Temperature-dependent memory characteristics of silicon–oxide–nitride–oxide–silicon thin-film-transistors

This study investigates the temperature-dependent memory characteristics of polycrystalline silicon thin-film transistors with oxide/nitride/oxide stack gate dielectrics and N+ poly-Si gate structures for nonvolatile memory application. As the device was programmed by Fowler–Nordheim tunneling at high temperature, some electrons captured in shallow traps could obtain enough thermal energy to de-trap to the gate, resulting in low programming efficiency. As the programming time increases, the hole injection through the blocking oxide from the gate would further lead the threshold voltage to decrease. In addition, the retention characteristic of the device programmed at higher temperature exhibits better charge storage ability. Because the electrons trapped in the shallow traps of the nitride layer can be easily de-trapped when temperature rises, the memory characteristics are mainly dominated by charges stored in the deep traps.