Organic and Printed Circuits Revolutionising Microelectronics
Plastics are an indispensable part of our everyday lives. They have highly modifiable material properties and are generally dimensionally stable in a wide range of forms—as thermoplastics, thermosets or elastomers, films or coatings, granular or expanded. As far as applications are concerned, they are used in everything from simple items of daily life to intricately designed structural elements in vehicles and buildings. With their functionally optimised physical and chemical qualities and their attractive appearance, they are constantly redefining the design paradigm for form and function which, in terms of the cost of mass production, is beyond the reach of traditional materials like wood or metal.
New functionalities
With suitable doping and molecular configuration, plastics are being used as electrical conductors and semiconductors. They serve as components in a new kind of microelectronics, that of organic and printed electronics.
These components are called organic because their minute circuitry structures, with myriad transistors, sensors and LEDs, are based on carbon derivatives—rather than silicon or gallium arsenide—as is the case with traditional electronic components.
They are termed printed because two-dimensional layouts of circuit patterns can be printed “from the reel” with structural fineness of currently just a few tens of micrometres onto light, flexible and also transparent substrates by using conventional mass printing processes (flexo, screen-printing and inkjet). Another currently favoured production method, for example for organic photoelectric cells, involves the sequential vacuum deposition of the functional layers in a vacuum.
Integration in objects
Printing and vapour deposition yield versatile, and electronically or photonically functionalised surfaces in the form of films or coatings that can be applied in any desired curvatures to all conceivable objects and even textiles. They form capacitive touch sensors and large-area luminous fields in the form of OLEDs (organic light-emitting diodes) as well as complete sensors and detectors for environmentally or medically important data, such as temperature and humidity. Or they operate as lightweight, flexible organic solar cells. Or as flat, printed batteries that power miniaturised devices. This means that electronics and data technology are no longer confined to specifically designed devices like PCs, tablets, mobile phones and game consoles. In fact, they can be seamlessly integrated into all suitable objects. This facilitates previously unknown and even exotic applications in “smart” objects and yields an appreciable expansion of their connectivity with the networking of even controlled or independently operating data systems in the “Internet of Things”.
Research-intensive field
All over the world, research consortiums and companies of the chemical, pharmaceutical, medical technology, electronics, automotive, consumer goods and packaging industries are working on the development of suitable materials and products and the associated production processes.
Organic and printed electronics constitute an extremely research-intensive sector with long development time-scales. The latest (fifth) edition of the Roadmap of the Organic Electronics Association (OEA), a work group of the VDMA (Verband Deutscher Maschinen- und Anlagenbau—the German Engineering Federation) on the applications and technologies of organic electronics, illustrates the state of progress and trends for the coming ten-year period.
With over 220 members worldwide, the OEA coordinates research and development projects and standardisation under the supervision of the IEC (International Electrotechnical Commission) TC119 and other organisations.
New plastics-based microelectronics have not yet fully arrived in all mass markets. But the first products, often not immediately visible to the user, are already available. The technology is regarded as a platform for a future industry that unites the fields of printing technology, electronics and materials research.
Innovations in the organic and printed electronics sector will be on show at the Printed Electronics Products and Solutions Pavilion at K 2013—the world’s largest trade fair for the plastics and rubber industry in Düsseldorf from October 16-23, 2013. This is where not only printing technologies but also functionalised surfaces such as RFID (radio frequency identification) solutions, flexible displays and OLEDs will be given a platform for presentation to trade visitors from processing and user industries.
OLED screens and displays, the first mass market
Small OLED displays in mobile phones and smartphones have already developed into a first, highly successful mass market for organic electronics. As a result, sales of organic electronics came to US$9 bn last year, says British market researcher Smithers Pira, which is forecasting growth of the sector as a whole into a global annual market of US$200 bn by 2025. This matches the order of magnitude achieved today by conventional silicon chips. Larger, colour-intensive and extremely high-contrast OLED 55-inch television screens have been announced or are already available (for example from Samsung and LG).
E-readers from Amazon and Sony that convincingly present e-books on “electronic paper” enjoy widespread popularity because of the energy-efficient, bistable principle of their electrophoretic displays. They are essentially ideal for presenting static content such as book pages on the basis of pioneer E-Ink’s e-paper. However, their continued distribution is now facing strong commercial pressure from the high-resolution and video-compatible Retina displays in the tablet PCs from Apple with less bright LCDs—a technology that they should have superseded long ago in the innovative logic of technological evolution.
Flexible displays
The next step that ought to move the e-paper display a big step forward is the development of lighter, more flexible and maybe even roll-up e-readers and tablets—without the heavy, breakable cover glass. The most progress here has been made by the British company Plastic Logic (with a fully automated production base in Dresden, Germany), which already masters the art of the backplane loaded with organic thin film transistors (OTFTs), that is to say the active matrix for the individual brightness control of the various display pixels. The latest milestone along the way is a thin, easily flexible 10-inch e-paper display that, with a resolution of 150 dpi (dots per inch), comprises a matrix of 1280 x 960 TFTs, ie a total of 1.2 million pixels.
In the organic sensor field, Plastic Logic in its cooperation with ISORG in France, an enterprise hived off from the large CEA-LITEN research complex in Grenoble, also clearly leads the field. The two of them recently unveiled a 4 x 4 cm image sensor with 89,30 pixels on a thin plastics substrate.
Sealed against water vapour
What is still hampering the development of flexible organic photovoltaics and display technology is the necessary hermetic encapsulation to provide protection from atmospheric water vapour that corrodes their electrode films and shortens their effective service life. So far, such encapsulation has only been possible with rigid cover glass. The appropriate solution for freely contourable solar cells and flexible displays is laminated films as barriers, for which transparent layers of amorphous silicon dioxide appear to be very well suited. These are being collaboratively researched and developed at various locations, for example at the Fraunhofer Polymer Surface Alliance (Polo) and at the Japanese National Institute of Advanced Sciences (AIST).
Application driving forces
The driving forces in the development of applications can be found, says the OE-A Roadmap, in four major industries—automotive, pharmaceutical, consumer electronics and manufacturers of “smart” packages for foods, medicines and other consumer items. With printed RFID tags, smart packages are capable of making merchandise management and its large-scale logistics more efficient. Moreover, with printed, dynamically updated display fields, they can communicate the best-before date to the consumer, draw attention to gaps in the cooling chain for sensitive goods or guarantee the authenticity of high-grade articles with their data links to traceable supply chains. The German company PolyIC is playing a leading role in this field with its development of RFID tags and their printed antennas and with conductive transparent organic films.
The OE-A Roadmap also mentions another current development. Some premium class cars are already fitted with printed antennas as well as printed sensors for seat occupancy integrated in the seat covers to trigger the airbags as necessary. They also detect the weight in order to distinguish children from adults. OLED displays for reversing cameras instead of the traditional mirrors are included in the cars’ equipment, as are the illumination of the instrument clusters on the dashboard and barely visible printed window de-icers.
Next in line for the car are organic displays and touch sensors as replacements for mechanical indicators and switches. The first strategies for reversing lights with OLEDs are already in the pipeline, among other things at Audi, so that today’s LED lights can be replaced to save energy and money. Also in discussion are large-area OLED fields as dimmable and colour-adaptable headliners or for the accentuation of door sills.
OLED lighting
Of the four large fields of application identified by the OE-A Roadmap—OLED lighting, organic photovoltaics, electrophoretic (e-paper) and OLED displays, and electronic components as a complement to classical silicon-based microelectronics—the OLED light sources are probably the most vigorously discussed and challenging elements, as they compete strongly with established LEDs and halogen lamps in the drive to save energy. Unlike LED and halogen spotlights, OLEDs promise dynamically colour-controllable light emitted over a large area. OLEDs can be attached in architecturally attractive ways to the surfaces even of familiar objects in the home, thus turning them into active light sources. OLED lights are already available in design studies and premium products, such as those from Osram and Philips.
Organic photovoltaics and batteries
Organic photovoltaics (OPVs) are developing in parallel with hybrid alternatives made of titanium oxide and dye-sensitised solar cells and with purely organic polymer-based cells. They are already commercially available. However, because of their relatively low efficiency, they are not intended for feeding power into the public grids, but as local supply sources (energy harvesting) and charging the batteries of mobile data and consumer devices and measuring stations. The long-term outlook of the OE-A Roadmap also envisages applications in the envelopes of vehicles and buildings (BIPV, building-integrated photovoltaics) as of 2021.
System components of organic electronics, whose favourable properties also make them suitable for hybrid integration in conventional circuitry, are available in printed data memories—for example, in the form of the ferroelectric, non-volatile memory films of the leading Norwegian manufacturer Thinfilm. This development as driven by Thinfilm is also an example of the system integration of organic components from different manufacturers into larger functional units on shared printed substrates. Thinfilm thus combines its memories with an also printed, first transistor logic produced at contract researcher PARC in California to yield a software-addressable memory module. The latter can also be extended with a printed thermistor as a temperature sensor and a display field (from the Swedish ICT Acre research institute) together with a printed battery to create a compact measuring system.
Slim and flexible batteries produced through printing are also a focus of development in the system integration of organic electronics. At present, the market is dominated by single-use zinc-carbon batteries, while rechargeable, lithium-based equivalents are still undergoing development. As an alternative, energy-rich supercapacitors are available for the temporary supply of power to devices. Their discharge behaviour comes close to that of batteries. Such power supplies can be integrated with display and luminous fields, touch sensors and solar cells in packages, textiles and other consumer items, elevating them to new levels of value and functionality.