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Comparativa e specifiche sulle Compact Flash Industriali

SLC vs. MLC: An Analysis of Flash Memory


2. Flash memory Explained

It is important to understand what makes up a Flash cell before explaining the variation between SLC and MLC Flash. Each cell consists of a single transistor, with an additional “floating” gate that can store electrons. Figure 2 shows the architecture of an SLC cell.

Figure 2: Flash Transistor Cell
A large voltage difference between the drain and the source, Vd – Vs, creates a large electric field between the drain and the source. The electric field converts the previously nonconductive poly-Si material to a conductive channel, which allows electrons to flow between the source to the drain.

The electric field caused by a large gate voltage, Vg, is used to bump electrons up from the channel onto the floating gate. As an electron travels closer to the drain, it gains more momentum and thus, more energy. But, this amount of energy is not enough to push an electron onto the floating gate. Electrons with high momentum near the drain can sometimes bump into Si (Silicon) atoms. This bump gives the electron enough energy to be pushed onto the floating gate.

The number of electrons on the floating gate affects the threshold voltage of the cell Vt. This effect is measured to determine the state of the cell.