Sang-Ryol Yang

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.

Characterization of novel SiO 2 /a-Si/a-SiOx tunnel barrier engineered oxide

We suggested the heterogeneously stacked oxide (HSO) for the future tunnel oxide of high density NAND flash memory. HSO has a structure of SiO2/a-Si/a-SiOx using the concept of tunnel barrier engineering. By employing HSO tunnel barrier, it was possible to fabricate the tunnel oxide, which is thicker physically and thinner electrically than the single layer tunnel oxide. The bandgap of a-SiOx can be modified, which made it possible to achieve tunnel barrier engineering without employing high-k material. By reducing the erase voltage, the reliabilities of NAND flash memory was improved.