OPERATION METHOD FOR NONVOLATILE SEMICONDUCTOR MEMORY DEVICE

摘要

PURPOSE: To obtain a control system for nonvolatile semiconductor memory device in which electric rewriting can be carried out reliably at high rate. CONSTITUTION: When information is written in a floating gate type nonvolatile memory cell or the information is erased therefrom, a writing or erasing voltage is split into a plurality of voltage pulses including at least one voltage pulse having a rising time different from those of other voltage pulses. Rising of voltage pulse is made gentle immediately after starting the writing operation and a switching is made to a steep voltage pulse in the way thus preventing excess rewriting of high rate bit while allowing high rate writing of low rate bit. Furthermore, a voltage pulse rising slowly is applied immediately after starting the rewriting operation in order to relax stress being applied to a gate insulation film thus prolonging the lifetime of a memory cell.