Online in the journal Advanced Materials, researchers from the Georgia Institute of Technology describe a new method of combining top-gate organic field-effect transistors with a bilayer gate insulator. This allows the transistor to perform with incredible stability while exhibiting good current performance. In addition, the transistor can be mass produced in a regular atmosphere and can be created using lower temperatures, making it compatible with the plastic devices it will power.
The research team used an existing semiconductor and changed the gate dielectric because transistor performance depends not only on the semiconductor itself, but also on the interface between the semiconductor and the gate dielectric.
“Rather than using a single dielectric material, as many have done in the past, we developed a bilayer gate dielectric,” said Bernard Kippelen, director of the Center for Organic Photonics and Electronics and professor in Georgia Tech’s School of Electrical and Computer Engineering.
The bilayer dielectric is made of a fluorinated polymer known as CYTOP and a high-k metal-oxide layer created by atomic layer deposition. Used alone, each substance has its benefits and its drawbacks.
CYTOP is known to form few defects at the interface of the organic semiconductor, but it also has a very low dielectric constant, which requires an increase in drive voltage. The high-k metal-oxide uses low voltage, but doesn’t have good stability because of a high number of defects on the interface.
So, Kippelen and his team wondered what would happen if they combined the two substances in a bilayer. Would the drawbacks cancel each other out?
“When we started to do the test experiments, the results were stunning. We were expecting good stability, but not to the point of having no degradation in mobility for more than a year,” said Kippelen.
The team performed a battery of tests to see just how stable the bilayer was. They cycled the transistors 20,000 times. There was no degradation. They tested it under a continuous bias stress where they ran the highest possible current through it. There was no degradation. They even stuck it in a plasma chamber for five minutes. There was still no degradation.
The only time they saw any degradation was when they dropped it into acetone for an hour. There was some degradation, but the transistor was still operational.
No one was more surprised than Kippelen.
“I had always questioned the concept of having air-stable field-effect transistors, because I thought you would always have to combine the transistors with some barrier coating to protect them from oxygen and moisture. We’ve proven ourselves wrong through this work,” said Kippelen.
“By having the bilayer gate insulator we have two different degradation mechanisms that happen at the same time, but the effects are such that they compensate for one another,” explains Kippelen. “So if you use one it leads to a decrease of the current, if you use the other it leads to a shift of the thereshold voltage and over time to an increase of the current. But if you combine them, their effects cancel out.”
“This is an elegant way of solving the problem. So, rather than trying to remove each effect, we took two processes that complement one another and as a result you have a transistor that’s rock stable.”
The transistor conducts current and runs at a voltage comparable to amorphous silicon, the current industry standard used on glass substrates, but can be manufactured at temperatures below 150°C, in line with the capabilities of plastic substrates. It can also be created in a regular atmosphere, making it easier to fabricate than other transistors.
Applications for these transistors include smart bandages, RFID tags, plastic solar cells, light emitters for smart cards – virtually any application where stable power and a flexible surface are needed.
In this paper the tests were performed on glass substrates. Next, the team plans on demonstrating the transistors on flexible plastic substrates. Then they will test the ability to manufacture the bilayer transistors with ink jet printing technologies.
Kippelen’s research team was comprised of Do Kyung Hwang, Canek Fuentes-Hernandez, Jungbae Kim, William J. Postcavage Jr. and Sung-Jin Kim.
The research was supported by Solvay, the Office of Naval Research and the National Science Foundation.
David Terraso | EurekAlert!
To improve auto coatings, new tests do more than scratch the surface
21.09.2018 | National Institute of Standards and Technology (NIST)
World's first passive anti-frosting surface fights ice with ice
18.09.2018 | Virginia Tech
The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.
This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.
Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...
Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.
"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...
A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.
Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...
Scientists have succeeded in observing the first long-distance transfer of information in a magnetic group of materials known as antiferromagnets.
An international team of researchers has mapped Nemo's genome, providing the research community with an invaluable resource to decode the response of fish to...
21.09.2018 | Event News
03.09.2018 | Event News
27.08.2018 | Event News
21.09.2018 | Physics and Astronomy
21.09.2018 | Life Sciences
21.09.2018 | Event News