Investigation of Geometric Effect Impact on SONOS Memory in a NAND Array Structure

Geometric effects on program/erase speeds, endurance, and charge retention of polysilicon-oxide-nitride-oxide-silicon-type memories are investigated with various structures, including Flash cells, capacitors, and NAND array strings of different dimensions. NAND strings with common word-lines or/and bit-lines were employed to characterize the Lg and W effect on device performance, which builds up the capability to extrapolate the cell properties of various dimensions. For a charge trapping storage device, it suggests that the evaluation carried out on a large-area device always leads to a conclusion more optimistic than the cell inside array of a real product in all aspects. In addition, a numerical model is proposed to elucidate the observed phenomena from a statistical viewpoint.