X-Message-Number: 24436
Date: Sun, 25 Jul 2004 11:25:34 -0700 (PDT)
From: Doug Skrecky <>
Subject: Breakthrough Yields Simple Way To Make Microscopic Electronics

[Cyberspace may become a big player in advancing medical research soon.]

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In a breakthrough that could lead to dramatically smaller memory chips
and other electronic components, Princeton scientists have found a way to
mass produce devices that are so small they are at the limit of what can
be viewed by the most powerful microscopes.

The achievement is an advance over current techniques, which require
expensive and time-consuming procedures to create anything so small. The
technique offers a relatively simple, low-cost production method that may
lead to greater memory capacity and lower costs for computers, digital
cameras and other devices. In addition, the scientists achieved
unprecedented success in packing the minute structures into dense

The researchers, led by engineering professors Stephen Chou and Stephen
Lyon, used a technique known as nanoimprinting, in which they press a
mold into a layer of softened plastic on a silicon wafer, making
microscopic patterns on the surface of the plastic. The patterns can then
be transferred to the silicon where they could form the basis of miniature
electronic circuits that store digital information.

The goal of the research was to determine how small and dense a pattern
could be pressed into plastic with nanoimprinting, said Chou, who
invented nanoimprinting in 1994. "This work really pushes the limit down
to a few molecules in size," he said.

The scientists published their results in the June 28 issue of Applied
Physics Letters. The other authors of the paper include graduate students
Michael Austin, Wei Wu, Mingtao Li and Zhaoning Yu and postdoctoral
researchers Haixiong Ge and Daniel Wasserman.

The researchers reported that they created tall, thin ridges only 5
nanometers (5 millionths of a millimeter) wide. The researchers believe
they made ridges even narrower than 5 nanometers, but could not confirm
the results with existing microscopes. "So we still do not know what the
absolute limit is," said Chou.

An important aspect of the achievement is not just the small size of the
ridges, but also the amount of space between the ridges, Chou said. The
spacing, known as "pitch," ultimately determines the density of
electronic memory that can be packed onto a chip. In their published
paper, the scientists reported that they achieved a 14-nanometer pitch
between ridges. They have since reduced it to 12 nanometers. That spacing
is a 20-fold reduction compared to the state-of-the-art techniques used
in making today's most advanced computer chips and would result in 400
times more memory in a two-dimensional memory chip, Chou said.

The current method for making nanoscale devices is to carve each piece
individually with a beam of electrons, a technique called electron-beam
lithography. That process does not achieve the 14-nanometer pitch of
nanoimprinting and requires equipment that is much more expensive than
anything used in Chou's technique.

The key to the result was the collaboration between the labs of Chou and
Lyon and the combination of their different areas of expertise. Chou, the
pioneer of nanoimprinting, was looking for improvements in the molds he
uses for pressing patterns into plastics. His standard method for making
a mold was to use electron-beam lithography to carve the desired pattern
in a piece of silicon, which is then pressed into plastic. This approach
is limited by the narrowness of the electron beam, which carves out a
U-shaped channel about 20 nanometers wide.

To improve on this level of precision, Chou turned to Lyon, an expert in
a technology called molecular-beam epitaxy, which Lyon uses to grow flat
sheets of crystals just a few molecules thick. Members of Lyon's lab grew
alternating layers of two materials until they had a wafer hundreds of
layers thick. Researchers in Chou's lab then cut the wafer, exposing the
edges of the layers. They applied a chemical that ate away one of the two
materials but not the other. The result was a very fine comb-like pattern
in which all the teeth and valleys were perfectly smooth and square with
atomic precision. The researchers used this creation as their mold.

This mold-making process, though time-consuming, would need to be done
only once in setting up a manufacturing process, said Chou. Once the mold
is made, it can be used to make countless copies very rapidly.

The research is the latest in a series of nanoimprinting advances Chou
has made in recent years. In 2003, Technology Review magazine, published
by the Massachusetts Institute of Technology, identified Chou's work with
nanoimprinting as one of "10 emerging technologies that will change the
world." His latest study was funded in part by the Department of Defense
Advanced Research Projects Administration.

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