Stable crosslinked gate electrodes for hygroscopic insulator OTFT sensors

Abstract

Organic thin film transistors, employing diverse device architectures, materials and form factors, have been demonstrated as effective sensors of a variety of analytes, including ions. In many such devices, it is essential to use materials with both electronic conductivity and ion permeability, that are also stable under aqueous conditions. Hygroscopic insulator field effect transistors (HIFETs) are simple, solution processable, and low-voltage transistors with promising sensing properties when the analyte is introduced into the device through a permeable top gate electrode. It is important that the gate electrode is water stable, to prevent loss or damage to the electrode in aqueous conditions and ensure consistent performance. Here, we report two different methods to fabricate stable gate electrodes for HIFETs using crosslinked PEDOT:PSS, a conductive and ion-permeable polymer. We compare the two common crosslinkers, divinyl sulfone (DVS) and (3-glycidyloxypropyl)trimethoxysilane (GOPS), and present methods to overcome challenges associated with using either for crosslinking a top gate electrode. We show that DVS crosslinking can take place at room temperature, but freestanding films need to be formed separately then attached to the transistor to avoid damage to underlying layers by the crosslinker. GOPS crosslinking requires high temperatures but can be done in situ and bonds well to underlying layers. Using these optimised methods, we show that the stable PEDOT:PSS films perform well as gate electrodes for HIFET sensors. Our report is a significant step forward in the development of stable HIFET-based sensors, and our methods may have broader applicability to similar stable organic electronic devices.