Monolithic Integration of Ion‐Selective Organic Electrochemical Transistors with Thin Film Transistors on Flexible Substrates

Organic electrochemical transistors (OECTs) are a promising class of devices for chemical and ionic sensing in aqueous media. Compared with conventional potentiometric techniques, OECT ion-sensors exhibit low output impedance that aids their miniaturization and integration in multi-sensor systems. However, in order to implement arrays of OECT sensors for multi-analyte detection or spatial mapping of analytes, it is critical that the sensors be integrated with an addressing system that minimizes the number of signal lines leaving the sensor array. In this work, an integrated system comprising miniaturized ion-selective OECTs (IS-OECTs) that are addressed by a simple multiplexing circuit composed of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) is reported. The resulting flexible sensor array accepts a set of voltage inputs that selects the currently active sensor, and the active sensor's measured ion concentration is outputted as a single voltage output. This simple readout circuit allows arrays of IS-OECTs to be monitored with low-cost electronic equipment, enabling their use in multi-ion sensing and high-resolution mapping of ion concentrations in fields ranging from biomedical research to environmental monitoring.