Less than six decades from its discovery in Bell Labs, the use of silicon as a semiconductor for electronic components has indeed been impressive, now applied ubiquitously from computers to telescopes, and from space craft to toys. The volume of silicon based components is increasing, as does its performance, following the famous Moore's Law theory for computing - the number of transistors on a silicon chip doubles every 18 months. However, challenges that this demand brings can no longer be ignored: R&D spend is increasing at approximately the same rate as Moore's law too; new silicon fabrication plants cost in excess of $3 billion; the cost of the cheapest silicon chip for the past twenty years has been typically 5-10 US cents; and despite developments in computers-on-chips, external power, resistors, capacitors and other components are still needed, meaning interconnects are required and hence more cost, process stages and areas of failure.
Other semi-conductive materials
Now over 50 companies, from start-ups to blue chips, are working on an alternative by using the semi-conductive properties of other materials such as organic semiconductors (e.g. conductive plastics) and inorganic semiconductors (e.g. carbon nanotubes). Organic semiconductors, the most popular of the flexible electronic options so far, are based on large or small molecule plastics which exhibit inherent conductivity. They can be deposited to form a functional transistor, and ever more functional and complex circuits. They can be printed using high resolution printing processes such as inkjet printing, lithography, gravure, and unlike silicon, other components, such as batteries, sensors, displays, etc, can be printed using similar materials and processes.
Other than this, the two main key benefits of printed electronics are:
Materials and manufacture costs very low
Circuits can be deposited onto flexible substrates such as plastic film and foils.
However, their performance, being several magnitudes less than that of silicon, currently limit their capability - don't expect printed Pentiums any time soon.
Printed electronics offer instead the possibility of using electronics in applications where the cost of silicon would have made it impossible or where silicon properties (size, rigidness, etc) are inadequate. Therefore applications include either "small area" such as the electronic sensors and the changing use-by date on a pack of meat; "large area" such as billboard size electronic displays, solar cells and sensors; or where flexible circuits are needed - such as displays for computers, signage, posters etc where the flexibility of the display adds much needed robustness.
Flexynet is a UK venture backed by the government to promote UK companies working with these electronics. Similar schemes also exist across Europe and in the US.
Speaking at the first Flexynet Meeting in June 2004, Tom McClean from Avecia, UK, presented some of the possible applications of the technology. Much attention is being focussed on displays, where organic LEDs (OLEDs) offer many advantages over traditional TFTs (Thin Film Transistors), such as being on flexible substrates (and therefore more robust than glass-based displays), being brighter, and having larger viewing angles.
Other printed display types include electrophoretic (see page 6), electroluminescent and electrochromic displays - this was used in a Valentines card sold by Marks & Spencer in 2003. However, Tom pointed out that predictions today for the impact of such displays are very difficult to judge, because several challenges with the technology still need to be overcome. As a result, he says, the actual volume sales could be five times less or more in reality than today's predictions. He summarises that the "killer" application for this technology may not even have been thought of yet, citing the example of lasers - which had limited applications 20 years ago but there are now several in most households. In response to a question asking how the conductive material suppliers intend to make money - since the plastics are very cheap and only small amounts are typically required - Tom replied that he expects a similar business model to that of the pharmaceutical industry - patents for these materials will be strongly protected and they will be sold based on their value and not production and core material costs.
Potential for large area displays
Bill Wilson from the British Outdoor Advertising Association spoke of the potential of printed electronics for large area displays for advertising. In the UK alone, there are two million large advertisements (e.g. billboards, advertisements on the side of buses etc), the total spend on these being £774 million in 2003. In addition, there are approximately 4.8 million advertisements in retail outlets, plus millions for information posters, timetables, etc. All of these have the potential to be replaced with colour moving displays which are updateable, flexible and much more effective in informing and appealing to people. Bill gave an example such as displays on the London Underground which could change according to the time of day, so that the advertisement can be tailored to the expected interests of the travellers.
Printing RFID tags
Raghu Das of IDTechEx presented on some of the potential applications of printed electronics beyond displays, namely RFID and electronic smart packaging, highlighting the challenges that still need to be overcome.
IDTechEx anticipate that eventually RFID tags will be manufactured in the same way as barcodes - the tag will be printed during the same process stages as the packaging graphics are printed, tagging every item. However, more than just an RFID tag can be printed. The printing process could include informative displays, sensors and other devices to provide on-package diagnostics and addition value for consumers.
Wolfgang Mildner of PolyIC, Germany, told the conference that they have now achieved a long‑life 200KHz oscillator. They are focusing on printed RFID tags.
OrganicID, a US startup, have also told IDTechEx that they expect to achieve a 13.56MHz RFID tag conforming to standards without compromise, and will be prototyping early next year. Both companies will be presenting on this at Smart Labels Europe 2004 which is held in Nice, France, in October. See www.smartlabelseurope.com for details.
For more information, IDTechEx are hosting a dedicated conference focussing on these technologies, paying special attention to the assessment of the applications and their roadmaps. Printed Electronics 2004 - covering the global view - will be held in New Orleans, USA, on December 6-8. Book now for the Early Bird Discount.
See www.printelec.com for details.
For further information on applications, read Electronic Smart Packaging, published by IDTechEx 2004. www.idtechex.com.