NONVOLATILE SEMICONDUCTOR MEMORY DEVICE HAVING CELL STRING WITH THE STRUCTURE FOR PREVENTING THE DEGRATION OF DIELECTRIC

摘要

A non-volatile semiconductor memory device with a cell string having a structure for reducing deterioration of an insulation layer is provided to improve identity of the operation characteristic of every memory cell included in one cell string by making every memory cell have an adjacent memory cell such that the memory cells have the same capacitance. A memory array includes a cell string which includes a plurality of serially connected normal memory cells(MC1-MC32), a ground select transistor(GST) and at least two dummy cells(DC1-DC4) serially connected between the normal memory cell at one end and the ground select transistor. The ground select transistor is gated to supply a source voltage to the normal memory cell. The normal memory cell is non-volatile, having a function for storing data. The dummy cell is excluded in storing the data. A wordline select block controls normal wordlines(WL1-WL32) for gating the normal memory cells of the memory array and dummy wordlines(DWL1-DWL4) for gating the dummy cells. In a program operation in which the normal memory cell at one end is selected, the dummy wordlines of the at least two dummy cells are controlled by sequential voltage levels between a voltage level of a signal for gating the ground select transistor and a voltage level of a normal wordline for gating the normal memory cell at one end. In an erase operation, the dummy wordlines are controlled by the same voltage level as that of the normal wordlines of the normal memory cells.