Nonvolatile semiconductor memory device comprising a memory transistor, a select transistor, and an intermediate diffusion layer

Abstract

A memory transistor and a select transistor are disposed side by side on a semiconductor substrate between source/drain diffusion layers thereof, with an intermediate diffusion layer interposed therebetween. The memory transistor includes: a gate insulating film having such a thickness as to allow tunneling current to pass therethrough; a floating gate electrode; an interelectrode insulating film; and a control gate electrode. The select transistor includes a gate insulating film and a select gate electrode. Tunneling current, allowing electrons to pass through the gate insulating film under the floating gate electrode, is utilized during the removal and injection of electrons from/into the floating gate electrode. As a result, higher reliability can be attained and rewriting can be performed at a lower voltage. Also, since the select transistor is provided, reading can also be performed at a lower voltage. Improvement of reliability and rewrite and read operations at respective lower voltages are realized for a nonvolatile semiconductor memory device, in which a memory cell includes a floating gate electrode and a control gate electrode.