Suppression of Threshold Voltage Fluctuation by Control of Channel Profile for NOR Flash Memory Scaling

The threshold voltage fluctuation of one cell in NOR flash memory is investigated for the first time. The threshold voltage fluctuation of one memory cell is significantly increased by the dopant fluctuation and random telegraph signal (RTS) as the cell size is scaled down. The threshold voltage fluctuation due to RTS occupied over 50% of the total variation of one NOR memory cell, and this impact continues to increase for smaller cell area, according to the experimental result. Furthermore, the RTS amplitude for the charge trap position in a tunnel oxide is investigated by device simulation, and it is revealed that the channel doping profile significantly affects the RTS amplitude. This result indicates that the threshold voltage fluctuation of one cell in NOR flash memory is one of the most critical issues in further cell size reduction, and it is expected to be suppressed by adopting an optimal channel doping profile.