Granular electron injection and random telegraph noise impact on the programming accuracy of NOR Flash memories

This work investigates for the first time charge-granularity effects during channel hot-electron programming of NOR flash memories, comparing the granular electron injection and the random telegraph noise limitations to the accuracy of the programming algorithm. The spread of the threshold voltage shift that is determined by the electron injection statistics is studied as a function of the channel hot-electron programming conditions, explaining the results by an analytical model accounting for the sub-Poissonian nature of the electron transfer to the floating gate. The scaling trend of the injection statistical spread is then investigated on NOR technologies ranging from 180 to 45 nm and its contribution to the width of the threshold voltage distribution in presence of a program verify level is separated from that given by random telegraph noise.