Investigation of Program Noise in Charge Trap Based 3D NAND Flash Memory

Abstract

The mechanisms and characteristics of program noise (PN) in charge trap based 3D NAND flash memory are investigated in this work. Electron injection statistics is found to be primarily responsible for PN. Moreover, it is found that PN gets worse after program and erase (PE) cycling in 3D charge trapping memory devices. A physical model is proposed to explain the observations. After heavy cycling stress, new traps are generated in the tunnel oxide, and more charges can be trapped. As a result, program speed increases and charge centroid shifts towards the tunnel oxide, which lead to worse PN. Furthermore, the upper part of Vt distribution is broadened after heavy PE cycling. The contribution of the worse PN to the upper part broadening after cycling is studied through Monte Carlo simulation.