Non-volatile semiconductor memory device with nand type memory cell

Abstract

An electrically erasable programmable read-only memory is disclosed which has programmable memory cells connected to parallel bit lines provided above a semiconductor substrate. The memory cells include NAND cell blocks each of which has a series array of memory cell transistors. Parallel word lines are connected to the control gates of the memory cell transistors, respectively. In a data write mode, a selection transistor in a certain NAND cell block including a selected memory cell is rendered conductive to connect the certain cell block to a corresponding bit line associated therewith. Under such a condition, electrons are tunnel-injected into a floating gate of the selected memory cell transistor, and the threshold value of the certain transistor is increased to be a positive value. A logical data is thus written in the selected memory cell transistor. The data in the selected cell transistor is erased by discharging carriers accumulated in the floating gate thereof to its drain or the substrate, so that the threshold value of the certain transistor is decreased to be a negative value.