Single Electron Transistor

The single electron transistor or SET is type of switching device that uses controlled electron tunneling to amplify current. A SET is made from two tunnel junctions that share a common electrode. A tunnel junction consists of two pieces of metal separated by a very thin (~1 nm) insulator. The only way for electrons in one of the metal electrodes to travel to the other electrode is to tunnel through the insulator. Since tunneling is a discrete process, the electric charge that flows through the tunnel junction flows in multiples of e, the charge of a single electron. [Source: Single-Electron Transistors, MITRE Nanosystems Group]