Copper Oxide Solution Sensor Formed on a Thin Film Having Nanowires for Detecting Ethanol in Water

Solution sensors are required to detect analytes in liquids with high sensitivity and response speed for environmental and health monitoring. In this study, we introduce the concept of a Cu oxide thin film having nanowires as a solution sensor for detecting ethanol in water. The Cu oxide sensor with grains and nanowires of different shapes was fabricated by a simple method of heating a Cu thin film and dropping an Ag conductive paste. Sensing parameters and mechanisms were evaluated by current-voltage and electrochemical impedance spectroscopy measurements. In the Cu oxide sensor formed on thin film having a large number of nanowires fabricated by heating at 400 °C for 5 h, the sensor sensitivity was 0.96 at 0.1 vol % ethanol concentration, and the response time was 313 s at a voltage of 0.1 V. The Cu oxide sensor detects ethanol by the change in electrical resistance caused by the reaction between ethanol molecules and the lattice oxygen on the Cu oxide surface. Therefore, the large nanowire surface area leads to a higher sensor sensitivity and a faster response time. Furthermore, the grain and nanowire regions on the thin film are represented by equivalent circuits. A high correlation was observed between the sensor sensitivity and the time constant calculated from the equivalent circuit. The proposed Cu oxide solution sensor and detection mechanism offer designs to improve the performance of chemical sensors.