| Hydrogen sensors are necessary for leak detection and concentration measurement. Pd gated metal-insulator-semiconductor (MIS) type sensors have been investigated for several decades. They are very sensitive to hydrogen. However, there are still some challenges with this technology as far as the response stability, dynamic range, and understanding the sensing mechanism. In this thesis, our goal is to use Pd alloy gates in an attempt to improve the sensor performance and elucidate the sensing mechanism in more detail.; Compared with the pure Pd gate, Pd-Cr and Pd-Ni alloys make the metal thin film smoother and more stable in the presence of hydrogen at high concentration. The alloy gated sensors can measure hydrogen concentration up to 5% and with quite satisfactory signal to noise down to 50 ppm. However, the response amplitude is reduced as compared to the Pd gated devices. Moreover, the metal gate structure with double layers does not affect the sensor's performance. Furthermore, the current sensing mechanism is modified, protons instead of the polarized hydrogen atoms are attributed to induce the hydrogen response and there is an endothermic step in the whole sensing process. With a simplified kinetic model, the alloy effect on the hydrogen response is related to the combined equilibrium constant.; In the selectivity study, the addition of oxygen shifts the response baseline for the all devices. With the increasing of the oxygen concentration, the hydrogen response amplitude decreases for the Pd and Pd-Cr gated devices. While oxygen up to 21% does not affect the hydrogen response for the Pd-Ni gated device. The addition of water vapor decreases the hydrogen response for the all devices and its effect is more obvious for the Pd-Ni gated device. Carbon monoxide and propane neither elicit a response nor have any detectable effect on the hydrogen response in our testing.; A general phenomenon, the reverse transient, in the hydrogen response is more obvious at high temperature. The activation energies for the turn-on reverse transient are 90 kJ/mol and 110 kJ/mol for Pd gated and Pd-Ni gated devices, respectively. This transient is possibly associated with the unintentional donor, oxygen, within the AIN layer.; In summary, our results showed the improvement in performance, especially in the dynamic range, through Pd alloy. This study also elucidates the sensing mechanism. |
