Novel application of sputtered (Ba,Sr)TiO₃ thin films for gas sensors: Influences of growth processing on dielectric properties

A novel type of metal-ferroelectric hydrogen gas sensor device was fabricated on platinum-coated silicon wafer with an amorphous ferroelectric (Ba_0.67Sr_0.33)TiO₃ layer using RF magnetron co-sputtering process. The BST films were characterized using X-ray diffraction and dielectric characterization, and the influence of the growth process on their dielectric properties was discussed. Experimental results showed that the microstructure and the dielectric properties were closely correlated to the deposition parameters. The microstructure was mainly determined by the deposition temperature, and the oxygen stoichiometry governing the dielectric properties was affected by the oxygen content of the plasma gas. The optimized films were prepared by depositing in 50% oxygen content just below the crystallization temperature. I-V performances exhibited the typical Schottky behavior, both in air and in hydrogen gas. Comparing to the results by sol-gel, it is believed that the electronic defects dominated by the grown process cause the degradation of the sputtered films to H₂ gas detection, and weaken the induced H₂ potential build-up across the space charge layer at the interface.