Semiconductor memory device for storing image data

Abstract

A first insulating film of a light-transmitting material is formed on a channel region between the source and drain regions on a semiconductor substrate. A floating gate electrode is formed on the first insulating film. A second insulating film is formed on the floating gate electrode. A control gate electrode is formed on the second insulating film. An opening is formed to extend through the control gate electrode, the second insulating film, and the floating gate electrode. The opening is filled with a light-transmitting material. Light incident on the memory cell is guided by the material onto the channel region. When light becomes incident on the channel region while predetermined voltages are applied to the control gate electrode and across the source and drain regions, electron-hole pairs corresponding to the amount of light incident on the memory cell are generated in the channel region, and the electrons are trapped in the floating gate electrode. The threshold value of the memory cell is changed in accordance with the amount of electrons trapped in the floating gate electrode. The memory cell stores digital data in accordance with the change in threshold value, i.e., corresponding to the amount of light incident thereon. When a plurality of memory cells are arranged in a matrix, image data can be two-dimensionally input and stored in the array.