Electrically erasable and reprogrammable read-only memory using the n-channel SIMOS one-transistor cell

The stacked-gate injection MOS transistor (SIMOS) uses a control gate stacked on the floating gate for selection of the cell during reading, programming, and erasure. Programming is achieved by the injection of hot electrons from the channel into the floating gate, resulting in a large upward shift in threshold voltage. In both states, operation is in the enhancement mode. Electrical erasure can be performed by injection of hot holes from an avalanche breakdown at the source-substrate junction and by Fowler-Nordheim electron injection from the floating gate to the source. Because the floating gate can be charged positively during the erasure, part of the channel is not covered by the floating gate, and in this way the enhancement mode of the SIMOS transistor after erasure is guaranteed. In a matrix array, the memory cell consists of the SIMOS transistor only. Decoders, read amplifiers, etc., can be integrated on the same substrate. Erasure can be performed as a block, or word-by-word. Different disturb effects on memory cells during programming and erasure are discussed. The cell area of the SIMOS memory is 850 µm². The photograph of a fully decoded 8192-bit SIMOS memory chip is presented.