A New Physical Model for Program Transients of Cylindrical Charge-Trap-Based NAND Flash Memories

A new physics-based model to explain program transient of NAND Flash memory cells is developed in this work. Unlike preexisting model, which incorporated structural features of cylindrical cell through an arbitrary adjustment of energy band offset in a planar one, our model is uniquely devised based on cylindrical coordinates, from the beginning. Electrostatic solution from 1-D Poisson equation is used to solve the continuity equation for the free carrier concentration inside charge trap nitride (CTN), and the memory cell is modeled as a capacitor with time-varying charge to track the behavior of its threshold voltage. It is shown that newly proposed model can also predict incremental step pulse programming (ISPP) slope degradation more precisely than the prior model, due to prediction of a larger electric field at the CTN -blocking oxide (BOX) interface, which leads to larger escaping current. The model shows a good fit between the experimental data of three-gate GAA test vehicles and modeling results, displaying a better fit than the previous model.