T. J. Jackson

Barium strontium titanate thin film varactors for room-temperature microwave device applications

Recent progress in the development of barium strontium titanate thin film varactors for room temperature tunable microwave devices applications is reviewed, with emphasis on efforts towards the improvement in the quality of BST thin films and the fabrication issues crucial for the performance of microwave devices based on BST varactors. The paper provides examples of tunable microwave devices employing BST varactors. Other thin film materials currently competing with BST thin films are discussed. Topics which deserve further investigation are suggested.

Oxide superconductor and magnetic metal thin film deposition by pulsed laser ablation: a review

A practical review of the use of laser ablation for the deposition of thin films of oxide superconductors and metals is presented. Details of the design and operation of a laser ablation deposition system are discussed, together with the influence of operating parameters such as laser wavelength and power density on the film growth, with the aim of assisting the researcher beginning to use and/or study laser ablation deposition.

Microwave properties of Ba0.5Sr0.5TiO3 thin film coplanar phase shifters

Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45 MHz–50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications.

BST-Varactor Tunable Dual-Mode Filter Using Variable

Ferroelectric materials like barium-strontium-titanate (BST) have become attractive for microwave tunable circuit applications. This letter presents an investigation of BST-varactor tunable dual-mode filter using variable characteristic impedance or ZC transmission line. The interdigital BST varactors are fabricated and modeled, which are then deployed to realize a bandpass filter with tunable bandwidth capability. The use of tunable impedance line provides additional flexibilities in the design of microwave tunable circuits. A tunable bandpass filter of this type with a center frequency of 1.8 GHz and a bandwidth tuning ratio of 1.15:1 is demonstrated experimentally.

{Z}_{C}

Abstract The oxidation state of a metal surface during the initial stages of deposition of an epitaxial oxide buffer layer is discussed from a thermodynamic viewpoint. The basic problem is one of minimizing oxidation of the surface of the metal while ensuring that the buffer layer oxide is able to form in the desired phase. Particular attention is paid to the deposition of CeO 2 , SrTiO 3 and Y 2 O 3 –ZrO 2 (YSZ) onto nickel. Such materials are candidates for use in the production of high- T c coated conductors. Calculation of the Gibbs free energy changes for the oxidation reactions, under various regimes of vacuum and gas supply, suggest conditions which are reducing for the metal oxide but under which the buffer layer oxide remains stable.

Transmission Line

Abstract An overview of recent developments and of the present status concerning low-energy μSR (LE-μSR) at the Paul Scherrer Institute is given. We also discuss some schemes of possible future developments, which are able to improve the potential of the LE-μSR method.

Oxidation thermodynamics of metal substrates during the deposition of buffer layer oxides

This paper presents an investigation of tunable bandstop filter using slotted ground structure. A Barium-Strontium-Titanate (BST) varactor chip is used to tune each resonator and its location is determined by electromagnetic simulation for an optimum frequency tuning. 2-pole bandstop filter is measured at the center frequency from 1.2 to 1.4 GHz and its rejection is more than 15 dB at the stop band while the insertion loss at the pass band is less than 1 dB.

Low-energy μSR at PSI: present and future

Vacancy defects in thin film laser ablated SrTiO3 on SrTiO3 were identified using variable energy positron annihilation lifetime measurements. Strontium vacancy related defects were the dominant positron traps and, apart from in the top ~ 50 nm, were found to be uniformly distributed. The surface layer showed an increase in annihilation from larger open-volume defects, large vacancy clusters or nanovoids.

BST varactor tuned bandstop filter with slotted ground structure

Low energy (16 keV) muons were used to probe the dynamic magnetic behaviour of iron nanoclusters embedded in a silver thin film matrix. The silver film was 500 nm thick and contained a volume fraction of 0.1% iron. Measurements were made in a field of 25 mT, applied normal to the plane of the film, in the temperature range 4.7 K to 300 K. At temperatures above 20 K thermal activation of the cluster moments was seen as a narrowing of the field distribution sensed by the implanted muons. An intrinsic cluster relaxation time of τ0 = 12 ± 4 ns and an activation energy of 51 ± 9 K were deduced from fits to the data. SQUID magnetometry of thicker (1.5 µm) but otherwise identical films on graphite substrates showed the clusters to have a volume of the order of 10-26 m3, from which a cubic anisotropy constant of K = 2.3 ± 0.4 × 105 J m-3 was calculated. Remanence measurements showed no evidence of a preferred orientation for the magnetization of the cluster assembly.

Identification of vacancy defects in a thin film perovskite oxide

Giant magnetoresistance of up to 9.5% in 1.5 T at 14 K has been observed in Co19Cu81, thin films prepared by pulsed laser ablation deposition from rotated, split targets. The as-grown films show a small GMR effect but this may be enhanced by a factor of 4 by appropriate annealing. The volume ratio of material in the target is found to be reproduced in the film. Measurements of the remanence and initial susceptibility of the films indicate a distribution of energy barriers to the rotation of the magnetic moments of the cobalt particles and also the presence of inter-particle interactions. The choice of operating parameters to control these effects and thus optimise the GMR is discussed.