Study on LiNbO3 Lateral Field Excited Humidity Sensors

• Main Authors: Tzu-Sheng Hsieh, 謝子笙
• Other Authors: Yung-Yu chen
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/28247904787429080855

碩士 === 大同大學 === 機械工程學系(所) === 104 === This thesis aims at developing a low-cost and high-sensitivity humidity sensor module which could work at room temperature by combining a Lithium Niobate (LiNbO3) lateral field excited sensor with ZnO nanowire sensing film. First of all, bulk waves in LiNbO3 are calculated using Christoffel equation for the determinations of cut angle and electric field direction. Besides, the vibration mode and frequency response of the LiNbO3 lateral field excited acoustic wave sensor are calculated through finite element analysis for the confirmation of cut angle and electric field direction. A dual delay line configuration is constructed for suppressing the interference from environmental factors. Then, the ZnO nanowires as humidity sensing film are prepared by hydrothermal method and spin coated on the 128°YX LiNbO3 wafer as the humidity sensing layer, and characterized using an X-ray diffraction (XRD) apparatus, scanning electron microscope (SEM). In the humidity sensing experiment, the LFE sensor is tested by passing the dry air and water into the chamber for evaluation of its sensitivity and repeatability. The result shows that in three testing cycles, the frequency shifts are all about 538.3 Hz when the change in the relative humidity is 66.5%. By changing relative humidity, the sensitivity of the LFE sensor to relative humidity is measured and shows a value of 11.74 Hz/%. In conclusion, the LFE humidity sensor developed in this study is successfully measured at room temperature, and shows great sensitivity, stability and repeatability.