By Will Soutter
Benefits of Printed
Materials used in
Fabrication Methods for
Printed electronics are made of electronic components which can be
processed in the form of a liquid solution, and printed onto a
substrate in the same way ink is printed onto paper. Whilst the concept
has been around for some time, the materials and techniques developed
by research into nanotechnology is making flexible circuits more of a
The materials used to form the resistors, capacitors, and other
components in a printed circuit can include semiconducting organic
compounds, metal nanoparticles, and carbon nanotubes - ongoing research
is uncovering more materials which can be used to make printable
electronics components every year.
The substrates used to print electronic circuits are usually
silicon, glass, ceramics, or polymer films. Polymer substrates have
received the most attention recently, as they allow circuits to be made
flexible, opening up a fascinating range of new applications.
|Figure 1. Flexible
printed circuits could be
used to add smart functionality to everyday objects. Image credit: ORNL.gov
Benefits of Printed
Printing electronic circuits, rather than using traditional
microfabrication techniques like vapour deposition and etching,
advantages, both in terms of the potential applications which are
opened up, and during the manufacturing process itself.
Fabrication of printed microelectronics can be achieved using
techniques which are very familiar to the graphics printing industry.
Roll-to-roll and sheet-fed methods are both possible. Start-up costs
are greatly reduced, and short runs of custom products can be
accommodated much more easily.
The operating temperatures are also much lower than conventional
microfabrication techniques, reducing the energy associated with
Electronic circuits manufactured using these techniques are unlikely
to be suitable for high-performance applications, where powerful
computing or high tolerance to temperature is required.
They will, however, open up a whole new area of low-powered,
low-cost applications. Flexible electronics will be able to add "smart"
functionality to packaging, labelling and garments. There is also much
interest in using them for displays, from large billboard-like screens
to portable flexible screens which can be read like a newspaper.
in Printed Electronics
Table 1. Materials used
printable electronic components
||Silver, silver alloys
||Copper, Gold, Silver
||- - -
||HfO2, TiO2, ZrO2
||- - -
||- - -
for Printed Electronics
Flexographic printing is affordable to set up, due to the use
cheap polymer plates. However, these are not always compatible with the
novel inks used for printed electronics.
Gravure printing is highly flexible - it can print layers
a wide range of thicknesses, from 5µm right down to 50nm. The available
resolution is also very high, allowing dense circuits to be printed.
Offset printing is well suited to more demanding
applications, as it allows a high degree of control, supports a
relatively high resolution,
and is suitable for rapid production on a large scale. The start-up
cost is higher than other methods, however, and a significant volume of
waste is produced.
Inkjet printing is the most common and widespread of these
technologies. Because of the robust understanding we have of it, it can
be adapted to work with a wide range of substrates and inks. It is also
much cheaper than the more specialist, advanced techniques listed here.
However, it is not clear yet how well it will scale-up to large
manufacturing operations. It is likely that inkjet printing electronics
will remain dominant for short-run, on-demand applications.
Screen printing is the most mature printing technique for
electronics. It is cheap and adaptable, but suffers from relatively
thick layer thickness (>20µm) and limited resolution.
The most significant challenge for printed electronics is the
development and optimization of the materials used. Only a handful of
potential substrates have been explored so far, and whilst researchers
are discovering nanomaterials with potentially useful electronic
properties, there is still a way to go in formulating these into
commercial, printable inks.
The manufacturing processes for printing electronics will also
require significant development. A few companies are beginning to
commercialize the printing of simple electronic systems, but the
processes will have to be improved considerably before we are capable
of printing complex circuits.
Many commentators believe that the most successful applications of
printed electronics will be in hybrid processes, combining printing
techniques with established processes like nanoimprint lithography,
which is used to create the latest generations of microprocessors. This
type of method could provide a reliable, cheaper way to produce
electronic components and circuit features on a scale of just a few
nanometres, which will be invaluable as our demands on computing
Printed electronics will have implications across a wide range of
industries. Displays, RFIDs, sensors, and wearable or biocompatible
electronic equipment are amongst the hottest research topics.
There is also a clear path to commercialization for this technology.
Whilst there is still development work to be done, the ubiquity of
large-scale techniques for regular printing means that the transition
to commercial scale production should be smoother than for most
burgeoning nanotechnology products.