Scientists have made headway in the development of organic electronic components by addressing what’s so far been the most significant obstacle to using organic semiconductors for thin-film transistors.
The breakthrough—from researchers at the Georgia Institute of Technology (Georgia Tech)--comes in the form of a nanostructured gate dielectric
that also protects the organic semiconductor, which is vulnerable to damage from the ambient environment. The twofold nature of the technology allows the transistors to operate with unprecedented stability, researchers said.
The new structure gives thin-film transistors stability comparable to those made with inorganic materials, allowing them to operate in ambient conditions--even underwater, Georgia Tech Senior Research Scientist Canek Fuentes-Hernandez told Design News.
Georgia Tech Senior Research Scientist Canek Fuentes-Hernandez (left) and Professor Bernard Kippelen examine a sample of organic thin-film transistors created with a new nanostructured gate dielectric that gives the devices unprecedented stability. (Source: Rob Felt, Georgia Tech)
In their work, the team set out to find semiconductor materials that could display an increased ability to transport charge carriers and not suffer from the instabilities displayed by amorphous silicon thin-film transistors, he explained. Researchers’ specific focus was the fabrication of large-area flexible displays.
“Organic semiconductors became a potentially attractive alternative because their ability to transport electricity can be tailored through chemical synthesis,” Fuentes-Hernandez explained. “And, in contrast to inorganic semiconductors, [they] can be processed at much lower temperatures--below 200 degrees Celsius--and from solution.”
Using such materials, researchers can fabricate organic thin-film transistors inexpensively at low temperature on a variety of flexible substrates using techniques such as inkjet printing. This ease of fabrication opens up new applications that take advantage of simple, additive fabrication processes.
Indeed, electrical engineering overall is moving toward electronic components made with organic materials, which will save on inorganic-material waste and enable smaller, high-performance form factors. The work from the Georgia Tech team advances that, said Bernard Kippelen, a professor in Georgia Tech’s School of Electrical and Computer Engineering.
"We have now proven a geometry that yields lifetime performance that for the first time establish that organic circuits can be as stable as devices produced with conventional inorganic technologies," he said. "This could be the tipping point for organic thin-film transistors, addressing long-standing concerns about the stability of organic-based printable devices."
To fabricate the dielectric, the new Georgia Tech architecture uses alternating layers of aluminum oxide and hafnium oxide-- five layers of one, then five layers of the other, repeated 30 times atop the fluoropolymer. Atomic layer deposition produced the oxide layers. The nanolaminate produced--about 50 nanometers thick--is virtually immune to the effects of humidity.
"While we knew this architecture yielded good barrier properties, we were blown away by how stably transistors operated with the new architecture,” Fuentes-Hernandez said. "The performance of these transistors remained virtually unchanged even when we operated them for hundreds of hours and at elevated temperatures of 75 degrees Celsius. This was by far the most stable organic-based transistor we had ever fabricated."
The team published a report on their work in the journal Science Advances.
Researchers used a glass substrate in the lab but report that they could use many other flexible materials, including polymers and even paper.
There are a number of applications for the transistors, but perhaps the most dramatic is in the development of very large, flexible displays that could be rolled up when not in use, researchers said.
Other applications include to control pixels in organic light-emitting displays (OLEDs) used in new smartphones. Currently, transistors fabricated with conventional inorganic semiconductors are used for this purpose.
The organic transistors also could have a place in Internet of things (IoT) devices, allowing for components to be produced with inkjet printers and other low-cost printing and coating processes.
Moreover, the nanolaminate technique enables development of inexpensive paper-based devices, such as smart tickets, that would use antennas, displays, and memory fabricated on paper through low-cost processes, researchers said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.