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Takahiro OHNAKADO Natsuo AJIKA
This paper reviews device technologies of flash memories, whose market has grown explosively due to the advantages of: (1) their low cost provided by availability of the single-transistor type cell with adoption of block-erase operation; (2) high functionality as electrically erasable and programmable non-volatile memories; and (3) high reliability with the mature floating gate technology. As for fast-random-access flash memories, their scaling issue, including a multi-level-cell technology, is discussed, and technologies for low power consumption, which is highly demanded for mobile electronic equipment, their major application, are described. Furthermore, device technologies of serial-access flash memories, which have achieved low cost with cell-size reduction, are also reviewed. Finally, a future promising technology of the NROM concept, which achieves a multi-storage-cell with low voltage operation and a simple process, is introduced.