Flash memory is a non-volatile solid state memory that maintains data even after all power sources have been disconnected. Non-volatile memory devices are currently in widespread use in electronic components that require the retention of information when electrical power is terminated. A typical flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. Each of the memory cells includes a floating gate field-effect
transistor capable of holding a charge. Each block of memory cells can store data used during system operations. To read the memory cells, a voltage is applied to the gate of the memory cells. By changing the threshold voltage of the memory cell transistor, the level of activation of the transistor can be measured using sense amplifier circuitry. Flash memory devices are generally classified into NAND flash memory devices and NOR flash memory devices. NOR flash memory devices include memory cells that are independently connected to bit lines and word lines and have an excellent random access time. The NAND array utilizes series strings of more than two memory cells, connected along with one or more select transistors between individual bit lines and a reference potential to form columns of cells. NAND flash memory devices have an excellent degree of integration and are mainly used in high-integrated flash memory devices. Flash memory is widely used in
personal computers,
notebook computers,
personal digital assistants (PDAs), various data communication devices,
digital cameras,
cellular telephones,
portable audio players, automobile sound systems, and similar types of equipment.
