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Purdue Scientsits Use Nanowires to Build Transparent Transistors for Displays

by Editor1 last modified June 28, 2007 - 11:01

Researchers from Purdue University are using single nanowires to create fully-transparent transistors and circuits for low-cost, flexible color screens for consumer electronics, displays for car windshields and even “electronic” paper. The transparent transistors are assembled from single "nanowires" put onto glass or thin films of flexible plastic.

Purdue Scientsits Use Nanowires to Build Transparent Transistors for Displays

Scientists at Purdue University's Birck Nanotechnology Center are using single nanowires to create fully-transparent transistors and circuits that could be used to build digital displays for car windshields, and other devices.

"The nanowires themselves are transparent, the contacts we put on them are transparent and the glass or plastic substrate is transparent," explained David Janes, a researcher at Purdue’s Birck Nanotechnology Center, and professor in the School of Electrical and Computer Engineering. Earlier research had succeeded is using nanowires to build transistors, but the electrodes weren’t transparent.

The work is published as “Fabrication of Fully Transparent Nanowire Transistors for Transparent and Flexible Electronics.

Birck Nanotechnology Center researchers say the “transparent transistor” technologies have three (3) areas of potential applications:
  • Transparent displays for uses such as heads-up displays on windshields and information displays on eyeglasses and visors. The displays enable drivers to see information without looking down at the dashboard and could project information on visors for workers without obstructing their view. Potential applications also include sports goggles for spectators to follow a particular player while having relevant statistics displayed and real-time interactive information for soldiers and surgeons.
  • Flexible displays for future "e-paper," promising to allow full-motion video. E-paper is a technology designed to mimic regular ink on paper. Unlike conventional flat-panel displays, which use a backlight to illuminate pixels, e-paper reflects light like ordinary paper and is capable of holding text and images indefinitely without drawing electricity while allowing the image to be changed later. Potential uses of e-paper include low-cost, energy efficient ways of displaying information and video as a replacement for paper in magazines, newspapers, books, electronic signs and billboards.
  • Transparent and flexible electronics for radio frequency identification tags, electronic bar codes and smart credit cards, which resemble ordinary credit cards but contain an embedded microprocessor. This microprocessor replaces the usual magnetic strip on a credit or debit card, increasing the security of data stored on the card and enabling computers to "talk" to the microprocessor. Such a technology could be used to display balances on cards and could be used for the free flow of people through transportation systems, avoiding the need of ticketing machines or validation gates. The cards could contain encryption software, secure data for use in pay phones and banking, and to contain health-care data for patients and allow tamper-proof identification information for workers.

Inside the Nanowires of Transparent Transistors

The nanowires are transparent because they are made of materials that do not absorb light in the visible range of the spectrum. In conventional electronics, transistors are connected to the rest of the circuitry by tiny lines of metal that act as wires. But in the new approach, the nanowires are the transistors.

Researchers used nanowires made of zinc oxide or indium oxide. The nanowires used in the research measure as small as 20 nanometers in diameter. A single nanometer is roughly the size of 20 hydrogen atoms strung together.
"This is a different kind of wire," Janes said. "It is basically taking the place of the silicon in silicon electronics." One reason for the higher performance realized in the new technology is that the devices have a better "on-off ratio" than previous thin-film technologies, Janes said.

"You can get high performance because the nanowires themselves give you some unique performance advantages, and you could still think of dispersing them down over large areas for displays, smart credit cards and other applications," Janes said.

[Unlike conventional computer chips, called CMOS, (complementary metal oxide semiconductors), the thin-film transistors could be produced less expensively under low temperatures, making them ideal to incorporate into plastic films, which melt under high-temperature processing. ]

Liquid crystal displays now used in applications such as color cell phone screens are made with thin-film electronics. This thin-film technology makes it possible to lay down electronic devices in large sheets containing individual pixels. Current thin-film electronics use technologies known as amorphous silicon and poly-silicon.

Researchers on the project include: Sanghyun Jui; Antonio Facchetti; Yi Xuani; Jun Liu; Fumiaki Ishikawa; Peide Yei; Chongwu Zhou; Tobin J. Marks; and David B. Janes. 

Research was funded by NASA through the Institute for Nanoelectronics and Computing, based at Purdue's Discovery Park, and at Northwestern University. Nanotechnology is critical for the advancement because electricity flows differently on the scale of nanometers, or billionths of a meter, than it does in larger wires.  Future research is expected to include work to integrate the thin-film transistors into large circuits and to develop ways to interconnect numerous transistors