computer hardware, consumer electronics, electronic components  

Flash memory

Nonvolatile memory is currently available in several forms, including electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), and flash EEPROM. Flash memory is a non-volatile type of memory which can be rewritten and retain its data content without power. Flash memory has been widely used for high volume data storage in devices such as personal computers, personal digital assistants (PDAs), digital cameras, and cellular telephones. Program code and system data such as a basic input/output system (BIOS) are typically stored in flash memory devices for use in personal computer systems. A typical flash memory comprises a memory array, which includes a large number of memory cells. Each of the memory cells includes a floating gate field-effect transistor capable of holding a charge. The cells are usually grouped into blocks. Each of the cells within a block can be electrically programmed in a random basis by charging the floating gate. A flash memory is provided with a high-voltage transistor and a low-voltage transistor for driving cells in view of a device's characteristic. A gate oxide film of the high-voltage transistor has a thick thickness, a gate oxide film of the low-voltage transistor has a thin thickness, and a gate oxide film of the cell has the same or similar thickness as those of the low-voltage transistor. Two common types of flash memory array architectures are the "NAND" and "NOR" architectures, so called for the logical form in which the basic memory cell configuration of each is arranged. In the NOR array architecture, the floating gate memory cells of the memory array are arranged in a matrix. The gates of each floating gate memory cell of the array matrix are coupled by rows to word select lines and their drains are coupled to column bit lines. A NAND array architecture also arranges its array of floating gate memory cells in a matrix such that the gates of each floating gate memory cell of the array are coupled by rows to word select lines. The memory cells of the array are coupled together in series, source to drain, between a source line and a column bit line. A flash memory card has a flash memory and a controller.

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