Team develops ‘world’s fastest’ thin-film organic transistor

Engineers have been trying to use inexpensive, carbon-rich molecules and plastics to create organic semiconductors capable of performing electronic operations at speeds comparable to costlier silicon-based technologies.

In the January 8 edition of Nature Communications, engineers from the University of Nebraska-Lincoln (UNL) and Stanford University show how they created thin-film organic transistors that could operate more than five times faster than previous examples of this experimental technology.

Research teams led by Zhenan Bao, professor of chemical engineering at Stanford, and Jinsong Huang, assistant professor of mechanical and materials engineering at UNL used their new process to make organic thin-film transistors with electronic characteristics comparable to those found in expensive, curved-screen television displays based on a form of silicon technology.

They are said to have achieved their results by altering the basic process for making thin film organic transistors. Typically, researchers drop a solution, containing carbon-rich molecules and a complementary plastic, onto a spinning platter. The spinning action deposits a thin coating of the materials over the glass platter used in this research.

In their paper, the collaborators describe two important changes to this basic process: they first spun the platter faster. Secondly, they only coated a tiny portion of the spinning surface, equivalent to the size of a postage stamp.

According to a statement, 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 researchers called this improved method “off-centre spin coating.” The process remains experimental, and the engineers cannot yet precisely control the alignment of organic materials in their transistors, or achieve uniform carrier mobility.

Off-centre spin coating produced 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.

Further improvements to this experimental process could lead to the development of inexpensive, high-performance electronics built on transparent substrates such as glass and, eventually, clear and flexible plastics.

The researchers have shown that they can create high-performance organic electronics that are 90 per cent transparent to the naked eye.