Abstract
A novel capacitive humidity sensor based on carbon black/polyimide composites is presented in this paper. The details of the fabrication, sensor characteristics, and effect of the carbon black additive are described. It was confirmed that the polyimide composite filled with a tiny amount of carbon black was suitable for a humidity sensing dielectric. The humidity sensors with three different dielectrics, which were pure polyimide, 0.01 wt% carbon black/polyimide, and 0.05 wt% carbon black/polyimide, were fabricated by a micro-electro-mechanical-system (MEMS) process. As the amount of the carbon black additive increased, the sensitivity of the humidity sensor increased. The humidity sensor with 0.05 wt% of carbon black had a much higher sensitivity of 15.21% (20–80% RH, 0.2535%/% RH) than that of the sensor with pure polyimide, which was 9.73% (0.1622%/% RH). The addition of carbon black also led to an enhancement in the hysteresis and response speed. The hysteresis of the humidity sensor decreased from 2.17 to 1.80% when increasing the amount of the carbon black additive. The response speed of the humidity sensor with 0.05 wt% of carbon black was measured to be ~10% faster than that of the sensor with pure polyimide. The long-term stability of the humidity sensors was demonstrated as well.
Highlights
It is confirmed that the carbon black/polyimide composite layer was patterned successfully without any problem arising from the carbon black additive
A novel capacitive humidity sensor based on carbon black/polyimide composites has been suggested
We have successfully demonstrated the possibility of using a carbon black/polyimide composite as a humidity sensing dielectric material to obtain high-performance capacitive humidity sensors
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Measurement of humidity, the amount of water vapor in air, is very important in many applications, including manufacturing, agriculture, climatology, and biomedical industry [1]. There are two ordinary measurements of humidity: absolute and relative humidity. Absolute humidity means a mass of water content in a unit volume of air. Relative humidity describes a ratio of the amount of water vapor to that of the saturated air at a given temperature. Since controlling relative humidity level is generally preferable, humidity sensors usually measure relative humidity rather than absolute humidity [2]
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