New Opportunities for Printed Transistors
A range of transistors using thin films of organic or organic compounds as the semiconductors and gate dielectrics are being pursued by organizations in more than 30 countries. The new IDTechEx report, “Printed and Thin Film Transistors and Memory,” studies the technologies, applications and progress of more than 150 companies in this sector.
According to the study, the rising interest in thin film transistor circuits (TFTCs) is of huge significance to everyone in the electronic, printing, merchandising and health care industries. TFTCs do not employ traditional crystalline or amorphous silicon, germanium or gallium arsenide and that can therefore be deposited at high speed onto low cost flexible substrates.
Flexible transistor circuits using new compounds
Traditionally, semiconductors are made as crystalline as possible to optimize their performance. The new transistors variously use thin films of organic or inorganic compounds as the semiconductors and gate dielectrics, enabling flexible transistor circuits. One printable inorganic semiconductor favored by Toppan Printing and Tokyo Institute of Technology is an amorphous combination of InGaZnO, for example, and it can be cured at a low temperature.
Similarities with old types of transistors
There are similarities with the old silicon chip and the amorphous silicon transistor array on the back of an LCD display today. The new transistors are field effect transistors (FETs). Most use the 40-year-old geometry where the controlled current passes horizontally, but some use vertical geometry to reduce feature size, increase frequency and current carrying capacity and/or reduce cost.
Almost all potential markets for these new transistors are for arrays of large numbers of transistors, not individual transistors. Although very high power versions for electrical use are also in prospect, they are not the largest potential market. Some of these circuits of hundreds to millions of transistors will involve other devices such as sensors, diodes and fuses deposited at the same time. All this is very similar to the old technologies. But there the similarities stop.
The new transistors can be deposited on low cost flexible substrates such as PET and PEN film, aluminum or stainless steel foil. As yet, they are much larger than today’s silicon transistors but they can be one hundredth of the cost, thinner and lighter in weight. Small runs and redesigns are still very low cost, in stark contrast to the situation with traditional transistors. Some are much more stable than amorphous silicon, even working for years without protection from the elements. Some will be stretchable and even biodegradable and made on paper thanks to Abo Akademi and Helsinki University in Finland, ACREO and Linkoping University in Sweden and others.
Those new transistors that are printed, such as the Hewlett Packard ones using zinc oxide-based transistors in thermal inkjet printers, can be made at very high speed, reel to reel over large areas. Such area is needed for driving the pixels of huge billboards and signage. Currently most of the new transistors are limited to frequencies around tens of megahertz, but this still embraces the most popular frequency for RFID, permitting sales of trillions to be contemplated rather than the limit of no more than tens of billions yearly imposed by the cost of the silicon chip in today’s RFID label.
According to the study, the new transistors are the key to huge new markets that the silicon chip will never reach. They will transform medicine, for example, making sophisticated diagnostic and drug delivery skin patches viable and a multitude of disposable testers of bodily fluids. They will herald the smart package for merchandising, with moving color images, sound and storage of books and videos as incentives.
The largest segment of the total printed electronics industry (encompassing displays, sensors, photovoltaics etc.) will be printed transistors and memory. They will drive lighting, displays, signage, electronic products, medical disposables, smart packaging, smart labels and much more. The chemical, plastics, printing, electronics and other industries are cooperating to make it happen.
Already, more than 150 organizations are developing printed transistors and memory, with first products being used in 2007. The market will take off slowly initially, reaching $40 million in 2009 then grow rapidly as technical challenges are overcome, reaching $8 billion by 2017. These transistors are the engine of the emerging printed electronics market.
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