SEMICONDUCTOR INTEGRATED CIRCUIT AND NONVOLATILE MEMORY ELEMENT

摘要

A nonvolatile memory element (130) constituting a flash memory is constructed such that a gate oxide film (GO2) and a gate electrode (GT2) of a transitor of another circuit formed over the same semiconductor substrate are a tunnel oxide film (GO3) and a floating gate electrode (FGT), respectively. One memory cell has a two-element one-bit construction composed of a pair of nonvolatile memory elements connected with paired complementary data lines. For the paired nonvolatile memory elements, threshold voltage states which are different from each other are set up so that they are differentially read. A word line voltage in reading operation is substantially equal to a threshold voltage (initial threshold voltage) in a thermal by equilibrium state of the non-volatile memory elements, desirably to an average of the low threshold voltage and the high threshold voltage of the memory elements. No matter whether the paired nonvolatile memory elements may be in the high threshold voltage state or in the low threshold voltage state, their threshold voltage are liable to approach the initial threshold voltage asymptotically to deteriorate in their characteristics. At this time, a word line selecting voltage is substantially equal to the initial threshold voltage, so that the read failure hardly occurs even if the characteristic deterioration of one memory element progresses relatively.