Polymer-derived microporous SiOC ceramic coated gallium nitride sensor for selective H2/CO detection

In this work enhancement of H2/CO selectivity of GaN sensors coated with amorphous microporous silicon oxycarbide (SiOC) filter layer has been studied. Amorphous SiOC ceramic has been synthesized by pyrolysis of vinyl-functionalized polysiloxane at 700 degrees C under argon. N2-adsorption measurement confirms formation of microporous SiOC ceramic. SiOC layer with a thickness of about 6 mu m was coated on GaN sensor substrate after two-fold coating/pyrolysis steps. Transient response characteristics and sensor signals of uncoated GaN and SiOC-coated GaN sensors were measured towards H2 (50, 500 and 1000 ppm) and CO (50, 70 and 100 ppm) in nitrogen at 400 degrees C. Uncoated GaN showed high sensor signal towards both H2 and CO whereas for SiOC-coated GaN almost no sensing towards CO was found.