Linearity and temperature dependence of large-area processed high-q barium strontium titanate thin-film varactors [Correspondence]

Ba_0.6Sr_0.4TiO₃ (BST) thin-films with large dielectric tunability as high as 4:1 were obtained using a large-area pulsed laser deposition process, with low loss-tangents below 0.01 at zero-bias and 10 GHz. This paper summarizes experimental results obtained on large-area processed BST thin films on 100-mm-diameter sapphire substrates characterized using a varactor shunt switch test structure. Varactors with 0.25-μm-thick BST films exhibited large dielectric tunability, the relative dielectric permittivity at zero bias of 990 tuned to 250 at an electric field of 320 kV/cm. The leakage current through the BST film was below 2 nA up to 6 V dc bias. The quality factor (Q) exceeded 300 at relatively low 6 V dc bias for the BST varactors at 1 GHz. These results confirm that large-area processed BST thin films are ready to compete with semiconductor varactors for commercial applications at RF, microwave, and millimeterwave frequencies.