A Study on Erase Speed Enhancement of 3D Vertical NAND Flash Memories by using Bulk-Erasable Electrodes

Abstract

A bit-cost scalable (BiCS) technology using a bulk erasing method instead of the conventional erase operation using gate-induced drain leakage (GIDL) is proposed to realize better cell characteristics and process feasibility for three-dimensional (3D) NAND flash memory. A novel 3-dimensional (3-D) vertical stacked type NAND flash cell arrays using the bulk erase method is proposed. This cell arrays consist of has an additional electrode layer for a bulk erase operation in the middle of a vertical channel string cell and several rows of NAND string share control gates. We investigated the I-V characteristics of the bulk erasable-BiCS structure using 3-D TCAD simulation tool, rely on the P+ bulk electrode for high speed Program/Erase operation and good read current margin. Here, we confirmed that this novel cell technology provides better cell characteristics and process feasibility for the 3-D vertical stacked NAND flash cell arrays. Morever, junction (P+/P/P+) engineering is achieved to realize a P+ poly-crystalline silicon layer of the P+ flat plate type as a bulk electrode for better design feasibility. As a result, we expect that a bulk erasable-BiCS technology using a P+ flat plate type erase electrode can be a promising candidate tera-bit 3-dimensional vertical stacked NAND flash memory technology in the near future.