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An investigation on the incorporation of two different kinds of high-κ dielectrics (HfO 2 and Ta 2 O 5 ) in the dielectric of Pd-WO 3 -SiC Schottky diode is presented. It is found that while the surface morphology of the WO 3 and WHfO films is almost the same, the WTaO film has the smoothest surface due to suppression of oxygen vacancies in WO 3 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 H 2 /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 WO 3 . From the kinetics analysis, it is demonstrated that more hydrogen atoms are accumulated at the Pd/WHfO and Pd/WTaO interfaces than their Pd/WO 3 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. [ABSTRACT FROM AUTHOR]

Abstract: Hafnium dioxide deposited by RF sputtering is used as the gate insulator of metal–insulator–silicon–carbide (MISiC) Schottky-diode hydrogen sensors. Sensors with different gate insulator thicknesses are fabricated for investigation. Their hydrogen-sensing properties are compared with each other by taking measurements at various temperatures and hydrogen concentrations using a computer-controlled measurement system. Experimental results show that for the same insulator thickness, the HfO2 sensor is more sensitive than its SiO2 counterpart. This should be mainly attributed to the larger barrier-height at the Pt/HfO2 interface which can reduce the current of the sensor before hydrogen exposure. Moreover, the sensitivity initially increases with the thickness of the HfO2 film because a thicker oxide layer can provide a larger barrier-height reduction upon hydrogen exposure. However, further increasing the thickness of the HfO2 dielectric beyond about 3.3nm reduces the sensitivity, possibly due to more trapped charges in thicker high-k dielectric which can screen the effect of the polarized hydrogen layer. [Copyright &y& Elsevier]

Abstract: A novel metal–insulator-SiC (MISiC) Schottky-diode hydrogen sensor with the interfacial insulator layer grown in oxygen and trichloroethylene (TCE) is fabricated. The sensitivity and response speed of the device are investigated at different temperatures and hydrogen concentrations. The sensor can quickly respond to hydrogen variation and can give significant response even at a low hydrogen concentration of 48ppm e.g., a sensitivity of 82% is achieved at 150°C and 1V. As compared to another sensor with the insulator grown in NO gas and the control without the insulator, the proposed sensor displays higher sensitivity and faster response. These improvements can be related to the effects of TCE on the quality and growth rate of the insulator layer. [Copyright &y& Elsevier]

Response mechanisms of hydrogen sensor based on a metal–insulator–SiC (MISiC) Schottky-barrier diode are analyzed. A physical model is established for the hydrogen sensor by combining thermionic emission with quantum-mechanical tunneling of charge carriers, and considering hydrogen-induced barrier-height modulation. Simulated results are in good agreement with experimental data. Relation between device performance and insulator thickness is investigated using the proposed model, and the optimal range of insulator thickness can be determined by taking into account the tradeoff between device sensitivity, reliability and resolution for high-temperature applications. [Copyright &y& Elsevier]