Ba_xSr_{1 − x}TiO₃ Thin Films for Tunable Microwave Devices in Cryogenic and Room Temperature Application

Abstract

The microwave properties of YBCO/Ba _0.05 Sr _0.95 TiO ₃ (BST5) and Ag/Ba _0.5 Sr _0.5 TiO ₃ (BST50) films were characterized at 80 K and 290 K. At zero bias, the BST5 had a permittivity of 400 and a loss tangent of 0.02; the BST50 had a permittivity of 900 and a loss tangent of 0.1. The respective tunabilities at 3.6 V μ m^{− 1} were 15% and 44%. Analysis of the performance of phase shifters and tunable filters based on these films showed that both conductor and dielectric losses need to be considered in the selection of materials for devices. A high tunability alone does not guarantee good performance.

Keywords:

• BST thin film
• ferroelectric
• phase shifter
• tunable filter

Acknowledgment

The authors wish to acknowledge the UK Engineering and Physical Science Research Council (EPSRC) for financial support under GR/S60471/01, funding from Australia Swinburne University of Technology under the Researcher Development Scheme and the assistance of Donna Holdom in sample lithography.