Numerical Simulation of Non-Volatile Memories

The trend towards ever decreasing geometries is making the non-volatile memory cell design task increasingly difficult. For reduced cost and time to market, simulation tools are essential to reduce the number of experiments on silicon wafers which are becoming increasingly expensive due to the increase in process complexity with each new generation [1]. A general purpose two-dimensional device simulator which allows the complete transient simulation of non volatile memories has been developed. Three models were identified which were necessary to simulate the electrical characteristics of EPROM, EEPROM and flash-EEPROM devices. These were Fowler-Nordheim tunneling, Band-to-Band tunneling and hot electron injection. All three models were incorporated into the drift-diffusion and hydrodynamic device simulator HFIELDS [2,3]. The models were carefully validated with appropriate measurements from test structures and devices. The enhanced program represented the first complete tool capable of modeling all the most important effects in floating gate memory devices.