06-08-2011, 10:22 AM
Abstract
The goal of this paper is to review in brief the basic physics of single-electron devices, as
well as their current and prospective applications. These devices, based on the controllable
transfer of single electrons between small conducting "islands", have already enabled several
important scientific experiments. Several other applications of analog single-electron devices in
unique scientific instrumentation and metrology seem quite feasible. On the other hand, the
prospect of silicon transistors being replaced by single-electron devices in integrated digital
circuits faces tough challenges and remains uncertain. Nevertheless, even if this replacement
does not happen, single-electronics will continue to play an important role by shedding light on
the fundamental size limitations of new electronic devices. Moreover, recent research in this field
has generated some exciting by-product ideas which may revolutionize random-access-memory
and digital-data-storage technologies.
Keywords - Single-electron tunneling, Fowler-Nordheim tunneling, single-electron
devices, Coulomb blockade, supersensitive electrometry, single-electron spectroscopy, dc current
standards, temperature standards, random access memories, floating-gate memories, logic
circuits, data storage.
I. INTRODUCTION: BASIC PHYSICS AND SCALING
The manipulation of single electrons was demonstrated in the seminal experiments by
Millikan at the very beginning of the century, but in solid state circuits it was not implemented until
the late 1980s, despite some important earlier background work [1-5]. The main reason for this
delay is that the manipulation requires the reproducible fabrication of very small conducting
particles, and their accurate positioning against external electrodes. The necessary nanofabrication
techniques have become available during the past two decades, and have made possible a new field
of solid state physics, single-electronics (see Refs. 6-8 for its general reviews).
Figure 1 illustrates the basic concept of single-electronics. Let a small conductor
(traditionally called an island) be initially electroneutral, i.e. have exactly as many (m) electrons as
it has protons in its crystal lattice. In this state the island does not generate any appreciable electric
field beyond its borders, and a weak external force F may bring in an additional electron from
outside. (In most single-electron devices, this injection is carried out by tunneling through an energy
barrier created by a thin insulating layer). Now the net charge Q of the island is (-e), and the
resulting electric field E repulses the following electrons which might be added. Though the
fundamental charge e » 1.6´10-19 Coulomb is very small on the human scale of things, the field E is
inversely proportional to the square of the island size, and may become rather strong
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