Substrate-current-induced hot electron (SCIHE) injection: a new convergence scheme for flash memory

Abstract

A new convergence scheme is designed to achieve a fast speed, low power and highly reliable operation for existing flash EEPROM technology. By applying a substrate bias and lowering the drain voltage, the gate injection is found to move from Drain-Avalanche-Hot-Carrier (DAHC) injection to Substrate-Current-Induced Hot Electron (SCIHE) injection. Compared to the well-known DAHC convergence scheme, the new SCIHE scheme shortens the convergence time over a hundred times, reduces the total drain and substrate currents significantly for block convergence, and makes the device degradation negligible. Bias conditions are optimized for flash cells with medium channel doping of about 3/spl times/10/sup 17/ cm/sup -3/, 0.85 /spl mu/m gate length and 73 /spl Aring/ gate tunnel oxide to realize convergence times under 250 /spl mu/s using this new low power scheme.