Low dielectric loss and enhanced tunability of Ba0.6Sr0.4TiO3 based thin films via material compositional design and optimized film processing methods

Low dielectric loss in conjunction with high tunability are simultaneous requirements for tunable device applications which have proved problematic to achieve. In this work, material compositional design and optimized film processing methods were employed to simultaneously lower the dielectric loss and enhance the, dielectric tunability of Ba0.6Sr0.4TiO3 (BST) based thin films without compromising the device impedance matching (epsilon(r)<500) and control voltage (<10 V) requirements. The films compositional design was achieved by Mg doping BST from 3 to 10 mol The Mg doped thin films were fabricated via the metalorganic solution deposition technique using carboxylate-alkoxide precursors and postdeposition annealing in an oxygen ambience at 750 degreesC for 60 min. The films dielectric loss at these doping levels was identical, tan deltasimilar to0.007. In contrast, the films permittivity (339-220), leakage current density (2.55 x 10(-8)- 2.43 x 10(-9) A/cm(2)), tunability (21.3%-5.7%), and grain size (75.2-61.55 nm) were observed to decrease with increasing Mg, concentration levels from 3 to 10 mol %, respectively. Device quality values of tunability, 40% and 32%, for the 3 and 7 mol % doped BST films, respectively, were achieved by elevating the applied bias from 237 to 474 kV/cm. This device quality tuning is compatible with voltage requirements of current semiconductor based systems. Our results suggest that the low level acceptor doping from 3 to 7 mol %, optimized precursor solution concentration (0.43 M), and oxygenated postdeposition thermal processing were found to work in concert to lower dielectric loss, limit defect density concentration, optimize film microstructure, and eliminate undesirable film/electrode interfacial phases. As a result, high quality BST thin films, with their resultant high breakdown fields, were realized. It is the excellent film quality (i.e., optimized composition and microstructure), which allowed the enhanced tunability at elevated dc bias to be achieved without risk of dielectric breakdown. The enhanced dielectric and insulating properties of the 3-7 mol % Mg doped BST thin films make them excellent candidates for integration into tunable devices.