Improvement of EEPROM cell reliability by optimization of signal programming

This paper presents an optimization study of electrically erasable programmable read-only memory (EEPROM) cell programming to increase the long-term reliability 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 electric field across the tunnel oxide of approximately 0.8 MV/cm, when using a particular programming waveform with a double rise ramp. We get the same simulated injected charge in write mode (+15 fC) and in erase mode (−12 fC) with the optimized programming signal rather than with the standard one. Threshold voltage measurements confirm the simulation results. Moreover, the endurance 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.