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PRINTED ELECTRONICS
There has been a huge increase in elements employed in
manufacturing printed electronics in order to meet the variety of
needs for all printed and potentially printed electronics. Not least
in flexible, low cost form, a rapidly increasing number of
elements are being brought to bear. Oxides, amorphous mixtures,
alloys and organics are particularly in evidence.
There are a number of promising elements currently being
employed by about 2000 organisations, double the number two
years ago, in research and production of printed devices. Some
of the most promising elements now employed for printed
electronics and their purpose are outlined here.
The chemistry of printed displays
Printed alternating current (ac) electroluminescent displays are
exhibiting better colours and longer life as the chemistry
improves but they will be overtaken by the growing
electrophoretic displays employing titanium dioxide, carbon and
organics to give exceptionally low power and good viewing in
sunshine. dyes, have been developed by Pacific Northwest National
Organic Light Emitting Diodes (OLEDs) have the potential to Laboratory in the USA and others. It has used organic phosphine
replace today’s TV and phone screens and to provide ubiquitous oxides as electron transport materials. These materials address
“wallpaper” lighting and even disposable electronic displays the critical issue of achieving high quantum efficiency at low
showing moving colour images on packaging. The first OLED voltages. One class of new OLED materials developed at PNNL
television displays have exceptionally vibrant colours, narrow is based on organic phosphine oxide compounds while another is
viewing angle and lack of pixilation when the camera is panned. based on organic phosphine sulphides. In addition to OLEDS,
However, OLEDs are a tough business to be in and those these materials have the potential to be used in other devices,
developing OLED lighting tend to be different companies from including photovoltaic cells and thin film transistors. It is not
those pursuing OLED displays, because the requirements are so unusual for an advance in materials for one device to be
different. Although over 200 organisations started to develop applicable to others. Another example of this is Kovio printed
OLEDs we now have attrition with several leaving the business in nanosilicon transistors opening up a new advance in
frustration every year because it is so tough to meet the required photovoltaics.
price and performance points.
Barrier layers
Fragile OLED chemistry Consider barrier layers for flexible OLEDs. They need to be
The leaders in OLED materials are investing huge amounts of better than those used for any other device. We mean 10-6
money to get on top of the fragile chemistry. Although versions grams per square meter per day of water and 10-5 cc per square
sandwiched in glass are selling well, profits are elusive. The meter per day of oxygen. Few currently believe that the
advent of mass produced, flexible, low cost OLEDs keeps slipping requirements of life, flexibility, large area, low cost and volume
further into the future. To extend life and improve electronic and manufacture have been met. Developers such as Vitex, Appliflex
optical performance, an ever widening choice of elements is and 3M in the USA and IMRE in Singapore use alternating
being employed by those in for the long haul. Fine chemical metal oxide or nitride and polymer layers, examples of the
companies concerned with inorganic materials are among those inorganic layers being the oxides of boron, aluminium and
coming to assist the device makers. titanium and there is interest in binding up the undesirables, not
In research and development, OLEDs now variously employ just preventing them from getting through. Not one of the
such materials as B, Al and Ti oxides and nitrides as barrier developers of barrier layers is able to use printing as yet and
layers against water and oxygen, Al, Cu, Ag and indium tin oxide samples are very hard to come by, according to various
as conductors, Ca or Mg cathodes and CoFe nanodots, Ir and Eu interested parties that IDTechEx has interviewed in the
in light emitting layers, for example. The organic chemistry is preparation of this article.The future is obviously rosy for printed
also sophisticated with both organic and inorganic dopants in electronics and with such extensive research occurring in the
organic hosts and different light emitting principles brought to global market there will be increasing opportunities in both
bear. Each layer of the device is a challenge, just as it is with manufacturing and application of printed electronics.
printed transistors being developed by over 360 organisations.
Versatile new materials
Market for printed electronics in 2008 and 2012
A fairly recent development by materials supplier Merck and
in billions of dollars
others is phosphorescent (triplet) technology for OLEDs. This
2008 2012
offers the prospect of high efficiency (a factor of 3-4 times over
Materials 0.63 3.84
fluorescents usually employed) while maintaining color purity
Production services and other 0.95 4.33
and long lifetime for red and green.
Total market 1.58 8.17
This promising triplet approach has been shown to be capable
of being adapted for printing using solution processes.
Source IDTechEx report “Printed Electronic Forecasts, Players, Opportunities 2008-2028”
Phosphorescent OLEDs, such as those employing iridium based
www.euroasiasemiconductor.com September 2008
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