Organic semiconductor is a high potential candidate for the next generation flexible electronics such as smart sensors health monitoring devices and etc. Recently, the team from HKU Mechanical Engineering Department led by Dr. Paddy Chan has collaborated with Prof. Xinran Wang’s team in Nanjing University and developed a high signal gain electrocardiogram (ECG) sensor based on the monolayer organic semiconductors field effect transistors. The PhD student of NJU, Zongzong Luo, has come to HKU as visiting graduate student for a year to learn about the fabrications and testing of these monolayer devices. The team has applied hafnium zirconium oxide and aluminum oxide hybrid dielectric in the flexible transistors, and employed solution processed monolayer C10-DNTT as the active layer. The device shows a record low subthreshold swing down to 58.6 mV/dec for the monolayer organic field effect transistors (OFETs). Based on these OFETs, they have further developed inverters with a gain higher than 10000. This high gain property is very important for measuring the weak signals like the electrophysiological signals from the human body. The team utilized the inverters as the ECG and pulse sensors. Their devices can sense the f-wave of a patient suffer from atrial fibrillation which cannot be easily sense by the standard commercially available ECG sensors as they can only be detected under extremely high sensitivity devices. The team is currently expanding this device to a more sophisticated flexible circuit for the neural sensor applications, and explore the diseases related to the brain. The paper was recently published in Nature Communications under the title “Sub-thermionic, ultra-high-gain organic transistors and circuits”.
(Left) Optical image of the OFET devices fabricated on the polyimide substrate. (Right) The flexible ECG sensor based on the organic inverter.