Sensitive humidity micro-switch based on polymers

We present a binary threshold sensor for humidity which is able to use the energy provided directly from the measured relative humidity of the ambient air to mechanically switch an electrical micro contact. This zero-power switching behavior is realized by using the humidity-sensitive volume swelling of a polymer layer as the detection element deflecting a mechanical deformable silicon boss structure, thus closing the electrical contacts of the switch. For the device considered here, a humidity-sensitive hydrogel blend was used. In this paper we introduce the inverse silicone stamping as versatile structuring technology for the hydrogel. It is suitable for thin silicon membranes of 20 µm in thickness, can handle the high volume shrinking of the hydrogel blend during the evaporation of the solvent and provides a high reproducibility of the printed pattern. Furthermore, an optimal parameter set for the boss structure was found based on analytical and numerical simulations.