Pd/Ta2O5/SiC Schottky-diode hydrogen sensors formed by using rapid thermal oxidation of Ta thin films

Abstract

Pd/Ta2O5/SiC Schottky-diode hydrogen sensors were fabricated, and their hydrogen gas sensing performance was investigated at 573 K and 773 K. Interfacial Ta2O5 films of 120 nm in thickness were formed by using rapid thermal oxidation (RTO) of the sputtered Ta films on SiC. The crystallinity of the Ta and the Ta2O5 films were characterized by using X-ray diffraction (XRD). As-sputtered Ta films on 4H-SiC are composed of α-Ta (body-centered-cubic) and β-Ta (tetragonal), and α-Ta (110) is the dominant orientation. After RTO at 573 K, the Ta films are converted to β-Ta2O5 (orthorhombic). The diode sensors show high sensitivity to H2 even at the low H2 concentration of 500 ppm, and the voltage change of the sensor upon H2 exposure is proportional to the H2 concentration in the range of 500 ∼ 2000 ppm at 573 K. The response voltage ΔV is shown to arise mostly from the change in the series resistance component of the sensor upon H2 exposure; the main origin of that change is believed to be the Ta2O5 interfacial layer. The response time t90 of the sensor at 573 K was estimated to be approximately 8 s.