CCVD thin film ferroelectric epitaxy and electrode/biasing structures performance effects on phase shifters and filters

This paper presents the combustion chemical vapor deposition (CCVD) growth and characterization of epitaxial BST films on sapphire. These thin films were used to fabricate phase shifters and tunable filters from 1GHz to 40GHz using planar gap capacitors. A 2:1 tunability was achieved for BST thin films under a DC bias of as low as 10 V and IMD as high as 50dBM can be achieved. Composition has a significant effect on loss and tunability with electrodes and bias structures also participating in performance. Coplanar waveguide (CPW) structures are fabricated onto BST are used to minimize electrode interface and better determine BST properties over frequency. S-parameters of the CPW were tested using a vector network analyzer, with dielectric constant and loss tangent being derived by comparing the measured data with electromagnetic (EM) simulation results. Optimization of the RF circuits, BST and electrodes have resulted in phase shifters with 60 to over 80 degrees/dB, tunable filters with 6 dB to less than 2 dB insertion loss, and good temperature stability.