| 摘要 |
PURPOSE: To make it possible to write four pieces of information in one memory cell by bring a transistor into or out of conduction depending on the presence or absence of a diffusion layer of a first conduction type joined with a diffusion layer of a second conduction type. CONSTITUTION: A p-type diffusion layer CD is formed in a memory cell MCi , i in junction with a n<+> -type diffusion layer D. A p-type diffusion layer is formed in a memory cell MCi-1 , i in junction with a n<+> -type diffusion layer Di and two p-type diffusion layers are formed in a memory cell MCi-1 , i-1 in junction with n<+> -type diffusion layers Di , Di-1 . When a word line WLi is selected, and a low voltage (VSS) and a high voltage (VDD) are applied to n<+> -type diffusion layers Di , Di+1 , respectively to make Di and Di+1 operate as source and drain, respectively, the memory cell MCi , i is brought out of conduction because its source is connected to the p-type diffusion layer CD and its threshold voltage is high. When Di-1 and Di are operated as a source and drain, respectively, the surface of the p-type diffusion layer CD joined with the drain of MCi , i is covered with a depletion layer extending from the n<+> -diffusion layer Di and thus MCi , i is brought into conduction. |
