Threshold Voltage Variability of NROM Memories After Exposure to Ionizing Radiation

Threshold voltage (Vth) behavior of nitride readonly memories (NROMs) was studied after irradiation with photons (γ- and X-rays), light and heavy ions. Both programmed and nonprogrammed single cells were investigated. The data suggest that two main physical phenomena are contributing to Vth variation and that the Vth loss and the variability can be modeled by a Weibull statistics with a shape parameter k~2.2 regardless of the irradiation species and total dose. The same peculiarities were found in large memory arrays, confirming the results from single-cell studies but with significantly larger statistics. Hence, once the irradiation dose is known, the Vth loss distribution can be obtained, thus providing a predictive model of the radiation tolerance of NROM memory arrays.