Thin film multilayer conductor/ferroelectric tunable microwave components for communication applications

Abstract

A study of Au/SrTiO₃/YBa₂Cu₃O_7-δ/LaAlO₃ and(Au,YBa₂Cu₃O_7-δ)/Ba_xSr_1-xTiO₃/LaAlO₃ (x=0, 0.50, and 0.40) multilayered structures is presented. At 1.0 MHz, the largest tuning of Au/SrTiO₃/YBa₂Cu₃O_7-δ parallel plate capacitors corresponded to single-phased, epitaxial 300–500 nm thick SrTiO₃ thin films deposited at 800 °C. For SrTiO₃/LaAlO₃ structures having SrTiO₃ films of similar quality, we observed that at 1.0 MHz and 77 K, interdigital capacitors exhibit higher tunabilities and lower losses than parallel plate configurations, but required higher dc voltage. For a 300 nm thick SrTiO₃ film, a 25 Ω YBa₂Cu₃O_7-δ/SrTiO₃/LaAlO₃ phase shifter exhibited a phase shift ∼2.6 times larger than its Au/SrTiO₃/LaAlO₃ counterpart. At 19 GHz and 32 V, a 360°phase shift could in principle be achieved with coupled microstripline sections only 7.0 mm long. At 14 GHz, 77 K and 260 V, for 1.0 μm and 300 nm thick SrTiO₃ films, 25 Ω 360° Au/SrTiO₃/LaAlO₃ phase shifters would be nominally 4.0 mm and 12 mm long, respectively. For a 2Λ YBa₂Cu₃O_7-δSrTiO₃/LaAlO₃ ring resonator a tuning rate of 0.7 MHz/Volt was achieved at 10 GHz and 77 K. The relevance of these structures for phased array antennas and as tunable elements in discriminator-stabilized oscillators is discussed.

Key Words:

• (HTS, metal)/ferroelectric structures
• tunable microwave components
• dielectric constant
• loss tangent
• parallel plate and interdigital capacitors
• phase shifters
• ring resonators