Modeling and optimization of a capacitive humidity sensor response in MEMS technology

The aim of this paper is the study of a capacitive humidity sensor in MEMS technology. It is designed primarily of two armatures; the first one is full, the other is lamellar thus facilitating the passage of water vapor. A layer of dielectric polymer sandwiched between two electrodes absorbs this vapor. The relative permittivity of the dielectric varies with humidity. The study is, in a first step, to determine the static response of the capacitive humidity sensor designed as shown before. In a second step, a finite element simulation using COMSOL software was done to determine the polymer giving a better absorption. Therefore several polymers have been studied. The study showed that the layer made of benzocyclobutene gives better absorption. Another simulation was done to determine the optimal geometric structure also leads to better absorption and a very short response time. The study showed that the structure consists of two electrodes 2 μm wide and spaced 2 μm (called structure2×2) leads to better absorption when it was compared with structures 3×3, 4×4 and 5×5.