Carbon Monoxide Gas Sensor Based on IGZO film Fabricated Atmospheric Pressure Plasma by Two-Step Annealing

• Main Authors: Chiang, Yi-Chou, 姜以洲
• Other Authors: Chang, Kow-Ming
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/xueq62

碩士 === 國立交通大學 === 國際半導體產業學院 === 107 === Indium gallium zinc oxide (IGZO) is one kind of transparent n-type metal oxide semiconductor material which is often utilized to the channel layer of thin-film transistors (TFT). IGZO is very sensitive to oxygen in air. Since the sensing mechanism of semiconductor metal oxide materials mainly depend on oxygen adsorption on the material surface, this property makes IGZO also be utilized as gas sensing layer of semiconductor gas sensors. In this study, we used atmospheric pressure plasma enhanced chemical vapor deposition (APECVD) system to deposit IGZO films on silicon oxide and as-deposited IGZO films were annealed in furnace. Samples which were fabricated in different conditions were exposed to carbon monoxide to measure the sensing performance. In the end we could finally develop the best process for IGZO sensors. The study is divided into five parts. First, we investigated the effect of film thickness on sensing performance and determined the best IGZO film thickness for CO sensing. Second, we studied the effects of N2 and O2 annealing with different gas flow rates on sensing performance. Third, we studied the effects of different annealing time on sensing performance. Fourth, we combined the advantages of N2 annealing and O2 annealing, and developed the brand-new two-step annealing process and determined the best annealing recipe for IGZO films. Finally, we tested the samples annealed by traditional annealing and two-step annealing in real-world environment and compared the results. In addition to CO sensing measurements, we used Scanning Electron Microscope (SEM) to observe the surface images of different annealing conditions. The images showed that excessively high annealing temperatures and excessively long annealing time would cause the grain size grow larger, resulting in smaller sensing surface area and lower sensing effect. X-ray photoelectron spectroscopy (XPS) is also used to analysis the oxygen bonds on IGZO film surface. It was reported that high proportion of surface oxygen vacancies can enhance sensing performance of the film. From XPS analysis we discovered that when IGZO films annealed by traditional annealing process, percentage of oxygen vacancies on the surface dropped to only half of it compare to as-deposited films. On the other hand, IGZO films annealed by two-step annealing process had almost same percentage of oxygen vacancies remained on the surface. By using the two-step annealing process we developed in this study, IGZO sensing films could still get the benefit from annealing but remove the side effect. Finally, in real-world environment CO sensing test two-step annealed samples also showed much higher sensitivity than traditional N2 annealed samples.