Variability in FG Memories Performance After Irradiation

Every time a heavy ion crosses a programmed Floating Gate (FG) in a nonvolatile memory array, it quickly discharges the FG and it produces a number of defects in the tunnel oxide, depending on its linear energy transfer (LET). These defects can build up a multitrap assisted tunneling path which allows electrons stored in the FG to escape it, every time the FG is programmed after irradiation [this phenomenon is called radiation-induced leakage current (RILC)]. We are showing by using retention and gate stress experiments that RILC has peculiar erratic characteristics, similar to those found for stress-induced leakage current (SILC). The erratic behavior is due to changes in the occupation states on defects, resulting in orders-of-magnitude changes in the tiny (Lt1 fA) current responsible for the FG discharge