| 摘要 |
A contactless mask programmable read-only memory (Mask ROM) is described, comprising a plurality of word lines extending in row direction and a plurality of diffusions arranged in rows and columns in a substrate. In the Mask ROM, two rows of diffusions are separated by a word line. Two adjacent diffusions in the same column, the word line between the two diffusions, and the substrate between the two diffusions together constitute a memory cell. The memory cells include a plurality of first memory cells and a plurality of second memory cells. The channel length, the gate oxide width or the channel dopant concentration of the first memory cells is different from that of the second memory cells, such that the threshold voltage of the first memory cells is substantially different from that of the second memory cells.
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