The influence of bottom oxide thickness on the extraction of the trap energy distribution in SONOS (silicon-oxide-nitride-oxide-silicon) structures

The charge retention characteristics of SONOS (silicon-oxide-nitride-oxide-silicon) nonvolatile memory cells at elevated temperatures were investigated. Assuming the thermal excitation model to be the dominant charge loss mechanism, the trap energy distribution in the nitride was determined. We present an improved model which includes the influence of subsequent tunneling of the charge carriers through the bottom oxide after being thermally emitted into the conduction band of the silicon nitride. The trap energy distribution was evaluated from samples with different bottom oxide thicknesses. Using this model it was found that the detected trap energy distribution is nearly identical despite the different tunneling probabilities from the various bottom oxide thicknesses.