Charging And Intrinsic-leakage Current Peaks In Thin Silicon-dioxide Films

A new leakage mode in thin SiO, films which may affect the retention characteristics of flash memories is examined. To improve the reliability of flash memories, electrical properties of the gate oxide were studied by using MOS capacitors. Since a transient current as well as a steady current is observed in a MOS capacitor under a constant gate bias, the time dependence of the current was measured to separate these currents. Through this operation, current peaks were found in both the transient and the steady current dependences on the gate bias. The peak for the transient current can be explained by resonant tunneling through traps near the oxide interface, and that for the steady current can be attributed to resonant tunneling leakage through traps distributed in the bulk oxide. The latter mechanism is a form of intrinsic leakage that affects the retention characteristics, and thus it should be considered in designing flash memories.