| 摘要 |
PURPOSE:To make it possible to record the data of 2 or more bits in one memory cell by forming source and drain regions of a MOS transistor, a memory cell, from regions which differ in either impurity density or diffusion depth or in both of them and by conducting ion implantation near a channel of the MOS transistor. CONSTITUTION:When the ions are implantated to the drain side of a transistor, the density of an LDD part 9 becomes lower and therefore the LDD part 9 becomes a depletion layer due to the potential difference between the LDD part 9 and a substrate 1. As a result, the LDD part 9 does not have much effect on the drain current ID. When the ion is injected to the source side of the transistor, on the other hand, the LDD part 9 is nearly at the same potential as the substrate and therefore it serves for a high resistance and the current is limited at the LDD part 9. As a result, ID is very small in the condition (b) and the written data is ignored in the inverse voltage-applied condition (a). Consequently, 2-bit data can be stored easily by the use of a single MOS transistor. |
