The next Silicon?: WFU conference spotlights ‘insulators’

Silicon built an industry and named a valley. But like athletes who have reached their performance thresholds, silicon and other semiconductors are nearing their limits.

Enter “insulators,” a different class of materials like diamonds that, with the addition of the right mineral impurities or “defects,” will be far more adept at handling the data- and image-processing demands of the Information Age.

How to better harness the power of insulators for tomorrow’s technology is the focus of the 13th International Conference on Defects in Insulating Materials (ICDIM96) July 15- 19 at Wake Forest University.

“Why are physicists from all over the world converging on Wake Forest University to study insulating materials and their defects?” said Richard Williams, Reynolds Professor of Physics and the conference’s co-chair with Eric Matthews, professor of physics.

“The need for more: More speed and power for computers, more storage on CDs, more distance in fiber optics, more sensitivity in medical imaging,” Williams said. “In order to make higher frequency lasers capable of recording, storing and transmitting much more information at far greater speeds, we need to move from narrow-gap semiconductors such as silicon to wide-gap materials based on insulators.”

Universities and companies worldwide have long eyed insulators for microprocessors and other devices because of silicon’s unsuitability for operation at high temperatures and frequencies.

Silicon is limited by its low “band gap,” the relatively small amount of energy required to loose the electrons bonded to its individual atoms. When silicon devices get hot, the thermal vibration itself is enough to free many electrons and short out the devices — a grave problem for radar, communications and any other equipment that requires continuous, uninterrupted power.

Because “wide-gap” insulators hold onto their electrons much more tightly, they can be operated at much higher temperatures. But in their pure crystal form, insulators are extraordinarily poor conductors of electricity. Which is why physicists add “defects,” or mineral impurities, to make extremely powerful semiconductors and lasers.

Electronics built from wide-gap insulating materials like diamond, gallium nitride, aluminum nitride and silicon carbide can tolerate far greater temperatures than silicon and operate at greater capacities and speeds.

“Temperature is very important because speed and power mean heat,” Matthews said. “The faster a computer processor operates, the more heat it produces. More powerful processors need to pack more devices into the same space, producing even more heat.

“If you can find a way to make these materials operate at higher temperatures, you can get faster and more powerful computers.”

Because of these advances, more electronics will be replaced with photonics — hybrids of electronics and optical devices that demand the transparency of insulators for using light instead of electrons to transmit and store information.

Insulators’ wider band gaps are also critical to the development of blue lasers, light emitting devices known as “LEDs,” better medical imaging machines and optical fibers.

While some defects make insulators excellent semiconductors, others limit their efficiency and reliability. For now, blue lasers exist only in the laboratory because the same power that allows them to store more than five times the information of infrared lasers creates defects in materials subjected to their immense energy. When Sony Corp. announced one of its blue-laser breakthroughs in January, the news was that the laser worked for 100 hours before self-destructing — a milestone, but a level of performance still not good enough for practical use.

Small band-gap materials like silicon can only be used for infrared lasers, and the long wavelength of their light limits the information that can be packed onto a CD-ROM. The shorter wavelengths of blue or ultraviolet lasers and LED’s mean denser storage on CDs and brighter flat-panel displays on monitors and televisions.

Insulator improvements are critical to telecommunications. Much of the nation’s phone traffic already passes over fiber optics, but the race is still on as to who will provide fiber to individual homes for telephone, cable television and Internet access. Since all fiber optics are insulators, improvements in insulating technologies mean longer-range transmission. The wider the band gap, the greater the flexibility in choosing the best wavelength for transmission.

Insulator improvements also mean better, and safer CAT scanners and other medical equipment. The better scintillators and phosphors within the machines are at detecting radiation, the lower the dose to the patient.

The annual ICDIM conference, last held in the United States in 1984, features 168 lectures and discussions and 113 poster presentations. Sponsors are Wake Forest University, the National Science Foundation, The International Science Foundation, Hughes Research Laboratories, AMP Incorporated and Newport Corporation.

The program committee and organizing committees are comprised of scientists from Cornell University, the Naval Research Laboratory, the Massachusetts Institute of Technology, the University of Utah, the University of Ottawa, the University of Georgia, Davidson College, the University of North Carolina at Chapel Hill and Vanderbilt University.

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