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Open AccessArticle

Polyimide-Based Capacitive Humidity Sensor

1
Fraunhofer EMFT, Research Institution for Microsystems and Solid State Technologies EMFT, Hansastraße 27d, D-80686 Munich, Germany
2
Institute of Electronic and Sensor Materials, Technische Universität Bergakademie Freiberg, Gustav-Zeuner-Str. 3, D-09599 Freiberg, Germany
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Physik-Department, Lehrstuhl für Funktionelle Materialien, Technische Universität München, James-Franck-Strasse 1, D-85748 Garching, Germany
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Physik-Department, Universität der Bundeswehr München, Werner-Heisenberg-Weg 39, D-85579 Neubiberg, Germany
*
Author to whom correspondence should be addressed.
Sensors 2018, 18(5), 1516; https://doi.org/10.3390/s18051516
Received: 4 March 2018 / Revised: 1 May 2018 / Accepted: 3 May 2018 / Published: 11 May 2018
(This article belongs to the Section Chemical Sensors)
The development of humidity sensors with simple transduction principles attracts considerable interest by both scientific researchers and industrial companies. Capacitive humidity sensors, based on polyimide sensing material with different thickness and surface morphologies, are prepared. The surface morphology of the sensing layer is varied from flat to rough and then to nanostructure called nanograss by using an oxygen plasma etch process. The relative humidity (RH) sensor selectively responds to the presence of water vapor by a capacitance change. The interaction between polyimide and water molecules is studied by FTIR spectroscopy. The complete characterization of the prepared capacitive humidity sensor performance is realized using a gas mixing setup and an evaluation kit. A linear correlation is found between the measured capacitance and the RH level in the range of 5 to 85%. The morphology of the humidity sensing layer is revealed as an important parameter influencing the sensor performance. It is proved that a nanograss-like structure is the most effective for detecting RH, due to its rapid response and recovery times, which are comparable to or even better than the ones of commercial polymer-based sensors. This work demonstrates the readiness of the developed RH sensor technology for industrialization. View Full-Text
Keywords: humidity sensor; flat polyimide; nanograss polyimide; rough polyimide humidity sensor; flat polyimide; nanograss polyimide; rough polyimide
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MDPI and ACS Style

Boudaden, J.; Steinmaßl, M.; Endres, H.-E.; Drost, A.; Eisele, I.; Kutter, C.; Müller-Buschbaum, P. Polyimide-Based Capacitive Humidity Sensor. Sensors 2018, 18, 1516.

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