New Method Will Help In Efforts To Find Better Insulators, Make Faster Microchips

Scientists at the Commerce Department's National Institute of Standards and Technology have devised a new method and built a new instrument to aid in the search for super-efficient plastic insulators that would make it easier to build tinier and more powerful computer chips.

Certain plastics are well-suited for the job, but they sometimes turn rubbery as the temperature rises. Because computers heat up when in operation, chips made with plastic insulators might fail in computer circuits.

Therefore, scientists must be able to study precisely how extremely thin layers of plastic polymers flow when heated. To accomplish that feat, a NIST scientist has formulated a new mathematical theory for measuring the viscosity of polymers in thin layers.

"The challenge became building an instrument that we could use to make those measurements," said Christopher White, an analytical chemist by training who works in the Polymers Division of the NIST Materials Science and Engineering Laboratory. "We had to design and build an entirely new instrument."

He is delivering a scientific paper today about the new measurement method and apparatus, called a twin-crystal resonator, during the ACS meeting. Wen-Li Wu, the leader of the Electronics Applications Group in the Polymers Division, has participated in the research and is a co-author of the paper.

"The exciting thing is that we are doing something that is relevant to an entire industry," said White, who introduced the mathematical theory as part of his doctoral thesis at the University of Wisconsin.

The point at which a plastic turns rubbery is called its glass transition temperature. Scientists recently have learned that when extremely thin layers of a polymer are created, this temperature may change.

"Some people say the transition temperature goes up; others say it goes down, with thickness," White said. "This needs to be better understood."

Scientists want to learn precisely at which temperatures and thicknesses certain polymers turn rubbery.

To that end, various researchers are using different methods. White's approach is to learn changes in the polymer's viscosity, which can be analyzed by coating quartz crystal with an ultrathin layer of plastic and then recording changes in the crystal's response to an oscillating electric current.

White and his colleagues discovered that the changes take place when polymers are produced in layers no thicker than 300 nanometers, or about four one-thousandths of a human hair's diameter. The technique has the potential to measure properties in far thinner films, researchers said.

White also will discuss his work during a meeting of The Society of Rheology in October. Rheology is the study of the flow and deformation of matter.

For more information, contact White at (301) 975-6016.

As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.