Vertical sensor design with amplified capacitive response for improved humidity sensing

Abstract

We propose a novel vertical capacitive humidity sensor capable of transducing the resistance variation of a humidity-sensitive material into a corresponding capacitance change. The proposed hydroxyethyl cellulose-based vertical structure expands the distribution of electric flux lines as the humidity increases, thereby overcoming the challenges of high output resistance at low humidity and the resultant incompatibility with commercial circuitry. The RC equivalent circuit model demonstrates that the effective length of the electric flux lines from the top-electrode edge increases with humidity, and the small inter-electrode spacing inherent in our design ensures amplified capacitance change. Over 10%–90% relative humidity, the capacitance change increased from 5 pF for the conventional interdigitated-electrode sensor to 114 pF for the vertical sensor, representing a 23-fold enhancement. Furthermore, we confirmed compatibility of the design with a wide range of humidity-sensitive conductive materials, indicating practical applicability of the proposed sensor design across a broad range of applications.