SUITABILITY OF SrTiO_3/YBa_2Cu_3O_(7-δ)/LaAlO_3 AND Ba_xSr_(1-x)TiO_3/LaAlO_3 THIN FILM MULTILAYER STRUCTURES FOR TUNABLE MICROWAVE DEVICES

摘要

We report on the characterization of thin film multilayer structures of SrTiO_3/YBa_2Cu_3O_(7-δ)/LaAlO_3 (STO/YBCO/LAO) and Ba_xSr_(1-x)TiO_3/ LaAlO_3 (BSTO/LAO), for x = 0, and x = 0.50, in terms of ferroelectric film deposition, device geometry and tunability. Material properties effects were assessed by varying the ferroelectric deposition temperature from to 800 to 250 ℃. Geometric aspects were considered by testing these structures in the parallel plate and interdigital capacitor configurations. Measurements of the relative dielectric constant (ε_r) and the loss tangent (tanδ) were made as a function of temperature (300 to 20 K), at a frequency of 1.0 MHz, and at dc electric fields from 0 to 3.5×10~5 V/cm. These measurements allowed us to determine (K = (ε_(max) - ε_(min))/rn(ε_(max))×(tanδ)~(-1) ), which is a figure of merit for the tunability to loss ratio of a given component. We observed that interdigital structures exhibited a larger K than parallel plate capacitors, but at the expense of a larger dc bias. Incorporation of a 300 nm thick ferroelectric film between the substrate and the conducting layer of non-tunable microwave components was investigated. The effect of the ferroelectric layer on the performance of a band reject, 20 GHz Au/STO/LAO ring resonator was minimal. Finally, an insertion phase shift of 17.5° and a frequency shift of 90 MHz were measured at 77 K and 20 GHz for Au/STO/LAO interdigital coupled microstrip line and ring resonator, respectively, for a dc bias of 100 V.