like nonvolatile memory is a strong candidate for future high density, high-performance, portable electronics.