Miniaturized High-Frequency Humidity Sensor Based on Quartz Crystal Microbalance

In this article, a high-frequency quartz crystal microbalance (QCM) detection unit is fabricated by dry thinning or wet etching, whose resonant frequency is about 61 MHz and the package size is only 5.0 mm long and 3.2 mm wide. After coating a mixed solution of sodium alginate (SA) and gamma-polyglutamic acid (PGA) as the humidity sensitive film over the detection unit, we obtain the proposed QCM sensor. Then, we analyze the variations of resonance frequency and relative humidity (RH), and the response/recovery time. By practical tests, the proposed sensor exhibits a very high sensitivity of 2727.41 Hz/% RH and a decent detection limit of 0.011%RH. The proposed QCM sensor could be widely applied to measure various environmental parameters for its high performance and portability. Due to its excellent performance and small size, we further prepared a 2 x 4 sensor array which will be more widely tested and applied in the future.