Zheng Zhou, Zhang Guodong, Wang Xiaomin, Kong Xu
College of Electrical Engineering and Automation, Shandong University of Science and Technology, Qingdao 266590, China.
Micromachines (Basel). 2022 Sep 30;13(10):1651. doi: 10.3390/mi13101651.
Humidity sensors with comprehensive performance are of great interest for industrial and environmental applications. Most sensors, however, have to compromise on at least one characteristic such as sensitivity, response speed, and linearity. This paper reports a gravimetric humidity sensor based on a capacitive micromachined ultrasonic transducer (CMUT) with exceptional all-around performance, and presents a side-by-side comparative investigation of two types of gravimetric humidity sensors for a better understanding of their characteristics and sensing mechanisms. For these purposes, a circular CMUT and a quartz crystal microbalance (QCM) with a resonance frequency of 10 MHz were designed and fabricated. Poly(vinyl alcohol) (PVA) was employed as the humidity sensing layer for its hydrophilicity and ease of film formation. The electrical properties of the sensors, including the electrical input impedances and quality factors, were characterized by a vector network analyzer. The relative humidity (RH) sensing performance of the sensors was evaluated and compared from RH levels of 11% to 97%. Both sensors exhibited good repeatability and low hysteresis. The unique microscale resonant structure of the CMUT humidity sensor contributed to a high sensitivity of 2.01 kHz/%RH, short response and recovery times of 8 s and 3 s, respectively, and excellent linearity ( = 0.973), which were far superior to their QCM counterparts. The underlying mechanism was revealed and discussed.
具有综合性能的湿度传感器在工业和环境应用中备受关注。然而，大多数传感器至少要在灵敏度、响应速度和线性度等特性上做出妥协。本文报道了一种基于电容式微机械超声换能器（CMUT）的具有卓越综合性能的重量法湿度传感器，并对两种重量法湿度传感器进行了并排比较研究，以更好地了解它们的特性和传感机制。为此，设计并制作了一个圆形CMUT和一个共振频率为10 MHz的石英晶体微天平（QCM）。聚（乙烯醇）（PVA）因其亲水性和成膜容易而被用作湿度传感层。传感器的电学特性，包括电输入阻抗和品质因数，通过矢量网络分析仪进行表征。在11%至97%的相对湿度（RH）水平下对传感器的RH传感性能进行了评估和比较。两种传感器都表现出良好的重复性和低滞后性。CMUT湿度传感器独特的微尺度共振结构使其具有2.01 kHz/%RH的高灵敏度、分别为8 s和3 s的短响应和恢复时间以及优异的线性度（ = 0.973），这远远优于它们的QCM对应物。揭示并讨论了其潜在机制。
