This paper presents the design, fabrication, and resonance characterization of three quartz crystal microbalance (QCM) configurations with different elliptical electrodes— symmetric elliptical electrodes, asymmetric elliptical electrodes, and asymmetric elliptical ring electrodes—for humidity sensing applications. A typical QCM humidity sensor consists of a quartz resonator and a humidity-sensitive material coated on the electrode surface. When the ambient humidity changes, the sensitive layer adsorbs or desorbs water molecules, causing a change in mass loading and consequently a shift in the resonant frequency, which can be used to characterize the relative humidity level. The dimensions of the symmetric elliptical electrodes were determined as 4×3.2mm through the finite element method. On this basis, the size of one side of the asymmetric elliptical electrode was determined as 2.7×2.16mm. The devices were fabricated using MEMS processes, and the resonant characteristics of the three configurations were characterized using an impedance analyzer. The vibration displacement uniformity and electric field distribution of the three electrodes were analyzed by finite element simulation.Experimental results demonstrate that the asymmetric elliptical ring electrode exhibits the best overall performance among the three configurations, combining a high quality factor (Q=34108) and a simulation-verified uniform vibration displacement distribution. The electric field simulation further indicates that this structure has enhanced fringing electric fields at the inner and outer edges of the ring. Previous studies have shown that asymmetric and ring electrode structures can enhance the fringing electric field and improve the humidity sensitivity of QCM. In this paper, an asymmetric elliptical ring electrode structure is further designed and implemented based on the symmetric elliptical electrode structure, providing a candidate electrode design for QCM humidity sensors. The humidity response of this specific structure still needs further experimental verification.

quartz crystal microbalance,elliptical electrode,ring electrode,quality factor,humidity sensing