Fabrication and Investigation of Coplanar Waveguide Based on HTSC / Ferroelectric Thin Film Structures

Abstract

Coplanar waveguide transmission lines were fabricated from YBa₂Cu₃O_7−δ / Ba_xSr_1-xTiO₃ bilayers deposited on 5×5 mm² LaAlO₃ substrates for investigation of the phase shift voltage tuning. As ferroelectric the solid solution Ba_xSr_1-xTiO₃ with x=0.05 (T_c ^f ∼70 K) was chosen. The epitaxial growth of both layers was confirmed by θ–2θ and φ-scan X-Ray Diffraction. At 10.117 GHz a low level of the insertion losses was obtained — less than — 0.5 dB — which evidences for the high-quality of the ferroelectric films and proves that this sort of devices can be successfully used at microwaves. Including a high ε_r ferroelectric layer in the CPW increased the effective dielectric constant and delays of 18–20 ps/mm could be realized. A tunability of several percents was registered — phase shifts of 3–5 degrees at 10.117 GHz, 17 V dc and T = 15–75 K.