In late July, researchers at the Center for NanoTechnology at University of Wisconsin - Madison's Synchrotron Radiation Center published a paper about a new manufacturing technique that could advance the development of nano-electronic processors. The technique enables greater control in the manufacture of nanometer-sized molecules, substantially reducing manufacturing costs.
The Wisconsin researchers found a way to combine two manufacturing techniques: lithography, and self-arranging block copolymers. Lithography, the usual method currently used for making semiconductors is difficult and expensive at nanometer dimensions. Self-assembly of block copolymers that arrange themselves into patterns on a given surface is inexpensive and routine, but prone to error. Researchers have been unable to get the molecules to arrange themselves into lines, but only in circles.
The Wisconsin researchers developed a hybrid method using used lithography to create patterns in the surface chemistry of a polymeric material. They then deposited a film of block copolymers on the surface, where the molecules arranged themselves into the underlying pattern without imperfections. The copolymers arranged themselves into straight lines. The technique created a circuit with 24-nanometer lines, a magnitude smaller than conventional manufacturing processes.
"Tremendous promise exists for the development of hybrid technologies such as this one in which self-assembling materials are integrated into existing manufacturing processes to deliver nanoscale control and meet exacting fabrication constraints," says Prof. Paul Nealey, the project's chief researcher. He added that the new technique has unimaginable potential for the nano-electronics industry.
Prof. Juan J. de Pablo, University of Wisconsin - Madison, Dept. of Chemical and Biological Engineering, said, "In terms of information storage, we're talking about PCs with 4,000 gigabyte memories." He said the facilities using the current manufacturing process increased in cost as chip size decreased.
Current semiconductors are 100-150 nanometers in size, and de Pablo has trouble imagining how current technology will produce 50-nanometer semiconductors. He and Nealey confirm that their technology is still a long way from being a viable manufacturing process.
The five-year University of Wisconsin research project was funded in part by National Science Foundation's Materials Research Science and Engineering Center and the Semiconductor Research Corporation, a consortium that sponsors university research worldwide, supported by IBM (NYSE:IBM, Intel (Nasdaq:INTL), Advanced Micro Devices (Nasdaq:AMD), Motorola (NYSE:MOT) and other chip makers.
"It's like sprouting peas"
Similar research is being conducted in Israel. Dr. Ernesto Joselevich from the Nanochemistry Group at the Weizmann Institute for Science, is conducting research on carbon nanotubes. He is trying to create a memory card from a network of nanotubes, Each junction would be a short distance between the horizontal and vertical tubes. An electrical current through the tubes would give opposing charges to the horizontal and vertical tubes, attracting them to each other and creating a contact. Sending a current with the same charge would separate the tubes. The result is a miniature network of junctions that are either in contact or separated - in other words, a memory.
Joselevich has so far developed a single switch prototype. He is currently concentrating on increasing the carbon nanotube vectors. "It's like sprouting peas," he says. "I insert a catalyst - iron balls of 3-5 nanometers in diameter each - at a particular point on the surface of the silicon wafer. I put them in the oven, fill it with a mixture of gases, one of which contains carbon. The gas molecule breaks down over the iron particles, which form in the shape of the carbon molecules. Carbon nanotubes begin forming from the particles. Simultaneously, I activate an electrical field parallel to the surface, which enables me to control the direction of the tubes' growth."
Repeating the technique in different directions with many cores could ultimately serve as nano-electrical printed circuits, by exploiting the fact that the nanotubes can be either conductors or semiconductors, under the control of the board builder. "I control the tubes placing, direction, and nature," says Joselevich.
Joselevich is one of the owners of the patent for the nanometer-memory network. He says Nantero and Nanosys have already bought rights to use the patent. "The fact that companies are buying the patent proves it has a future. Someone is prepared to put money on it," he says.
The question is when we'll see the results. "It's hard to say, but I think will happen eventually," replies Joselevich. "Silicon was discovered over 100 years ago. Think how many years passed until the first transistor was built, and how many years passed between the first transistor and Pentium's launch. A lot or research was needed along the way. Carbon nanotubes were discovered in 1991, and the techniques for building them, like the ones I'm working on, were first published in 1996. The technique for building nanotubes on silicon wafers was published in 1998. It's very new. It took 100 years from the discovery of silicon to the creation of the first transistor, and decades more to build the Pentium processor. Patience is needed, but it will happen."
Nanometer magnets
Another recently published nanotechnology discovery actually began in another field altogether. Dr. Ehud Gazit and his student Meital Rechess from the Tel Aviv University Department of Molecular Microbiology and Biotechnology were researching the formation of amyloid fibril from proteins, a key factor in Alzheimer's and other diseases.
The researchers discovered that the proteins created nanometer-sized hollow tubes. This was the first research that confirmed a hypothesis of the late Nobel Laureate Prof. Max Perutz that depressions in patients' brains were actually water-filled tiny tubes.
In additional to possible applications for treating Alzheimer's patients, Gazit and Rechess launched another line of research. They added the nanotubes to boiling ionic silver solution, reduced the silver with citric acid to create silver nanowires inside the tubes. These silver nanowires could be used to create nanosized electrical circuits.
The researchers are now trying to use the casting molds to create nanometer magnets. If they succeed, it could be the first step in creating far tinier memory cards than is currently possible.
"We're conducting very basic research to answer preliminary questions about self-assembling structures," says Gazit. "We've developed a new type of nanotube that has advantages over carbon nanotubes for electrical circuits and mechano-optical circuits. At this stage, we know how to make nanometer castings from various materials. We began with silver nanowires, and we're now examining casting from magnetic, semiconducting, and other materials. The great challenge is to combine them into a functional circuit."
Research funding comes from both academic and industry sources. "Industry is interested in this, national-level academe is increasingly interested, as governments realize that this is a technology of the future, and controlling it will be crucial. Countries with a nanotechnological edge will have clear advantages. Everyone wants to be at the forefront of this ongoing revolution. There are definite indications that applications are on the horizon."
Asked how long before the research leads to regular nanotechnology production lines, Gazit replied, "I feel that I'd mislead you if I said it was very close. But we're preparing the foundations for creating these things, and it's hard to know at what pace they'll develop. I think that we're now in a period similar to the first days of microelectronics, when it took ten years from the invention of the first transistor to commercial applications. Things are much faster nowadays, however."
When the semiconductor industry becomes a nanosemiconductor industry, it will be interesting to see what will happen to Moore's Law: Will the pace of shrinking circuits accelerate with the transition to nanoscale processors?
"This is one of the empirically tested laws that has been consistently proved over many years," says Gazit. "Moore's Law has been true throughout the period of linear development, during which there haven’t been any quantum leaps. There was gradual development of latent technology, miniaturizing and improving it. It's possible that the transition from microelectronics and micromechanics to nano-electronics and nanomechanics will lead to a quantum leap in the law.
"My sense is that mathematically, there will be a jump, and then we'll revert to the logarithmic scale that will duplicate itself. It would be rather audacious to be more precise today. There are various approaches in nano research, and we're holding onto the most conservative approach."
Joselevich concurs, saying, "There is something interesting and paradoxical in Moore's Law. It's said that the curve in Moore's Law must be broken by the year 2015, in order to reach dimensions that cannot be created with existing technology, and electrical current will be by single electrons. At that point, quantum behavior, which doesn't allow for operations of the present type, comes into play.
"On the other hand, we've built smaller structures than predicted by Moore's Law. In other words, there has been acceleration. In to preserve the pace, and avoid the anticipated pitfalls, we have to move to molecular electronics, and that's what we're doing. At some point, that too will be over. After all, you can't build anything smaller than an atom."
Published by Globes [online] - www.globes.co.il - on August 14, 2003