Fully printed carbon nanotube transistor circuits for displays

ScienceDaily (Nov. 30, 2011) — Since the invention of liquid crystal displays in the mid-1960s, display electronics have undergone rapid transformation. Recently developed organic light-emitting diodes (OLEDs) have shown several advantages over LCDs, including their light weight, flexibility, wide viewing angles, improved brightness, high power efficiency and quick response.

OLED-based displays are now used in cell phones, digital cameras and other portable devices. But developing a lower-cost method for mass-producing such displays has been complicated by the difficulties of incorporating thin-film transistors that use amorphous silicon and polysilicon into the production process.

Now, researchers from Aneeve Nanotechnologies, a startup company at UCLA's on-campus technology incubator at the California NanoSystems Institute (CNSI), have used low-cost ink-jet printing to fabricate the first circuits composed of fully printed back-gated and top-gated carbon nanotube-based electronics for use with OLED displays. 

The startup includes collaborators from the departments of materials science and electrical engineering at the UCLA Henry Samueli School of Engineering and Applied Science and the department of electrical engineering at the University of Southern California.

In this innovative study, the team made carbon nanotube thin-film transistors with high mobility and a high on-off ratio, completely based on ink-jet printing. They demonstrated the first fully printed single-pixel OLED control circuits, and their fully printed thin-film circuits showed significant performance advantages over traditional organic-based printed electronics.

"This is the first practical demonstration of carbon nanotube-based printed circuits for display backplane applications," said Kos Galatsis, an associate adjunct professor of materials science at UCLA Engineering and a co-founder of Aneeve. "We have demonstrated carbon nanotubes' viable candidacy as a competing technology alongside amorphous silicon and metal-oxide semiconductor solution as a low-cost and scalable backplane option."

This distinct process utilizes an ink-jet printing method that eliminates the need for expensive vacuum equipment and lends itself to scalable manufacturing and roll-to-roll printing. The team solved many material integration problems, developed new cleaning processes and created new methods for negotiating nano-based ink solutions.

For active-matrix OLED applications, the printed carbon nanotube transistors will be fully integrated with OLED arrays, the researchers said. The encapsulation technology developed for OLEDs will also keep the carbon nanotube transistors well protected, as the organics in OLEDs are very sensitive to oxygen and moisture.

The technology incubator at the CNSI was established two years ago to nurture early-stage research and to help speed the commercial translation of technologies developed at UCLA. Aneeve Nanotechnologies LLC has been conducting proof-of-concept work at the tech incubator with the mission of developing superior, low-cost, high-performance electronics using nanotechnology solutions that bridge the gap between emerging and traditional platforms.

The research was published this month in the journal Nano Letters.

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The above story is reprinted from materials provided by University of California - Los Angeles.

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Journal Reference:

Pochiang Chen, Yue Fu, Radnoosh Aminirad, Chuan Wang, Jialu Zhang, Kang Wang, Kosmas Galatsis, Chongwu Zhou. Fully Printed Separated Carbon Nanotube Thin Film Transistor Circuits and Its Application in Organic Light Emitting Diode Control. Nano Letters, 2011; : 111122151948003 DOI: 10.1021/nl202765b

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Proton-based transistor could let machines communicate with living things

ScienceDaily (Sep. 21, 2011) — Human devices, from light bulbs to iPods, send information using electrons. Human bodies and all other living things, on the other hand, send signals and perform work using ions or protons.

Materials scientists at the University of Washington have built a novel transistor that uses protons, creating a key piece for devices that can communicate directly with living things. The study is published online in the interdisciplinary journal Nature Communications.

Devices that connect with the human body's processes are being explored for biological sensing or for prosthetics, but they typically communicate using electrons, which are negatively charged particles, rather than protons, which are positively charged hydrogen atoms, or ions, which are atoms with positive or negative charge.

"So there's always this issue, a challenge, at the interface -- how does an electronic signal translate into an ionic signal, or vice versa?" said lead author Marco Rolandi, a UW assistant professor of materials science and engineering. "We found a biomaterial that is very good at conducting protons, and allows the potential to interface with living systems."

In the body, protons activate "on" and "off" switches and are key players in biological energy transfer. Ions open and close channels in the cell membrane to pump things in and out of the cell. Animals including humans use ions to flex their muscles and transmit brain signals. A machine that was compatible with a living system in this way could, in the short term, monitor such processes. Someday it could generate proton currents to control certain functions directly.

A first step toward this type of control is a transistor that can send pulses of proton current. The prototype device is a field-effect transistor, a basic type of transistor that includes a gate, a drain and a source terminal for the current. The UW prototype is the first such device to use protons. It measures about 5 microns wide, roughly a twentieth the width of a human hair.

"In our device large bioinspired molecules can move protons, and a proton current can be switched on and off, in a way that's completely analogous to an electronic current in any other field effect transistor," Rolandi said.

The device uses a modified form of the compound chitosan originally extracted from squid pen, a structure that survives from when squids had shells. The material is compatible with living things, is easily manufactured, and can be recycled from crab shells and squid pen discarded by the food industry.

First author Chao Zhong, a UW postdoctoral researcher, and second author Yingxin Deng, a UW graduate student, discovered that this form of chitosan works remarkably well at moving protons. The chitosan absorbs water and forms many hydrogen bonds; protons are then able to hop from one hydrogen bond to the next.

Computer models of charge transport developed by co-authors M.P. Anantram, a UW professor of electrical engineering, and Anita Fadavi Roudsari at Canada's University of Waterloo, were a good match for the experimental results.

"So we now have a protonic parallel to electronic circuitry that we actually start to understand rather well," Rolandi said.

Applications in the next decade or so, Rolandi said, would likely be for direct sensing of cells in a laboratory. The current prototype has a silicon base and could not be used in a human body. Longer term, however, a biocompatible version could be implanted directly in living things to monitor, or even control, certain biological processes directly.

The other co-author is UW materials science and engineering graduate student Adnan Kapetanovic. The research was funded by the University of Washington, a 3M Untenured Faculty Grant, a National Cancer Institute fellowship and the UW's Center for Nanotechnology, which is funded by the National Science Foundation.

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Washington. The original article was written by Hannah Hickey.

Journal Reference:

Chao Zhong, Yingxin Deng, Anita Fadavi Roudsari, Adnan Kapetanovic, M.P. Anantram, Marco Rolandi. A polysaccharide bioprotonic field-effect transistor. Nature Communications, 2011; 2: 476 DOI: 10.1038/ncomms1489

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