Performance Analysis of Surface Acoustic Wave Hydrogen Sensor Functionalized with Pd, ZnO, and Pd/ZnO Films
摘要
With the fast depletion of fossil fuels, hydrogen appears to be the most promising renewable energy source, whose demand is expected to rise in the forthcoming years. Due to the flammable nature and safety risks of hydrogen, the need for hydrogen sensors is very crucial. Micro-electromechanical systems (MEMS)-based hydrogen sensors have multiple advantages over traditional sensors. They have fast response and recovery times owing to their small size, low power consumption, and long-term stability, and can be mass-produced making them cost-effective. The present work reports on the comparative performance of MEMS-based surface acoustic wave (SAW) hydrogen sensors with different functionalization layers. SAW hydrogen sensors are fabricated on 128° YX-lithium niobate (LiNbO3) wafer with palladium (Pd), zinc oxide (ZnO), and Pd on ZnO (Pd/ZnO) as sensing layers. Unlike earlier research, which has focused on single-layer sensing materials, this study systematically assesses temperature-dependent performance, examining sensor response at both ambient temperature and 150 °C. The sensors displayed a detection limit of up to 20,000 ppm, which is half the hydrogen safety level, highlighting their industrial importance. At room temperature for 20,000 ppm hydrogen, the sensor exhibited resonant frequency shifts of 10, 19, and 25 KHz with ZnO, Pd, and Pd/ZnO films, respectively. At 150 °C, the Pd/ZnO bilayer showed a sizable shift of 110 kHz, whereas the ZnO- and Pd-sensing layers exhibited 22 and 60 kHz, respectively. All the devices exhibited a linear shift in resonant frequency and good repeatability with the concentration of hydrogen. Further, this study demonstrates the Pd/ZnO bilayer’s outstanding sensing capabilities, particularly in high-temperature settings, making it a promising candidate for next-generation high-performance SAW hydrogen sensors.