New transistors for flexible smart devices offer enhanced performance at lower cost

- High-performance vertical organic transistors developed -

The Korea Research Institute of Standards and Science (KRISS, President Hyun-Min Park) developed a new method of vertical stacking of organic transistors, a key element of flexible smart devices*, and succeeded in improving performance. This is expected to accelerate the commercialization of next-generation smart devices.

  * Flexible smart device: Refers to a flexible next-generation smart device that has a foldable surface, can be rolled up for convenient storage, or has a stretchable screen.

The team comprised of senior researcher Kyung-Geun Lim of the KRISS Interdisciplinary Materials Measurement Institute, Dresden University of Technology, and the Chinese University of Hong Kong achieved vertical stacking of organic transistors using a simple electrochemical process. Compared to conventional, planar transistors, the proposed organic transistors offer superior performance such as faster operation speed, increased current, and decreased voltage.

▲ Senior researcher Kyung-Geun Lim of the KRISS Interdisciplinary Materials Measurement Institute is showing organic transistors stacked vertically.

Commercial foldable phones have hinged flexible displays. To bend and wear the device like a wristwatch or to roll it up like a scroll, information processors, information storage semiconductors, and batteries must all be flexible.

The performance of smart devices is largely determined by transistors, which are responsible for information processing and storage. As such, it is necessary to develop high-performance transistors that are both affordable and flexible.

 ? Transistor performance determines response time of displays, processing speed of computers, data storage capacity, and power consumption.  

Organic transistors made from flexible organic materials are light and flexible, and are affordable enough to be mass produced. However, they have shown limited performance as they require greater power for operation and are slower than inorganic semiconductors.

For dense arrangement of semiconductors, many companies and research institutes rely on photolithography and through-silicon vias. However, such technologies are highly complicated and expensive. Developed for inorganic semiconductors, they are also difficult to apply to organic semiconductors.

To address the above issues, the joint research team applied anodizing to field-effect transistors (FET). Chemical reactions were used to stack components from bottom to top, achieving a vertical architecture, unlike the conventional planar method of connecting individual components.

 ? Anodizing is a process that creates an oxide layer on the electrode surface by applying a voltage to a device with aluminum electrode patterns in a solution.

This approach allows easier fabrication of electrodes, arranged with a spacing in nanometer units, based on electrochemical reactions alone, and improves transistor performance by effectively controlling the flow of electrons.

 ? Compared to conventional, planar organic transistors, the proposed transistors achieved a 100 times faster operation speed, a 10,000 times larger maximum current, and 1/3 smaller driving voltage. The results were consistent for p-type semiconductors, n-type semiconductors, small-molecule semiconductors, and polymeric semiconductors.

Senior researcher Kyung-Geun Lim said, “This technique will usher in the age of next-generation smart devices including flexible displays, sensors, and semiconductors.”