Flexible Polymer Transistors 'Printed' Using Ultraviolet Light

Dec 19, 2008 By Laura Mgrdichian feature
The procedure for creating UV-printed polymer transistors. (a) A PEDOT-coated mold is placed in contact with the pre-polymer-coated flexible substrate (b) They are illuminated with UV light (c) Upon removing the mold, PEDOT source-drain layers are transferred onto the substrate (d) Active and dielectric layers are "spin coated" on top of the source-drain layers (e) and (f) Using a PEDOT-coated glass substrate, the self-aligning gate layer is contact-printed on the dielectric layer. Image by Hong Lee, © American Institute of Physics

(PhysOrg.com) -- Computer and television displays made using flexible, bendable polymer materials are technologies of the future, promising roll-up computer monitors and other innovations. Scientists are making progress toward bringing these technologies into our homes and offices.

A research group at Seoul National University in Korea recently created a flexible polymer transistor that is printed using a simple process involving ultraviolet (UV) light, described in the November 20 online edition of Applied Physics Letters. Creating transistors in this way is an important avenue toward flexible electronics, as transistors form the basis of most modern electronic devices. Computer processing chips, for example, consist of more than 200 million transistors.

"Our printing method is low-cost and could be scaled to the manufacturing level -- a requirement for most technologies," said Hong Lee, the paper's corresponding author, to PhysOrg.com. "It performs as well as non-flexible polymer transistors and better than similar transistors produced by other research groups."

The researchers started with a commercially available polymer mold etched with a "source-drain" pattern, forming locations for two of the three electric terminals that make up a transistor: the source, drain, and gate. They then coated the mold with a very thin layer (just 100 nanometers) of a conducting polymer material, known in abbreviated form as PEDOT.

Next they coated a flexible substrate -- a surface on which to build the transistor -- with a "pre-polymer" liquid layer. The pre-polymer is key to the process because it hardens and binds to the PEDOT layer when illuminated with UV light.

Applying no pressure, the researchers brought the mold and the substrate into contact and exposed them to UV light for 20 minutes. When the mold was removed, the researchers saw that the PEDOT on the mold's raised areas had been transferred to the substrate, forming the transistor's source and drain.

But unlike ink deposited onto paper by a stamp, in which the paper's surface remains flat, the substrate underwent topological changes caused by the physical bonding between the pre-polymer and the PEDOT under the UV light during the hardening process. Where the raised parts of the mold met the substrate, the substrate's surface developed "low" areas. And across from the mold's low areas, the substrate developed a raised mound between the source and drain, which acts as a channel between them.

The substrate was coated with two additional polymers, an "active" current-carrying layer and a dielectric, a material used in transistors to control the flow of current.

Finally, the substrate was flipped over and put in contact with PEDOT-coated glass. PEDOT "ink" was transferred to the substrate's raised area, completing the four-layer printed transistor structure.

This method departs from the inkjet-style approaches commonly used to print polymer transistors, in which a printer head moves back and forth across the substrate, depositing the polymer layers in tiny droplets. Inkjet printing has been successful, but ensuring the overall transistor pattern is properly aligned before the ink is dispensed can be difficult. The UV method does not require this step because the formation of the raised mound after the mold and substrate are combined and illuminated acts as a self-alignment mechanism.

Citation: Applied Physics Letters 93, 203308 ( 2008) link.aip.org/link/?APPLAB/93/203308/1

Copyright 2008 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Explore further: The unifying framework of symmetry reveals properties of a broad range of physical systems

add to favorites email to friend print save as pdf

Related Stories

A cool approach to flexible electronics

Jul 10, 2014

A nanoparticle ink that can be used for printing electronics without high-temperature annealing presents a possible profitable approach for manufacturing flexible electronics.

Nano-imaging probes molecular disorder

Jun 13, 2014

Using a newly developed imaging method, LMU researchers show that thin-film organic semiconductors contain regions of structural disorder that could inhibit the transport of charge and limit the efficiency ...

Scientists developing electronic skin

May 30, 2014

Once a topic explored exclusively in science fiction, the notion of restoring sensory feelings to humans and to machines is now approaching reality. Scientists around the world are developing artificial organs ...

Recommended for you

What time is it in the universe?

5 hours ago

Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some ...

Watching the structure of glass under pressure

Aug 28, 2014

Glass has many applications that call for different properties, such as resistance to thermal shock or to chemically harsh environments. Glassmakers commonly use additives such as boron oxide to tweak these ...

Inter-dependent networks stress test

Aug 28, 2014

Energy production systems are good examples of complex systems. Their infrastructure equipment requires ancillary sub-systems structured like a network—including water for cooling, transport to supply fuel, and ICT systems ...

Explainer: How does our sun shine?

Aug 28, 2014

What makes our sun shine has been a mystery for most of human history. Given our sun is a star and stars are suns, explaining the source of the sun's energy would help us understand why stars shine. ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Dec 22, 2008
not rated yet Jan 05, 2009
Well written article about subject. The PhysOrg reviews are usually a much better, then usual sterile reprints of news without value added.