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September 9, 2003
Printing Plastic Circuits Stamps Patterns in Place
New York – When Benjamin in “The Graduate”
was told to go into plastics,
computers were in their infancy and silicon technology
ruled. Now,
conducting organic polymers are infiltrating the electronics
sphere and the
watchword is once again plastics, according to Penn
State researchers.
“For plastic circuits we cannot use the old processing,”
says Dr.
Qing Wang, assistant professor of materials science
and
engineering. “Photolithography and silicon technologies
require harsh
environments and plastics cannot hold up to them.”
Wang, working with Ziqi Liang and Kun Li, graduate students
in
materials science and engineering, are looking into
novel processing
methods for production of organic conducting polymer
circuits. One method
that is low cost, easy to do, fast and adaptable to
large areas and
non-flat surfaces, is micro contact printing.
“We use conducting polymers that are functionalized,”
Wang told
attendees today (Sept. 9) at the annual meeting of the
American Chemical
Society in New York. “They have functional groups
attached that allow them
to be soluble and to attach to the surface.”
The researchers used poly (p-phenylene vinylene), PPV,
which was
modified by adding alkyoxy side chains and amino end
groups. Altering the
polymer allows it to dissolve in a variety of organic
solvents. The amines
act as reaction points where the polymer can attach
to another chemical.
Attachment is important as most polymers are slippery
and do not
want to adhere to surfaces. In conventional ink printing,
ink is held onto
the paper by surface interactions, but not by chemical
reactions. When
printing a plastic electronic device, surface interactions
are not strong
enough to hold the polymer “ink” onto the
surface.
Wang used a gold substrate onto which an organic acid,
16-mercaptohexadecanoic acid, was placed in a self-assembled
monolayer. This single layer of molecules of MHA provides
specific
chemical groups to which the amino end groups of the
polymer can attach.
In conventional printing, ink is placed on the plate
and then the
ink and paper are brought together for a very short
time during which the
wet ink is transferred to the paper. When printing polymers
on organic
acid coated gold, the process is different. The researchers
used a pliable
stamp of the submicron pattern they wish to transfer.
They then applied
the polymer “ink” to the stamp surface and
dried it. The stamp and the
substrate are held in contact for 30 minutes while the
polymer transfers to
the substrate.
Because the stamp is pliable, this printing method is
applicable
to curved surfaces. A wide variety of opto-electric
devices are possible,
including light-emitting diodes, field effect transistors,
lasers, solar
cells and chemical and biological sensors.
Wang has investigated the resulting patterns using a
variety of
macroscopic techniques to ensure that the pattern created
on the surface is
continuous and usable. Micro contact printing does create
patterns with
some defects, but the researchers believe that the resultant
product is usable.
“Micro-printed patterns of conducting polymer need
to be used in
applications where some defects can be tolerated,”
says Wang. “Although we
do optimize the printed pattern as much as possible.”
The Commonwealth of Pennsylvania’s Lehigh/Penn
State Center for
Optical Technologies supported this work.
**aem**
EDITORS: Dr. Wang is at 814-865-1443 or at by e-mail.
A'ndrea Elyse Messer
Science & Research Information Officer
Penn State
814-865-9481
814-865-9421
aem1@psu.edu
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