SELECT GATE MATERIALS HAVING DIFFERENT WORK FUNCTIONS IN 3D NAND NON-VOLATILE MEMORY

摘要

In a 3D stacked non-volatile memory device, multiple smaller drain-end selected gate (SGD) transistors replace one larger SGD transistor. The SGD transistors have different work functions in their control gates so that, during a programming operation, a discontinuous channel potential is created in an inhibited NAND string. The SGD transistor closest to the bit line has a higher work function so that the channel potential under it is lower, and the next SGD transistor has a lower work function so that the channel potential under it is higher. The different work functions can be provided by using different control gate materials for the SGD transistors. One option uses p+ polysilicon and n+ polysilicon to provide higher and lower work functions, respectively. Metal or metal silicide can also be used. A single SGD transistor with different control gate materials could also be used.