Room‐Temperature Solid‐State Grown WO_3−δ Film on Plastic Substrate for Extremely Sensitive Flexible NO₂ Gas Sensors

Abstract Due to the increased world‐wide threat to health from air pollution, as well as the need for personalized diagnostic and physiological monitoring of exhaled breath, flexible gas sensor nodes have become an emerging area of critical importance for wearable electronics applicable. In this study, WO 3−δ films are prepared on flexible substrates at room temperature using a single‐step, solid‐state deposition, granule spray in vacuum (GSV) process. The GSV‐WO 3−δ films are successfully utilized to fabricate an ultrasensitive flexible gas sensor. The performance of the sensor can be enhanced by its increased surface area and large number of defect sites on the surface utilizing high‐impulse hollow sphere granules. The gas sensor is extremely responsive and selective to low concentration of NO 2 . The gas‐sensing responses are linear for the concentrations ranging from sub‐ppm to tens of ppm with detection limit of 1.88 (±0.128) for NO 2 . The response time is on the order of few seconds for gas detection (17 s) and recovery (25 s). Beyond this sensing performance, the GSV‐WO 3−δ film is highly advantageous in terms of production cost and time for the realization of mass production of flexible sensing devices, compared to conventional gas sensors that require high‐cost and time‐consuming processes.