Croucher engineer develops miniaturised organic semiconductor for flexible electronics

11 November 2020

Be it foldable phones or bendable televisions, electronics manufacturers see enormous potential market appeal in “flexible electronics”.

The technological components behind these flexible electronics are organic field effect transistors (OFETs), which form the building blocks of electronics that use organic semiconductors to generate an electric current. Compared with non-organic field effect transistors, they are mechanically flexible, highly sensitive, biocompatible, tunable, and can be fabricated at low cost, providing a competitive edge for the production of wearable electronics, conformal health monitoring sensors, and bendable displays.

However, mass production has previously proved elusive due to the difficulty in miniaturising OFETs while retaining performance.

Now, Dr Paddy Chan Kwok Leung (Croucher Studentship 1994), of the University of Hong Kong (HKU), and his research team in the Department of Mechanical Engineering have devised a solution to miniaturise organic semiconductors that overcomes this hurdle by developing a staggered structure monolayer OFET.

The new transistor demonstrates a low normalised contact resistance of 40 Ω -cm. Compared with conventional devices with a contact resistance of 1,000 Ω -cm, the new device can save 96 per cent of power dissipation at contact when running the device at the same current level.

In addition to saving energy, heat generated in the system can be greatly reduced, minimising the chances of semiconductor failure.

The findings have been published in Advanced Materials and a US patent filed for the innovation.

“On the basis of our achievement, we can further reduce the dimensions of OFETs and push them to a sub-micrometre scale, a level compatible with their inorganic counterparts,” Chan said, pointing out that the new OFETs would also still function effectively with regard to their unique organic properties. This was critical for commercialisation of related research, he noted.

“If flexible OFETs work, many traditional, rigid-based electronics, such as display panels, computers, and cell phones, [could be] transformed to become flexible and foldable.” These future devices would be much lighter and cost less to produce. “Moreover, given their organic nature, they are more likely to be biocompatible for advanced medical applications, such as sensors tracking brain activities or neural spike sensing, and in precision diagnosis of brain-related illnesses, such as epilepsy,” Chan said.

Chan’s team is currently working with researchers at the HKU Faculty of Medicine and biomedical engineering experts at City University of Hong Kong to integrate miniaturised OFETs into a flexible circuit on a polymer microprobe for neural spike detections in-vivo on a mouse brain under different external stimulations. They also plan to integrate the OFETs with surgical tools, such as catheter tubes, to sense brain activities directly in order to locate abnormal brain activation.

“Our OFETs provide a much better signal-to-noise ratio. Therefore, we expect [to be able to] pick up some weak signals that could not be detected before using a conventional bare electrode for sensing,” Chan explained.

According to Chan, the researchers’ goal has been to connect applied research with fundamental science and extend the horizons of OFET research and applications. Now, OFETs were ready for applications related to large area display backplanes and surgical tools, he said.

Dr Paddy KL Chan is Associate Professor of Mechanical Engineering at the University of Hong Kong. He received both his MSc in Electrical Engineering and Computer Science and PhD in Mechanical Engineering from the University of Michigan. He was awarded a Croucher Studentship in 1994.

To view Dr Chan’s Croucher profile, please click here.