Multilevel vertical-channel SONOS nonvolatile memory on SOI

Abstract

A first multilevel vertical-channel silicon-oxide-nitride-oxide-silicon (MLVC-SONOS) memory cell is proposed and fabricated using 0.12-μm silicon-on-insulator (SOI) standard logic process for Flash memory cell with ultrahigh density. If NAND array structure is used, the unit cell size of MLVC-SONOS is 4F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Further reduction of cell size is possible by using the multilevel concept which is originated from the steady states by two carrier transports from both the substrate and the gate. The program threshold voltages and their windows are uniform and controllable depending on the negative gate bias conditions. In addition, we propose a new endurance measurement method for multilevels and report the retention characteristics for multilevel memory operation.