Titanium and silver contacts on thermally oxidized titanium chip: Electrical and gas sensing properties

► Ti–TiO2 contact is ohmic in all atmospheric conditions and temperatures. ► Ohmic Ag–TiO2 contact becomes highly nonlinear in oxidizing atmosphere. ► Forward biased Ag–TiO2 was experimentally analyzed to result barrier height. ► Reverse current in Ag–TiO2–Ti diode increases 105 times in reducing atmospheres. Ti–TiO2 structure has been utilized in the fabrication of many TiO2-based devices such as solar cells, electrocatalytic electrodes and noble metal–TiO2–Ti chemical sensors. While the ohmic behaviour of Ti–TiO2 is assumed in the description of many TiO2-based devices, direct experimental evaluation has not yet been carried out. We have fabricated Ti–TiO2–Ti and Ag–TiO2–Ti structures on a thermally oxidized titanium chip and assessed their electronic behaviours at different biasing, thermal and atmospheric conditions. The junction areas at the opposite sides of the Ti–TiO2–Ti structure were different and the linearity of the I–V characteristics of the structure, at both biasing directions, approved the ohmicity assumed. This was compared to the behaviour of Ag–TiO2 junction which varied from a high energy barrier Schottky diode to an ohmic contact, depending on the composition of the surrounding atmosphere. It was established that the ionic current due to the field assisted silver ion migration in the forward biased device causes the behaviour of the Ag–TiO2 junction to deviate from that of a Schottky diode.