Impact of Cell Shape on Random Telegraph Noise in Decananometer Flash Memories

This paper presents a comprehensive numerical study of the impact of cell shape on random telegraph noise (RTN) in nanoscale Flash memory devices. The statistical dispersion of the RTN fluctuation amplitude is computed using both classical and quantum-corrected 3-D TCAD simulations of devices featuring three different active-area shapes (planar, rounded edges, and full rounded), with self-aligned or surrounding floating gate. For both the floating-gate geometries, results show that RTN immunity is enhanced by increasing the rounding of the active-area edges in the width direction, due to a more uniform source-to-drain conduction during read. For this analysis, the importance of quantum-mechanical corrections for the correct evaluation of the RTN distribution of sharp-edge devices is highlighted. Finally, the reduction of RTN by cell shape engineering is shown to be anticorrelated with the reduction of cell threshold-voltage variability.