NONVOLATILE ANALOG MEMORY

PURPOSE:To obtain a nonvolatile analog memory of holding characteristic stable for a long time and sufficient output width by a method wherein the shift width of threshold voltage and beta of a memory element are set at a specific value, with the threshold voltage as the center immediately after manufacture. CONSTITUTION:A nonvolatile memory by an FET having a floating gate 4 and a control gate 6 can store the analog value, since the threshold voltage Vt varies according to the writing voltage Vd, and the drain current Id at the time of readout varies in response to Vt. Vt set by write is converged into the threshold value V0 immediately after manufacture by being left to stand, and the shift width is larger as Vt is larger. At the time of the voltage VG impressed on the control gate 6, Vt=(2Id/beta)-VG, and the values of changes of the Vt shift width and the holding characteristic are approximately proportional. Sudden increase of drift is restrained by setting the Vt shift within a width of 1.83V, and decrease of output Id due to the reduction of widths is prevented by setting beta>100. By this constitution, a nonvolatile memory for storing analog values of holding characteristic stable for a long time and sufficient output width can be obtained.