Piezoelectric micro diaphragm based high performance humidity sensor

This paper presents a novel humidity sensor based on a piezoelectric micro diaphragm (PMD) resonator integrated with a zinc oxide (ZnO) sensing layer, demonstrating exceptional performance through stress-based sensing mechanisms. Unlike conventional mass-loading based sensors, our design uniquely leverages the PMD's flexible vibration modes combined with a ZnO sensing layer to achieve unprecedented sensitivity. The sensor exhibits dual-mode operation at low frequencies of 0.17 MHz and 0.68 MHz, where the second mode demonstrates remarkable humidity sensitivity reaching 638–4110 Hz/%RH and achieves outstanding figure of merit (FOM) values of 943–6080 ppm/%RH from low relative humidity range (0.6 % RH∼80 % RH) to high relative humidity range (80 % RH∼90 % RH), surpassing current state-of-the-art technologies by more than an order of magnitude. Systematic characterization reveals fast response characteristics with T₆₃ absorption/desorption times of 5/11 s and excellent selectivity against common gases. The enhanced performance of the second mode is attributed to its complex modal pattern enabling more effective stress distribution, as verified through finite element analysis and experimental validation. This work establishes PMD architecture as a promising platform for high-performance humidity sensing applications, offering an optimal balance between sensitivity, response time, and system integration capabilities. Additionally, the versatile stress-based sensing mechanism can be adapted for detecting various gas molecules of societal importance by simply modifying the sensing layer, enabling broader environmental monitoring applications.