AL-AL2O3-PD JUNCTION HYDROGEN SENSOR

Al-Al2O3-Pd MIM (metal insulator metal) junctions fabricated on a glas s substrate were tested as hydrogen sensors. The I-V (current versus v oltage) characteristics of the junctions were measured at room tempera ture in a vacuum of 10(-5) Torr and in H-2 gas of 10(-2)-10(0) Torr. A significant increase in the current was observed upon introduction of H-2 gas. This phenomenon is believed to occur due to the work functio n lowering of the hydrogen-absorbed Pd top electrode. The rise time wa s on the order of minutes, while the recovery time when hydrogen was p urged was more than 20 h. However, when the junction was placed in an oxidizing ambient such as air, the recovery time was drastically reduc ed to the order of minutes, indicating that the device is operative as a hydrogen sensor in the atmospheric ambient. Hydrogen adsorption and desorption behavior of the Pd film was also investigated using a Pd c oated quartz microbalance, and the results explained the current respo nse of the Pd MIM junction to hydrogen in the presence of oxygen.