Simulation analysis and experimental verification for sensitivity of IDE-QCM humidity sensors

This paper proposes a new, simple, and effective approach that uses both an interdigital electrode (IDE) and a quartz crystal microbalance (QCM) as sensitive components to improve humidity sensitivity. First, a simulation analysis of the equivalent electronic circuit was used to verify that the frequency response of the IDE-QCM humidity sensor is the sum of that of the QCM and interdigital electrode-piezoelectric quartz crystal (IDE-PQC) sensors. Then, cellulose nanocrystals (CNCs) were used as humidity-sensitive materials deposited on IDE and QCMs, respectively, to fabricate several PQC sensors. The humidity-sensing performances of all sensors were tested at room temperature, including the dynamic response, sensitivity, response/recovery time, repeatability, and long-term stability. The experimental results prove the superposition relationship and can be used to enhance the humidity sensitivity. The maximum sensitivity of the IDE-QCM sensor reaches 262.21 Hz/%RH in the humidity range of 11.3 %-97.3 %, which is higher than that of all frequency-modulated piezoelectric quartz crystal humidity sensors. Moreover, the humidity hysteresis (similar to 8.1 %RH) and response/recovery time (68/4 s) did not significantly increase compared with the IDE-PQC and QCM sensors. All the sensors exhibited good repeatability and long-term stability. Finally, the humidity-sensing mechanism of the CNC-based IDE-QCM sensor is discussed in detail. This work demonstrates that using both IDE and QCM as sensitive elements is a simple and effective method to improve the humidity sensitivity of frequency-modulated piezoelectric quartz crystal sensors. This superposition relationship of capacitance-inductance frequency modulation to enhance sensitivity also provides an excellent reference for the design of other high-performance sensors.

Automated summary

This paper proposes a new method using an interdigital electrode and a quartz crystal microbalance to improve the sensitivity of humidity sensors. By using cellulose nanocrystals as humidity-sensitive materials, the experimental results demonstrate high sensitivity and stability of the sensor.