Abstract
The microwave tunable capability and its related material optimization of (Ba,Sr)TiO3 thin films in the parallel-plate capacitor form is discussed in terms of the dependence of barium concentration, acceptor doping and in-plane film stress, based on developed wide GHz-band characterization technique under bias field. The barium-content dependence indicates the tradeoff between tunability and dielectric loss, and the notable field-induced loss in SrTiO3 is confirmed as intrinsic Quasi-Debye contribution. The Mg dopant incorporated into perovskite lattice shows almost no effectiveness for tunable device performance except for enhanced insulation as electron acceptor, while less field-sensitivity of the dielectric loss suggests the possibility of partial occupation of the alkaline-earth ion site by Mg. The reduction of in-plane thermal stress controlled by the sputtering deposition pressure leads to higher permittivity and tunability, while the microwave loss remains unchanged, revealing the applicability of sputtering stress control to the microwave device.
