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Breaking Through

Printable electronics is attracting growing interest and is gearing up for commercial applications

by Alexander H. Tullo
February 13, 2006 | A version of this story appeared in Volume 84, Issue 7

On A Roll
Credit: PolyIC Photo
A worker prints demonstration circuits at PolyIC's headquarters in Erlangen, Germany.
Credit: PolyIC Photo
A worker prints demonstration circuits at PolyIC's headquarters in Erlangen, Germany.

In the 2002 science fiction film "Minority Report," the protagonist, John Anderton, is in no mood for the noisy, animated cartoon characters on the front of a cereal box, so he flings the offending package out of sight. The movie, set in 2054, also features automatically updating electronic newspapers and billboards that pitch to particular individuals in a crowd.

If the future does see technologies like these, it will likely be thanks to printable electronics. By being potentially much cheaper and more physically flexible than conventional electronics, printable electronics can make electronics, already ubiquitous today, more commonplace and perhaps even disposable.

Conventional silicon-based semiconductors are manufactured in clean-room environments through costly processes like photolithography and plasma etching. Though the performance of chips manufactured this way is without peer, there is a limit to how inexpensively they can be made.

Printed electronics, at least conceptually, represent a step change in production costs. Semiconductors would be based on organic inks printed on flexible plastic substrates similar to how labels and newspapers are made. But instead of words and pictures on paper, layers of semiconductor inks would be applied, building active electronic components such as transistors. "The premise is that if you are able to use solution deposition, you will be able to make this transistor on this circuit much cheaper than you would if it were silicon," says Beng Ong, a research fellow at Xerox Research Centre of Canada in Mississauga, Ontario.

Chemistry is playing a crucial role in making printable electronics come to life. And many chemical and materials companies-including BASF, Dow Chemical, Cabot Corp., DuPont, Degussa, Merck KGaA, and Sun Chemicals-have taken a keen interest in this nascent sector. Companies like these are developing their own technologies or investing in small start-up firms in the field.

Peter Harrop, chairman of the U.K.-based consultancy IDTechEx, says real-life applications of printed electronics won't be as frivolous as the ones shown in "Minority Report." He says printable electronics may make conventional "use by" dates on drug and food packaging obsolete. Instead, a bottle of pills may record the temperatures it has experienced, and an electronic display can advance or delay the expiration date accordingly.

The potential of printable electronics is bounded only by the imagination. The technology might be used to make radio frequency identification (RFID) tags inexpensive enough to be printed on just about everything, helping to foil counterfeiters or enable Wal-Mart managers to keep inventories continually accurate. Tags on sweaters may someday tell washing machines how they should be washed. And window shades may someday double as photovoltaic power sources.

Harrop predicts that sales of organic chips will eventually eclipse sales of silicon chips, which were nearly $230 billion last year, according to the Semiconductor Industry Association. He forecasts that organic electronics will be a $30 billion market by 2015, at which point major applications will be logic circuits, displays, and lighting. The market, he predicts, will grow to $96 billion by 2020 as uses like billboards and power generation emerge. By 2025, Harrop says, the organic electronics market will be about $250 billion.

According to Harrop, conventional chipmakers won't have to worry about competing head-to-head with organic semiconductors for another 15 years. The initial growth will come from new-to-the-world applications that wouldn't be commercially possible without cheap, printable electronics.

Some commercial applications for printable electronics are hardly futuristic. In fact, rudimentary applications such as toys that incorporate printable circuitry are already commercial, Harrop points out. More sophisticated applications, such as displays and RFID tags, may be less than two years away.

Plastic Logic, launched in 2000 in Cambridge, England, is working on technologies to make applications like animated posters and electronic newspapers become a reality. The company was spun off the same research team-Richard Friend's group at the University of Cambridge-that spawned the organic light-emitting diode (OLED) technology company Cambridge Display Technology in 1992.

Credit: Plastic Logic Photo
Credit: Plastic Logic Photo

Plastic Logic takes materials from a host of sources-nanosilver inks from Cabot, for example, and polyethylene terephthalate sheet from DuPont Teijin Films-and uses them to design and make backplanes for flexible displays. These backplanes consist of arrays of transistors that turn specific pixels in the display on and off, just as in semiconductor-based liquid-crystal displays.

The application is tricky. Stuart M. Evans, Plastic Logic's chief executive officer, explains that the surfaces of flexible substrates tend to be more distorted than flat surfaces like silicon. In normal printing, he adds, this isn't a problem because the eye doesn't notice imperfections on very small scales. "In electronics, you are trying to get things down to the precision of a few microns," he says. "A drop of the wrong material in the wrong place can lead to a devastating short circuit."

The company can point to some successes. In collaboration with electronic paper developer E Ink, Plastic Logic made the world's largest flexible organic active-matrix display. The display's backplane contains 480,000 transistors to activate pixels on a 10-inch black-and-white screen.

Evans hopes to have commercial products available in stores sometime in 2008. He is confident about the commercial scale-up of the process, largely because the construction of a $15 million prototype line went smoothly. "It was very pleasing last year to realize that a lot of the equipment that we used was off the shelf," he says.

The CEO estimates that a manufacturing plant could be constructed for less than $100 million, an order of magnitude less than the cost of building a liquid-crystal display factory.

Evans is optimistic that electronics makers will be receptive to flexible displays and predicts a market for the backplanes of about $3 billion by 2010. "One of the curious challenges that we had in the early days was this sense that we hadn't spotted what the gigantic applications would be, but I have given up worrying about that," he says. "There are 400 million newspapers read every day."

Plastic Logic's optimism is shared by several stalwart investors. Among them are Dow Chemical and BASF, both of which participated in a recent $28 million funding round.

Both Dow and BASF have other ties to printable electronics as well. Dow had been developing light-emitting polymers, although it sold the business to Sumitomo Chemical. In 2004, Dow spun off Aveso, a company that is developing ultrathin displays based on a modification of electrochromic technology.

In September, BASF concluded a project with Lucent Technologies' Bell Labs and Printed Systems GmbH that resulted in a fully printed ring oscillator, a component that produces pulses in a circuit. BASF will now work with Printed Systems to explore printable electronics applications.

Like Plastic Logic, PolyIC designs printable electronic circuits and is developing technologies for full-scale manufacturing. The Erlangen, Germany-based firm, a joint venture between Siemens and German printer Leonhard Kurz, is focusing on plastic RFID tags and hopes to launch its first commercial products early next year.

Last December, the company announced a major breakthrough toward this goal: prototype tags that work at 13.56 MHz, a standard RFID frequency. "Half a year ago, people were saying that this frequency might not be reachable with organic electronics," says Wolfgang Mildner, PolyIC's managing director.

To make organic RFID tags commercially viable, PolyIC still needs to perfect the roll-to-roll manufacturing process to lower fabrication costs and bring the process to commercial scale. The company's goal is to eventually get the cost of its tags down to 5 cents each, Mildner says. Standard RFID tags cost about 20 to 30 cents apiece and can't be made below 10 cents per tag, he says.

Chemical firms that would supply raw materials to the sector are also gearing up. These firms say they have made a lot of progress in developing materials such as organic semiconductors and printable connectors and are now fine-tuning properties for industrial-scale production.

Among them is Plextronics, a Pittsburgh-based company founded in 2002 to commercialize the work of Richard D. McCullough's group at Carnegie Mellon University in conductive regioregular polythiophenes.

Shawn P. Williams, the firm's vice president of technology, says several companies are working with polythiophenes in printable electronics applications. He explains that they work as semiconductors because the conjugated bonds in polythiophenes form band gaps much like those in silicon-based semiconductors. Plextronics' regioregular polythiophenes boast smaller band gaps and more tunable conductivities compared with regiorandom polythiophenes and other materials, he says.

Andrew W. Hannah, Plextronics' president and CEO, says his company's technology lends itself to OLED and photovoltaic applications. In particular, he says Plextronics' polymer, by being nonacidic and solvent-based, is ideal for the OLED's hole injection layer-the part of an OLED assembly that furnishes a positive charge for the electron to combine with to create light. "We actually extend the lifetime of OLEDs and make them easier to manufacture," he says.

Hannah says the same properties that help Plextronics materials enable OLEDs is also a sought-after property for photovoltaics. "Longer term, we think the biggest impact that we will have is on thin-film photovoltaics," he says. The company is also supplying semiconductors to PolyIC for the first printable RFID applications.

Xerox is also working with polythiophenes. Ong says Xerox also uses inorganic materials that are potentially more stable and cheaper than organics.

Xerox' goal is to develop semiconductor materials that can be processed in ambient conditions in the presence of air. Ong's group in Ontario sends its materials to Xerox' Palo Alto Research Center for fabrication into circuits. "We have used our materials all the way to printing circuits under ambient conditions," he says. "And we have used an ink-jet printer to print a transistor circuit using our materials."

Ong says Xerox' materials are nearly ready for commercialization. "The current performance characteristics of our materials should be able to allow for making circuits for displays and even suitable for use in applications such as RFID tags," he says.

But there are still obstacles. "In the lab and under certain conditions, it works," Ong says. "But when you bring it to the manufacturing stage, you have to make the printed circuits at high speed."

Ong says it is also unknown whether printed electronics will deliver on their promise of being cheaper than conventional silicon-based electronics. "There are still a lot of unknowns with respect to manufacturing," he says. "Everything is based on the premise that a solution process such as printing will be able to lower the costs. But when you go to actual manufacturing, whether you can lower the costs or not is still an open question."

Other companies working on electronics semiconductors include Bayer's H. C. Starck unit, which is developing polythiophene-based materials. Its poly-(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT/PSS) is being used as a hole-injection layer in OLED applications.

Merck KGaA is another company that uses thiophene-based materials for organic semiconductors. It also works with polyarylamines and other semiconductor materials as well as dielectric and interface materials compatible with its semiconductors.

In addition to its own research program in organic semiconductors dating back to 2000, the company acquired additional materials in its purchase last year of OLED technology developer Covion from Avecia. Merck is also partnering with the Technical University of Darmstadt, in Germany, to develop inorganic composite materials.

Merck is honing organic semiconductor properties such as stability, processibility, and mobility-the speed-enhancing ability of the semiconductor to scatter electrons. The company says some of its materials have mobilities similar to that of amorphous silicon.

Merck's target markets include display backplanes, RFID, and photovoltaics. "Some of our industry partners believe that, with the materials we currently have available, the first applications can be realized," says Udo Heider, who heads new business activities in Merck's chemicals arm.

Meanwhile, Degussa has an effort under way in semiconductor materials based on hybrid materials incorporating silicon nanoparticles. It is also working on conductive material systems based on indium tin oxide. The company recently signed a collaboration agreement with a German research center in Karlsruhe for the development of the nanoparticle materials.

"We are convinced that future applications will have an added value by combining new nanomaterials with established materials," says Frank Martin Petrat, senior project manager for printable electronics at Creavis Technology & Innovation, a Degussa unit that develops nanomaterials.


Among Degussa's targets are disposable electronics for RFID tags. But Petrat admits there is still some work to be done. "There are different technical hurdles that have to be addressed in the materials, such as charge carrier mobility, processibility, and stability, just to name a few of them," he says. Degussa is also buying a stake in Printed Systems, which is developing keyboards printed on paper and also working with BASF.

Chemical and material companies also aim to apply the innovative chemistry of conductive inks to passive components of printable electronics such as connectors and resistors.

Cabot already has a business dedicated to printable electronics and displays. It is the result of the firm's 2004 acquisition of Albuquerque-based Superior MicroPowders, which had been developing powdered materials for electronics as part of U.S.-government-sponsored programs.

The first product that Cabot is developing for printable electronics is nanosilver ink. The material is made of polymer-coated silver nanoparticles in a solvent.

Silver normally has a melting point of more than 900 °C. But according to Chuck Edwards, general manager of the Cabot unit, the nanoparticles, up to 500 atoms across, are relatively unstable and can sinter together at 200 °C. "What you end up with is a layer of tiny particles that have welded together so they become a network of silver particles," he says. The spongelike layer of particles has about half the conductivity of silver metal and can serve as a wire.

The company is also developing nanoparticle nickel, which Edwards says would be easier to solder than silver. Additionally, the company is exploring other electronic components, such as resistors, where Cabot may employ its carbon expertise.

Sun Chemical is developing connectors for the printed electronics industry. But according to Andy Parkinson, manager of new developments in conductive inks, its approach differs from Cabot's because Sun uses silver flakes with water-based, solvent-based, and UV-curable binders.

There is a trade-off in terms of performance versus nanoparticle materials, Parkinson admits, but the Sun materials claim their own advantages. "In some cases, flakes work better from a cost/performance standpoint," he says. Moreover, they can process at lower temperatures. Some substrates and organic semiconductors can't be processed at temperatures over 125 °C, he says.

The next year, Parkinson says, will be a moment of truth for the printable electronics industry. "By midyear, we'll see a different environment," he says. "This year, we will see it fly up, or we will be able to say conclusively that it is not going to happen for another two or three years."

PolyIC's Mildner agrees that the nascent business is on the verge of big things. And he notes that many companies are entering the sector. About 55 companies, he notes, have formed a trade association. "Of course, this is a technology that is not yet there and not yet mature," he says. "But there is a whole market working in this direction."


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