In ancient times, technologically speaking, three scientists at Bell Laboratories in Murray Hill, N.J., announced they had discovered the transistor. It was 1947, and the research of John Bardeen, Walter Brattain and William Shockley soon put an end to the use of bulky vacuum tubes and ushered in the age of high-speed microelectronics. Their seminal work earned them the Nobel Prize in physics in 1956. Fast-forward to the present and three University of Toronto professors: Sajeev John, a physics theorist, Geoffrey Ozin, a materials chemist, and laser physicist Henry van Driel. Backed by a team of 11 Canadian and Spanish researchers, the trio successfully synthesized a silicon crystal capable of “caging” light which could one day, according to
Three University of Toronto scientists make a bold leap towards developing a super-fast optical chip
Ozin, do to the transistor what the transistor did to vacuum tubes. “Most people would agree,” says Ozin, “this is the Holy Grail.”
It is too early to say whether the teams accomplishment will earn any of its members a Nobel Prize, nor are they inclined to suggest it will. For now, John, Ozin and van Driel are content in knowing they and their colleagues have accomplished something no one else has managed in more than a decade of trying. Together, they have produced a three-dimensional structure out of silicon which could lead to the development of an optical microchip—a semiconductor capable of controlling the flow of light the way todays microchips handle the flow of electrons. Their breakthrough, says Paul Corkum, a physicist at the National Research Council of Canada in Ottawa, “might well have a huge impact.”
The basis for the Toronto team’s discovery dates back to 1984, when Sajeev John outlined his theory for caging light in his PhD thesis at Harvard University. Three years later, John refined his work while at Princeton, introducing the concept of a photonic band gap—essentially a means of blocking the path of light particles, or photons, in a fashion similar to what semiconductors do with electrons. John’s theory touched off a worldwide race to synthesize a silicon crystal to channel light in the way his theory predicted was possible.
The need for so-called photonic crystals is pressing. Scientists have steadily shrunk computer chips to such an extent
that certain physical limitations are now unavoidably on the horizon. In about 12 years, microchips are expected to be so powerful and small that beyond a certain threshold they will begin to overheat and short-circuit. But with a chip based on light, it should be possible to develop smaller and faster computers, as well as far more efficient, all-optical telecommunications systems.
The synthesized material had to meet four criteria to be deemed a success:
• The crystal had to be made of silicon, one of the world’s most abundant elements and the most common material used to make microchips.
• It had to harness light at the same frequency as light passing through fibre-optic cables used in today’s telecommunication networks.
• There had to be a way of taking the tiny experimental structures and building them into larger structures suitable for building circuits.
• It had to be inexpensive.
The team’s discovery meets all the basic requirements, succeeding where teams with more money have failed. “Many groups around the world have aimed for the sky,” says John, “but only reached the tree tops.”
The collaborative effort was aided by the Canadian Institute for Advanced Research, which brings top scientists together from around the world to work in their respective fields. While John and Ozin taught at the same university, they had yet to join forces. It was the institute that suggested they team, through its program in nanoelectronics, the science of developing circuits and devices only a few billionths of a metre in size. Ozin initially felt it would be impossible to develop the crystal, but as he reconsidered its potential, he figured on two years’ work.
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Its creators liken this cube to Swiss cheese. The computerized rendition depicts the silicon photonic crystal synthesized by Sajeev John’s University of Toronto team, who hope it will control light the way today’s microchips control electrons. In reality, it is less than one-tenth the width
of a human hair. Each of the silicon wafer’s spheres, and the tiny holes within each sphere, allow the crystal to “cage” light, shown in red. The breakthrough could lead to an optical microchip and smaller, very fast computers.
The process, it turned out, took only seven months, beginning with John contacting colleagues in Spain, where templates essential to the work were made. The templates consisted of stacks of tiny round beads made of silica, forming a thin wafer. Each bead was less than one hundredth the width of a human hair. Ozin then injected silicon-based gas into the tiny spaces between the beads. He did this gradually, depositing the silicon around the beads in layers, similar to die rings of an onion. Once the silicon crystallized, Ozin added hydrofluoric acid, which ate away the beads, leaving the injected silicon untouched. The end result was a three-dimensional silicon wafer filled with regularly spaced—and extremely tiny—air holes that could be used to control the passage of light.
But would it work? That question fell to van Driel, whom John asked to join the team. Using a variety of lasers and other light sources, van Driel analyzed the wafers, observing how they reflected and transmitted light and whether they conformed to Johns theory. The first wafers were not up to snuff, as the team struggled with its technique. But through brainstorming, and trial and error, John, Ozin and van Driel finally accomplished
'Most people would agree this is the Holy Grail'
their feat last November, and announced their discovery to the world in the May 25 issue of the prestigious science journal, Nature. “For us older folks, so to speak, it was a once-in-a-career type of event,” says van Driel. “I joke with the grad students and say, to have this happen this early in their career probably gives them a distorted idea of how difficult science is.”
There is still difficult science ahead. An optical microchip is perhaps five or more years away. In the short term, the team will attempt to further refine their technique. They will deliberately incorporate imperfections into the silicon crystals that could aid in controlling the light. If they are successful, computers could process data and network solely with light, at about 1,000 times the speed currendy possible. That success would likely translate into sizable profits: John has filed for three patents in various combinations with Ozin, graduate students and the Spanish researchers.
Like most scientific challenges, getting there will take money. John, Ozin and van Driel lament the fact that research funding can be difficult to come by in Canada. But they agree there is also something to be said for teamwork, or as John puts it, the triumph of “brain power over the big bucks.” Ozin savours the lead his team now has, but is cautious. “We definitely have an advantage at the moment,” says Ozin. “It doesn’t mean that we will maintain that advantage, and that’s one of the challenges of the field—you have to be very nimble.” And work at the speed of light. EH
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