A novel buried-channel FinFET BE-SONOS NAND Flash with improved memory window and cycling endurance

In NAND flash, devices are normally erased to negative Vt and then programmed to positive Vt. In this work we introduce a novel depletion-mode (normally on) buried-channel, junction-free n-channel NAND flash device. The buried-channel NAND flash shifts the P/E Vt ranges below those for the conventional surface-channel device, and is more suitable for the NAND Flash memory design. Due to the lower initial Vt, the device shows faster erase speed and higher immunity to read disturb. Furthermore, the buried-channel device has significantly improved cycling endurance, because the buried channel is insensitive to the interface state (Dit) generation during program/erase stressing. A lightly doped shallow n-type channel serves both as the buried bit line and as the source/drain of the junction-free structure. The short channel effects are overcome by using FinFET. The buried-channel NAND flash uses a simple program-inhibit method by directly raising the buried bit line potential without introducing a deep depletion in the conventional self-boosting method. A successful sub-30 nm buried-channel FinFET BE-SONOS NAND flash with MLC is demonstrated.