Architectures for Molecular Electronic Computers: 1. Logic Structures and an Adder Built from Molecular Electronic Diodes
July 1999
James C. Ellenbogen, The MITRE Corporation
J. Christopher Love, The MITRE Corporation
ABSTRACT
Recently, there have been some significant advances in the fabrication and demonstration of individual
molecular electronic wires and diode switches. This paper shows how these demonstrated molecular devices
might be combined to design molecular-scale electronic digital computer logic. The design for the demonstrated
rectifying molecular diode switches is refined and made more compatible with the demonstrated wires through
the introduction of intramolecular dopant groups chemically bonded to modified molecular wires. Quantum
mechanical calculations are performed to characterize some of the electrical properties of the proposed
molecular diode switches. Explicit structural designs are displayed for AND, OR, and XOR gates that are built
from molecular wires and molecular diode switches. These diode-based molecular electronic logic gates are
combined to produce a design for a molecular-scale electronic half adder and a design for a molecular-scale
electronic full adder. These designs correspond to conductive monomolecular circuit structures that would be
one million times smaller in area than the corresponding micron-scale digital logic circuits fabricated on
conventional solid-state semiconductor computer chips. It appears likely that these nanometer-scale molecular
electronic logic circuits could be fabricated and tested in the foreseeable future. At the very least, these
molecular circuit designs constitute an exploration of the ultimate limits of electronic computer circuit
miniaturization. In that connection, examination of these designs suggests that diode switches alone probably
will not be sufficient to operate such extended molecular electronic circuitry. Three-terminal switching devices
that produce power gain probably are required. Nonetheless, molecular diode switches and diode-based logic
are likely to be important components of future molecular electronic digital circuits, if only because they demand
many fewer interconnects and, consequently, should make such ultra-dense circuitry much easier to design and
to fabricate. In its treatment of the foregoing innovations and analysis, this work addresses two of the
architectural issues that will be encountered in the fabrication and operation of a molecular electronic computer:
the issues of design and interconnects. A more complete enumeration of such issues is discussed, with a view
to considering the assembly of a molecular electronic computer using logic gates similar to or based upon those
designs proposed here.
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