'Cascading molecules' drive IBM nanotech circuits

Researchers at IBM Corp. have developed what they say is the world's smallest working computer circuit, which measures 12 nanometers by 17 nanometers and uses carbon monoxide molecules to transfer information across the circuit.

Other groups have demonstrated atomic-scale logic circuits, but the group of four scientists at IBM's Almaden Research Center in San Jose, California, are the first to integrate multiple logic circuits, said Andreas Heinrich, staff scientist at IBM and one of the researchers involved in the two-year project.

The result is a functioning circuit that is 260,000 times smaller than integrated circuits developed on 0.13 micron process technology, the current leading standard for chip production, Heinrich said. It consumes 1 electron-volt of energy, a tiny sliver of the power used by current PC processors. "One hundred thousand times less energy is consumed in this circuit than in modern processors," Heinrich said.

While the announcement appears to represent a breakthrough in the field of nanotechnology, the molecular circuit model is far from becoming part of a PC. It will take around ten years to get this circuit into a computer, Heinrich said.

The researchers did not embark upon the project with the stated goal of developing the world's smallest circuit, Heinrich said. "This really came out because we were allowed to do this type of exploratory research, and we were quite surprised we were able to reach this level of integration so quickly," he said.

The scientists used a scanning tunnelling microscope to arrange the molecules on a copper surface in patterns that IBM calls "chevrons," which are groups of three molecules in a slightly crooked line, Heinrich said. Using the microscope, a single molecule was knocked into the lattice spacing next to the first group of three molecules, landing very close to the middle molecule. Carbon monoxide molecules naturally repel each other, so the middle molecule is moved away from its previous position, landing next to the center molecule of the next group of three molecules.

When viewed from overhead, the cascading process resembles the effect created by patterns of toppling dominoes. By linking several groups of three molecules, the researchers were able to start a chain reaction of cascading molecules. These cascading molecules were then connected to create arrays.

Computers, despite what the average user might think, are actually very simple, and the basics of computation haven't changed since computers were the size of large rooms. Varying levels of electricity flow through the transistors on a processor, opening and closing logic gates. The different voltage levels designate whether a gate's terminal, or its inputs and outputs, is in a low binary position, designated as a "0", or a high binary position, designated as a "1." Different combinations of logic gates allow processors to perform operations.

In this case, the researchers set up the circuit so a cascaded array could be interpreted as a "1," and an upright array as a "0." The arrays intersect at certain intervals, where logic gates were created. The circuit created by the researchers is a three-input sorter, which requires three triggers to start the cascading process.

Several hurdles remain before the IBM researchers can bring this technology into PCs.

The test was carried out 4 to 10 degrees above absolute zero (-459 degrees Farenheit or -273 degrees Celsius), which would be an austere computing environment. There is no reason why the circuit itself can't function at room temperature, but the microscope used to arrange the atoms requires that level of intense cooling to operate, and a similar tool that can work at room temperature will have to be engineered, Heinrich said. Even then, the cascades require two to three hours to set up, as each individual atom is dragged into place with the microscope, he said.

The largest obstacle to overcome, according to Heinrich, is figuring out a way to re-arrange the atoms once they have been toppled. After the atoms move across the circuit once, they must be manually reset. The researchers don't know right now how to create an automatic loop circuit, but Heinrich thinks the answer may lie in the application of magnetic fields to the atoms.

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Tom Krazit

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