Study of electron and hole injection statistics of BE-SONOS NAND Flash

Abstract

The electron and hole injection statistics of BE-SONOS NAND Flash is studied for the first time using a 75 nm charge-trapping NAND Flash test chip. By using the incremental step pulse programming (ISPP) method the impact of device variations are minimized and the electron number ( N ) fluctuation can be identified. We find that both electron and hole injection statistics well follow the Poisson statistics ( Sigma ∞ √N, where Sigma corresponds to the distribution width). However, due to the 3D fringing field effect the small transistors require more charge injection to obtain the same memory window, and this reduces the proportional factor of Sigma. We also found that the hole injection distribution is slightly broader than the electron injection, and can be explained by the lower charge centroid in nitride which leads to the larger proportional factor. Based on these results, we can also simulate the distribution for various technology nodes.