UF Team Achieves Milestone In Design Of New Semiconductors

The engineers' achievement -- which also may prove important to 21st century automobiles and cutting-edge military hardware -- is described in the December 1998 issue of "Compound Semiconductor," a leading industry journal.

Four UF professors of materials science and engineering and two professors of chemical engineering designed a basic electronic structure called a "metal oxide semiconductor field effect transistor" using a material called gallium nitride.

The only engineers to achieve the feat to date, the UF team and another team from the University of California at Santa Barbara also were the first to design and demonstrate a related structure known as a "bi-polar transistor."

The achievements are important steps in an ongoing effort to create gallium nitride semiconductor switches that will ensure the future's high-quality electricity in a deregulated utility system, said Stephen Pearton, a UF materials science and engineering professor and one of the researchers involved.

Pearton said the nation's utility grid currently uses two methods to transfer electricity from one place to another: large mechanical relay switches and silicon switches. Both have serious flaws, he said. The relay switches create "spikes" in the electricity when they turn on and off, forcing power companies to operate the grid well below capacity. The silicon switches cannot sustain high voltages or temperatures above 150 degrees Fahrenheit, meaning they require very expensive and bulky cooling equipment while operating, he said.

Under the regulated utility system, customers usually have few options of where they can purchase power, so utilities do not do a lot of electricity switching, Pearton said. That will change when the system is deregulated. Florida residents, for example, will be able to buy power from a New York company with a cheaper rate than a local company. As a result, utility companies would like to set their product apart by marketing it as "high quality," or guaranteeing that it will be uninterrupted and without spikes in power levels.

The way to achieve such seamlessness is to replace the mechanical and silicon switches with gallium nitride electronic switches, Pearton said.

"If you could replace all those mechanical switches with electronic switches, the electricity could be switched much faster with fewer problems, and you could raise the power level up so the whole thing is running closer to its rated value," he said.

The UF team showed they could create gallium nitride metal oxide transistors and bi-polar transistors and that the devices would continue to function at high temperatures, said Fan Ren, associate professor of chemical engineering.

However, many obstacles remain, such as increasing the size of the gallium nitride wafers, currently too small to be used for power switches, Ren said.

Pearton said high-voltage, high-temperature switches gallium nitride switches also are likely to help make automobiles more efficient. Currently, he said, computer chips in automobiles are housed a few feet from the engine because they cannot withstand the heat generated by internal combustion. This results in a delay between the information the chips receive and the signals they send back. Gallium nitride chips could be situated directly on the engine block, eliminating this delay and making the engine more efficient, he said.

The chips also may have important uses in the military, which often requires equipment that can operate at high temperatures in harsh conditions. For example, they could reduce the weight of surveillance airplanes, which require heavy electronic equipment.