A Novel nand Flash Memory With Asymmetric S/D Structure Using Fringe-Field-Induced Inversion Layer

A NAND flash memory device for sub-40-nm-node technology and beyond utilizing an asymmetric source/drain (S/D) structure to suppress short-channel effects and improve the th distribution is presented in this paper. The asymmetric S/D structure consists of a diffused junction and inversion layer which is induced by the fringe field of the gate bias voltage during NAND operation. To reduce the area overhead caused by the select transistors, a 64-cell NAND string, which is twice the number of cells used in conventional NAND devices, is also evaluated. The proposed NAND memory device is demonstrated by a 32-Mb test chip which is fabricated using a 60-nm NAND flash technology. It exhibits subthreshold slope characteristics that improved by 37% and a programmed th distribution width that improved by 35% while almost maintaining multiple-level-cell NAND flash performance requirements.