Separate assessment of chemoresistivity and Schottky-type gas sensitivity in M–metal oxide–M′ structures

Maximum response levels reported for chemoresistive sensors span from less than 10 to over 108. These differences are attributed to either the different micro- and nano-structured oxide pallets used or the properties of the metal–metal oxide junctions provided. Here, we report separate measurements and model-based estimations of the chemical responses arising from these different origins. The results quantitatively connect the observed responses to the parameters of the metal and metal oxide components of the device. It is shown that while the peak chemoresistive response is microstructure-dependent, the highest attainable Schottky-type gas sensitivity is almost microstructure-independent and is determined by the intrinsic properties of the materials involved. Measurements carried out on different Ag–TiO2–Ti, Au–TiO2–Ti and Ti–TiO2–Ti structures verified the estimations: While chemoresistive responses in TiO2 can hardly rise over 102, atmosphere-sensitive noble metal–TiO2 junctions can cause responses as high as ∼107.