Going miniature is the trend of the new millennium, and electrical engineering professor Stephen Chou is leading the way. His nano-imprinting breakthrough is endowing computer chips with speed and power several orders of magnitude greater than was previously possible.
Chou has uncovered a way to make transistors with nanoscale features for computer chips — in just 20 billionths of a second. His process, called Laser-Assisted Direct Imprint (LADI), replaces the more costly method of photolithography, which requires up to twenty minutes to etch one silicon computer chip.
The process is essentially similar to that of a cookie cutter, Chou said. "It's an old idea, but to work on a nano scale, new technology had to be developed."
To create transistors with features that are 10 times smaller than those currently fabricated, Chou directs an excimer laser through a quartz mold, which shapes nanopathons in a layer of silicon or polymer. The smallest ridges are as small as 10 nanometers wide.
The classical method of creating transistors uses light radiation to etch nanopathons, with the assistance of chemicals, which limited the degree of miniaturization.
With his newly researched technique, Chou is no longer constrained by such limitations.
Chou has been involved in nanotechnology for almost twenty years. After receiving his bachelor's degree in physics at the University of Science and Technology of China in Beijing in 1978, he received a master's degree at SUNY Stony Brook in 1982 and a Ph.D. from the Massachussets Institute of Technology in 1986, where his thesis was concerned with nanotechnology.
After working at Stanford University and then the University of Minnesota, he joined Princeton's faculty in 1997.
Chou expresses an interest in the sciences that began to flourish in his childhood.
"I always liked to fix things," said Chou. "I started engineering [after my undergraduate years] because I like to build things."
Chou worked on a team with four other grad students at the NanoStructures Lab, including Jian Gu GS and Chris Keimel GS.
Chou's accomplishment lies not only in working on an extremely small scale, but, perhaps more importantly, in making nanotechnology practical.
"The breakthrough I have made," Chou said, "is to provide a solution to nanomanufacturing, to make the commercialization and application of nanotechnology much faster."
The importance of Chou's discovery was recognized by the scientific industry and media, among them MIT's Technology Review, a publication that included LADI in its list of "ten emerging technologies that will change the world."
"We were looking at nanotechnology and what is needed to drive nanotechnology forward and make it practical," said David Rotman, executive editor of Technology Review. "We were very familiar with his research and had followed it for several years."
Recognition
Chou's research was also deemed the most significant nanotechnology breakthrough of 2002 by the Forbes/Wolfe Nanotech Report.
"It's a survey . . . between 50 and 60 of the leading researchers in nanotechnology in academia, research and the government," said Rob Paul, cofounder and managing partner of Lux Capital, which releases the Forbes/Wolfe Report.
"We asked them to look at the fundamental strength of the patent as well as market value. The most important metric was the fundamental science breakthrough," Paul said.
"This is not only recognition from the business community, but also from his peers in the scientific world," he added.
Chou's name is ubiquitous in the field of nanotechnology. The December 2002 issue of Scientific American chose Chou's work as one of 2002's top 50 significant technologies or companies.
"He is at the forefront of nanoimprinting technology," said University professor Zhigang Suo of the mechanical and aerospace engineering department.
If one were to randomly choose five of the most recent scientific papers on nanoimprinting, Chou is cited either first or second, Suo added.
The mechanical simplicity of LADI, as well as the efficient production rates and low costs associated with the process, have astounded many in the scientific world.
"People are really amazed that this is so simple and works," Chou said. "People don't understand much of the fundamental science . . . because classic theory doesn't apply. Nanotechnology means you can enter new territory no one has ever explored before."
Chou has collaborated with other Princeton scientists to figure out the laws and science at work behind this technology, and to improve what has already been produced. This loosely-knit group includes Jim Sturm, a fellow electrical engineer, as well as Dan Tsui, a nobel laureate and member of the electrical engineering faculty, Professor Zhigang Suo, Professor Bob Austen of the physics department, as well as professors Rick Register and graduate school dean Bill Russel of the chemical engineering department.
Suo is a specialist in nanomechanics and is currently performing research on how substances deform on a nano scale.
The challenge
"The laws that govern big structures often fail when you study small structures," Suo said. "On a large scale you have some intuition."
The LADI technology is especially essential at a time when polymer substances are quickly replacing silicon and other traditional substances.
"A lot of organic materials, polymers, will enter into devices," said Suo. "Traditional devices are made of silicon and metal, and you use chemicals to etch [these surfaces]. Now if you have polymers, chemicals almost always destroy the device. Therefore it will be desirable to have a mechanical way to imprint polymers."
The LADI technology is currently used by a few external companies, and Chou himself owns two startups. Princeton-based Nanonex provides tools to the nanotechnology industry, and Nano-opto uses those tools to make new optical technology.
Chou also organized the first international conference on nanoimprinting, which took place in San Francisco in December. Over 200 scientists shared more than 80 papers in an effort to foster the development of the emerging science.
"The whole world is working on this nanotechnology," Chou said. "It is not limited to one field. Biology, chemistry, and physics [are all involved]."
Moore's Law
The development of faster and denser computer chips did not take the scientific community entirely by surprise.
According to Moore's Law, the density of computer chips will double every 18 months, approximately. Gordon Moore, co-founder of Intel, first identified the periodic doubling trend in 1964, which applied since the invention of silicon chips.
Moore's Law has held to this day, and with the materialization of Chou's enhanced computer chips, the rate of growth might even increase.
The application of Chou's technology to other products will also cut the development cycle for new products from a few years to a few months, said Chou.
Even with all of the publicity and acclaim that Chou's research has received in recent times, there is still work to be done.
"In order to make many technologies more available to the public," Chou said, "other things need to develop, including tools and understanding."
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