Diode-type NAND flash memory cell string having super-steep switching slope based on positive feedback

Abstract

A positive feedback (PF) mechanism was adopted for the first time in the cell string of a 3-D NAND flash memory where n(+) and p(+) regions are formed on both ends of the string to implement a diode-type cell string. The body consists of a tube-type poly-Si channel. To generate the PF in the channel during a read operation, a new read operation scheme is proposed. In this paper, the simulator was calibrated in terms of trap density (D-it) of a poly-Si channel extracted from fabricated 3-D NAND flash memory cells. By utilizing the PF, a NAND flash memory cell in a cell string has a steep subthreshold swing of <1 mV/decade.