Researchers in Hong Kong have developed a single layer organic transistor for flexible medical and wearable systems.
The engineering team led by Dr Paddy Chan Kwok Leung (above) at the Department of Mechanical Engineering of the University of Hong Kong (HKU) used a staggered crystallized organic monolayer to reduce the size of the Organic Field Effect Transistors (OFET).
A US patent has been filed for the 1L-OFET material.
While large OFET devices have been demonstrated, the performance drops significantly with a reduction in size, partly due to the problem of contact resistance. As the device gets smaller, the contact resistance will become a dominating factor. The channel length varies from 8µm to 140µm in the HKU devices.
The staggered structure monolayer OFETs created by Dr Chan’s team demonstrate a record low normalized contact resistance of 40 Ω cm. This compares to a contact resistance of 1000 Ω cm in other OFETs, bringing a 96 percent reduction in power dissipation at the contact when running the device at the same current level. This also avoids the excess heat generation that is a major problem for OFETs. At a high bias load, a maximum current density of 4.2 µA/µm is achieved by the only molecular layer as the active channel, with a current saturation effect being observed.
“On the basis of our achievement, we can further reduce the dimensions of OFETs and push them to a sub-micrometer scale, a level compatible with their inorganic counterparts, while can still function effectively to exhibit their unique organic properties. This is critical for meeting the requirement for commercialisation of related research,” said Chan.
“If flexible OFET works, many traditional rigid based electronics such as display panels, computers and cell phones would transform to become flexible and foldable. These future devices would be much lighter in weight, and with low production cost. Also, given their organic nature, they are more likely to be biocompatible for advanced medical applications such as sensors in tracking brain activities or neural spike sensing, and in precision diagnosis of brain related illness such as epilepsy,” said Chan.
His team is currently working with researchers at the HKU Faculty of Medicine and biomedical engineering experts at CityU to integrate the miniaturised OFETs into a flexible circuit onto a polymer microprobe for neural spike detections. They also plan to integrate the OFETs onto surgical tools such as a catheter tube to sense direct brain activity.
“Our OFETs provide a much better signal to noise ratio. Therefore, we expect we can pick up some weak signals which cannot be detected before using the conventional bare electrode for sensing. “It has been our goal to connect applied research with fundamental science. Our research achievement would hopefully open a blue ocean for OFETs research and applications. We believe that the setting and achievement on OFETs are now ready for applications in large area display backplane and surgical tools,” he said.
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