상온 구동용 SnO2 및 실리콘 기반 반도체 가스 센서의 성능 향상을 위한 마이크로/나노 하이브리드화를 이용한 새로운 접근방법

Abstract

In past few decades due to fast industrialization and urbanization, the development of gas sensors has attracted continually for applications in areas environmental monitoring, medical diagnostics and food inspection. Many kinds of gas sensors have been developed by many researcher until now. Among various gas sensors, the semiconductor gas sensors have drawn much attention due to their good sensitivity, excellent mechanical stability and low manufacturing costs. Nevertheless, the gas-sensing properties of pure metal oxide materials are not sufficient to identify a given gas due to its high operation temperature (200-400oC) and low selectivity, which have disadvantages such as long term stability and the additional power consumption when they are used for long time or exposed at high temperature. To overcome these problems, various additives such as metal, metal oxide have been incorporated into the sensor matrix materials for decreasing operating temperature. In addition, the morphology modification of material has been widely studied because the sensing property was primarily determined by the controlled morphology. However, the techniques controlling morphology and incorporating additives on sensor matrix material have commonly disadvantages such as the complex process and expensive equipment. Besides, after additives were incorporated, the temperature drop of optimal operation temperature of sensing material was low. For this reason, it is difficult to commercialize low-cost gas sensor. For commercialization of gas sensor, it is necessary to develop sensing materials of high sensitivity, selectivity and reliability at room temperature. The first objective of this dissertation is to decrease high operation temperature of the general semiconductor sensing materials and to enhance the sensing performance by controlling sensing material morphology using simple synthesis process. First, we have focused on fabricating sensor based on vertically aligned SnO2 nanorod thin films having extended active sites and investigating their morphology and electric property with synthesis conditions. Second, in order to simplify the synthesis process of catalyst materials on SnO2 film, we suggested 1) tilted sputter process and 2) spray process. Tilted sputter process was used to synthesize the selectively doped domains of Pt nanoparticles on the SnO2 surface and spray process was used to synthesize the ultra-thin CuxO nanolayers with a thickness less than 5 nm scattered on the extended surface of SnO2 nanorods. The morphology of synthesized sensing materials using simple process were analyzed. The mechanism of the H2S gas sensing was elucidated with respect to the unique hierarchical surface morphology and generation of active sites. Fabrication of novel catalyst deposited porous silicon gas sensor to ensure low cost and reliability is the second objective of this dissertation. Porous silicon is used as sensing device due to high specific surface area and high surface chemical activity. Because it is difficult to have excellent sensing property with only porous silicon, metal and non-metal catalysts on porous silicon were added to improve sensing property. Aiming the synthesis of silicon with controlled porosity, we chose as process of combined technology of electrochemical etching and metal assisted chemical etching, which can easily control porous diameter and thickness. To design highly selective porous silicon complex, other components such as palladium (Pd) and graphene were deposited on porous silicon substrate. 1) The porous silicon was used as H2S gas sensor materials unlike the existing H2 or NO2 gas sensing materials. A variety of sensing properties such as response speed, recovery speed, detection limit and selectivity were examined at room temperature. In addition, reaction mechanism of between Pd particles on porous silicon and H2S gas was explained. 2) The graphene deposited nanoporous silicon substrate for low ppm H2 gas detection by an inexpensive synthesis route was proposed, where the porous silicon substrate of large specific area was utilized as sensor matrix materials and graphene as catalyst materials. The sensitivity of the graphene deposited porous silicon substrate were examined in terms of the graphene contents in porous silicon substrate and gas concentration at room temperature. The possibility of gas sensor was confirmed by interpretation of sensing mechanism.