Design and Fabrication of MEMS Microheater for Gas Sensing Applications

Abstract

Recent technological advancements have adverse effects on mankind including environmental (air) pollution due to rapid industrialization, chemical pollution due to increased use of pesticides in agriculture and some unforeseen effects of genetically modified food stuff affecting the health of living organisms as well as the ecosystem. Hence, efficient sensors are essentially required to detect these pollutants at the first step only. Nowadays, efforts are continuing towards the realization of smart and intelligent systems which combine sensors with necessary electronics to make a portable or wireless sensor. Acetone vapours/gas having a pungent and irritating smell is toxic if inhaled directly. Acetone is released in environment both by the natural and anthropogenic (man-made) sources. The main sources of acetone emission are industrial sources as a result of chemicals manufacturing, non-ferrous materials, plastic products, printing processes, and sewage and drainage services and also from coal mining. The other natural sources are volcanic gases and forest fires. The acetone is also present in the vehicle exhausts and also from railway operations, and even from tobacco smoke. Acetone being highly flammable and/or explosive in nature when mixed with some peroxides or strong oxidants, is also present in the consumer products such as paint and varnish removers, thinners, paints and primers etc. Thus, there will always be need to detect the leakage of the acetone in any form within a premises or environment. As acetone is heavier than air, it may travel along the surface to a hot equipment or flames which can caught fire causing distant ignition even in lowered concentrations. Hence, to prevent a disastrous situation the acetone sensor must be installed to detect any leakage. Sensors of this kind have a simple design that makes mass production feasible and is strongly linked to the availability of better sensing materials with improved functional properties. The phenomenon of change in the resistance of semiconducting sensing element in the presence of a reducing or an oxidizing gas while being operating at elevated temperatures is the basic principle of operation of semiconducting metal oxide gas sensors. Later, demand for enhanced sensitivity and fast response speed led to the development of thin film based sensing devices. Currently, worldwide efforts are focused in both the basic as well as applied areas and there is continued interest in developing new sensing materials along with novel design structures for obtaining improved sensing response characteristics. The fabricated sensor is then tested with a newly designed coplanar architectured for inter digitated electrodes and the microheater for improving the sensing efficiency of the sensor by improving the increased uniform area for heating of the sample. Finally the results are discussed for each sensor fabricated in respective sections.