Engineering team develops novel miniaturized organic semiconductor
An important breakthrough essential for future flexible electronic
devices

Date:
October 8, 2020
Source:
The University of Hong Kong
Summary:
An engineering team has made an important breakthrough in developing
the staggered structure monolayer Organic Field Effect Transistors,
which sets a major cornerstone to reduce the size of OFETs.



FULL STORY ========================================================================== Field Effect Transistors (FET) are the core building blocks of modern electronics such as integrated circuits, computer CPUs and display
backplanes.

Organic Field Effect Transistors (OFETs), which use organic semiconductor
as a channel for current flows, have the advantage of being flexible
when compared with their inorganic counterparts like silicon.


========================================================================== OFETs, given their high sensitivity, mechanical flexibility,
biocompatibility, property tunability and low-cost fabrication, are
considered to have great potential in new applications in wearable
electronics, conformal health monitoring sensors, and bendable displays
etc. Imagine TV screens that can be rolled up; or smart wearable
electronic devices and clothing worn close to the body to collect vital
body signals for instant biofeedback; or mini-robots made of harmless
organic materials working inside the body for diseases diagnosis, target
drug transportations, mini-surgeries and other medications and treatments.

Until now, the main limitation on enhanced performance and mass production
of OFETs lies in the difficulty in miniaturising them. Products currently
using OFETs in the market are still in their primitive forms, in terms
of product flexibility and durability.

An engineering team led by Dr Paddy Chan Kwok Leung at the Department of Mechanical Engineering of the University of Hong Kong (HKU) has made an important breakthrough in developing the staggered structure monolayer
Organic Field Effect Transistors, which sets a major cornerstone to
reduce the size of OFETs. The result has been published in the academic
journal Advanced Materials. A US patent has been filed for the innovation.

The major problem now confronting scientists in reducing the size of OFETs
is that the performance of the transistor will drop significantly with
a reduction in size, partly due to the problem of contact resistance,
i.e. resistance at interfaces which resists current flows. When the
device gets smaller, its contact resistance will become a dominating
factor in significantly downgrading the device's performance.

The staggered structure monolayer OFETs created by Dr Chan's
team demonstrate a record low normalized contact resistance of 40
? -cm. Compared with conventional devices with a contact resistance of
1000 ? -cm, the new device can save 96% of power dissipation at contact
when running the device at the same current level. More importantly, apart
from energy saving, the excessive heat generated in the system, a common problem which causes semiconductors to fail, can be greatly reduced.

"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." Dr Chan said.

"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." "Moreover, 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." Dr Chan added.

Dr Chan's 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 in-vivo on a mouse brain under different external stimulations. They also plan to integrate the OFETs onto surgical tools
such as catheter tube, and then put it inside animals' brains for direct
brain activities sensing to locate abnormal activation in brain.

"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." Dr Chan concluded.


========================================================================== Story Source: Materials provided by The_University_of_Hong_Kong. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Boyu Peng, Ke Cao, Albert Ho Yuen Lau, Ming Chen, Yang Lu, Paddy
K. L.

Chan. Crystallized Monolayer Semiconductor for Ohmic Contact
Resistance, High Intrinsic Gain, and High Current Density. Advanced
Materials, 2020; 32 (34): 2002281 DOI: 10.1002/adma.202002281 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201008104224.htm

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