Florian Paul

Influence of Fe–F-co-doping on the dielectric properties of Ba0.6Sr0.4TiO3 thick-films

Abstract The influence of Fe acceptor and Fe – F acceptor – donor co-doping on the dielectric response of screen-printed Ba0.6 Sr0.4 TiO3 thick-films on alumina substrates has been investigated. The Ba0.6 Sr0.4 TiO3 powders were synthesized by freeze-drying of sols. Permittivity, dielectric loss, and tunability were investigated at kHz frequencies with a planar metal-insulator-metal capacitor structure, and at GHz frequencies up to 40 GHz using coplanar waveguide structures. Pure acceptor doping by Fe was found to have a distinct influence on permittivity and dielectric loss-factor at kHz-frequencies and at GHz frequencies due to an internal bias field and pairs of associated defects. Co-doping with F significantly suppresses the influence of the internal bias field and defect-associates at low and microwave frequencies. The commutation quality factor at 10 GHz and Eeff = 5.8 V μm-1 was increased by co-doping the thick-films with Fe and F. Such doped Ba0.6 Sr0.4 TiO3 films show a high potential for tunable microwave applications.

Barium strontium titanate thick-films: dependency between dielectric performance and their morphology

The paper is focused on the influence of the morphology of barium strontium titanate (BST) thick-films on their effective dielectric properties. Therefore two BST thick-films are made with a minor deviation in sinter temperature, and hence their mean grain size of the films and their sintering necks. By modeling the meso-structure using a Nonlinear 3D Finite-Difference Time-Domain field solver the assumed effect of the morphology on the effective dielectric properties are confirmed. The simulation results show the potential for a further improvement of the dielectric tunability of BST thick-films.

Tunable dielectrics for microwave applications

This paper gives a short introduction into tunable dielectrics for microwave applications based on nematic liquid crystal and Barium-Strontium-Titanate (BST) thin- and thick-films. Due to their tuning voltage dependent electromagnetic properties, both are very promising material candidates for tunable passives in the microwave and millimeter-wave regions. For applications, such as frequency-agile communications and sensor systems we illustrate the challenges of optimization BST films based on a multi-scale view for material, processing, device and application design.

Thickness variation of electrophoretically deposited strontium titanate films for photoelectrochemical energy conversion

Photoelectrochemical cells consisting of strontium titanate (SrTiO3) films on nickel substrates in potassium hydroxide electrolyte have been developed. SrTiO3 film thicknesses in the range of 1 μm–8 μm have been realized by electrophoretic deposition (EPD). The EPD process enables to produce such films in only 12 s with very high reproducibility. The samples have been studied with the focus on their photocurrents under illumination with different wavelengths. Samples with a film thickness of 5 μm show the best performance, because the trade-off between high absorption and low recombination is highest. Under 365 nm illumination, these samples show light to current efficiencies of 8% and external quantum efficiencies of 23.6%.

Distribution of the Local Electric Field during Electrophoretic Deposition of an Alumina Suspension on a Membrane

The spatially distributed local electric field strength during the electrophoretic deposition (EPD) of alumina suspensions on a membrane is within the scope of the present article. The water-based alumina suspensions were optimized in order to achieve stable suspensions, high deposition rates and maximum green densities of the deposited bodies. In-situ measurements of the local potential drop inside the EPD-cell were carried out using a computer assisted process control set-up with electronic data acquisition. The behaviour of the spatial- and time-dependent electric field distribution was calculated from measured potential drops. The influence of varrying input voltages on the output parameters, such as deposition rate and green density for EPD on membranes was investigated and is discussed. It is shown that the distribution of the local electric field depends on the applied voltage and on time for the case of higher voltages. A dependance of the local electrical fields on the deposition rate is suggested as well.