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EDN, May 26, 2011

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pulse R Researchers claim replacement for rare material indium-tin oxide esearchers at Eindhoven University of Technology (Eindhoven, Nether- lands) claim to have discovered a replacement for ITO (indium- tin oxide), a material that finds use in electronics displays and solar cells (Reference 1). The transparent conducting oxide has electrical conductivity and optical transparency that engi- neers can deposit as a thin film. Indium is a rare material, and industry participants expect the depletion of available supplies within as little as 10 years. The team of researchers produces the transparent, conducting film-replacement material in water and bases it on electrically conducting car- bon nanotubes and plastic nanoparticles. The research- ers combine low concentra- tions of carbon nanotubes and conducting latex in a low-cost polystyrene film. The nano- Cor Koning (left) and Paul van der Schoot (right) developed a four-point conductivity measurement of a trans- parent conducting film. The black pot contains a dispersion of carbon nanotubes in water, and the white pot contains the conducting latex. tubes and the latex account for less than 1% of the weight of the conducting film. A high concentration of carbon nano- tubes makes the film black and opaque, so the concentration must be as low as possible to achieve transparency. The researchers use stan- dard, commonly available nanotubes, which they dis- solve in water. They then add conducting latex—poly- mer beads in water— with a binder in the form of polystyrene beads. When the mixture is heated, the polystyrene beads fuse together to form the film, which contains a conducting network of nanotubes and beads from the conducting latex. Using freeze-drying tech- niques, the research- ers remove the water, which serves as a dispersing agent in production. The researchers claim that the conductivity of the transpar- ent film is still 100 times lower than that of ITO but expect that they can quickly close that gap. "We used standard carbon nanotubes—a mixture of metallic conducting and semiconducting tubes," says Cor Koning, a polymer chem- TI, National pairing: a bright idea for LED lighting What might Texas Instruments' purchase of National Semiconductor (www.national.com) mean for the world of LED lighting? IMS Research (www.ims research.com) puts TI and National at numbers 1 and 2, respectively, in the LED-IC-driver market, with TI accounting for 19% and National for 7% of what IMS terms a $1 billion market. However, that $1 billion represents the whole LED-IC-driver market, including backlighting; you can bet that IC drivers for solid- state illumination are a much smaller piece of the pie. I've found National Semiconductor drivers in the high- volume, relatively low-cost EcoSmart brand that Home Depot (www.homedepot.com) carries, but I've found none from TI. National is now most likely the stronger player in this market. TI's acquisition of National Semiconductor is inter- esting because the future of LED lighting is decid- edly digital, and National Semiconductor hasn't done well in the digital arena, but TI has excelled at it. In power management, digital has two applications: the control of the PWM (pulse-width-modulation) loop in power conversion and regulation and the communi- cation path between the power-conversion/regula- tion controller and the overall system. Both of these pieces will become dominant in solid-state lighting as the market moves beyond thinking about replace- ment bulbs for incandescent lights to lighting as an integral part of building and environment manage- ment. TI is one of the key players in digital-power control, whereas National Semiconductor's LED driv- ers are currently all analog. With control networks, TI is a long-time market leader, but it also brings a portfolio of energy-harvesting and ultra-low-power design chops, both of which will be keys in lighting applications. Imagine TI's MSP430 microcontroller in every bulb or luminaire; that's the future of lighting. Solid-state lighting is now just a tiny piece of the electronics road map, and TI didn't buy National Semiconductor just for its LED-driver smarts, but the market will become significant, and these two compa- nies make a beautiful pairing.—by Margery Conner ▶Texas Instruments, www.ti.com. ist on the research team. "As soon as you start to use 100% metallic tubes, the conductivity increases greatly." The researchers have discov- ered that manufacturers have recently developed production technology for 100%-metallic tubes and expect the price to fall rapidly. The conductivity of the film is good enough for use as an antistatic layer for dis- plays, for EMI (electromagnetic- interference) shielding to pro- tect devices and their surround- ings, and for flexible displays. —by Suzanne Deffree ▷Eindhoven University of Technology, www.tue.nl. REFERENCE 1 Kyrylyuk, Andriy V; Marie Claire Hermant; Tanja Schil- ling; Bert Klumperman; Cor E Koning; and Paul van der Schoot, "Controlling electri- cal percolation in multicom- ponent carbon nanotube dispersions," Nature Nano- technology, April 10, 2011, http://bit.ly/hcLtHK. 16 EDN | MAY 26, 2011 05.26.11

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