Molecular Electronics and Technology:

Some proposed distinctions and terms

Originated from neXus

Third International Symposium
on Molecular Electronic Devices

6 - 8 October 1986

"Molecular electronics" spans several broad fields; it overlaps with several more. The paper titles in this conference show the great diversity of phenomena being studied and applications being contemplated. To facilitate communication within our emerging research community, it seems useful to draw some distinctions and to suggest terms to use when the distinctions prove useful.

Molecular Electronics

The field of molecular electronics covers everything from the development of optical discs based on films of bistable biomolecules to the conceptual design of computers based on molecular wires and switches. It seems important to distinguish between systems based on the bulk properties of aggregates of molecular devices, on the one hand, and systems based on the connection of molecular devices to form molecular-scale circuits, on the other. Both of these need to be distinguished from proposed computational systems based on patterns of diffusing, reacting chemicals, and from those based on living cells. Hence the following suggested terms and definitions:

Molecular electronics proper

Molecular electronic materials research: The study, design, and synthesis of molecules which, when aggregated, yield materials and films having such useful properties as bistability, nonlinearity, or transduction abilities in the optical or electronic domains.

Molecular computation research: The study, design, and construction of signal-processing systems having distinct, atomically-defined components of molecular size. Projected products include molecular circuits, memory arrays, and computers. (Some proposals for molecular computation are based on molecular machines rather than on molecular electronics.)

Biochip research: A subset of molecular computation research in which the atomically-defined components are of biological origin.

Other ideas

Biological computation research: Work aimed at building computers from living cells; what the media reports often seem to mean by "biochip." In reality, this field seems virtually nonexistent.

Chemical computation research: The study, design, and construction of signal-processing systems based on the dynamics of chemical reaction and diffusion.

Small and Molecular Machinery

A technology base that enables construction of molecular circuits will likely enable construction of molecular machines. In some proposals, this technology base would itself make use of molecular machines. As in molecular electronics, some distinctions are needed.

Molecular machinery

Nanomachines (or molecular machines): Machines built to complex atomic specifications, making possible mechanical components on a sub-nanometer scale. By analogy with molecular machines in the cell, nanomachine technology is expected to include the full range of components required to construct complex, power-driven mechanical systems.

Molecular assemblers: Nanomachines able to build systems to complex atomic specifications by accurately positioning reactive molecules under programmable control; products may include more assemblers. Ribosomes may be considered a primitive instance.

Other small-scale machinery

Micromachines: Machines small by ordinary standards, but whose components lack atomically-specified structures and do not approach the atomic scale. Typically, they are made using extensions of microelectronic technology and lack motors, rotary bearings, and so forth.

Small and Molecular Technologies

Molecular electronics and molecular machinery fall within the broad field of small-scale technology. Distinctions between bulk and molecular technologies again seem useful, together with finer distinctions within these domains.

Molecular technologies

Protein engineering: The design and modification of proteins to serve novel mechanical, chemical, or electronic functions.

Macromolecular engineering: The design and synthesis of large molecules to serve novel mechanical, chemical, or electronic functions.

Supramolecular engineering: The design and synthesis of molecules (such as proteins) that self-assemble into systems able to serve novel mechanical, chemical, or electronic functions.

Nanotechnology: Technology based on assemblers able to build systems to complex atomic specifications. Individual parts serving distinct functions may thus range down to sub-nanometer size. Expected products include molecular circuits and nanomachines.

Small-scale bulk technologies

Microtechnology: Technology characterized by micron-scale parts, including modern microelectronics and micromachines.

Sub-micron technology: Microtechnology extended into the sub-micron or multi-nanometer domain, characterized by the refinement of techniques for selective deposition, irradiation, and etching. While unable to build complex, atomically-defined components and systems, these techniques can yield feature sizes that overlap with macromolecular dimensions.

The above distinctions are intended to follow natural lines in the field; the terms are more tentative, but are intended to follow usage in the relevant literatures. In making these distinctions, it is important to recognize the essential unity of the interdisciplinary field of molecular science and technology. A given piece of research may have significance in many areas.

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K. Eric Drexler
MIT Artificial Intelligence Laboratory
Visiting Scholar, Stanford University