Improvement of EEPROM cell reliability by optimization of signal programming

This paper presents an optimization study of electrically erasable programm able read-only memory (EEPROM) cell programming to increase the long-term r eliability of the device. Based on a charge-sheet model of the memory cell, we suggest that our result show that it is possible to decrease the electr ic field across the tunnel oxide of approximately 0.8 MV/cm, when using a p articular programming waveform with a double rise ramp. We get the same sim ulated injected charge in write mode (+15 fC) and in erase mode (-12 fC) wi th the optimized programming signal rather than with the standard one. Thre shold voltage measurements confirm the simulation results. Moreover, the en durance test shows that this new programming signal improves the endurance of the memory cell without any change in the device technology, memory cell lifetime becomes four times longer. (C) 2001 Elsevier Science B.V. All rig hts reserved.