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Although planar floating gate (FG) device using high-K IPD has been proposed, our study indicates that out tunneling through IPD due to the high electric field is inevitable, leading to programming/erasing saturation. Moreover, charge trapping in IPD is a major concern. In this work, we propose a completely different approach - using a trapping IPD for storage. Our concept is to combine the merits of CT and FG - CT for good retention and scaling to few-electron regime and FG for edge effect immunity and faster erase. The planar “fusion” FG/CT devices are fabricated by replacing the conventional IPD ONO of a FG device by a CT BE-SONOS structure. Both simulation and experimental results indicate that most of the stored electrons are trapped inside the SiN trapping layer instead of the FG. The CT storage provides excellent retention even for a very thin tunnel oxide (≪5nm). On the other hand, the thin FG provides an equipotential channel that screens any non-uniform injection effect. Excellent memory window, scalability and reliability are demonstrated.

Sub-30nm TFT CT NAND flash devices have been extensively studied. Although TFT devices were often believed to have much worse performance than bulk devices, our results show that as devices scale down to sub-30nm, the DC characteristics (such as read current and subthreshold slope (S.S.)) approach those of the bulk devices because sub-30 nm TFT devices often contain no grain boundaries. The memory window is also larger than the bulk planar devices due to the tri-gate structure that enhances the electric field during programming/erasing. However, a fair percentage of devices contain grain boundaries with poorer S.S. and g m . Interestingly, this only affects the DC characteristics but does not impact the memory window. Furthermore, grain boundaries do not increase the random telegraph noise. The most serious drawback of grain boundaries is the impact on self-boosting window caused by junction leakage. A sub-30 nm TFT BE-SONOS NAND device with MLC capability and good retention is demonstrated