Charge loss after 60Co irradiation of flash arrays

Flash memories are the most important among modern nonvolatile memory technologies. We are showing new results on the threshold voltage shifts in Flash memory arrays after ⁶⁰Co irradiation. A (relatively) high total dose, exceeding 100 krad (SiO₂), is needed to induce errors in the array, but threshold voltage shifts are all but negligible even at lower doses. These shifts can be accurately described by using a model which considers the charges generated by irradiation in all the oxides surrounding the floating gate. We are also showing that cycling (endurance) and total ionizing dose effects mutually add.