January 9, 2014
Production Process Changes Make Faster Thin-Film Organic Transistors
redOrbit Staff & Wire Reports - Your Universe Online
Research teams from a pair of US universities have joined forces to develop the world’s fastest thin-film organic transistors, demonstrating that this type of experimental semiconductor technology could become the foundation for low-cost high-resolution television screens and similar electronic devices.The developers, who hail from the Stanford School of Engineering and the University of Nebraska-Lincoln (UNL), explained in Wednesday’s edition of the journal Nature Communications how they created thin-film organic transistors capable of operating five-times more quickly than previous models.
Engineers from all over the world have been attempting to create organic semiconductors capable of performing high-speed electronic operations using inexpensive, carbon-rich molecules and plastics. The study authors used a new process to create organic thin-film transistors comparable to those found in curved-screen televisions, then altered the basic organic transistor development process in order to achieve their speed boost.
“Typically, researchers drop a special solution, containing carbon-rich molecules and a complementary plastic, onto a spinning platter – in this case, one made of glass. The spinning action deposits a thin coating of the materials over the platter,” the California-based university explained in a statement.
However, Stanford professor of chemical engineering Dr. Zhenan Bao, UNL assistant professor of mechanical and materials engineering Dr. Jinsong Huang, and their colleagues made key changes to this process: they spun the platter faster, and coated a smaller portion of the spinning surface -- roughly equal to the size of a postage stamp.
“These innovations had the effect of depositing a denser concentration of the organic molecules into a more regular alignment. The result was a great improvement in carrier mobility, which measures how quickly electrical charges travel through the transistor,” the university said.
The process, which Dr. Bao and Dr. Huang have dubbed “off-center spin coating,” is still experimental. Currently, the engineers are unable to precisely control the alignment of organic materials in their transistors, and they have not been able to achieve uniform carrier mobility.
Even so, their technique was able to produce transistors “with a range of speeds far above those of previous organic semiconductors and comparable to the performance of the polysilicon materials used in today's high-end electronics,” the researchers said.
Future refinements to the process could allow them to create inexpensive, high-performance electronics constructed on transparent substrates such as glass and plastics, which are flexible and transparent. Despite being at an experimental stage, their organic electronics are already 90 percent transparent to the naked eye.
Other members of the development team include UNL postdoctoral associate Yongbo Yuan, Stanford graduate assistant in chemical engineering Gaurav Giri and Alex Ayzner, a postdoctoral researcher at the Stanford Synchrotron Radiation Lightsource.