Chemical sensing with ZnO nanowire FETs

Zinc oxide nanowires are configured as n-channel field effect transistors. These transistors are implemented as highly sensitive chemical sensors for detection of various gases such as O2, NO2, NH 3, and CO at room temperature. They show oxidizing sensing property to oxygen and nitrogen dioxide. Nanowires' ammonia sensing behavior is observed to switch from oxidizing to reducing when temperature increased from 300 to 500 K. This effect is attributed to the temperature dependent chemical potential shift. Carbon monoxide is found to increase the nanowire conductance in the presence of oxygen. Due to a Debye screening length comparable to the nanowire diameter, the electric field applied over the back gate significantly affects the sensitivity as it modulates the carrier concentration. A strong negative field is utilized to refresh the sensors by an electro-desorption mechanism. In addition, different chemisorbed species could be distinguished from the "refresh" threshold voltage and the temporal response of the conductance. These results demonstrate a refreshable field effect sensor with a potential gas identification function