New Accurate Method to Analyze both Floating Gate Charge and Tunnel Oxide Trapped Charge Profile in NAND Flash Memory

Abstract

New method to extract the amount of floating (FG) charge (Q(FG)) apart from oxide trapped charge (Q(OX)) generated by program and erase (P/E) cycles is proposed, for the first time. Q(FG) shift by P/E cycling shows asymmetry between programmed and erased states as follows; vertical bar Q(FG)vertical bar exhibits the peak at similar to 100 cycles in programmed state, while vertical bar Q(FG)vertical bar monotonically reduces in erased state. Next, the midgap voltage (V-mid) shift of the cell caused by the generation of Q(OX) is also extracted by this method. Therefore, it enables to analyze the profiles of the hole and electron-trap separately across the oxide in detail. It is demonstrated that the hole-trap is mainly distributed near to Si surface and the centroid of electron-trap is located near to the middle of oxide. In addition, it is found that hole-trap near to Si has strong dependence on erase bias.