Memory traps in MNOS diodes measured by thermally stimulated current

Abstract

Thermally stimulated current was measured to determine trap distribution and charging and discharging mechanisms in a Metal-Nitride-Oxide-Semiconductor (MNOS) diode with 16 Å oxide thickness. By changing gate voltage, heating rate and the initial flat-band voltage, the memory traps near the nitride-oxide interface were separated from the others. The general formula was derived for the thermally stimulated current in an MNOS diode and was applied to obtain the trap distribution as well as effective emission time constants. The results indicate that the memory traps are distributed 50 Å deep into the nitride film from the nitride-oxide interface. The energy level lies at around 2·55 eV from the bottom of the nitride conduction band. The charging and discharging mechanism is the cascade connection of tunneling and thermal excitation or trapping. The obtained trap distribution and the charge transfer mechanism are successful for interpreting the write-in and retention characteristics.