Pd thin films on flexible substrate for hydrogen sensor

• Pd thin films fabricated by RF sputtering on both flexible and hard substrates.
• Structural deformation observed for films on hard substrate after exposing 10% H2.
• 6 nm Pd film on flexible substrate shows reversible sensor response up to 10% H2.
• H2 sensing properties of film on flexible substrate investigated depending on temperature and concentration.
• The sensitivity of the film decreased with increasing operation temperature.

In this work, palladium (Pd) thin films were prepared via RF sputtering method with various thicknesses (6 nm, 20 nm and 60 nm) on both a flexible substrate and a hard substrate. Hydrogen (H2) sensing properties of Pd films on flexible substrate have been investigated depending on temperatures (25–100 °C) and H2 concentrations (600 ppm – 10%). The effect of H2 on structural properties of the films was also studied. The films were characterized by Scanning Electron Microscopy (SEM) and X-ray diffraction. It is found that whole Pd films on hard substrate show permanent structural deformation after exposed to 10% H2 for 30 min. But, this H2 exposure does not causes any structural deformation for 6 nm Pd film on flexible substrate and 6 nm Pd film on flexible substrate shows reversible sensor response up to 10% H2 concentration without any structural deformation. On the other hand, Pd film sensors that have the thicknesses 20 nm and 60 nm on flexible substrate are irreversible for higher H2 concentration (>2%) with film deformation. The sensor response of 6 nm Pd film on flexible substrate increased with increasing H2 concentration up 4% and then saturated. The sensitivity of the film decreased with increasing operation temperature.