| Tunneling is used to alter the placement of | | | | entire chip or to predetermined sections known as |
| electrons in the floating gate. An electrical charge, | | | | blocks. This erases the targeted area of the chip, |
| usually 10 to 13 volts, is applied to the floating | | | | which can then be rewritten. Flash memory works |
| gate. The charge comes from the column, or | | | | much faster than traditional EEPROMs because |
| bitline, enters the floating gate and drains to a | | | | instead of erasing one byte at a time, it erases a |
| ground. This charge causes the floating-gate | | | | block or the entire chip, and then rewrites it. |
| transistor to act like an electron gun. The excited | | | | You may think that your car radio has Flash |
| electrons are pushed through and trapped on | | | | memory, since you are able to program the |
| other side of the thin oxide layer, giving it a | | | | presets and the radio remembers them. But it is |
| negative charge. These negatively charged | | | | actually using Flash RAM. The difference is that |
| electrons act as a barrier between the control | | | | Flash RAM has to have some power to maintain |
| gate and the floating gate. A special device called | | | | its contents, while Flash memory will maintain its |
| a cell sensor monitors the level of the charge | | | | data without any external source of power. Even |
| passing through the floating gate. If the flow | | | | though you have turned the power off, the car |
| through the gate is greater than 50 percent of | | | | radio is pulling a tiny amount of current to |
| the charge, it has a value of 1. When the charge | | | | preserve the data in the Flash RAM. That is why |
| passing through drops below the 50-percent | | | | the radio will lose its presets if your car battery |
| threshold, the value changes to 0. A blank | | | | dies or the wires are disconnected. Mark Haskins |
| EEPROM has all of the gates fully open, giving | | | | MSc.Electron.Eng.(UCT) |
| each cell a value of 1. The electrons in the cells of | | | | B.Mus.(RCM) |
| a Flash-memory chip can be returned to normal | | | | Record Producer |
| ("1") by the application of an electric field, a | | | | Songwriter |
| higher-voltage charge. Flash memory uses in-circuit | | | | REcord Label Owner. |
| wiring to apply the electric field either to the | | | | |