Fabrication of an ammonia microsensor based on zinc oxide

The ammonia microsensor is fabricated by the 0.35 μm complementary metal oxide semiconductor (CMOS) process. The sensor is composed of a sensitive film and polysilicon electrodes. Area of the ammonia microsensor is about 1 mm². The sensitive film of the ammonia microsensor is zinc oxide prepared by hydrothermal method. The sensor requires a wet etching process to remove the sacrificial oxide layer and coats the zinc oxide sensitive film on the polysilicon electrodes after the CMOS process. The ammonia microsensor is resistive type. When the sensitive film absorbs or desorbs ammonia gas at room temperature, the sensitive film generates a change in resistance. Experimental results present that the sensitivity of the ammonia microsensor is about 12.6 Ω/ppm at room temperature.