Van der Waals Assembled Solution‐Processed Organic Monolayer Single‐Crystal Transistor for Electrocardiograph Sensing

Abstract Solution‐processed organic semiconductors (OSCs) promote the development of the next generation of large‐area, low‐cost flexible electronics. To date, the properties of the flexible substrates such as chemical compatibility, roughness, and surface energy are still big challenges for the solution process, especially for high‐performance ultrathin monolayer OSCs. Herein, van der Waals assembled organic field‐effect transistors (OFETs) with layer‐by‐layer lamination processes are reported. The active layer is an ultrathin single molecular layer 2,9‐Didecyldinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (C 10 ‐DNTT) which maintains decent electrical fidelity with mobility of 10.4 cm 2 V –1 s –1 after transfer. With the active layer transfer technique, the bias stability of OFETs can be significantly improved by tuning diverse hydrophobic self‐assembly monolayers (SAMs) onto the dielectric which is a challenging task before the solution processing organic monolayer. A small subthreshold swing (SS) of 63 mV decade −1 is achieved by low surface energy phosphonic acid SAMs on high‐κ AlO x dielectric. We further demonstrate a high‐gain organic inverter amplifier that can be powered up by a coin cell on the 1.5 μm conformal parylene substrate and apply it for high‐resolution electrocardiograph (ECG) sensing. The ECG sensors can provide a signal‐to‐noise ratio as high as 34 dB. It is believed that our device demonstrates the prospect of continuous monitoring for human health management.