There has been significant advancement in the fabrication and demonstration of individual molecular electronic wires and diode switches [5,6]. This paper shows how these demonstrated molecular devices might be combined to design molecular scale electronic digital computer logic .
Explicit structural designs are displayed for AND, OR, and XOR gates that are built from molecular wires and molecular diode switches which are combined to produce a design for a molecular scale electronic half adder and a full adder. These designs correspond to molecular structures that would be one million times smaller in area than the corresponding micron scale digital logic circuits. Their designs constitute an exploration of the ultimate limits of electronic computer circuit miniaturization.
Polyphenylene-based molecular wires and switches involve chains of aromatic benzene rings that have shown to conduct small electrical currents. While polyphenylene-based molecular wires do not carry as much current as carbon nanotubes, polyphenylenes and their derivatives are much smaller molecules and thus will go a long way in helping realize the nano-supercomputing capabilities.
Molecular scale logic gates are based upon a mechanism that involves perturbing the equilibrium electronic charge distribution to change the electrostatic potential of a molecule. The present work is the molecular scale analogous of micron-scale conductive circuitry with the exception that the circuits discussed takes advantage of quantum effects like tunneling that would impair micron scale circuits.
The circuit for a Molecular Electronic Full Adder has been discussed along with the molecular AND, OR, XOR gates (using a molecular Resonance Tunneling Diode) and molecular half-adder . The Molecular Full Adder using a Polyphenylene derivatives based spatial arrangement occupies an area of about 25nm*25nm which is a minute fraction of the current area occupied by the solid state circuits.
The design challenges for the such Molecular Logic circuits are also discussed and include the problems of combining individual molecular devices without altering their properties, the non-linear I-V behaviour of individual devices, dissipation of electron energy into the vibrational modes of the molecule etc[1,3].
1. James C. Ellenbogen, J. Christopher Love, "Architecture for Molecular Electronic Computers - Logic Structures and an adder built from molecular electronic diodes"
2. MITRE Nanosystems Group, http://www.mitre.org/technology/nanotech
3. Cees Dekker (Delft), Jim Heath (UCLA), Jim Hutchbi (SRC), "Lecture Notes"
4. Electronics For You, http://www.electronicsforu.com
5. David Goldhaber Gordon, Michael S. Montmerlo, J. Christopher Love, et al, "Overview of Nanoelectronic Devices"
6. R.W.Keyes, "The miniaturization of Electronics and Its Limits"
7. W.Broad, "Incredible shrinking transistor nears its ultimate limit"