First Observation of Hydrogen sensing by Trap Assisted Conduction Current in Pd/TiO2/SiC Capacitors at High Temperature

This paper reports the first observation of gas sensing using the leakage current through a capacitor fabricated on silicon carbide (SiC). The dielectric layer used in this sensor has a titanium dioxide layer in addition to the thermally grown silicon dioxide (SiO₂) and this operates as an adhesion promoting layer to the catalytic metal gate contact. We have shown that the leakage current through this Pd/TiO₂/SiO₂/SiC capacitor structure is controlled by a trap assisted tunneling mechanism, using a single barrier height and trap density. This barrier height is lowered in the presence of hydrogen gas at high temperatures, whilst the trap density in the dielectric remains unchanged. This shows that the formation of a charge dipole layer under the contact is responsible for the observed change in characteristics in the hydrogen environment, rather than a change to the bulk properties of the dielectric layer. Further, we show that this technique is not affected by the influence of interface traps, which dominate the low voltage capacitance characteristics at high temperatures, offering the opportunity for a simple, more rugged detection method.