A hydrogen-sensitive Pd-gate MOS transistor

An n-channel MOS transistor with palladium gate was fabricated. The threshold voltage of this transistor was found to depend on the partial pressure of hydrogen in the ambient atmosphere. At a device temperature of 150 °C, 10 ppm hydrogen in air is easily detected, and in nitrogen or argon the sensitivity is considerably larger. A model, based on hydrogen adsorption on the palladium–silicon dioxide interface, is proposed. This model explains the device behavior and is also able to predict the absolute sensitivity for hydrogen in argon.