Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
1998-10-27
2002-02-19
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
Reexamination Certificate
active
06348700
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention is directed to a monomolecular rectifying diode structure and monomolecular electronic digital logic gates and higher Boolean functions based upon the monomolecular rectifying diode structure. More particularly, the present invention directs itself to a molecular conducting wire having a plurality of primarily aromatic rings that is chemically doped to integrally form a rectifying diode embedded into the molecular conducting wire. The molecular wire consists of a plurality of substantially identical aromatic ring structures bonded or linked together. The wire is chemically doped by bonding at least one electron donating group and/or an electron withdrawing group, to respective discrete portions of the molecular wire, the two portions being separated from each other by an insulating aliphatic or semi-aliphatic bridging group. The present invention also pertains to monomolecular logic gates constructed from combinations of the aforementioned rectifying molecular wire structures. Further, the present invention relates to molecular logic structures which can be formed by combination of the aforementioned logic gates to construct a larger individual molecular structure that performs a higher digital function, as, for instance, a monomolecular electronic HALF ADDER and a monomolecular electronic FULL ADDER.
PRIOR ART
For the past forty years, electronic computers have grown more powerful as their basic sub-unit, the transistor, has shrunk. However, the laws of quantum mechanics and the limitations of fabrication techniques may soon prevent further reduction in the size of today's conventional field effect transistors. Many researchers project that during the next 10-15 years, as the smallest features on mass-produced transistors shrink from their present approximate length range of 100 nanometers to 250 nanometers, the devices will become more difficult and costly to fabricate. In addition, they may no longer function effectively in ultra-densely integrated electronic circuits. In order to continue the miniaturization of circuit elements down to the nanometer scale (nanoelectronic), perhaps even to the molecular scale, researchers are investigating several alternatives to the solid state transistor for ultra-dense circuitry. However, unlike today's FETs, which operate based on the movement of masses of electrons in bulk matter, the new devices take advantage of quantum mechanical phenomena that emerge at the nanometer scale.
There are two broad classes of alternative nanoelectronic switches and amplifiers:
(a) solid state quantum-effect and single electron devices, and
(b) molecular electronic devices.
Devices in both classes take advantage of the various quantum effects that begin to dominate electron dynamics on the nanometer scale. Despite the novelty of the designs of solid state quantum-effect and single electron devices, researchers already have been able to develop, fabricate, and employ in circuitry several promising new device types by building upon 50 years of industrial experience with bulk semiconductors. Such solid-state quantum-effect devices change the operating principles for ultra-miniature electronic switches, but they still bear the difficult burden of requiring that nanometer-scale structures be “carved” out of amorphous or crystalline solids.
Molecular electronics is a relatively new approach that would change both the operating principles and the materials used in electronic devices. The incentive for such radical change is that molecules are naturally occurring nanometer-scale structures. Unlike nanostructures built from bulk solids, molecules can be made identically, cheaply, and easily that will be needed for industrial scale production of ultra-dense computers. Two of the significant challenges are to devise molecular structures that act as electrical switches, and to combine these molecules into a more complex circuit structure needed for computation of applications.
Presently, there are two primary types of small molecules that have been proposed and/or demonstrated for use as molecular scale electrical conductors. These two types of molecular-scale conductors are: (a) polyphenylene-based conductors, and (b) carbon nanotubes.
Polyphenylene-Based Conductors
Polyphenylene-based molecular wires involve chains of organic aromatic benzene rings bonded to each other, shown in
FIG. 1A
or linked to each other by acetylene spacers, as shown in FIG.
1
B. Until recently, whether such small molecules had appreciable conductance was an open question. However, over the last two or three years, molecules of this type have been shown by several research groups to conduct small electrical currents.
An individual benzene ring, shown in
FIG. 2
, has the chemical formula C
6
H
6
. When a benzene ring is drawn, as shown in
FIG. 3A
, with one of the hydrogen atoms removed (e.g., to form C
6
H
5
), so that it can be bonded as a group to other molecular components, such a ring-like substituent group is termed a phenyl group. When two hydrogen atoms are removed from a benzene ring (e.g., C
6
H
4
), a phenylene ring is obtained, as shown in FIG.
3
B. By binding phenylenes to each other on both sides of the respective rings and terminating the resulting chain-like structures with phenyl groups, a polyphenylene-based molecule is thus formed. Thus, molecules made primarily from two or more phenyl groups are known as polyphenylenes.
While polyphenylene chains do not carry as much current as carbon nanotubes, they are very conductive small molecules. Also, polyphenylenes have the great advantage of a very well-defined chemistry and great synthetic flexibility, based upon more than a century of experience accumulated by organic chemists in manipulating such aromatic compounds. Recently, James M. Tour has refined the synthetic techniques for conductive polyphenylene chains (or molecular wires) by developing precise synthetic methods that produce enormous numbers of these molecules, approximately 10
23
, every one of which is of exactly the same structure and length. Such polyphenylene-based molecular wires, shown in
FIGS. 1A and 1B
, have come to be known as Tour wires. While the Tour wires provide conductive leads, the molecular-scale electrical devices that they interconnect must have a structure and chemistry that is compatible therewith.
The source of the conductivity for a polyphenylene-based wire is the conjugated pi-type orbital that lies above and below the plane of the molecule when it is in its planar or near planar conformation, as shown in FIG.
4
. In such a conformation, the pi-orbitals associated with the individual ring-like phenyl groups overlap to create a single pi-orbital that runs the length of the molecule, because of the significant energetic advantage that arises from delocalizing the pi-electrons over the length of the entire molecule. Because this long pi-orbital is both out of the plane of the nuclei in the molecule, and it is relatively diffuse compared to the in-plane sigma molecular orbitals, the pi-orbital forming a “channel” or “conduction band” that can permit transport of additional electrons from one end of the molecule to the other when it is under a voltage bias. In
FIG. 5
, such a pi-type conduction channel is sketched for a Tour wire.
In practice, as shown in
FIG. 1B
, triply bonded acetylenic linkages often are inserted as spacers between the phenyl rings in the Tour wire. These spacers eliminate the steric interference between hydrogen atoms bonded to adjacent rings. Otherwise, these steric interferences would force the component rings in the Tour wire to rotate into a non-planar conformation that would reduce the extent of conjugation between adjacent rings, break up the electron channel, and decrease the conductivity of the wire. The acetylenic linkages themselves, because of their own out-of-plane pi-electron density become a part of the electron channel, and thus, they permit the conductivity to be maintained throughout the length of the molecule.
Alip
Ellenbogen James C.
Love John Christopher
Meier Stephen D.
The Mitre Corporation
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