Development of a Zinc Oxide Gas Sensing Device with an Integrated Microplasmas Generation Unit

• Main Authors: Fei-Hung Huang, 黃非紅
• Other Authors: 徐振哲
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/45770676916090335419

碩士 === 國立臺灣大學 === 化學工程學研究所 === 105 === Atmospheric microplasma system has numerous advantages, for example, the operation under atmospheric pressure avoids the use of vacuum equipment, the small discharge volume with high electron density and reactivity provides the capability of local treatment and low power consumption, the characteristic of non-thermal equilibrium plasma offers us an option of low temperature process, etc. Therefore, atmospheric microplasma system becomes one of the most attractive plasma systems operated under atmospheric pressure. In this thesis, we integrate the microplasmas generation unit (MGU) with the gas-sensing element on one device. The gas-sensing element is zinc oxide (ZnO), which is widely used as conductometric gas sensors based on its semiconducting property. In this device, the discharge location of microplasmas is also the deposition position of the precursor film of ZnO, thus the MGU provides on-site treatment of the precursor film and converts the film to ZnO film with low processing temperature. This process enables ZnO film fabrication even when the device or substrate suffer from the disability of low temperature tolerance. In this thesis, the MGU is classified as the dielectric-barrier-discharge (DBD)-type microplasma system. The device was fabricated by double-sided copper clad laminate (CCL), which consists of two copper laminates with one insulting layer between. Through toner transfer process, we are capable to design and fabricate the electrodes’ patterns, as we desire. While the high voltages (AC) are applied across the dielectric layer, microplasmas breakdown along the edge of the electrodes under atmospheric pressure. Because of the capability of user-defined electrode patterns on CCL, we can integrate the MGU with the gas-sensing element on one device. We placed one pair of electrodes on one side of the CCL and one electrode on the other side. The paired electrodes on the same side of the CCL were separated by a 200-μm-wide gap from each other; moreover, on the other side of the gap was electrode. After spraying zinc nitrate, the precursor of ZnO, over the gap for deposition of the precursor film, microplasmas generated along the edge of electrodes and diffuse to the gap, and microplasma post-treatment converted the film to ZnO. Therefore, the film could be treated as a gas-sensing element. In this thesis, ethanol vapor was the representative gas for the test of gas sensing performance. We changed the microplasma post-treatment time, the ambient for plasma generation, the pattern design of electrodes, etc., to alter or modify the sensing performance. For example, when we used the pattern of interdigitated electrodes and the microplasmas generate under ambient air, for only 10 minutes of microplasma treatment, the sensor detected around 100 to 16000 ppm ethanol vapor with the resistance ranging from about 100 MΩ to 100 GΩ. Besides, comparing the gas sensing performances with the results of element analysis by energy dispersive spectrometer of scanning electron microscope, we concluded that the precursor films successfully transform to semiconductor ZnO.