New NO 2 sensor based on Au gate field effect devices

Abstract

A new NO 2 field effect gas sensor based on Au gates is demonstrated and the influence of gate morphology on sensor response is evaluated. A sensitization mechanism, for non-catalytic continuous gates, based on grain boundary diffusion is proposed. The sensors are fabricated as MOS (metal-oxide-semiconductor) capacitors with sputtered or thermal evaporated Au gates (at different substrate temperatures) with thickness between 75 and 960 nm. The devices’ sensitivity, in the range of 15–200 ppm of NO 2 in dry air, depends strongly on gate morphology; shorter response times and larger voltage shifts are correlated with smaller grain sizes. Scanning-electron-microscope (SEM) images show that the microstructure is very stable after 5 months of gas exposure at temperatures up to 200°C. The sensors are selective to NO 2 (with NO, H 2 and CO as interfering gases) and selectivity depends also on gate structure.