The threshold voltage fluctuation of one memory cell for the scaling-down NOR flash

Abstract

The threshold voltage (Vth) fluctuation for the NOR flash memory scaling is investigated. The Vth fluctuations for one memory cell in 45nm node are dramatically increased to 350% compared to 90nm generation due to the reduction of channel area and the increase of channel doping level. Here, as the cell size is scaled, the impact due to random telegraph noise (RTN), Dopant Fluctuation and etc become more critical. In 45nm technology, the RTN results in the Vth fluctuations of 60% from the measurement results. Furthermore, we also propose one solution with the channel doping engineering to suppress the Vth fluctuations. It is confirmed that maximum RTS amplitude at the center can be significantly decreased to below 20% in 45nm technology by the modification of channel doping profile. From this result, the Vth fluctuations within one NOR flash cell are the most critical issue for the cell size scaling, and can be effectively suppressed by the optimal channel engineering.