Highly Fast Response of Pd/Ta₂O₅/SiC and Pd/Ta₂O₅/Si Schottky Diode-Based Hydrogen Sensors

Herein, the fabrication of a novel highly sensitive and fast hydrogen (H₂) gas sensor, based on the Ta₂O₅ Schottky diode, is described. First, Ta₂O₅ thin films are deposited on silicon carbide (SiC) and silicon (Si) substrates via a radio frequency (RF) sputtering method. Then, Pd and Ni are respectively deposited on the front and back of the device. The deposited Pd serves as a H₂ catalyst, while the Ni functions as an Ohmic contact. The devices are then tested under various concentrations of H₂ gas at operating temperatures of 300, 500, and 700 °C. The results indicate that the Pd/Ta₂O₅ Schottky diode on the SiC substrate exhibits larger concentration and temperature sensitivities than those of the device based on the Si substrate. In addition, the optimum operating temperature of the Pd/Ta₂O₅ Schottky diode for use in H₂ sensing is shown to be about 300 °C. At this optimum temperature, the dynamic responses of the sensors towards various concentrations of H₂ gas are then examined under a constant bias current of 1 mA. The results indicate a fast rise time of 7.1 s, and a decay of 18 s, for the sensor based on the SiC substrate.