Engineers Tackle the Challenge of Miniaturizing Organic FETs

October 24, 2020 by Luke James

A Hong Kong engineering team claims to have made an important breakthrough in developing staggered structure monolayer organic field-effect transistors, which they say are important for future flexible electronic devices.

Field-effect transistors (FETs) can be found at the core of all modern electronics from ICs to CPUs and even displays. Researchers are eager to engineer a replacement for bulky and brittle silicon FETs that have a limited utility in flexible and wearable electronics. 

Organic field-effect transistors (OFETs), which use organic semiconductors as a channel for current flows, could be this replacement. Not only are they flexible compared to their silicon counterparts but they are also highly sensitive, biocompatible, tuneable, and cheap to manufacture.

These metrics mean that they could have considerable potential in new applications in wearable electronics, health sensors, and bendable electronics, to name a few.


A Miniaturization Problem

Until now, realizing the enhanced performance and mass production of OFETs has been stifled by a miniaturization problem—that is, it’s difficult to reduce the size of OFETs. In addition, products and applications currently in the market that utilize OFETs are still in their very early, primitive forms.

And while large OFET devices have been demonstrated, their performance drops significantly when size is reduced, partly due to contact resistance. 


Dr. Paddy Chan

Dr. Paddy Chan of the Department of Mechanical Engineering at the University of Hong Kong. Image used courtesy of the University of Hong Kong


However, an engineering team led by Dr. Paddy Chan Kwok Leung at the University of Hong Kong (KHU) claims to have made an “important breakthrough” with the development of a single layer organic transistor—a staggered structure monolayer OFET—that overcomes this size challenge. 

Published in the journal Advanced Materials, the KHU team’s research describes how they used monolayer (1L) organic crystals and non-destructive electrodes to overcome the problems experienced when downscaling OFETs.

Compared with conventional devices with a contact resistance of 1000 Ω cm, the team’s new OFETs demonstrate a “record low” normalized contact resistance of only 40 Ω cm, a 96% decrease. This also avoids excess heat generation, something that’s a major problem with other OFETs.


OFETs at a Sub-Micrometer Scale

According to the research team’s leader Dr. Chan, their results demonstrate that they can further reduce the dimensions of OFETs and “push them to a sub-micrometer scale, a level compatible with their inorganic counterparts,” while maintaining their effective function and unique organic properties. 


Image of monolayer organic transistors

Image of monolayer organic transistors. Image used courtesy of the University of Hong Kong 

If flexible OFETs can be advanced and brought to the market, many traditional "rigid" electronics, which is most of them, could transform to become flexible and foldable where necessary or beneficial. These devices would also be much lighter in weight and cheaper to produce.


A Possible Solution for Neural Spike Sensing

"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 illnesses such as epilepsy." Dr. Chan added.

Dr. Chan’s team is currently working to integrate their miniaturized OFETs into a flexible circuit onto a polymer microprobe for neural spike detections in-vivo on the brain of a mouse under different external stimulations. They also plan to integrate their OFETs into surgical tools and achieve their goal of connecting applied research with fundamental science, opening up a “blue ocean for OFETs research and applications.”