Microstructure and hydrogen gas sensitivity of amorphous (Ba,Sr)TiO3 thin film sensors

Ferroelectric (Ba0.67Sr0.33)Ti1.02O3 thin films have been prepared by the sol–gel technology and characterized using TGA, DTA, XRD, TEM, dielectric characterizations, and gas sensing properties. The (Ba0.67Sr0.33)Ti1.02O3 thin film devices are made on Pt-coated Si substrate to detect hydrogen gas and to study gas sensing mechanism. Experimental results show that the diode I–V behavior appears in these Pd/amorphous (Ba,Sr)TiO3 (BST) thin film/metal capacitive devices, and that the enhanced voltage shift as large as 4.5 V at 1042 ppm hydrogen gas in air has been observed. Compared with the available data in the literature, this obtained value of voltage shift in our experiment is about seven times larger than the best one reported under similar testing conditions. It has been clearly shown that the hydrogen-induced voltage shift is closely correlated with the microstructure of ferroelectric thin films and the enhancement of this polarization potential is mainly attributed to the high dielectric constant of amorphous ferroelectric thin films. In this paper, we report our experimental results of this new hydrogen gas sensor and discuss the relationship between microstructure and hydrogen gas sensitivity in these ferroelectric thin film sensors.