A gas sensor corresponds to the role (the olfaction) of "a nose", if it compares to the five senses of the human being. The resistance value of the oxide semiconductor changes by the interaction between various gases and the surface of the oxide semiconductor. There is correlation between the gas concentration and the resistance value of the oxide semiconductor (the sensor resistance value). Therefore, gas concentration can be detected from sensor resistance. The gas sensor can detect even odorless gas, although it is impossible for the olfaction to detect odorless gases. The representative H2
, CO and methane in reducing gases are odorless. Accordingly, CO poisonous and gas explosion and other accidents occur if it cannot detect existences of these gases certainly. Also, the representative O3
, NOX etc in oxidizing gas cause accidents after all if they cannot detect at low concentration although they have foul-smell. The exclusive sensors are necessary for each gas.
The technologies of these gas sensors have being applied for the air environment improvement inside of automobile and the other in our company. Also, the O3
sensors of our company have been diffused widely as those safety devices, although O3
is applied in an air environment improvement, water treatments, sewage treatment, food industries or semiconductor industry etc.