Novel hydrogen gas sensing by palladium electrode on dielectric capacitor coupled with an amorphous InGaZnO thin-film transistor

Palladium (Pd) is well known for its capability to selectively detect hydrogen (H₂) gas, where the detection process involves absorbing hydrogen gas molecules to form compound palladium hydrides. Such Pd-H interaction leads to the increase of electrical resistance and volume of Pd, simultaneously lowering its work function. These Pd-based hydrogen sensors would be more beneficial when connected to conventional semiconductor integrated circuits. Here, we utilize the Pd film as H-sensing electrode for metal/SiO₂/p⁺-Si (MIM) capacitor, since we found the H-induced chain reactions in Pd/SiO₂/p⁺-Si capacitor:Pd volume expansion, Pd-SiO₂ contact are change, and the capacitance change. This capacitance change is connected to the gate of an electrically stable amorphous InGaZnO (a-IGZO) thin-film transistor (TFT). As a result, H-induced output as the drain current of a-IGZO TFT was statically and dynamically measured through the capacitance signal change from Pd-MIM sensor. This output current signal was converted to voltage when a load resistor was connected to the a-IGZO TFT in series. These sensor circuit configurations are regarded promising and novel because of their simplicity and practicality.