THE STUDY OF HUMIDITY SENSOR BY SAW DELAY LINE

• Main Authors: Shih-Hsuan Tseng, 曾士軒
• Other Authors: Mu-Shian Wu
• Format: Others
• Language: en_US
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/73030189463456435755

碩士 === 大同大學 === 電機工程研究所 === 88 === Reliable humidity or gas detection is becoming great important in environment control. In particular, precise humidity detection is necessary in the industry of high technology and food. Among the commercialized semiconductor material, Tin dioxide is usually been fabricated as resistive type or capacitive type detector to detect oxidizing/reducing gas due to high sensitivity of gas or humidity at high temperature. But it has some disadvantages like operating at high temperature and slow response time. These disadvantages could be improved by using the SAW based sensor and SAW sensor has other wider applications. These are the motivation of this thesis. SAW, firstly discovered by Lord Rayleigh in 1887, has been widely used in communication field such as radar, pager and mobile phone. Recently, the application of SAW sensor is more and more important. SAW sensor, not only has the advantage of operating at room temperature and high sensitivity but also the wireless detection application of poison gas in poor environment due to its RF outstanding characteristics. The SAW delay-line structure with uniform IDT overlap is facilitate to design and fabricate among various SAW device. It is considered that raising the successful probability of fabricating and lowering the cost of SAW device when using this simple structure. Zinc Oxide, which has strong piezoelectric effect and can be sputtered on a variety of substrates, is a nature choice as the piezoelectric film layer in recent years. The Corning 7059 glass substrate, whose thermal expansion coefficient is nearly equal to that of ZnO single crystal, is usually chosen as the substrate for ZnO thin film. According to the above reasons, we use the piezoelectric ZnO thin film accompanying Corning 7059 glass substrate with similar thermal expansion coefficient as the main structure of SAW delay-line in this thesis. Through highly preferred orientation ZnO thin film and the interdigital transducers fabricated by lift-off process to form the SAW delay-line structure. Depositing the sputtered SnO2 and spin coated hygroscopic polymer between two IDTs to observe the humidity sensing characteristics in frequency, insertion loss and phase by network analyzer. Besides, the discussing of the influence of humidity using different combinations of semiconductor thin films and the interaction mechanism between water vapor and different sensing materials will be included in this thesis.