Molecular-wire crossbar interconnect (MWCI) for signal...

Details Molecular-wire crossbar interconnect (MWCI) for signal... Molecular-wire crossbar interconnect (MWCI) for signal...

1999-03-29

2001-11-06

Nelms, David (Department: 2818)

Static information storage and retrieval

Systems using particular element

Molecular or atomic

C365S153000, C365S175000

Reexamination Certificate

active

06314019

ABSTRACT:

TECHNICAL FIELD
The present application relates generally to making integrated circuits of electronic devices whose functional length scales are measured in nanometers, and, more particularly, to crossbar interconnects based on crossed nanometer-scale wires joined by bi-stable molecular scale switches at the intersecting junctions.
The silicon (Si) integrated circuit (IC) has dominated electronics and has helped it grow to become one of the world's largest and most critical industries over the past thirty-five years. However, because of a combination of physical and economic reasons, the miniaturization that has accompanied the growth of Si ICs is reaching its limit. The present scale of devices is on the order of tenths of micrometers. New solutions are being proposed to take electronics to ever smaller levels; such current solutions are directed to constructing nanometer-scale devices.
Prior proposed solutions to the problem of constructing nanometer-scale devices have involved (1) the utilization of extremely fine scale lithography using X-rays, electrons, ions, scanning probes, or stamping to define the device components; (2) direct writing of the device components by electrons, ions, or scanning probes; or (3) the direct chemical synthesis and linking of components with covalent bonds. The major problem with (1) is that the wafer on which the devices are built must be aligned to within a small fraction of the size of the device features in at least two dimensions for several successive stages of lithography, followed by etching or deposition to build the devices. This level of control does not scale well as device sizes are reduced to nanometer scale dimensions. It becomes extremely expensive to implement as devices are scaled down to nanometer scale dimensions. The major problem with (2) is that it is a serial process, and direct writing a wafer full of complex devices, each containing trillions of components, could well require many years. Finally, the problem with (3) is that high information content molecules are typically macromolecular structures such as proteins or DNA, and both have extremely complex and, to date, unpredictable secondary and tertiary structures that cause them to twist into helices, fold into sheets, and form other complex 3D structures that will have a significant and usually deleterious effect on their desired electrical properties as well as make interfacing them to the outside world impossible.
The problem of building a physical digital circuit, as opposed to only a set of digital devices, is to connect a set of devices with a physical interconnect which is topologically equivalent to the logical net list of the logic design that is being implemented. The lithographic creation of integrated circuits does this, but at great expense for nanometer-scale objects. Direct write methods using electron or ion beams can create nanometer scale interconnect, but they do so one wire at a time in a serial fashion which is clearly inadequate for wiring a circuit with trillions of components. The use of nanoscale devices means that the ability to fabricate circuits with trillions of components is required.
An intrinsically parallel solution to the problem of creating nanoscale interconnect is to chemically fabricate an extremely regular structure, and then to configure that structure so that the wiring paths through it are determined by a set of programmable configuration bits. This can be done using a crossbar switch. A crossbar is an array of switches that connect each wire in one set of parallel wires to every member of a second set of parallel wires that intersects the first set (usually the two sets of wires are perpendicular to each other, but this is not a necessary condition).
There has only been one published idea about building a crossbar switch using molecular components; see, J. R. Heath, et al, “A Defect-Tolerant computer Architecture: Opportunities for Nanotechnology”,
Science,
Vol. 280, pp. 1716-1721 (Jun. 12, 1998). The problem with that idea was that it required making an intimate contact among five different nanometer-scale components: two address wires, two data wires, and a quantum dot.
Contemporary crossbar switches use several transistors to store a configuration bit and control the flow of current between the two data wires. This requires a large area for a circuit, a factor of 20 to 40 times the area of the wire intersection itself, to control the crossbar switch. This heavy penalty in circuit area is one of the major issues limiting the use of crossbar switches and defect tolerant schemes in modern circuits.
Thus, there is a need for providing a physically parallel means of constructing an interconnect for signal routing and communications at nanometer-scale dimensions, that can be used to readily and cheaply form complex circuits and systems from nanometer-scale devices.
DISCLOSURE OF INVENTION
In accordance with the present invention, a molecular-wire crossbar interconnect (MWCI) for signal routing and communications between a first layer of wires and a second layer of wires in a molecular-wire crossbar is provided. The molecular wire crossbar comprises a two-dimensional array of a plurality of nanometer-scale switches. Each switch is either singly configurable or reconfigurable and self-assembling and comprises a junction formed by a pair of crossed wires. The junction is formed where one wire crosses another. At least one connector species connects the pair of crossed wires in the junction.
The electronic switch of the present invention, in one realization, is a quantum-state molecular switch comprising an electrically adjustable tunnel junction between two wires. Only at the intersection of the two wires is an actual device defined. The exact position of this intersection is not important for this architecture. The molecular devices sandwiched between the wires can be electrochemically oxidized or reduced. Oxidation or reduction of the molecule forms the basis of a switch. Oxidation or reduction will effect the tunneling distance or the tunneling barrier height between the two wires, thereby exponentially altering the rate of charge transport across the wire junction. Some types of molecules can be cycled reversibly (reconfigurable), while others will act irreversibly (singly configurable). The chemical state of the molecular switches determines the tunneling resistance between the two wires. Each switch consists of two crossed wires sandwiching an electrically addressable molecular device. The approach is extremely simple and inexpensive to implement, and scales from wire dimensions of several micrometers down to nanometer-scale dimensions. This method requires only a set of bi-stable switches which can control electrical contact between the two layers of wires approximately perpendicular to the two parallel planes defined by the crossbar wires (Z direction).
The above description is directed to controlling connections between layers. Controlling connections within a layer are essential for realizing a practical crossbar. In order to create an arbitrary circuit from a highly ordered set of wires and switches such as a crossbar, it is necessary to make cuts at specific locations to break the electrical continuity along certain wires (in the plane of the crossbar). This enables functions in one part of the regular array of wires and switches to be isolated from those of other parts, and in conjunction with open switches between the two layers of a crossbar allows electrical signals from different finctions to be routed through each other without interfering. Given the fact that the crossbars described herein are made from junctions, which are essentially electrochemical cells, between sets of crossing wires, such cuts can be made by over-oxidizing a particular junction to consume a localized region of the wire to be cut, and thus form an insulating gap that breaks the electrical continuity of that wire at the desired location. Thus, there are at least three different voltage levels (which may be different magnitudes of th

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