Investigation of ultra thin polycrystalline silicon channel for vertical NAND flash

We have investigated thin film transistors (TFTs) with ultra-thin polycrystalline silicon (poly-Si) of 77 Å - 185 Å. The TFT charge transfer characteristics such as ON current and effective mobility are dominated not by the thickness itself but by the grain size of poly-Si channel. When the poly-Si channel thickness is decreased with the same grain size, the sub-threshold TFT characteristics are improved without degradation of ON current and reliability properties. These results give us appropriate criteria to establish an excellent poly-Si channel in vertical NAND flash memory.