Radiation effects in nitride read-only memories

We report on the influence of different types of radiation on the nitride read-only memories (NROM (R)). The memory cells were irradiated by light ions (Boron). X-rays and gamma-rays. Memory transistor parameters, such as threshold voltage and subthreshold drain leakage were studied as a function of the accumulated radiation dose and compared to the as-programmed (-erased) devices parameters. Their time evolution was registered in the range from few hours up to 5 months after the irradiation. The NROM cells showed good radiation robustness up to high accumulated doses. Sufficient program margin (difference of threshold voltage in the programmed state and the read-out voltage level) remained after gamma or X irradiation for absorbed doses exceeding 50 krad(Si) and 100 krad(Si), respectively. For Boron irradiation, the programmed devices remained stable up to the fluence of 10(11) ions/cm(2) (equivalent to 1 Mrad(Si) of TID tolerance).