Ultra-High Sensitivity to Low Hydrogen Gas Concentration With Pd-Decorated IGZO Film

Abstract

To enhance the performance of semiconducting metal oxides, as hydrogen (H2) sensor, we introduced a high carrier concentration ( ${N}_{d}$ ) metal oxide, indium-gallium–zinc oxide (IGZO), combined with palladium (Pd) catalysis. This allowed the detection of low concentrations of H2 at room temperature. The base current level was linearly increased with the Pd thickness. As a result, a high sensor sensitivity of $6.1 \times 10^{6}$ % at 5% H2 concentration was obtained using a 1-nm-thick Pd-decorated IGZO film. Comparative studies with a zinc oxide (ZnO) counterpart showed that the ${N}_{d}$ of IGZO ( $8 \times 10^{18}$ cm $^{-3}$ ) is significantly higher than that of ZnO ( $2 \times 10^{16}$ cm $^{-3}$ ), indicating a closer location for the Fermi level of IGZO to the conduction band. Therefore, a relatively small amount of electron-donating H2 was required to overcome the energy barrier in IGZO. Consequently, the 1-nm-thick Pd-decorated IGZO sensor responded to a gas level as low as 0.01% (100 ppm) and demonstrated a 70-fold higher sensitivity compared with ZnO sensor at all H2 concentrations.