Room-temperature hydrogen sensors based on ZnO

Thin-him ZnO (0.3-1.0 mu m) has been deposited on various substrates by an indigenously developed spray-chemical vapour deposition (CVD) method. The film is polycrystalline and non-stoichiometric in nature with a fairly high resistivity of 125-150 ohm cm. Two new kinds of sensor structures, viz., a Pd/ZnO/p-Si heterojunction and Pd/ZnO/Zn metal-active insulator-metal (MIM) have been fabricated and tested for hydrogen sensor applications. The results show that both the structures can detect hydrogen efficiently and reproducibly between 2000 and 20 000 ppm in air at room temperature. The MIM sensor shows better performance than the heterojunction one. The sensors have been tested in CO, CO2 and LPG and are found to be insensitive.