Flash memory is non-volatile, that no power needed to maintain the information stored in the chip. In addition, flash memory offers fast read access times (though not as fast as volatile DRAM memory used for main memory in PCs) and flash memory is better shock resistance than other hard disks. These characteristics explain the popularity of flash memory for applications such as storage on battery-powered devices.
1.1 Operation Principles
The information is stored in Flash memory as an array of floating gate transistors, called "cells", each of which traditionally stores one bit of information. Newer flash memory devices, sometimes referred to as multi-level cell devices, can store more than 1 bit per cell, by varying the number of electrons placed on the floating gate of a cell.
1.2 Structure and Operation of Flash Memory
Flash memory uses memory cells similar to an EPROM, but with a much thinner, precisely grown oxide between the floating gate and the source (see Figure 1). The flash memory cell functions by storing charge in the floating gate. The presence of charge will then determine whether the channel will conduct or not. During the read cycle a "1" at the output corresponds to the channel being in its low resistance or ON state. The Control gate is used to charge up the gate capacitance during the write cycle.