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Effects of TiO2 buffer layers on the dielectric and tunable properties of Ba0.6Sr0.4TiO3 thin films prepared by pulsed laser deposition

The dielectric properties of Ba0.6Sr0.4TiO3 (BST) thin films were greatly affected by interfacial layers between the electrodes and BST thin films. Our previous work shows that the dielectric loss of the BST system can be decreased by an excess of Ti contents. In this paper, TiO2 buffer layers were grown between BST thin films and the Pt coated silicon substrate, which are expected to improve the interfacial conditions by providing a certain amount of titanium. Both BST and TiO2 films were prepared by pulsed laser deposition. Different substrate temperatures of 550°C, 600°C, 650°C, 700°C and different oxygen pressures of 1mTorr, 10mTorr, and 100mTorr were used for the deposition of TiO2 buffer layers. XRD pattern shows that all the samples have crystallized into the perovskite structure and the (110) peaks become sharper with increasing substrate temperature, indicating better crystallization along this direction. The increased tunability and lower loss of BST thin films with TiO2 buffer layers prepared at the optimized temperature and oxygen pressure achieve about 45.9% and 0.01 at the field of 200kV/cm and 1 MHz. The figure of merit of BST thin films is significantly improved to 45.9 upon using TiO2 buffer layers, which is only about 18.2 for BST thin films prepared directly on the substrates. Our results indicate that TiO2 buffered BST thin films are expected to have better dielectric and tunable properties.