October 2002
Popular Science: Writing About S&T for the Public

Making Faster Computer Chips

When Galaxies Collide

Understanding Life by Understanding Proteins

Summer at the Bench

The Roundabout Path

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Bryn Mawr College
A quarterly newsletter on research, teaching, management, policy making and leadership in Science and Technology

Making Faster Computer Chips
By Dorothy Wright

If then-Bryn Mawr Physics Department Chair Walter (Mike) Michaels had told Patricia M. Mooney Ph.D. ’72 that she would become one of IBM's principal researchers, she would not have believed him. Yet today Mooney is a research staff member at IBM’s T.J. Watson Research Center in Yorktown Heights, N.Y., focusing on defects and impurities in semiconductors and their effects on the electronic and optical properties of these materials. Since she joined the research center in 1980, Mooney has earned two Outstanding Technical Achievement Awards from IBM for her contributions to the development of faster computer chips.

Patricia M. Mooney,
Ph.D. ’72

"I think it is amazing that I ended up here," Mooney observes. "Most people working in research laboratories such as IBM's went to MIT, Berkeley or other big research universities, even as undergraduates. In the 1960s and '70s, few women studied science at these kinds of universities, and very few women earned Ph.D.s in physics. In general, women were not encouraged to go into the physical sciences. Even now, fewer than 10 percent of the people in my environment are women."

As an undergraduate at Wilson College, a small women's college in Chambersburg, Pa., Mooney excelled in math and science, graduating with honors in physics. "I think what made me decide to go on to graduate school was doing research as an undergraduate for Paul Ganley, a physics professor who came to Wilson from Bryn Mawr during the summer before my junior year. I did a senior project measuring the electroluminescence of oxide films on aluminum electrodes. I realized that I liked working in a lab, building and measuring things."

Mooney's physics professors encouraged her to apply to graduate school. "I was encouraged to apply to Bryn Mawr by Paul," she recalls. "During my senior year, Paul had also introduced me to Priscilla and Ken Laws, Bryn Mawr Ph.D. alums who were teaching at nearby Dickinson College."

After earning her Ph.D. in solid-state physics in 1972, Mooney taught physics for six years, first at Hiram College, then at Vassar. "I had learned a lot about teaching from Mike, and he encouraged me to go into college teaching," she says. "He was well known for physics teaching and was a very strong influence on the whole Bryn Mawr Physics Department, which has always taught physics in ways that are creative and interesting."

The Rewards of Research

While at Vassar, Mooney heard about Jim Corbett, a physics professor who specialized in semiconductors at the State University of New York (SUNY) Albany. She joined Corbett's team as a senior research associate in the summer of 1976 studying radiation-induced defects in silicon (Si). This was of interest because satellites were powered by Si solar cells, which degrade over time as they are exposed to radiation in the upper atmosphere. The team used a high-energy electron beam to introduce and then identify defects in Si. "There were visitors from all over the world," she recalls. "I began to see that research is an activity involving an international community of scientists. That interaction is stimulating."

Mooney had her first taste of life at an industrial lab in 1977 in a visiting summer faculty position at IBM's T.J. Watson Research Center, where teams of researchers were studying the processes for fabricating the integrated circuits used in computers. "The real heart of semiconductor activity at the time was in places such as IBM," she says. "Semiconductors are their bread and butter, so they had the best resources."

Three years later, on the basis of the research she did at SUNY Albany and during a year at the University of Paris working on radiation-induced defects in Si, germanium (Ge) and gallium arsenide (GaAs), Mooney was recruited for a full-time position at IBM. There she continued to develop her research specialties, initially studying process-induced defects in Si and GaAs and later investigating impurities in epitaxially grown semiconductor films, most notably the "DX" center in aluminum GaAs. "For most of the 1980s I was part of a group studying these compound materials to see whether they would be better than silicon for use in digital electronic circuits," Mooney says.

Mysterious Atom "X"

Aluminum gallium arsenide (AlGaAS) was being considered for several applications. "But the material is not a good conductor at low temperature unless you shine a beam of light on it," Mooney explains. "When the light is turned off, the material remains conducting; we were trying to understand this phenomenon, known as persistent photoconductivity. People thought silicon, the electron donor, was interacting with something else in the material — substance 'X' — to create the so-called DX center."

Mooney's team was competing with physicists around the world to explain this phenomenon. "We learned that as you add more and more aluminum to the crystal, the silicon atoms lowered their energy by changing their position in the silicon crystal lattice," she says. "Mysterious atom 'X' was not needed to explain this behavior." As a result, IBM presented Mooney with her first Outstanding Technical Achievement Award.

Mooney has discovered that competition can be heady stuff. "You don't work at IBM if you don't like competition," she laughs. "But the competition is between teams, and I am always working with collaborators on my own team. As problems become more complex, the solutions require people with different training and perspectives to work together, and I like that."

Faster, but Not Smaller

Recently Mooney has studied the characteristics and effects of straining, or stretching, semiconductor materials, which permits electrons — and, thus, information — to move faster. "Until now, we've made silicon chips faster by shrinking the size of the transistors," she explains. "At this point, the dimensions are close to the atomic scale. So we are studying ways to make transistors faster without making them smaller. Using silicon germanium as a template for growing strained silicon is a possible alternative." Mooney earned her second Outstanding Technical Achievement Award for demonstrating this possibility.

Active in professional societies, Mooney is a fellow of both the American Physical Society (APS) and the American Association for the Advancement of Science (AAAS) and a member of the Materials Research Society (MRS). She is past chair of the Division of Materials Physics (DMP) of the APS. She currently serves on the editorial boards of Physical Review B and the Journal of Materials Science: Materials in Electronics. Mooney has also authored more than 100 research publications.

Mooney expects to retire within 10 years, but shows no sign of slowing down. "Every year I tell myself that I am going to work less, but it doesn't happen," she laughs. "One reason is because I like what I'm doing; the other is that it is a very competitive field, and we want to be first."

Assessing her career, Mooney concludes, "I was a slow starter. I got more involved and more interested in what I was doing as time went on. One thing always leads to another."

About the Author

Dorothy Wright contributes news and feature articles on science, technology, engineering and general interest topics to a variety of publications, including Civil Engineering, Engineering News Record and Bryn Mawr Now.

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