Application of Single Electron Devices Utilizing Stochastic Dynamics

Application of Single Electron Devices Utilizing Stochastic Dynamics

Shigeo Sato (Tohoku University, Japan) and Koji Nakajima (Tohoku University, Japan)
DOI: 10.4018/978-1-60960-186-7.ch006
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Abstract

Single electron devices utilizing the Coulomb blockade phenomenon have attractive features such as extreme low power consumption, one by one electron flow controllability, small device size, etc. However, besides promising applications such as the current standard and charge detection, it is not easy to apply the single electron devices to conventional computational tasks due to its stochastic operation and low amplification capability. Therefore, it is important for us to consider suitable applications of single electron devices. In this paper, we show three applications such as a noise generator, a stochastic neural network, and a charge detector employing stochastic resonance. Trough these applications, we see the advantages of single electron devices and study the direction of applications.
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Theoretical Background And Simulation Methods

Coulomb Blockade

Operation of single electron devices is based on the Coulomb blockade phenomenon on ultra small tunnel junctions (Likharev, 1988; Averin & Likharev, 1991; Grabert & Devoret, 1992). Let us consider a junction whose electrostatic capacity is C. Its charging energy is given as E = Q2/ 2C, where Q is the charge on the junction. When an electron tunnels, the energy change is given as, (1) where e and V(= Q/C) denote the elementary charge and the voltage across the junction, respectively. The second term in the right side can be viewed as the work done by a voltage source. The fact that an electron tunneling accompanies energy dissipation gives the relation ΔE < 0. Therefore tunneling does not occur if

. (2)

Therefore, this is called Coulomb blockade. There are two conditions required for us to observe a Coulomb blockade with a real device. The charging energy must be larger than thermal noise as given as, (3) where kB is the Boltzmann constant and T is the temperature, respectively. Also, the tunnel resistance RT must be larger than the resistance quantum RK as given as, (4) where h is the Planck constant. In general, a tunnel junction with capacitance of the order of aF shows the blockade property at room temperature.

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