Hydrogen sensing properties of SnO2 varistors loaded with SiO2 by surface chemical modification with diethoxydimethylsilane

Effects of chemical surface modification with diethoxydimethylsilane (DEMS) on the H2 sensing properties of pure SnO2 and Pd/SnO2 as a varistor-type sensor have been investigated. The DEMS treatment resulted in an increase in the breakdown voltage, especially in air, and in an improvement in H2 sensitivity for both SnO2 and Pd/SnO2 varistors. A.C. impedance measurement has revealed that variations in potential barrier height per grain boundary, Vgb, with H2 concentration are well coincident with the breakdown voltage shift induced by the presence of H2. Thus, it was confirmed that the improved H2 sensitivity arose from the increased Vgb in air induced by the SiO2 thin film coating by the DEMS treatment. The limitation of neck growth between SnO2 particles by the SiO2 thin film coating is anticipated to be responsible for the increased Vgb.