A field effect gas sensor for hydrogen

A description is presented of investigations with a sensor consisting of a metal-insulator-semiconductor (MIS) diode with palladium as gate metal. For the preparation of the MIS diodes, silicon disks were oxidized at 1100 C in humid oxygen. Contact areas consisting of Al-Ti-Ag or Au were obtained on the reverse side of the specimens with the aid of a vapor deposition procedure. The front side of the device contains on top of the SiO2 a palladium layer and an aluminum contact. In the experimental study of the prepared gas sensors, stepwise changes could be produced in the pressures of the gases employed in the tests. The reaction of the sensor was observed until equilbrium values were reached. The test gases used included nitrogen with different concentrations of hydrogen, pure hydrogen, oxygen, and nitrogen. The results of the investigation show that MIS diodes with a palladium gate are suited for the detection of hydrogen. It is possible to replace the MIS diodes for the considered application also by field effect transistors or Schottky diodes with palladium.