Channel Stacked Array NAND Flash Memory With Vertically Stacked String Selection Line (SSL)

Abstract

Three-dimensional (3D) stacked memory devices are representative solutions that can lead to reduce bit cost of NAND flash memories. Recently, many groups have proposed various types of 3D stacked NAND flash memory devices. In this thesis, we propose a novel 3-D STacked Array (STAR) NAND flash memory featuring Gate-All-Around (GAA) structure with single crystalline Si channel. In Chapter 1 and 2, we introduce a newly designed structure, compact STAR, and address the advantages of compact STAR over other types of 3D stacked NAND flash memories. By using TCAD simulation, we demonstrate that the proposed array structure can support fully compatible device operation with conventional NAND array. In Chapter 3 and 4, we investigate the advantages of metal gates in a 3D stacked NAND flash memory compared with poly-Si gates in terms of the variation of dopant concentration. Also, we show the fact that NAND flash memory cells featuring a GAA structure are less sensitive to the variation of the gate dimensions than cells featuring a DG structure. In Chapter 5, we investigate the cell characteristics with respect to physical dimensions of channel and gate experimentally. Poly-Si channel with GAA structure flash memory cells are successfully fabricated.