As the size scale for microelectronics continues to decrease, standard architectures will reach the limits of efficiency, and alternative device architectures will be required. One avenue of exploration has been storing state information with single electron charges, as in a quantum dot cellular automata. A different approach to storing information is to use superconducting nanostructured arrays in a magnetic field where positions of the vortices define the logic state. When a magnetic field is applied to a superconductor, the flux enters in the form of individual quantized vortices which repel each other. Individual vortices can be trapped by nanofabricated dots of nonsuperconducting material, or by antidots etched from the superconductor. If a row of elongated dots is created, the vortices will move to the top or bottom of adjacent dots, forming an alternating pattern.
A single logic element is composed of two dots, one labeled a and one labeled b. By definition, a vortex at the top of a dot in position a (every other dot) is in the logic state "1." A vortex at the bottom of a dot in position a is in the logic state "0." The logic convention is reversed for the dots in position b. Thus, in the structure illustrated above, all of the dots are in the logic state "1."
In order to create a logic device in which a signal can propagate at a constant rate, allowing a constant clock speed to be implemented, we use three different types of dots in sequence, which are colored red, green, and blue in the figures and movies. A single logic element is still composed of two of these dots. The red wells are narrow, while the green and blue wells are wide, with the green well having an overall tilt in the potential to the left side of the well and the blue having a tilt to the right side, illustrated in (b) above. A three-stage alternating current pushes the vortices to the left or right sides of the green and blue wells, altering the spacing between the vortices in the wells. As a result, a vortex in an individual well interacts more strongly with its left or right neighbor, cyclically, allowing a signal to propagate through the structure in a controlled fashion.
In order to make a complete logic architecture, the basic units include a fanout and a NAND gate. In the fanout, shown above, a single input pipeline splits into two pipelines at the output. An MPEG movie of the fanout operation is available below. In the movie, the gate is initially in logic state "1." Logic state "0" is input on the left side of the gate, and propagates down both channels of the fanout output. The current logic state of each well is indicated above the well in the movie.
In the AND gate, two input pipelines interact at the gate location and produce two synchronized output pipelines with the desired signal. The AND gate can be converted into a NAND gate, illustrated above, simply by adding an additional well, which serves as an inverter for the vortex logic. MPEG movies of the operation of the AND gate for three different inputs which start on the left side of the gate and produce synchronized outputs on the right side of the gate are available below. The current logic state of each well is indicated above the well in the movies.
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Last Modified: 10/31/02