A gas sensor comprising two back-to-back connected Au/TiO2 Schottky diodes

Aminiature, but sturdy, gas sensor capable of operation at temperatures as high as 600 degrees C is presented. The device comprises two back-to-back connected gold/rutile Schottky diodes, which are fabricated on the opposite bases of a self-standing 100 mu m-thick pellet of polycrystalline rutile. The rutile layer is formed by the direct oxidation of titanium metal in air at 900 degrees C, and the Au/rutile diodes are formed by the diffusion bonding of the gold wire segments to the pellet bases. The current versus voltage diagrams and gas sensing properties of the Au/rutile/Au structured device are recorded at different voltage sweeping frequencies and operating temperatures. The interesting features of these diagrams are explained based on an equivalent circuit of the device, which considers Schottky-type contacts at both bases and memristive conduction for the rutile in between. The device current is controlled by the leakage current of the reverse biased diode, which depends on the concentration of the oxygen vacancy at the Au/rutile interface and, hence, on the composition of the surrounding atmosphere. The device current increases 15 times in response to the presence of 1000 ppm of ethanol vapor in air. Consisting only of bulk gold and bulk rutile, the device is resilient to harsh environments and elevated temperatures; a suitable gas sensor for in-exhaust installation.