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The
goal of etching high performance electronic circuits using standard
silicon-based techniques on a piece of flexible plastic has eluded
researchers for quite some time. This is because silicon chips require
processing temperatures high enough to melt any plastic base holding the
silicon crystals in place. But, thanks to pioneering research on
nanowires at Caltech, the goal of producing complex silicon circuits on
flexible plastic substrates is now within reach.
A
paper recently published in Nature Materials(1) by
the James Heath Research Group at Caltech describes a method for etching
nanowires into a wafer of silicon, then peeling them off and
transferring them to plastic. This method results in high-performance
electronics on low-cost, flexible, and transparent plastic substrates.
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| James
Heath, Ph.D., of Caltech is regarded as the world’s
foremost expert on molecular electronics and nanowire
fabrication technologies. |
The
Caltech research holds significant promise because the consumer and
medical markets are developing an appetite for flexible electronics.
Experts predict that this market could easily top $120 billion by the
year 2020(2).
And the race to satisfy demand for enabling technologies, including new
chip designs, is heating up.
Digital
Living: The New Investment Craze?
Established
firms, such as Intel, IBM, Kodak, Motorola, and Xerox, are pouring
millions of dollars into internal research and scouting academic
research labs around the world in pursuit of tools heralding the age of
“digital living.” Ideas include flexible displays that promise to
disrupt everything from newspaper publishing to mobile phones(3),
flexible batteries for efficient energy generation(4),
architectural electronics, and a host of other tools to endow everyday
products --
from food and medicine containers to fabric and paper -- with a
modicum of computer smarts(5).
Entrepreneurial
startups with VC-backing also see the opportunity. One recent example
featured in Red Herring(6) is
the British startup Plastic Logic, which succeeded in lining up $100
million from top VCs, including Oak Investment Partners, Amadeus
Capital, and hedge fund Tudor Investment Corporation. All attention is
on producing e-paper, i.e., flexible displays that you can roll up and
put in your pocket. The idea was attractive enough to lure other
investors such as Intel Capital, Bank of America, and BASF Venture
Capital.
In
the biomedical field, San Francisco Bay Area-based Bioident and
Nanoident have lined up venture backers to invest in plastic chips for
biometrics and chemical agent detection(7).
Taking a different approach is Los Angeles-based ORFID, which is using
an organic chip platform to produce flexible displays for RFID
applications in hospital settings as well as for tagging medicine
containers(8).
Nanowires
to the Rescue:
The
ability of established and entrepreneurial companies to meet demand for
flexible electronics is restrained by the limitations of prevailing
plastic chip technology. Devices, such as e-paper and roll-up displays
for mobile devices, rely on transistors made of either organic polymer
printed like ink on plastic substrate or amorphous, noncrystalline,
silicon.
According
to Mike McAlpine, Ph.D., lead author of the Caltech paper, most of these
chips have limitations. Although organic transistors can be processed at
low temperatures, “they perform poorly because of their propensity to
degrade over time,” he said. And, when it comes to speed, these chips
don’t fare well either. “The mobility [speed] of silicon is 1000
times higher than organics. Furthermore, since they are inorganic
materials, they are much more stable in air than organics,” he added.
To
overcome the limitations of organic chips, the Caltech team resorted to
nanotechnology to combine high quality semiconductors with plastic.
Their approach involved etching nanowires —1000 times smaller than
|
 |
The
production of Caltech's plastic chip required unprecedented advances in
assembly, integration, and device reliability of nanoscale materials.
|
 |
| Michael
McAlpine, Ph.D., a member of the James Heath Research Group
at Caltech and lead author of the Nature Materials article, was
first to conceive of the nanowire-on-plastic process while at
Charles Lieber’s lab at Harvard five years ago. |
a
human hair — into a wafer of silicon of the same quality as that used
in Intel computer chips. These nanowires were then transferred to
plastic at room temperature.
In
fact, the Caltech team is the first to assemble such well-ordered,
densely packed nanowires on a piece of flexible plastic. The resulting
product is not only much more stable thermally and chemically, but also
expected to perform much faster than chips made of organics or hybrid
materials.
According
to McAlpine, the Caltech team takes pride in the fact that the
production of its plastic chip “required unprecedented advances in
assembly, integration, and device reliability of nanoscale materials.”
Nonetheless, the team believes that the micro-fabrication procedures
involved are compatible with large-scale industrial production. These
procedures are expected to result in competitively priced, yet
high-performance, electronics.
As
for applications, the Caltech researchers think the sky is the limit.
Imagine a myriad of new gadgets with important applications in
biosensing and medicine. Examples include highly portable chemical and
biological threat detectors and DNA sensors that could be packed into a
small chip to spot pathogens in blood samples. Furthermore, since
plastic is biocompatible, the Caltech team believes that the chip could
one day facilitate the commercial production of fully implantable or
wearable continuous health monitoring systems.
Footnotes
-
Michael C. McAlpine, Habib Ahmad, Dunwei Wang & James R. Heath, “Highly
Ordered Nanowire Arrays on Plastic Substrates for Ultra-sensitive
Flexible Chemical Sensors,” Nature Materials, April,
2007
- US Display Consortium, Dec. 19, 2006
-
Olga Kharif, “Computing’s New Screen Gems: Display Technologies Are
Moving Rapidly to Thinner, More Flexible, and Efficient Systems. Even
CRTs Are Getting Rethought,” Business Week, June 8, 2004
-
Battery Innovations: The Current Scene,” ePower, Sep – Oct,
2003.
-
Otis Port, Rachel Tiplady, Faith Arner “Just Two Words: Plastic Chips,” Business
Week, May 10, 2004.
-
Ken
Schachter, “Plastic Logic Lands $100M,” Red Herring,
January 4, 2007
-
Adena
DeMonte, “Nanoident: Plastic Chip Plant,” Red Herring,
March 13, 2007.
-
Jeyling
Chou, “Los Angeles-Based Startup Combines UCLA Research with High-Tech
Company’s Savvy & VC Funds,” SoCalBio Synergies,
Summer 2004.
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