Transient response of a transistor-based hydrogen sensor

The transient phenomenon of hydrogen-sensing of a Pd-oxide-InGaP metal-oxide-semiconductor field-effect transistor (MOSFET) is studied. In an environment of N₂ carrier gas, the sensing signal is logarithmically proportional to the hydrogen concentration over a temperature range from 30 to 160 °C. Due to a high activation energy needed for initiating the reverse hydrogen releasing process, the responsive current signal during hydrogen detection does not always go back to the baseline. Over the high temperature region, the recovering curve can be divided into three parts: (i) the initial, (ii) the accumulation, and (iii) the revival stages. Because the recombination process of hydrogen atoms is very slow, a large amount of desorbed hydrogen atoms are appeared and accumulated on the Pd metal surface. A long desorption time is observed. However, in the presence of oxygen, a high speed desorption phenomenon is observed. The hydrogen adsorption rate is also enhanced. In addition, the same shift of drain current baseline for two carrier gas systems (N₂ and air) is found even at high temperature.