Development of a sensor for environmental monitoring using a semiconductor thin-film

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A sensor for environmental monitoring has been developed. A sensing film is deposited on a tri-layered SiO_2/Al_2O_3/SiO_2 diaphragm by rf sputtering ; the diaphragm is formed on an Si wafer with micro-machining technology. The sensing film is composed of double-layered Fe_2O_3-based film and SnO_2-based one. The patterning of the sensing film is carried out with photolithography technique. A micro-heater is formed on another diaphragm in a similar way. It is used to heat the sensing film up to about 300℃.The electrical conductance of the fabricated sensor changes when a pollutant gas such as CO and NO_x is introduced. It also changes when cigarette smoke or exhausted gas is introduced. It steeply increases and then slowly decreases when a piece of pollen is adsorbed on the surface of the sensing film. It is also sensitive to volatile organic compounds (VOCs) such as formaldehyde, toluene and xylene.Thus the sensor is found to be promising as a small, low-powered, inexpensive sensor for environmental monitoring.The selectivity to the kind of environmental pollution should be improved in a future study.