This paper provides an overview of research developments toward nanometer-scale electronic switching devices for use in building ultra-densely integrated electronic computers. Specifically, two classes of alternatives to the field-effect transistor are considered: 1) quantum-effect and single-electron solid-state devices and 2) molecular electronic devices. A taxonomy of devices in each class is provided, operational principles are described and compared for the various types of devices, and the literature about each is surveyed. This information is presented in nonmathematical terms intended for a general, technically interested readership

We show how evolutionary methods can help in the design of singleelectronic circuits with an example of evolving a simple NOR gate. Evolutionary algorithms, capturing the bare essentials of Darwinian evolution, work differently from conventional design methods, and have the potential to explore new territory. Our preliminary evolved circuit is far from an ideal NOR gate, but has interesting properties. It was evolved to work at a temperature of 340mK, and its performance deteriorates if the temperature is lowered, as well as if it is increased. This is contrary to the usual behaviour of single-electronic circuits, which generally improve with decreasing temperature. We hypothesise that the circuit exploits or relies upon the simulated effects of the particular thermal energies of the electrons at around 340mK.

During the last decade the field of single electron devices has matured from pure theoretical ideas of elements working at very low temperatures (milli Kelvin range) to fabricated devices operating at room temperature. These ideas are moving now from the experimental physics to the electronic circuits domain. New applications are sought and single electron devices may become a replacement for standard CMOS in several areas. This thesis presents a possible approach to this goal. A brief introduction of the aspects and general problems of current digital logic devices and a detailed background on single electronics theory and applications are presented. The fabrication issues of nanometer scale structures are discussed followed by a brief account on the estimation of electric parameters of such devices. A novel multi-valued adder circuit is introduced, where the emphasis is on its implementation for decimal addition. A detailed analysis and simulation results indicating its sensitivity...

The differences between electronics design through artificial evolution and through conventional methods have the consequence that evolved circuits may take unusual leverage from the physics of their medium of implementation. This can occur even if there is no tractable analytical model to predict how the overall behaviour will emerge from the interactions of the components. This is alluring for singleelectron circuit design, and a first case-study is presented: the evolution of a NOR gate. Although the results to date are far from ideal or practical, it appears that the particular thermal energies of the electrons are exploited. Whether desirable or not, this indicates that evolution can explore new kinds of designs not seen before in the literature. 1 Introduction This paper discusses the use of evolutionary algorithms to design single electron systems, and describes a first exploratory experiment. Although evolutionary design does not circumvent all of the design challenges faced ...

To benefit from the reduction of the devices ' feature sizes new circuit concepts can be introduced. These new circuits will require new devices, such as singleelectronic devices. Single-electronics devices are capable of controlling the transport of only one electron. In this manner, the charge transfer through the device is quantized. However, single-electronics is still a highly experimental technology. As an example of single-electronics we discuss circuits based on the so-called single-electron tunneling (SET) device, including tunnel junctions.

Abstract. Single-electron tunneling devices can detect charges much smaller than the charge of an electron. This enables phenomenally precise charge measurements and it has been suggested that large scale integration of single-electron devices could be used to construct logic circuits with a high device packing density. Here the operation of the two basic types of single-electron tunneling transistors is reviewed. The applications of singleelectron tunneling in precision measurements and in general purpose computation is discussed. Particular attention is paid to the characteristics of single-electron tunneling transistors in the superconducting state.