Nonvolatile semiconductor memory and method of rewriting data thereto

Abstract

The promotion of reduction of the power source voltage for use in a nonvolatile semiconductor memory is attained by using a method wherein memory cells each of which includes a control gate having a floating gate above a channel region, and a source constituted by an N-type impurity diffusion layer enclosed with a high impurity concentrated P-type diffusion layer containing impurities the impurity concentration of which is higher than that of a P-type well are formed in double wells made up of an N-type well and the P-type well which are formed in a P-type silicon substrate, the electric potentials at the N-type well and the P-type well are controlled independently to each other to write data to the memory cell by utilizing the tunnel phenomenon, the electrical potential at the P-type well is made negative, and under this condition, a relatively low positive voltage and a high voltage are respectively applied to the control gate and the source and the hot electrons generated in the vicinity of the source are injected into the floating gate through the channel region by utilizing the tunnel phenomenon to erase the information stored in the memory cell.