ABSTRACT
In this chapter, the concepts of electrostatic potential energy, Fermi energy, quantum confinement energy, and free energy are introduced. The capacitance of a spherical conductive island is calculated. It is shown that for an island of a few nm radius, the electrostatic energy is very high so that the Coulomb blockade effect can be observed at room temperature. The tunnel junction and its equivalent circuit are described. Considering a double tunnel junction, the equation for free energy change is derived, and it is shown that by increasing the supply voltage the free energy must be made negative to enable tunneling across the tunnel junction. The working of the double tunnel junction is explained with reference to its energy-band diagram. Ascending and descending staircase-like current-voltage characteristics appear when the two tunnel junctions have different tunnel resistances. Extending the double tunnel junction analysis further, a single-electron transistor (SET) circuit with two gates is examined. When the supply voltage is fixed, a change in the gate voltage is necessary to enable tunneling by rendering free energy change negative. The rhombus enclosing the Coulomb blockade region is called the Coulomb diamond. The stability plot of the SET is drawn and the production of Coulomb oscillations is shown. A nanowire-based fabrication process for SET capable of operating up to a temperature of 430 K is described.
