Abstract
Fast-response humidity sensors using nanomaterials are attractive and have been intensively studied. Among the various nanomaterials, nonporous inorganic nanoparticles are suitable for use in humidity sensitive films for sensors. Here, we focus on a nonporous inorganic nanoparticle film and investigate a humidity sensor using the film. Hysteresis error and a dynamic response to a change of humidity are fundamental specifications of humidity sensors. A humidity sensor using a 50 nm silica nanoparticle film shows a hysteresis error of 2% at 85% RH and a response/recovery time of 2.8/2.3 s in 30% RH to 70% RH. We also summarize response/recovery times and hysteresis errors of state-of-the-art humidity sensors. As compared to those of commercial sensors and porous nanoparticle-based sensors evaluated using saturated salt solutions, the fabricated sensor shows a comparative hysteresis error and shorter response time.
Highlights
Humidity sensing has been of great importance in environmental monitoring, planting in factories, and human care [1,2]
Because the dynamic response is limited to the diffusion of water molecules inside/outside of a polymer film, the response/recovery time of commercial sensors is usually more than 5 s
We investigate the humidity hysteresis and response time of a nonporous inorganic nanoparticle-based humidity sensor
Summary
Humidity sensing has been of great importance in environmental monitoring, planting in factories, and human care [1,2]. Detecting mechanisms of humidity in conventional sensors are based on the adsorption/desorption of water molecules inside a humidity-sensitive film. In the case of a commercial polymer-based sensor, a humidity-sensitive film typically has electrolytes which produce mobile ions using water molecules [5]. The electrical resistance of a film is dependent on the humidity in air. While this mechanism has been widely used, a dynamic response to a humidity change has not been studied well. Because the dynamic response is limited to the diffusion of water molecules inside/outside of a polymer film, the response/recovery time of commercial sensors is usually more than 5 s. There have been intensive studies to improve the dynamic response of humidity sensors. The number of publications reporting a fast/ultrafast response of humidity sensors has rapidly increased
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