Fabrication and characterization of doped barium strontium titanate thin films for tunable device applications

Summary form only given. Barium strontium titanate (BST) is a promising material for tunable microwave devices such as phase shifters. The tunability of this material arises because dielectric constant varies with application of an electric field. Tunable low loss (tan δ=0.006) bulk ceramic BST/MgO composite phase shifter materials have been demonstrated at 10 GHz. Utilization of these BST/MgO materials as phase shifting elements in this bulk ceramic form, is still quite limited due to the large voltages, of the order of 1000 V, needed to bias these bulk materials in a microstrip geometry. However, fabrication of this BST/MgO based material in the thin film form, reduces the needed bias voltages to less than 10 V, which is compatible with the voltage requirements of present semiconductor based systems. Additionally, the thin film material regime allows high frequency device operation (>15 GHz) thereby enhancing the S/N ratio and direct integration opportunities with other semiconductor components and devices. This investigation reports on the evolution of the dielectric, insulating, structural and microstructural properties of metalorganic decomposition (MOD) fabricated dope BST thin films as a function of film composition. Our results demonstrated that dielectric loss, tunability, leakage current, and film microstructure changed significantly as a function of dopant concentration. The details of the dielectric, electrical, microstructural, and compositional properties are examined, correlated and discussed. Additionally, the trade-off between film composition, tunability and dielectric loss is evaluated for phase shifter applications.