Excellent emission characteristics of tunneling oxides formed using ultrathin silicon films for flash memory devices

Abstract

A novel technique using oxidized ultrathin rugged polysilicon films on silicon substrates has been appied to significantly improve the tunneling efficiency of thin oxides. As compared with oxidized amorphous silicon films, these rugged polysilicon films can achieve a higher emission current. High-resolution transmission electron microscopy (HRTEM) was used to observe the atomic-scale microtips at the SiO2/Si and polysilicon/SiO2 interfaces. According to the extracted geometry parameters of the microtips, a two-dimensional numerical simulator based on the finite difference method using the curved emitting surface of microtips can well explain the remarkable current asymmetry of the dielectrics. This suggests that the oxidized rugged polysilicon films can form higher microtips and smaller tip angles, resulting in better emission characteristics that will enable potential applications to future 5-V-only nonvolatile memories.