Epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/ heterostructures grown on LaAlO/sub 3/ substrate by pulsed laser deposition for voltage tunable microwave filter applications

The performance of microwave devices containing electrically tunable layers of strontium titanate has been evaluated for samples produced by pulsed laser ablation over a range of deposition temperatures on [001] LaAlO/sub 3/ substrate. At zero bias the samples which exhibited the highest agility also exhibited the highest loss. It has been observed that the SrTiO/sub 3/ lattice parameter is the relevant parameter in determining both the frequency agility of the sample and its dielectric loss. Furthermore, it was seen that whilst the SrTiO/sub 3/ lattice parameter is dependent on deposition temperature, it has a maximum, and that samples grown at higher/lower temperatures around this maximum exhibit similar electrical properties for similar lattice parameter. A sample was then processed by a high temperature annealing of the SrTiO/sub 3/ layer prior to YBCO deposition and it was found that dielectric loss is reduced over the whole range of agility without deterioration of the frequency agility.