The Development of Quantum-Dot Cellular Automata - Field-Coupled Nanocomputing: Paradigms, Progress, and Perspectives - page 2

The Development of Quantum-Dot
Cellular Automata

Craig S. Lent ( & )

and Gregory L. Snider

Department of Electrical Engineering, University of Notre Dame,
Notre Dame, IN 56556, USA
[e-mail]

Abstract. Quantum-dot cellular automata (QCA) is a paradigm for connecting
nanoscale bistable devices to accomplish general-purpose computation. The
idea has its origins in the technology of quantum dots, Coulomb blockade, and
Landauer's observations on digital devices and energy dissipation. We examine
the early development of this paradigm and its various implementations.

Quantum-dot cellular automata (QCA) Molecular electronics Keywords:

1 Introduction

Quantum-dot cellular automata (QCA) is a means of representing binary information
in cells, through which no current flows, and achieving device performance by the
coupling of those cells through the electromagnetic field. Information is stored in the
arrangement of charge (or magnetic dipoles) with in the cell. Importantly, cells have
no monopole moment and are designed to be bistable, having two low energy states
with different dipole or quadrupole orientation which can encode a binary 1 or 0. For
large scale structures it is necessary to guide the switching of the cells with a clocking
field that controllably switches the cells between a null state and an active state (either
0 or 1). Clocking provides power gain necessary to restore signal energies which
would otherwise decay due to inelastic losses. The interaction energy between two
cell, that is the energy difference between neighboring cells holding the same or
opposite bits, is termed the kink energy, and determines thermal stability. Raising the
kink energy entails moving to smaller geometries, with molecular QCA providing the
limit of device density and requiring the ultra-low power dissipation made possible by
adiabatic switching of QCA.
Here we sketch the origins of the QCA idea, its early development, and subsequent
evolution into several implementations and many research fronts. This is in no way a
comprehensive review, but is particularly focused on the perspective of the Notre
Dame group which originated the idea, and the basic trajectories that have arisen from
the early work. We mean no slight by mentioning only a few of the major subsequent
investigators. The elaboration of all the other contributors to this volume is necessary
to give a fuller picture.