Threshold Voltage Setting Method for Layer Selection by Multi-Level Operation in Channel Stacked NAND Flash Memory

In this paper, we propose a modified channel-stacked array with a layer selection by multi-level operation (LSM) and a new string select transistors (SSTs) threshold voltage (V-th) setting method that all the SSTs on each layer are set to target V-th by using boosted body operation. To verify the validity of the new method in LSM, TCAD simulations are performed. It is verified that the V-th values of SSTs are set to the target V-th values by the new method. Moreover, memory operations are examined in TCAD simulation by the new method. As a result, stable memory operations are obtained successfully without the interference between stacked layers.