Ferroelectric (Ba,Sr)TiO₃ thin films for H₂ gas detection by sol-gel and RF sputtering

Ferroelectric (Ba,Sr)TiO₃ thin films for hydrogen gas detection have been prepared by sol-gel and RF sputtering methods, and characterized using X-ray diffraction, dielectric characterization, and gas sensing measurements. The sol gel approach can easily produce BST amorphous films for H₂ gas detection, however, no amorphous films, but partially crystallized ones, have been obtained using our RF sputtering coating system. Experimental results show that the Schottky I-V behavior appears in these Pd/amorphous BST thin film/metal capacitor devices, both in air and in diluted hydrogen gas. The sol-gel prepared films display an excellent gas sensitivity and the turn-on voltage shift as large as 4.5V at 1024 ppm H₂ gas in air has been observed due to the H₂ blocking effect by amorphous BST films. The relatively poorer performance of the RF sputtered films to H₂ gas detection may originate from the trapped charges in these partially crystallized films, and therefore, weaken the induced H₂ potential build-up across the space charge layer at the interface.