A comparative study of Hf and Ta incorporations in the dielectric of Pd-WO3-SiC Schottky-diode hydrogen sensor

An investigation on the incorporation of two different kinds of high-κ dielectrics (HfO2 and Ta2O5) in the dielectric of Pd-WO3-SiC Schottky diode is presented. It is found that while the surface morphology of the WO3 and WHfO films is almost the same, the WTaO film has the smoothest surface due to suppression of oxygen vacancies in WO3 by the Ta incorporation, as supported by XPS analysis. The current-voltage characteristics are examined under a wide range of temperature and hydrogen concentration. Upon exposure to 10,000 ppm H2/air, the diodes based on WHfO and WTaO show a maximum hydrogen response of 89 and 147 respectively, both higher than that (31) of the control sample with WO3. From the kinetics analysis, it is demonstrated that more hydrogen atoms are accumulated at the Pd/WHfO and Pd/WTaO interfaces than their Pd/WO3 counterpart due to larger enthalpy change for hydrogen adsorption on passivated surface, resulting in a greater barrier-height variation at the interface and thus better sensing performance for the two devices with ternary oxide.