Printed electronic test circuit manufactured on a flexible plastic substrate at the Cavendish Laboratory, University of Cambridge. Image: Enrico Gili |
The sense of touch is something we take for granted. The
sensitive nerves in our finger tips generate a flow of information to our
brains that enables us to do things that require extraordinary precision.
Reaching out for an object in the darkness, we are able to tell in a split
second what we’re touching and how to respond. Artificial skin with the ability
to process information—such as texture and temperature—has long been the holy
grail of researchers working on the next generation of electronics. Artificial
skin, which has potential in areas such as robotics, and other products are now
within our grasp as the result of recent research into the exciting field of
plastic electronics.
Initially discovered in the late 1970s, plastic electronics is
an expanding technology that is bringing us a myriad of products incorporating
flexible and transparent electronic circuits in which the active materials are
deposited as printable inks onto polymer-based substrates using various
printing technologies. Rather than relying on conventional, rigid, and brittle
silicon chips to process information, plastic technology relies on novel
organic materials which can be printed, just as colored inks can be printed on
paper. Plastic electronic circuits have the potential to be printed in a small
laboratory containing one or two printing tools, whereas state-of-the-art
microchip factories are about the size of three football fields and require
purpose-built facilities.
However, the full commercial potential of plastic electronic
circuits has been hampered by their lower speed and by the requirement of high
supply voltage (of the order of 100 V), which meant that they were unable to
compete with conventional silicon-based electronics especially in off-the-grid
applications, which are the most attractive for this technology.
A breakthrough by researchers at the University of Cambridge’s
Cavendish Laboratory lays the foundation for plastic electronic circuits that
are fast, flexible, and have low power consumption—as well as being cheap and
relatively straightforward to produce. Physicists Auke Kronemeijer, PhD, and Enrico
Gili, PhD, working in the Cambridge team led by Professor Henning Sirringhaus,
have developed a technology based on solution-processed organic semiconductors
that will find a wide range of applications in everyday life—from radio
frequency identification (RFID) tags on supermarket packaging to transparent
displays embedded in car windscreens displaying vehicle speed or satellite
navigation directions.
Put simply, the new technology provides a simpler way to
fabricate plastic electronic circuits with relatively high performance. Kronemeijer
said: “Our research shows that it’s possible to produce electronic circuits
using a new class of ambipolar organic materials that simplify considerably the
fabrication process compared with more traditional materials. Typically, to
fabricate high-performance plastic electronic circuits you need two different
active materials. Our technology obtains the same result using only one
material. This is an ink that can be printed and requires little more than room
temperature to reach its peak performance. Conventional silicon chips, on the
other hand, typically require more than 1,000 C to be fabricated. The
robustness and flexibility of our new material opens up the possibility for
developing all kinds of intelligent products such as clothing items that
interact with their wearer.”
Countless reports have predicted a future in which we will enjoy
roll-up TV screens in our homes and buy phones with rollable display screens.
But so far, these products have been restricted by the reliance of plastic
electronics on high voltage power supplies which makes them cumbersome and
impractical. Typically such circuits would operate at a speed of a few hundred
Hz and would require input voltages of several dozens of volts—while the
consumer would expect the devices to have embedded printed batteries able to
supply all the power needed. The new circuits developed by Kronemeijer and Gili
exhibited the fastest operation published to date using this class of materials
(a few hundred KHz) and reduced the power supply requirements by approximately
one order of magnitude so that they can already be operated using a standard 9-V
battery.
The physicists are confident that they will be able to reduce
the power supply requirements further to make this technology suitable for
ubiquitous electronic devices incorporating printed power supplies. This was
achieved by using new ambipolar organic materials developed by Martin Heeney’s
team at Imperial College,
London,
exhibiting carrier mobility in excess of 1 cm2/Vs. Moreover, these
materials conduct both electron and holes, making the use of two different
materials (such as in complementary logic circuits) redundant.
The integration potential of the new technology will open up
possibilities for the production of entirely new products as well as lighter,
more flexible versions of existing products. Gili explained: “Take an item such
as a hand held solar powered calculator. This requires several discrete
components contained in a bulky casing, such as a solar cell, back-up battery,
silicon chip, and LCD display. Using plastic electronic technology, all these
components could be integrated on a single plastic substrate by simply printing
different inks in different areas. Moreover, the end result would be a
transparent piece of flexible plastic performing similar operations to the
original, bulky calculator. Although the circuitry may not be powerful enough to
perform very complex calculations, this opens up a multitude of novel
applications, such as interactive playing cards or self-powered customizable
business cards.”
Forty years after the introduction of microchips which have revolutionized
our life with consumer products such as computers, mobile phones and TVs, it’s
hard to remember a world without them. Will this new generation of plastic
electronics replace the technologies used in the day-to-day products that we
have come to rely on? Gili said: “The new technology has broad applications in
areas such as display technology and ubiquitous sensor networks. It is not
likely to replace silicon chips in computational-hungry applications such as
PCs, but is has the potential to open up a whole new range of exciting
applications of plastic electronics which will be cheaper and easier to
manufacture, flexible and easy to customize.”
This research was published in Advanced Materials.
