U.S. TECH OCTOBER 2016 ISSUE

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www.us-tech.com

October, 2016

Carbon Nanotube Transistors Continued from page 1

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communications, and other semicon- ductor electronics technologies.” This advance could pave the

way for carbon nanotube transistors to replace silicon transistors and con- tinue delivering the performance gains the computer industry relies on and that consumers demand. The new transistors are particularly promising for wireless communica- tions technologies that require a lot of current flowing across a relatively small area. As some of the best elec- trical conductors ever discovered, carbon nanotubes have long been recognized as a promising material for next-generation transistors. Carbon nanotube transistors

should be able to perform five times faster or use five times less energy than silicon transistors, according to extrapolations from single nanotube measurements. The nanotube’s ultra- small dimension makes it possible to rapidly change a current signal travel- ing across it, which could lead to sub- stantial gains in the bandwidth of wireless communications devices. However, researchers have

struggled to isolate purely carbon nanotubes, which are crucial, be- cause metallic nanotube impurities act like copper wires and disrupt their semiconducting properties — in effect performing like a short in an electronic device. The UW-Madison team used polymers to selectively sort out the semiconducting nan- otubes, achieving a solution of ultra- high-purity semiconducting carbon nanotubes. “We’ve identified specific conditions in which you can get rid of nearly all metallic nanotubes, where we have less than 0.01 percent metallic nanotubes,” says Arnold. Placement and alignment of the

nanotubes is also difficult to control. To make a good transistor, the nan- otubes need to be aligned in just the right order, with just the right spac- ing, when assembled on a wafer. In 2014, the UW-Madison researchers overcame that challenge when they announced a technique called “float-

ing evaporative self-assembly” that gives them this control. The nanotubes must make good

electrical contacts with the metal elec- trodes of the transistor. Because the polymer the UW-Madison researchers use to isolate the semiconducting nan- otubes also acts like an insulating lay- er between the nanotubes and the electrodes, the team “bakes” the nan- otube arrays in a vacuum oven to re- move the insulating layer. The result: excellent electrical contacts to the nanotubes. The researchers also de- veloped a treatment that removes residues from the nanotubes after they’re processed in solution. “In our research, we’ve shown

that we can simultaneously over- come all of these challenges of work- ing with nanotubes, and that has al- lowed us to create these ground- breaking carbon nanotube transis- tors that surpass silicon and gallium arsenide transistors,” says Arnold. The researchers benchmarked

their carbon nanotube transistor against a silicon transistor of the same size, geometry and leakage cur- rent in order to make an apples-to- apples comparison. They are continuing to work on

adapting their device to match the geometry used in silicon transistors, which get smaller with each new gen- eration. Work is also underway to de- velop high-performance radio fre- quency amplifiers that may be able to boost a cellphone signal. While the re- searchers have already scaled their alignment and deposition process to 1 x 1 in. (25.4 x 25.4 mm) wafer, they’re working on scaling the process up for commercial production. Arnold says it is finally reaching the point where re- searchers can exploit the nanotubes to attain performance gains in actual technologies. “There has been a lot of hype

about carbon nanotubes that hasn’t been realized, and that has kind of soured many peoples’ outlooks,” he says. “But we think the hype is de- served. It has just taken decades of work for the materials science to catch up and allow us to effectively harness these materials.” The researchers have patented

their technology through the Wiscon- sin Alumni Research Foundation. r

Contents

Tech-Op-Ed ........................... 4 Tech Watch ........................... 10 Supply Chain ........................... 12 People.................................... 14 Business News......................... 16 Business Briefs........................ 17 Management......................... 18 EMS .................................... 20 ElectronicMfg. Prods............. 24 Production............................ 44 Partnering............................. 46 Distribution........................... 48 New Products....................... 86 High-Tech Events................... 96 Editorial Calendar.............. 96 Advertisers Index................... 98

Special Focus: Components and Distribution.. 50 Product Preview: electronica, The Assembly...... 62

See at electronica, Hall B1, Stand 106

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