A Quartz Crystal Microbalance (QCM) Humidity Sensor Based on a Pencil-Drawn Method With High Quality Factor

In this work, we, for the first time, propose a quartz crystal microbalance (QCM) humidity sensor that is prepared by a one-step method based on pencil drawing. The scanning electron microscopy (SEM), atomic force microscope (AFM), and Raman spectra confirm some graphite flakes, and a layer of sensing film is formed, demonstrating the successful preparation of the QCM sensor. A series of experiments were performed by means of oscillating circuit and impedance analysis at room temperature. The impedance analysis method demonstrates that the QCM humidity sensor exhibits an excellent stability with a quality factor ( ${Q}$ ) that only drops from 47 923 to 43 849 in the whole humidity range, which is better than ever reported QCM humidity sensors. In addition, the sensor shows a good long-term stability with a maximal frequency deviation of less than 5% in a long-term test. Furthermore, the sensor displays a rapid response time ~8s and a recovery time less than 5 s. The underlying reasons for these excellent properties of the proposed sensor are analyzed and discussed. This research demonstrates that the pencil-drawn method is a simple, green, and cost-effective way for constructing a QCM humidity sensor with high performance.