Design of a Dual-Technology Fusion Sensor Chip with a Ring Electrode for Biosensing Application

Effect of Electrode Thickness on Quality Factor of Ring Electrode QCM Sensor

As a key type of sensor, the quartz crystal microbalance (QCM) has been widely used in many research areas. Recently, the ring electrode QCM sensor (R-QCM) with more uniform mass sensitivity has been reported. However, the quality factor (Q-factor) of the R-QCM has still not been studied, especially regarding the effect of electrode thickness on the Q-factor. Considering that the Q-factor is one of crucial parameter to the QCM and it is closely related to the output frequency stability of the QCM, we study the effect of different electrode thicknesses on the Q-factor of the R-QCM in this paper. On the other hand, we clarify the relationship between the electrode thickness and the Q-factor of the R-QCM. The measurement results show that the average Q-factor increases with increases in the thickness of ring electrodes generally; however, the resonance frequency of the QCM resonator decreases with increases in the thickness. The low half-bandwidth (2Γ < 1630 Hz) of the R-QCM shows that the frequency performance is good. Additionally, the R-QCM has a higher Q-factor (Q > 6000), which indicates that it has a higher frequency stability and can be applied in many research areas.

Uniform Mass Sensitivity Distribution of Elliptically Designed Electrodes Based on a Quartz Crystal Microbalance

Uniformization of mass sensitivity distribution is conducive to the application of the quartz crystal microbalance (QCM) in some fields. However, the sensitivity of the QCM sensor surface perpendicular to the displacement direction is higher that of the displacement direction in the mass sensitivity distribution of ring and double-ring QCMs, which leads to poor reproducibility of the sensor. Considering the effect of the electrode structure on the mass sensitivity distribution, we found that for ring- and double-ring-type QCMs, when the elliptical single ring and double-ring electrode structures are combined, an approximately uniform mass sensitivity can be obtained in all directions. Therefore, this study proposes the elliptical single-ring and elliptical double-ring electrode structure design. Through theoretical calculations and three-dimensional finite element analysis verification, a systematic investigation is carried out to quantify the effect of the ratio of the minor axis to the major axis of the elliptical electrode on the mass sensitivity distribution in different directions, and the optimal ratio is found to be 0.8. Comparing the mass sensitivity of the new type of electrodes and the original electrodes, the result shows that the mass sensitivity distribution of the elliptical double-ring electrode structure is more uniform. Hence, these specially designed electrodes are conducive to improving the repeatability.