Physical origin of long-term charge loss in floating-gate EPROM with an interpoly oxide-nitride-oxide stacked dielectric

The long-term charge loss characteristic in a floating-gate EPROM cell with an oxide-nitride-oxide (ONO) interpoly stacked dielectric has been studied quantitatively. It is found that trapped electrons at the nitride-oxide interface can directly tunnel through a thin approximately 30-AA top oxide. The estimated tunneling barrier height is about 2.6 eV, which is consistent with the previous result based on MNOS studies. The thermal activation of the long-term charge loss is believed to be caused by the availability of trapped electrons at the top oxide-nitride interface. The thermal activation energy of the long-term charge loss is about 0.37 eV, which is similar to the activation energy of the second phase. It is believed that the trapped electron density at the top oxide-nitride interface becomes larger at higher temperatures due to the activated electron movement during the second phase.<>