A Flexible Smart Sensor System Based on Hybrid Integration of Organic and Metal-Oxide Transistors

Over the last decade, flexible electronic technology has been developed intensively and applied in sensor electronics. The use of sensors in a wide range of environments has been demanding a more compact and flexible platform. This article demonstrates a flexible smart sensor system integrating a p-type polymer field-effect transistor (FET) sensor and a flexible operational amplifier using complementary n-type metal-oxide and organic p-type FETs. The fabricated flexible operational amplifier (OpAmp) showed high differential voltage gain (>100 V/V) and successfully converted the sensing current to output voltage. The sensing functions are integrated in a thin and flexible card format with power provided by a small photovoltaic (PV) module and we demonstrate successful PV-powered operation and detection of gaseous molecular analytes, such as ethanol. The system detects the sensing current change from 114 nA (without ethanol) to 86 nA (with ethanol) and transforms to an output voltage of ~1.2 V through the OpAMP. The ethanol sensing output is displayed on an electrophoretic display (EPD) implemented in the system.