Langmuir analysis on hydrogen gas response of palladium-gate FET

A field effect transistor with a thin palladium electrode annealed in a high hydrogen concentration atmosphere was characterized as a hydrogen gas sensor at the operation temperature of 100 degrees C in flowing dry air mixed with hydrogen gas ranged from 1 to 10 000 ppm. The response of threshold voltage from the base level to the steady-state was achieved within 1 min, and the recovery time to the 1 ppm level was 2-4 min. The base level drift observed in the continuous operation over 3 months was smaller than 30 mV per month. The dipole model adapted to the Langmuir equation well describes the observed hydrogen response of the FET gas sensor, and the one-point calibration in the implementation of the hydrogen detector may be possible by use of the Langmuir relationship.