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Electrochemical
transistors made of plastic open myriad possibilities.
Since both electrons and ions are active, they can
function as a bridge between traditional electronics
and biological systems. A new dissertation from Linköping
University in Sweden describes a simple and inexpensive
humidity sensor that can be manufactured in a printing
press.
Electrically conducting plastic
is used today in field effect transistors, light-emitting
diodes, electrochemical components, and batteries.
Organic semiconductors are better than silicon because
they can be applied to soft surfaces, even paper,
using printing technology. What’s more, the components
can be recycled in the same way as regular paper and
plastic.
In an electrochemical transistor,
both electrons and ions serve as charge bearers. It
can be used in sensors, analytical tools, logical
circuits, and smart displays. The current is controlled
by a reduction/oxidation process, which means that
it uses low-voltage current, roughly one volt, and
is not dependent on small dimensions. Moreover, it
has a memory function.
This dissertation by David
Nilsson, from the Department of Science and Technology,
describes an electrochemical humidity sensor, produced
using purely organic materials. Depending on the humidity
of the air, the conducting capacity of the electrolyte
changes, as does the response from the transistor.
The same concept can be used to gauge acidity (pH)
or the content of ions and glucose.
The vision is for the sensor,
the battery, and the display to be pressed simultaneously
on paper or other flexible surfaces. In that way it
would be possible to produce cheap electronic “litmus
paper” or reaction strips for blood and glucose testing.
Intelligent image units (pixels)
are another interesting application of electrochemical
transistors. Varying the current alters the color
of the display and thereby the content of the image
or text. The technology can be used to develop smart
labels and advertising signs.
David Nilsson is a member of
Professor Magnus Berggren’s research team in organic
electronics. In collaboration with the electronics
research institute Acreo, the team has developed printing
technology for electronics on paper. Recently the
Swedish Research Council provided funding for another
printing press under the project Electronic Paper
Printing House.
Notes
The dissertation is titled: An organic electrochemical
transistor for printed sensors and logic. The public
defense will take place on February 17.
David Nilsson can be reached
at phone: +46 11-36 30 54, davni@itn.liu.se.
Magnus Bergren phone: +46 11-363637, cell phone +46
709-783430, magbe@itn.liu.se.
http://www.bibl.liu.se/liupubl/disp/disp2005/tek921s.pdf>
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