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.

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Cost effective and high quality processes are needed for further development of flexible electronic systems. Applications of these structures are e. g. in the field of high density interconnection foils or polymer electronics. In this paper a lithography process for patterning copper on flexible foils using reel-to-reel methods is presented. The process allows the fabrication of well defined copper structures with typical feature sizes from 15 to 40 µm using either etching or electro plating technology. Properties of the dry film photoresist used in the process as well as details of the technology are described. Influences of photol ithography and etching on dimensional accuracy and resolution are given and some consequences on design rules are shown