Measurement uncertainty of piezoresistive beam-type humidity sensors

In this work, the reliability and accuracy of a sensor design which exploits the volumetric changes of polymeric films due to the uptake of water vapor for humidity measurement is investigated. In this case, the humidity sensing element is a thin polymer film deposited and bonded to the surface of four cantilever beams that are bulk micromachined from the surrounding silicon substrate. For this purpose, the performance of sensors as a function of climatic conditions was experimentally studied. The main results showed a good repeatability of all sensors, positive temperature coefficients of offset voltage, and negative temperature coefficients of humidity sensitivity. The reliability and stability of the beam-type sensor design is compared with bimorph humidity sensors which use the similar piezoresistive readout.