| 摘要 |
PROBLEM TO BE SOLVED: To provide a multivalent mask ROM of higher degree of integration. SOLUTION: This is a mask ROM which stores at least trivalent or more data, with a memory central transistor arranged in matrix form, and impurities in the concentration geared to each data value to be stored, out of at least three kinds of concentration being varied, according to the storage data values, are injected severally into the channel region of each memory cell transistor, and the threshold voltage value of each memory cell transistor is set. To be concrete, in the memory cell transistor in which to set the threshold voltage lower, the quantity of implanted ions is set small, and in the memory cell transistor in which to set the threshold voltage higher, the quantity of implanted ions is set large. |
