A Highly Sensitive Humidity Sensor Based on Ultrahigh-Frequency Microelectromechanical Resonator Coated with Nano-Assembled Polyelectrolyte Thin Films

Wenpeng Liu,Hemi Qu,Wei Pang,Jizhou Hu,Hao Zhang,Xuexin Duan

doi:10.3390/mi8040116

Abstract

We developed a highly sensitive humidity sensor based on the combination of ultrahigh-frequency film bulk acoustic resonator (FBAR) and nano-assembled polyelectrolyte (PET) thin films. The water molecule absorption efficiency was optimized by forming loosely-packed PET nanostructures. Then, the humidity sensing characteristics were analyzed in terms of sensitivity, linearity, reversibility, stability and detection limit. As a result, PET-coated FBAR exhibits excellent humidity sensitivity of 2202.20 Hz/ppm, which is five orders of magnitude higher than quartz crystal microbalance (QCM). Additionally, temperature dependence was investigated with the result that PET-coated FBAR possessed a higher sensitivity at low temperature. Furthermore, we realized the selective detection of water vapor from volatile organic compounds (VOCs) with respect to the polarity property. Owing to the high sensitivity, miniaturized size and ultrahigh operating frequency, PET-coated FBAR is uniquely favorable as a wireless humidity sensor node to integrate into wireless sensor networks (WSNs).

Highlights

Monitoring of environmental humidity is crucial in fields ranging from meteorology, agriculture and industry to medicine/healthcare development and food science [1,2,3]
film bulk acoustic resonator (FBAR) usually operates at two orders of magnitude higher frequency than quartz crystal microbalance (QCM) and is cable of detecting small mass changes at even pictogram order
The compatibility with conventional complementary metal oxide semiconductor (CMOS) technology promotes the mass production of FBAR with low cost

Summary

Introduction

Monitoring of environmental humidity is crucial in fields ranging from meteorology, agriculture and industry to medicine/healthcare development and food science [1,2,3]. FBAR usually operates at two orders of magnitude higher frequency than QCM and is cable of detecting small mass changes at even pictogram order It has been extensively employed for fundamental science and practical engineering [13,14]. The compatibility with conventional complementary metal oxide semiconductor (CMOS) technology promotes the mass production of FBAR with low cost All these advantages make FBAR a good candidate as humidity sensor to integrate into WSNs in the development of internet of things. The FBAR-based humidity sensor reported in the literature suffers from the poor sensing characteristics with respect to the sensitivity, detection limit and stability [11,12,15]

Methods

Results

Conclusion