A novel double-density single-gate vertical-channel (SGVC) 3D NAND flash featuring a flat-channel device with excellent layer uniformity

Abstract

We have developed a novel single-gate vertical channel (SGVC) 3D NAND Flash architecture. The device is a single-gate, flat-channel TFT charge-trapping device with ultra-thin body. The ultra-thin body TFT device enables tight initial Vt distribution as well as excellent short-channel effect that is comparable to and sometimes superior than the more prevailing gate-all-around (GAA) macaroni devices of other 3D NAND architectures. Unlike GAA device for which the electric field is a function of channel hole curvature, the flat cell is insensitive to etching CD, thus SGVC device is very tolerable to the non-ideal vertical etching and has shown superb layer-to-layer device uniformity. Even without help from curvature (like in GAA) our SGVC flat cell achieves excellent P/E window of >10V with only modest interferences that can support TLC (3 logic bits per cell) operation. Owing to the double-density in a single WL trench and much more efficient array design with minimal overhead, SGVC architecture offers 2 to 4 times memory density than GAA VC 3D NAND at the same stack layer number.