New NO2 sensor based on Au gate field effect devices

A new NO2 field effect gas sensor based on Au gates is demonstrated and the influence of gate morphology on sensor response is evaluated. A sensitizat ion mechanism, for non-catalytic continuous gates, based on grain boundary diffusion is proposed. The sensors are fabricated as MOS (metal-oxide-semic onductor) capacitors with sputtered or thermal evaporated An gates (at diff erent substrate temperatures) with thickness between 75 and 960 nm. The dev ices' sensitivity, in the range of 15-200 ppm of NO2 in dry air, depends st rongly 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 degreesC. The sensors are selective to N O2 (with NO, H-2 and CO as interfering gases) and selectivity depends also on gate structure. (C) 2001 Elsevier Science B.V. All rights reserved.