Introduced by Toshiba Corporation in 1987, NAND Flash memories contain a transistor array with 16 to 32 transistors in series. The name for these devices also stems from their cell structure, in that the bit line goes to a logic low level only if all the transistors in the corresponding word lines are turned on. This functionality is similar to that of a NAND logic gate, and that is where the name "NAND Flash" for these devices comes from. NAND Flash devices also feature memory cells that occupy a smaller area per bit than their NOR Flash counterparts. The programming current into the floating gate is very small because NAND Flash devices use Fowler-Nordheim tunneling for both programming and erasure. Therefore, the power consumption for programming does not significantly increase even as the number of memory cells being programmed is increased. As a result, many NAND Flash memory cells can be programmed simultaneously so that the programming time becomes very short. The architectures in use at a commercial level in this field are SLC (Single Level Cell) and Multi-Level Cell (MLC) designs. Some companies are researching and have patented enhanced technologies, such as a 4-bit-per-cell technology, which may gain more popularity in the future. The main suppliers of NAND Flash memory products at this time (June 2007) are Samsung, Toshiba, SanDisk, Hynix, and ST Microelectronics. In addition, a number of other manufacturers manufacture memory cards and modules, as well as adapters appropriate to these cards and modules.

Contributed By:

Farzin Jahed
Applications and Product Engineer
Statek Corporation