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

Abstract

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.