| 摘要 |
<p>An accumulation region (15) comprises many dispersed dots (15a) whose surface density is higher than that of structural pin-holes produced in a tunnel insulating film (14a). Alternatively, the number of dots (15a) in the accumulation region (15) is determined to be five or more. Alternatively, a conduction region (13c) is formed in a polysilicon layer (13) whose surface roughness is greater than 0.1 nm and less than 100 nm. The number of dots (15a) in the accumulation region (15) is larger than the number of grains in the conduction region (13c). Even if defects, such as pin-holes, occur in the tunnel insulating film (14a) and charges accumulated in some dots leak, the charges accumulated in the dots in the regions where no defect is present do not leak. Therefore, information can be held for a long time.</p> |
