NONVOLATILE MEMORY CELL AND ADJUSTING METHOD FOR ITS THRESHOLD VALUE, ADJUSTING METHOD FOR THRESHOLD LEVEL OF PLURAL TRANSISTORS, NONVOLATILE MEMORY AND ITS OPERATIONAL METHOD

摘要

PURPOSE:To obtain a nonvolatile semiconductor memory using nonvolatile memory cells in which a threshold level can be easily and accurately adjusted and its operational method. CONSTITUTION:A memory transistor 1 provided with a floating gate is connected to a selecting transistor 8, a memory node N is provided with a capacity element 9 consisting of parasitic capacity or the like. After a drain electrode D of the memory transistor 1 is kept at a high potential, the memory transistor 1 is made a floating state, gate voltage of pulse-like swinging from positive to negative is applied to a gate electrode 2, and a threshold level of the memory transistor having a different level is adjusted to the prescribed level.