Effects of previous ionizing radiation exposure on programming EPROMS

Different effects are observed for FGMOS cells exposed while in "0" and "1" states. If reprogrammed to the "0" state, cells exposed in the 1 state take longer to erase under UV exposure than those cells exposed in the "0" state. This difference in UV-erasure time is attributed to charge removal from the floating gate in the "0" state cells. This difference in erasure time between the "0" and "1" states is proportional to the absorbed dose and is not dependent on annealing and temperature, a big advantage in most dosimetry applications. Cells exposed in the "1" state are also observed to fail to program at very low doses if programming is attempted within a few days of exposure.