Charge Storage Mechanism in Nano-Crystalline Si Based Single-Electron Memories

Abstract

AbstractA memory device sensitive to a single electron stored in a nanocrystalline Si dot has been synthesized allowing for the study of charge retention lifetime. A 50 nm by 20 nm transistor channel is synthesized by E-beam lithography followed by reactive ion etching of thin (20nm) Silicon-on-Insulator (SOI) channel. This small area of the narrow channel allows for the isolation of a single nano-crystalline Si dot and elimination of channel percolation paths around the screening charge. Remote Plasma Enhanced CVD is used to form 6±2nm diameter nc-Si dots in the gas phase from a pulsed SiH4 source. Electrons stored in a dot results in an observed discrete threshold shift of 90 mV. Analysis of lifetime as a function of applied potential and temperature show the dot to be an acceptor site with nearly Poisson lifetime distributions. An observed 1/T2 dependence of lifetime is consistent with a direct tunneling process, thus interface states are not the dominant mechanism for electron storage in this device structure. Median lifetimes are modeled by a direct tunneling process, which is influenced by gate bias and dot size.