Susanne Hoffmann

Dielectric properties, leakage behaviour, and resistance degradation of thin films of the solid solution series Ba(Ti1-yZry)O3

Abstract Barium titanate zirconate thin films were grown on Pt-coated Si-substrates by a chemical solution deposition (CSD) method at temperatures of 750°C. The crystal structure and the morphology of these films with respect to the Ti/Zr ratio were studied by means of glancing incidence X-ray diffraction analysis, scanning and transmission electron microscopy. The dielectric properties were analyzed as a function of the composition and the applied electric field. Using transient impedance analysis, the dielectric relaxation, leakage, and resistance degradation of the thin films were investigated with respect to the Ti/Zr ratio. The measurements show that thin films of the composition Ba(Ti0.7Zr0.3)O3 exhibit an improved DRAM charge storage behaviour compared to the pure BaTiO3 films.

A novel integrated thin film capacitor realized by a multilayer ceramic-electrode sandwich structure

Abstract In this work a method will be presented to increase the capacitance of an integrated capacitor per chip area using a sandwich multilayer structure, which is successfully employed for ceramic multilayer capacitors used as surface mount devices. On a Pt coated Si/SiO2 wafer polycrystalline SrTiO3 films deposited by a chemical solution deposition (CSD) method and sputter deposited Pt layers have been alternatingly arranged. Connecting all even Pt electrode layers and all odd, respectively, leads to an equivalent circuit of several high permittivity SrTiO3 thin film capacitors in parallel.

Functional graded high-K (Ba1−xSrx)TiO3 thin films for capacitor structures with low temperature coefficient

Abstract The high dielectric constant of perovskite-type alkaline earth titanates makes them attractive for use in integrated thin film capacitors for microwave circuits. The application temperatures of those devices such as resonators, filters and phase shifters range from cryogenic temperatures for superconducting devices up to 250°C for semiconducting ICs. Significant material modifications have to be introduced to bring the pure components such as BaTiO3 and SrTiO3 into formulations which have a suitable temperature coefficient of the dielectric constant. For conventional powder based industrial processes, usually solid solution adaptations and heterogeneous mixtures are employed. The deposition processes of thin films, especially the low cost Chemical Solution Deposition (CSD) technique, offer the possibility to build thin films of graded compositions. We will show that in those films the composition gradient can be tailored in order to fit the designated temperature characteristics.

Structural and electrical properties of wet-chemically deposited Sr(Ti1-yZry)O3 (y=0…1) thin films

Abstract Polycrystalline thin films of SrTiO3—SrZrO3 solid solutions were prepared along a new wet-chemical deposition route using β—diketone and propandiole as chelating agents. The structural properties of the films were studied by X-ray diffraction analysis, scanning and transmission electron microscopy. The thin film density was correlated with the permittivity using Maxwells dispersion rule. The temperature coefficient of the capacitance as well as the dielectric losses were studied. Using transient impedance analysis, the dielectric relaxation, leakage, and resistance degradation of the thin films were investigated with respect to the Ti/Zr ratio.

High-frequency dielectric response of SrTiO3 crystals, ceramics and thin films

Abstract Far infrared (FIR) soft-mode dielectric responses of bulk SrTiO3 single crystal, flux-grown plate-like crystal, bulk ceramics and several thin films in the 10-300 K range are measured and compared. Huge differences among the samples are observed, particularly below the antiferrodistortive transition, where the soft mode frequency in films and ceramics levels off near - 60 cm−1. The reason for it is connected mainly with internal stresses induced by the transition, however quantitative estimates are missing. Soft mode spectroscopy is shown to be extremely sensitive to the quality of the film.

Far infrared and Raman spectroscopy of ferroelectric soft mode in SrTiO3 thin films and ceramics

Abstract The ferroelectric soft mode behaviour was studied in several SrTiO3 (ST)films on sapphire substrates using far infrared (FIR) transmission measurements and in the bulk ST ceramics using Raman and FIR reflectivity measurements down to 15 K. The recently established dramatic differences in softening and soft mode width compared to single crystal behaviour were confirmed in all the cases. Clear evidence of polar clusterappearance in the pure bulk ceramics indicates that the main reason for the observed differences in thin films are inhomogeneities due to the appearance of polar clusters or even a macroscopic ferroelectric transition at about 130 K in the case of well orientedinjection MOCVD film.

Mechanism Theory in Architecture Education

In mechanical engineering tasks concerning motion and moving parts are very common, thus of course topics like kinematics and mechanism theory are content of teaching in various lectures, exercises and laboratories. At RWTH Aachen University besides mandatory basic courses for all engineering students, continuative courses for students specialized on engineering design or automotive engineering impart profound knowledge. In architecture education the focus lies on the design of buildings in consideration of social, functional, esthetical and statical aspects. Although due to the demand of sustainable and adapting buildings the importance of deployable structures and kinematic parts is increasing, these topics are rarely found in education. Suitable opportunities to bring interested prospective architects in touch with mechanism theory are design projects scheduled for master students. Following an existing cooperation in the research field of foldable structures the Chair of Structures and Structural Design (Faculty of Architecture) and the Department of Mechanism Theory and Dynamics of Machines (Faculty of Mechanical Engineering) offered in the winter semester 2012/13 an interdisciplinary task of designing a foldable bridge to a group of architecture students. The focus of this student project was on the design of a new foldable bridge, but in order to enable the students to solve this unusual task some preliminary activities were performed. The project started with analyses and presentations of existing solutions followed by lectures and workshops providing contents from architecture, arts and mechanism theory. Observations of the project showed that thanks to this preparation students considered kinematic issues as well as architectural ones from the very beginning. The aim of this paper is to present how mechanism theory can be integrated into Interdisciplinary education, which content the authors consider being important for students and which influence can be observed in students’ results.

Faltung und Origami - Prinzipien für Konstruktionen in Architektur und Ingenieurwesen

Prinzip des Faltens ist allgegenwärtig und findet sich in Natur, Alltag, Design sowie in der Technik in einem großen Variantenreichtum. In der Natur wird es sowohl als optimiertes Leichtbauprinzip für immobile, tragende Strukturen als auch für wandelbare oder flexible Konstruktionen eingesetzt. So sind beispielsweise Palmenblätter aufgrund ihrer Struktur aus in Längsrichtung verlaufenden – longitudinal – verlaufenden Falten steife aber zugleich auch nachgiebige und veränderbare sowie sehr robuste Gebilde. Marienkäfer können ihre empfindlichen Flügel schützen, indem sie diese unter die Deckschalen einfalten. Im Alltag begegnen uns Faltstrukturen zum Beispiel als Faltenbälge an Zügen und Bussen. Faltkartons nutzen die Wandelbarkeit des Faltprinzips und lassen sich von einem flächigen in einen voluminösen Zustand überführen. Auch im Ingenieurwesen gibt es Faltungen. In der Bautechnik stellen Wellbleche, Trapezbleche und Spundwandprofile gefaltete Halbzeuge dar, im Fahrzeugbau werden Cabriodächer einund ausgefaltet und die Medizintechnik entwickelt Implantate wie Stents, die in den menschlichen Körper eingeführt werden und sich am endgültigen Bestimmungsort auffalten. Faltungen in der Architektur In der Architektur findet das Prinzip des Faltens Anwendung bei weit gespannten Tragwerken, temporären Bauten und bei Fassadenelementen. Bis in die 80er Jahre des letzten Jahrhunderts wurden zahlreiche großmaßstäbliche Faltwerke aus Beton realisiert. Die geodätischen Kuppeln des Architekten Buckminster Fuller (1895-1983) waren große, aus Kunststoffelementen oder aus Metallblechen zusammengesetzte facettierte Kuppeln, deren Geometrie auf Archimedischen Körpern beruhten und als Raumfaltwerke bezeichnet werden. In der zeitgenössischen Architektur findet dieses Leichtbauprinzip leider nur noch selten – manchmal noch in der Messeoder Ausstellungsarchitektur – Verwendung. Da in Zukunft angesichts sich zusehends verknappender Ressourcen dem Thema materialsparender Konstruktionen eine zentrale Bedeutung zukommen wird, lohnt sich die intensive Auseinandersetzung mit dem Strukturformprinzip der Faltung umso mehr. Faltungen und Origami Prinzipien für Konstruktionen in Architektur und Ingenieurwesen Susanne Hoffmann, Martin Trautz