Effect of String Tapering on Threshold Voltage Distribution and Its Mitigation in a Vertical Channel 3D NAND Flash Memory

Abstract

In this work, we have investigated the impacts of taper angle and channel doping on the performance parameters of a vertical channel 3D NAND flash memory. It is found that string current and threshold voltage (VT) distribution of the word lines (WLs) along the string is influenced by both, taper angle and channel doping. Therefore, nonuniformity in VT distribution of different WLs due to string tapering is minimized by optimizing the channel doping along the string from top to bottom. Moreover, optimized channel doping leads to an improved string current. These results are crucial for the designing of high performance and reliable future 3D NAND flash memories.