The development of radio frequency integrated circuits (RFICs), especially the dream of integrating analog, digital and radio frequency (RF) components on the same chip that is commonly known as System-on-a-Chip (SoC), is crucial to mobile communications of the future. Such SoC approach offers enhanced performance, greater reliability, and substantially less power consumption of integrated circuits while reducing overall physical size and thus manufacturing cost. However, the progress has been stalled by the lack of miniaturized inductor elements. Rise of unwanted parasitic effects limits down-scaling of the inductor structures and leaves the use of magnetic coating as a viable and attractive option to enhance the inductance and thus inductance density. It is also essential to shift from perm alloy and other amorphous alloys to ferrites and hex ferrites as the core material because of their very high electrical resistivity so as to keep losses in check, a criterion that cannot be compromised on in GHz frequency applications. This is viable, however, only if the integration of the magnetic core (film), particularly a ferrite film, is fully compatible with the CMOS fabrication process. Various approaches have been taken to meet this requirement, including investigations of employing layers of ferrite materials to envelop the inductor loop. However, the deposition of thin films of ferrites, whether by PVD or CVD, usually calls for the deposited ferrite layer to be annealed at an elevated temperature to crystallize the layer so that its magnetic characteristics are appropriate for the optimum performance of the circuit element. Such annealing is incompatible with CMOS process flow required for aggressive device geometries, as the inductor element is added after the active semiconductor circuit is processed, and any exposure of the processed circuit to elevated temperatures risks disturbing precise doping profiles employed and the integrity of the inter-layer dielectrics. What is called for is a low-temperature process for the deposition of a ferrite layer on top of the patterned inductor element – a layer of thickness such that most of the fringe field is encapsulated – while ensuring that the layer comprises crystallites of uniform size that leads to uniform magnetic behaviour. Recognizing the difficulty of meeting the various stringent requirements, it has recently been remarked that such a goal is a formidable challenge. In an attempt to address this challenge, in this work, we have adopted a counter-intuitive approach - the deposition of the desired ferrite composition on a processed die (that contains the inductor structures along with active semiconductor circuits) by immersing it into a chemical (reactant) solution, followed by a brief irradiation of microwave frequency. However, to identify the desired ferrite composition and the appropriate recipe to deposit them, a systematic effort had to be made first, to understand the inter-relationship between synthesis process, structure of resulting material, and its physical and chemical properties. Therefore, at the beginning, a general introduction in which key concepts related to the magnetic-core inductors, the microwave-irradiation-assisted synthesis of nanostructures, the ‗state of the art‘ in the field of integration of appropriate magnetic material to the RFICs, are all outlined. As a proof of concept, microwave-irradiation-assisted solution-based deposition of zinc ferrite thin films on the technologically important Si (100) substrate is demonstrated. The highlight of the process is the use of only non-toxic metal organic precursors and aqua-alcoholic solvents for the synthesis, which is complete in 10 minutes @< 100 °C, without any poisonous by-products. Effects of various process parameters such as solute concentrations, surfactant types, and their concentrations are investigated. A wide range of deposition rates (10 - 2000 nm/min) has been achieved by tweaking the process parameters. The simultaneous formation of zinc ferrite nanocrystallites (ZFNC) along with deposition of thin film is the hallmark of this synthesis technique. Unlike its bulk counterpart, both film and powder are found upon investigation to be rich in magnetic behavior– owing to plausible cationic distribution in the crystal lattice, induced by the inherently quick and far-from-equilibrium nature of the process. The accurate estimation of magnetic characteristics in film is, however, found to be difficult due to the high substrate-to-film mass ratio. The simultaneously prepared ZFNC is examined to arrive at the optimized process recipe that imparts the desired magnetic properties to the zinc ferrite system. The crystallographic cationic distribution in zinc ferrite powder is, however, difficult to study due to the nanoscale dimension of the as prepared material. To enable crystal growth, slow and rapid annealing in air at two different temperatures are employed. The effects of these annealing schemes on various attributes (magnetic properties in particular) are studied. Rapid annealing turns out to be an interesting pathway to promote rapid grain-growth without disturbing the crystallographic site occupancies. The presence of inversion, i.e., the amount of Fe3+ in the ‗A‘-sites in the spinel structure that ideally is zero in normal spinel structure of zinc ferrite, is evident in all annealed ZFNC, as determined by Riveted analysis. Such partially inverted ZFNC exhibits soft magnetic behavior with high saturation magnetization, which can easily be ―tuned‖ by choosing appropriate annealing conditions. However, a few unique strategic modifications to the same microwave-irradiation-assisted solution-based synthesis technique are tried for the formation of nanocrystalline powder with desired sizes and properties without the necessity of anneal. The approach eventually appears to pave a way for the formation of oriented structures of zinc ferrite. The effects of anneal, nevertheless, are studied with the help of neutron powder diffractometry and magnetic measurements. The magnetic ordering at various temperatures is analyzed and connected to the magnetic measurements. The study shows that long-range magnetic ordering, present even at room temperate, originates from the distribution of cations in the partially inverted spinel structures, induced by the rapid and kinetically driven microwave synthesis. Keeping the mild nature (<200 °C) of the processing in mind, a large degree of inversion (~0.5) is a surprise and results in a very high saturation magnetization, as much as 30 emu/g at room temperature (paramagnetic in bulk), in the ZFNC system. Based on the knowledge of process-structure-property interrelationship, a recipe for the deposition of ferrite thin films by the microwave-assisted deposition technique is optimized. Successful deposition of smooth and uniform zinc ferrite thin films on various substrates is, then, demonstrated. The mystery behind the strong adherence of the film to the substrate - an unexpected outcome of a low-temperature process - is probed by XPS and the formation of silicates at the interface is identified as the probable reason. The uniformity and consistency of film composition is also examined in this chapter. Another salient feature of the process is its capability to coat any complex geometry conformally, allowing the possibility of depositing the material in a way to ―wrap around‖ the three-dimensional inductor structures of RF-CMOS. Integration of nanostructure zinc ferrite thin films onto on-chip spiral inductor structures has been demonstrated successfully. The magnetic-core inductors so obtained exhibit the highest inductance density (700 nH/mm2) and the highest Q factor (~20), reported to date, operate at 5 GHz and above, by far the highest reported to date. An increase in inductance density of as much as 20% was achieved with the use of just 1 µm thick film of zinc ferrite covering only the ―top‖ of the spiral structure, i.e., up to 20% of chip real estate can potentially be freed to provide additional functionality. The microwave-assisted solution-based deposition process described in this thesis is meant for ‗post-CMOS‘ processing, wherein the film deposited on some specific electronic components can add desired functionality to or improve the performance of a component (circuit) underneath. However, the effect of such ‗post-CMOS‘ processing on the active MOS devices, interconnects, and even inter-layer-dielectrics fabricated prior to the deposition has to be mild enough to leave the performance of delicate MOS characteristics intact. Such CMOS-compatibility of the present deposition process has been tested with a satisfactorily positive result.

[pt] No presente trabalho foi feita inicialmente uma revisão bibliográfica sobre a formação e redução da ferrita de zinco. Em seguida fez-se um estudo cinético e termodinâmico da sua formação a partir da mistura dos óxidos de ferro puro, Fe2O3 e de zinco puro, ZnO, em proporção mássica estequiométrica ã do composto Fe2O3/ZnO = 2/1, considerando que este composto tem sido considerado como o constituinte de maior porcentagem em peso nos pós de aciaria elétrica (fornos elétricos a arco).A ferrita de zinco, que geralmente se forma no aquecimento de diferentes proporções de misturas dos óxidos constituintes, incluindo a estequiométrica, foi caracterizada térmica (DTA-TGA) e estruturalmente (XRD). A temperatura onde começou a se formar a ferrita de zinco e os resultados quantitativos das conversões da sua síntese, foram calculadas pelo software Topas 2,1 Difracc Plus, usando o método Reitveld XRD. Os seguintes resultados da análise cinética da formação de ferrita de zinco, foram obtidos; a baixas temperaturas (650-730 graus Celsius) as conversões obtidas ajustaram-se ao modelo de reação de interface ou modelo topoquímico, sendo a reação química o mecanismo de controle obtendo-se uma Ea = 65,6 kcal / mol e um k = 2,32 x 10-3 K-1 ; nas altas temperaturas (750 - 1000 graus Celsius) o ajuste ao modelo de crescimento populacional modificado, foi o mais adequado, sendo o mecanismo de controle o difusional e obtendo-se uma Ea =16,1 kcal /mol e k = 570 K -1. Finalmente encontrou-se um estágio de transição entre os dois mecanismos numa temperatura aproximada de 745 graus Celsius (controle misto). Foram gerados vários diagramas operacionais de predominância de fases (DOPF)necessários para orientar os trabalhos perimentais. Estes diagramas consistiram de uma análise termodinâmica da redução de misturas de ZnO e Fe2O3 pelos gases redutores CO e H2, focando primordialmente à formação e a redução da ferrita de zinco. Foram utilizados os seguintes software: HSC versão 5,0 e Mathcad versão 6,0. Os resultados desta avaliação foram os DOPF dos seguintes sistemas: Zn-C-O, Zn-H-O, Zn-C-H-O, Fe-C-H-O e Zn-Fe-C-H- O com a variação das atividades de suas fases metálicas e de seus óxidos. / [en] The present work includes initially a bibliographical revision on the formation and reduction of the zinc ferrite. Further a thermodynamic and kinetic study was made, focusing its formation from an equimolar mixture of pure iron oxide Fe2O3, and pure zinc oxide ZnO, due to the fact that this substance is often the major constituent in the electric arc furnace dust. The zinc ferrite that is formed during the operation of the electric arc furnaces doesn t necessarily results from an equimolar mixture; it could be produced from a wide range of constituents compositions. Initially the equimolar mixture was characterized thermally (DTA-TGA) and structurally (XRD). The temperature where this compound began its formation and the quantitative results regarding the zinc ferrite synthesis conversion were calculated by the software Topas 2,1 Difracc Plus, using the Reitveld XRD method. The following experimental results from the kinetic analysis of the zinc ferrite formation were obtained: at low temperatures (650-730 Celsius Degree) the phenomena fitted the interface reaction model, or topochemical model, being the chemical reaction the control mechanism. The obtained data in this case was: Ea equal 65,6 kcal / mol and k equal 2,32 x 10-3 K-1. On the other hand, at high temperatures (750-1000 Celsius Degree) the modified population growth formalism showed the best fit, being the diffusional mechanism the controlling process. Again the obtained data was: Ea equal 16,1 kcal / mol and k equal 570 K-1. Finally a transition between the two mechanisms was found to happen at approximate 744 Celsius Degree (mixed control). Several DOPF (phase predominance operational diagrams) were obtained based upon the thermodynamic analysis of the Fe2O3 - ZnO mixtures reduction driven by CO and H2 reducing gases, focusing the formation and reduction of zinc ferrite compound. For that purpose the softwares HSC 5,0 and MathCAD 6,0 were utilized. The DOPF for the systems: Zn-C-O, Zn-H-O, Zn-C-H- O, Fe-C-H-O and Zn-Fe-C-H-O, considering the activities of their metallic and their oxides phases, were generated and discussed.

[pt] O presente estudo foca o comportamento da redução da ferrita de zinco produzida em laboratório e a contida nos pós de aciaria elétrica (PAE) pelo CO puro e misturas COCO2, esta última tomada como exemplo de um caso real. Este trabalho se iniciou com a caracterização dos principais compostos presentes no PAE (óxido de ferro (III), óxido de zinco e ferrita de zinco) usando técnicas, metodologias e equipamentos para caracterizações térmica (ATD-ATG), estrutural (DRX), microscópica (MEV-MET analise de EDS), física (porosidade do briquete, massa especifica, tamanho médio e área superficial específica das partículas) e química. Constatou-se que as partículas dos materiais estudados são predominantemente de geometria esférica e, em particular o estudo via MET da ferrita de zinco, revelou aglomerados micrométricos e homogêneos tipo clusters, formados por partículas arredondadas e constituídas por alguns monocristais com tamanhos da ordem de 100 nm. Com a finalidade de estudar a cinética de redução da ferrita de zinco, foram realizados ensaios de redução por CO puro e misturas gasosas formadas por: 75 por cento CO-25 por cento CO2 e 50 por cento CO-50 por cento CO2 nas temperaturas de 1073, 1173, 1223, 1273 e 1373K. O tempo máximo de redução foi de 105 min. Os resultados obtidos permitiram propor uma sequência cinética de redução, ao longo da qual os principais produtos de redução da ferrita de zinco foram caracterizados via MEV, visando estabelecer a fenomenologia/morfologia da redução. Conclui-se que a fenomenologia morfológica e cinética da redução da ferrita de zinco, embora complexa, é similar a da redução dos óxidos de ferro, dependendo das composições gasosas, temperatura e tempo de reação. O estudo morfológico permitiu constatar que a redução da ferrita de zinco evidencia sua decomposição nos óxidos constituintes (ZnO e Fe2O3), na faixa de 1073 a 1273K e a redução sequencial do óxido de zinco e dos óxidos de ferro. Os típicos produtos sólidos da redução são: óxido de zinco (ZnO), wüstita (FeO), óxidos mistos do tipo (Zn, Fe)O e ferro metálico. O estudo cinético estabeleceu ainda que ocorre uma rápida redução do óxido de zinco, liberando zinco gasoso, evidenciando a seguinte sequência de redução: primeiramente, o óxido de zinco se reduz, seguido dos óxidos de ferro. Isto ocorre significativamente nas temperaturas entre 1223 e 1373K. Estabeleceu-se um modelo geral de redução da ferrita de zinco usando a metodologia de superfície resposta (RSM), que envolveu o planejamento estatístico fatorial 3(4) para avaliar a influência dos fatores preestabelecidos sobre a (porcentagem) Redução (temperatura e tempo de reação, composição gasosa, e massa da amostra). Os modelos cinéticos que melhor ajustaram os mecanismos de redução foram: o modelo de reação química de interface-simetria esférica, seguido pelo modelo exponencial de reação contínua, representados por: [1 - raiz cúbica de (1 -alfa)] = kt e −ln(1 -alfa) igual a kt , respectivamente. O modelo de reação química de interface - simetria esférica, representado por: [1 - raiz cúbica de (1 - alfa)] = kt foi o que melhor adequou-se à redução da ferrita de zinco sintética. Os parâmetros cinéticos obtidos foram: (a) 100 por cento CO: Ea de 55,60 kJ/mol e A igual a 8,833 mHz; (b) 75 por cento CO-25 por cento CO2: Ea igual a 88,21 kJ/mol e A igual a 127,74 mHz; (c) 50 por cento CO-50 por cento CO2: Ea igual a 95,21 kJ/mol e A igual a 193,37 mHz; De maneira similar, no caso da redução da ferrita de zinco presente no PAE, o modelo que melhor representou o processo, também foi o modelo de reação química de interface - simetria esférica, representado por: [1 - raiz cúbica de (1 - alfa)] igual a kt , sendo, Ea (energia de ativação aparente) e A (constante pré-exponencial de Arrhenius), os parâmetros cinéticos obtidos: (d) 100 por cento CO: Ea igual a 52,34 kJ/mol, e A igual a 4,98 mHz; (b) 75 por cento CO-25 por cento CO2: Ea igual a 66,70 kJ/mol e A igual a 76,06 mHz; (c) 50 por cento CO-50 por cento CO2: Ea igual a 86,28 kJ/mol e A igual a 289,59 mHz. A comparação entre as energias de ativação aparente, permitiu concluir que tanto a redução da ferrita de zinco sintética como a redução dos Pós de Aciaria Elétrica-PAE, tiveram como etapa controladora da reação global a redução dos óxidos de ferro, particularmente para a redução com 100 por cento CO. No caso da redução com misturas COCO2, isto não foi observado para a ferrita de zinco sintética, embora possa ser válida para os Pós de Aciaria Elétrica-PAE, considerando seu baixo teor de zinco. Assim, para o caso da redução da ferrita de zinco por misturas CO-CO2, propõe-se como etapa controladora a redução simultânea do óxido de zinco e dos óxidos de ferro. / [en] This work deals with the behavior of the synthetic zinc ferrite reduction as well as a case study for the same process using electric arc furnace dusts (EAFD). These processes were conducted under pure CO atmosphere and CO-CO2 gas mixtures. The research here reported onsets with the characterization of the compounds present in EAFD - Iron (III) oxide, zinc oxide and zinc ferrite - using techniques, methodologies and equipments for thermal characterization (DTA-TGA), structural (XRD), microscopic (SEM-TEM coupled to EDS), physical (briquette porosity, specific gravity, average size and particle specific surface) and chemical analysis. It was found that the studied materials particles showed predominantly spherical geometry and in particular, the TEM scans in the zinc ferrite, reveled cluster type micrometric and homogeneous agglomerates formed from single crystal round particles having the size of circa 100 nm. Aiming at the study of the kinetics of the zinc ferrite reduction experiments were conducted using synthetic and EAFD materials submitted to pure CO gas and mixtures of it with CO2 in the following proportions: 75 per cent CO-25 per cent CO2 e 50 per cent CO-50 per cent CO2. The runs were conducted at the temperatures 1073, 1173, 1223, 1273 e 1373K and the maximum reaction time was 105 min. The obtained results permitted the proposal of a kinetic reduction reaction chain. In the course of the study, also, the main zinc ferrite reduction products were characterized by the SEM analysis. This analysis also permitted the observation of phenomenological and morphological correlations during the process. It was concluded that the morphological and kinetic zinc ferrite reduction, in spite being a complex process, it is similar to iron oxides reduction, meaning, dependent on the gaseous compositions, temperature and reaction times. The morphological prism permitted to propose that the zinc ferrite reduction denounces its instantaneous decomposition in their constituent oxides (ZnO and Fe2O3) when submitted to temperatures in the range of 1073 to 1273K and also the sequential reduction of zinc and iron oxides. The typical reduction products were zinc oxide (ZnO), wüstite (FeO) and mix oxides type (Zn, Fe) O and metallic iron. Again, the kinetic study established that a rapid reduction of the zinc oxide occurs, as compared to the other present oxides, through the sequence: firstly the zinc oxide reduction takes place, and this is followed by the iron oxides reduction. The last processes occur significantly for temperatures in the range of circa 1223 to 1373K. A general model of the zinc ferrite reduction by the gaseous mixture of CO-CO2 was proposed using the response surface methodology (RSM) for the factorial analysis 3(4). This was done evaluating the effect of the following variables: temperature, reducing atmosphere composition, specimen mass and reaction time over the (percentage)Reduction. The kinetic models that presented the better adjustment for the reduction were the boundary chemical reaction model for spherical symmetry (BCRM ss) with the equation [1 - cubic root (1 - alfa)] equal kt and the model of simple exponential continuous reaction obeying the relation: − ln(1 - alfa) equal kt . The kinetic parameters obtained (Ea, apparent activation energy, and A, Arrhenius preexponential frequency fator) were for the first model, that is synthetic zinc ferrite: (a) 100 per cent CO gas: Ea equal 55,60 kJ/mol & A equal 8,83 mHz; (b) 75 per cent CO-25 per cent CO2: Ea equal 88,21 kJ/mol and Aequal 127,74 mHz; (c) 50 per cent CO-50 per cent CO2: Ea equal 95,21 kJ/mol and A equal 193,37 mHz. And for the second material, zinc ferrite contained in the EAF dusts: (a) 100 per cent CO gas: Ea equal 52,34 kJ/mol and A equal 4,98 mHz; (b) 75 per cent CO-25 per cent CO2: Ea equal 66,70 kJ/mol and A equal 76,06 mHz; (c) 50 per cent CO-50 per cent CO2: Ea equal 86,28 kJ/mol and A equal 289,59 mHz. The comparison between the apparent activation energy obtained from the best fitting kinetic models permitted to conclude that the zinc ferrite reduction as well as the electric arc furnace dusts reduction global reactions rates are controlled by iron oxides reduction, this in particular for the case of the reduction with 100 per cent CO. As for the reduction with the CO-CO2 gas mixtures, this was not observed for the synthetic zinc ferrite, although, for the reduction of the electric arc furnace dust, this could be the case due to their low zinc content. Considering these facts and the experimental results of this work, it is suggested that the zinc ferrite reduction by CO-CO2 gas mixtures has the global reaction rate controlled simultaneously by the reduction of both zinc and iron oxides.

Nickel zinc ferrites (NZF) have been considered as one of the basic components in high frequency electromagnetic applications especially in the field of telecommunications. In the present study, the aim was to produce high quality nickel zinc ferrite ceramics at low soaking temperatures. For this purpose, conventional ceramic manufacturing method based on mixed oxide precursors was followed using calcium fluoride, CaF2, as sintering additive. During the sintering studies, it was noticed that both the microstructure and the electromagnetic properties of the NZF ceramics were modified to a great extent by CaF2. Therefore, material characterization studies involving microstructural, dielectric and magnetic properties were conducted with respect to CaF2 content of ceramics and soak duration. The results showed that due to the presence of CaF2 in ceramics, significant improvements were achieved not only in kinetics of sintering but also in the parameters / DC electrical resistivity, dielectric constant and dielectric loss factor. For example, 1.0 wt% CaF2 added NZF ceramic produced in this study had a DC electrical resistivity of 1011 &amp / #61527 / -cm which was 100,000 times bigger than the one attained in pure NZF ceramic. On the other hand, the dielectric constant exhibited a flat behavior up to 40 MHz with a value around 16. In addition, no resonance peak was observed in dielectric loss factor spectra, and the typical values of dielectric loss factor lied below 0.01. Besides the achievements mentioned, the magnetic properties such as relative magnetic loss factor and hysteresis parameters were also improved.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work, zinc ferrite oxide was performed (ZnFe2O4) was synthesized by the solvothermal conventional method and the microwave-assisted solvothermal route. The influence of different synthesis as well as their variables on the physical properties of the material were investigated. The powders were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption/desorption measurements by the Brunauer-Emmett-Teller method (BET), and atomic force microscopy (AFM). The produced ferrite was used as catalyst and its activity was investigated in the photo-Fenton reaction for the degradation of textile organic dye (Procion Red H-E7b) under visible light irradiation. In the experiments, different process variables such as dye and hydrogen peroxide concentrations, pH and reaction time were analyzed. The rate constants for the photo-Fenton reactions were determined for both materials prepared by different routes. The synthesis results demonstrated the formation of particles with different physical properties such as surface area, pore volume and size. The experiments of photo-Fenton reaction indicated that the materials prepared in this work present satisfactory activity for the degradation of organic pollutant, 97% de decolorization and 60% de mineralization, in aqueous solution. All studied variables of the reaction process significantly influenced on the catalytic process. / Neste trabalho, foi realizada a síntese do óxido ferrita de zinco (ZnFe2O4) pelo método solvotérmico convencional e pela rota solvotérmica assistida por microondas. A influência das diferentes rotas de síntese, bem como de suas variáveis de síntese sobre as propriedades físicas do material foi investigada. Os pós obtidos foram caracterizados por difração de raios-X (DRX), espectroscopia no infravermelho (FTIR), medições de adsorção-dessorção de nitrogênio pelo método Brunauer-Emmett-Teller (BET), e microscopia de força atômica (MFA). A ferrita produzida foi usada como catalisador e sua atividade foi investigada na reação de foto-Fenton para a degradação de um corante orgânico têxtil (Vermelho Procion H-E7B) sob irradiação de luz visível. Nos experimentos, foram analisadas diferentes variáveis de processo, tais como concentrações de corante e peróxido de hidrogênio, pH e tempo. As constantes de velocidade das reações de foto-Fenton foram determinadas para ambos os materiais preparados pelas diferentes rotas. Os resultados das sínteses demonstraram a obtenção de partículas com diferentes propriedades físicas, tais como área superficial, volume e tamanho de poros. Os testes da reação foto-Fenton indicaram que o material preparado neste trabalho apresenta satisfatória atividade para a degradação do poluente orgânico, até 97% de remoção de cor e 60% de mineralização, em solução aquosa. Todas as variáveis do processo reacional estudadas influenciaram significativamente no processo catalítico.

Die vorliegende Arbeit befasst sich mit magnetischen Tunnelkontakten (magnetic tunnel junctions, MTJs) auf Basis des Oxids Zinkferrit (ZnxFe3-xO4). Dabei soll das Potential dieses Materials durch die Demonstration des Tunnelmagnetowiderstandes (tunnel magnetoresistance, TMR) in zinkferritbasierten Tunnelkontakten gezeigt werden. Dazu wurde ein Probendesign für MTJs auf Basis der „pseudo spin valve“-Geometrie entwickelt. Die Basis für dieseStrukturen ist ein Dünnfilmstapel aus MgO (Substrat) / TiN / ZnxFe3-xO4 / MgO / Co. Dieser ist mittels gepulster Laserabscheidung (pulsed laser deposition, PLD) hergestellt. Im Rahmen dieser Arbeit wurden die strukturellen, elektrischen und magnetischen Eigenschaften der Dünnfilme untersucht. Des weiteren wurden die fertig prozessierten MTJ-Bauelemente an einem im Rahmen dieser Arbeit entwickeltem und aufgebautem TMR-Messplatz vermessen. Dabei ist es gelungen einen TMR-Effekt von 0.5% in ZnxFe3-xO4-basierten MTJs nachzuweisen. Das erste Kapitel der Arbeit gibt eine Einführung in die spintronischen Effekte Riesenmagnetowiderstand (giant magnetoresistance, GMR) und Tunnelmagnetowiderstand (TMR). Deren technologische Anwendungen sowie die grundlegenden physikalischen Effekte und Modelle werden diskutiert. Das zweite Kapitel gibt eine Übersicht über die Materialklasse der spinellartigen Ferrite. Der Fokus liegt auf den Materialien Magnetit (Fe3O4) sowie Zinkferrit (ZnxFe3-xO4). Die physikalischen Modelle zur Beschreibung der strukturellen, magnetischen und elektrischen Eigenschaften dieser Materialien werden dargelegt sowie ein Literaturüberblick über experimentelle und theoretische Arbeiten gegeben. Im dritten Kapitel werden die im Rahmen dieser Arbeit verwendeten Probenpräparations- und Charakterisierungsmethoden vorgestellt und technische Details sowie physikalische Grundlagen erläutert. Die Entwicklung eines neuen Probendesigns zum Nachweis des TMR-Effekts in ZnxFe3-xO4-basierten MTJs ist Gegenstand des vierten Kapitels. Die Entwicklung des Probenaufbaus sowie die daraus resultierende Probenprozessierung werden beschrieben. Die beiden letzten Kapitel befassen sich mit der strukturellen, elektrischen und magnetischen Charakterisierung der mittels PLD abgeschiedenen Dünnfilme sowie der Tunnelkontaktstrukturen.

La miniaturisation des antennes s'accompagne d'une dégradation leurs performances (bande passante, gain, efficacité), surtout avec l'utilisation de substrats matériaux diélectriques. Pour relever le défi « intégration / performances », la conception de nouveaux matériaux tels que les ferrites magnétoélectriques constitue une alternative des plus prometteuses. Ce travail met en avant les principaux paramètres à l'élaboration de ferrite spinelle par coprécipitation. Un traitement thermique modéré a permis l'obtention de céramiques semi poreuses pour la montée en fréquence. En parallèle, l'anisotropie magnétocristalline, liée à la composition (rapport Nickel / Zinc, Cobalt, Fer 2+…) ; ainsi que l'anisotropie magnétoélastique lors de l'application d'une contrainte, étendent encore le domaine des faibles pertes des ferrites de Nickel-Zinc de 400 MHz à plus de 1 GHz. Ces matériaux ont ainsi pu équiper des antennes sur les fréquences du DVH-H (470 – 830 MHz) et répondent aux normes du DVB-H. De façon à profiter pleinement de la miniaturisation, nous avons proposé une antenne imprimée. Une bonne corrélation est trouvée entre les résultats de simulation et de mesure, ainsi que des relations adaptées aux antennes patch. Enfin dans le domaine émergent des communications On / Off bodies, nous avons développé des antennes flexibles sur un substrat de type PDMS. Pour assurer une bonne efficacité de l'antenne, celle-ci est encapsulée, ce qui évite une métallisation hasardeuse (fissures, manque d'adhérence). / Antenna miniaturization, especially with dielectric substrates, is accompanied by a radiation loss (bandwidth, gain, efficiency). To meet the challenge "integration / performance", the design of new materials such as magnetodielectrics ferrites is a promising alternative. To satisfy these requirements, this work highlights the main parameters of ferrite spinel development by coprecipitation. A moderate thermal treatment leads to semi porous ceramics. In parallel, the magnetocrystalline anisotropy, related to the composition (ratio Nickel / Zinc, Cobalt, Iron 2+ ...), and the magnetoelastic anisotropy with application of stress, extend the field of low-loss from 400 MHz to over 1 GHz, in the Nickel-Zinc ferrite. These materials were able to equip antennas on DVH-H frequencies (470-830 MHz). In order to take full advantage of miniaturization, we proposed a printed antenna. A good correlation between simulation results and measurement is obtained, together with relations adapted to patch antennas. Finally, in the emerging field of communications On / Off bodies, we have developed flexible antennas on PDMS substrate. To ensure good antenna efficiency, it is encapsulated, thereby avoiding a hazardous metallization (cracks, loss of adhesion).

O uso das ferritas de manganês zinco em fontes de potência de carregadores de bateria vem crescendo nos últimos anos, devido a suas baixas perdas magnéticas em induções da ordem de 0,2 T. Estas ferritas pertencem à categoria de ferritas moles, são óxidos ferrimagnéticos, policristalinos com estrutura cúbica tipo espinélio. Pós desse material foram compactados em prensa uniaxial e em prensa automática de produção para anel e toróide, respectivamente. Foram realizados dois ciclos de queima variando o teor de oxigênio entre 5 e 15%, no patamar de sinterização, com o propósito de avaliar seu efeito na densidade, microestrutura, perdas magnéticas em altas induções (0,2 T) e permeabilidade. Amostras sinterizadas em posições mais quentes do forno resultaram em maior densidade e maior tamanho de grão, conforme esperado, mas resultaram em maiores perdas a 25 °C. O aumento do teor de oxigênio entre 5 e 15% não alterou sistematicamente a densidade, mas resultou num pequeno aumento do tamanho de grão. Já a correlação entre teor de oxigênio e perdas foi complexa. Foi observado que existe uma temperatura de mínimo nas perdas totais por volta de 60 °C. O mesmo comportamento foi observado na curva da perda histerética, compatível com a variação da constante de anisotropia magnetocristalina (K1). Foram realizados ensaios de curvas de histerese a partir de 25 até 100 °C, a 0,2 T com o objetivo de avaliar o efeito da temperatura nas duas parcelas da perda histerética. Amostras sinterizadas a 1290 °C com a menor pressão de oxigênio apresentaram menor temperatura de mínimo de perda. As técnicas de análise química do teor de Fe2+ não foram capazes de estabelecer, inequivocamente, a esperada relação entre essa variável e o teor de oxigênio da atmosfera de sinterização. / The use of manganese zinc ferrite in power sources of battery chargers is growing, due to its low magnetic power losses at inductions around 0.2 T. These ferrites belong to the soft magnetic materials group, they are polycrystalline ferromagnetic oxides with face centered cubic structure. Powders of this material were compacted in uniaxial press and in automatic press of production, by ring and toroidal form, respectively. Two firing cycles, varying the atmosphere oxygen content between 5 and 15%, were applied to evaluate its effect on microstructure, density, magnetic losses in high induction and permeability. Samples sintered in warmer positions inside the furnace resulted in higher density and larger grain size, as expected, but higher losses at 25 °C were achieved. Increasing the atmosphere oxygen content from 5 to 15% did not alter density significantly, but resulted in a slight increase in grain size. On the other hand, the correlation between oxygen content and losses was complex. There are lower losses, at 60 °C. Similar behavior was observed with hysteresis loss, which is compatible with the change in magnetocrystalline magnetic anisotropy (K1). Measurements were performed from 25 to 100 °C, at 0.2 T, aiming at the evaluation of the effect of temperature on the two parcels of hysteresis loss. Samples sintered at 1290 °C with low atmosphere oxygen content showing a minimum on the losses versus temperature curve. The available techniques to analyze Fe2+ content were not capable of establishing, unequivocally, the expected relation between this variable and the oxygen content of the sintering atmosphere.

O uso das ferritas de manganês zinco em fontes de potência de carregadores de bateria vem crescendo nos últimos anos, devido a suas baixas perdas magnéticas em induções da ordem de 0,2 T. Estas ferritas pertencem à categoria de ferritas moles, são óxidos ferrimagnéticos, policristalinos com estrutura cúbica tipo espinélio. Pós desse material foram compactados em prensa uniaxial e em prensa automática de produção para anel e toróide, respectivamente. Foram realizados dois ciclos de queima variando o teor de oxigênio entre 5 e 15%, no patamar de sinterização, com o propósito de avaliar seu efeito na densidade, microestrutura, perdas magnéticas em altas induções (0,2 T) e permeabilidade. Amostras sinterizadas em posições mais quentes do forno resultaram em maior densidade e maior tamanho de grão, conforme esperado, mas resultaram em maiores perdas a 25 °C. O aumento do teor de oxigênio entre 5 e 15% não alterou sistematicamente a densidade, mas resultou num pequeno aumento do tamanho de grão. Já a correlação entre teor de oxigênio e perdas foi complexa. Foi observado que existe uma temperatura de mínimo nas perdas totais por volta de 60 °C. O mesmo comportamento foi observado na curva da perda histerética, compatível com a variação da constante de anisotropia magnetocristalina (K1). Foram realizados ensaios de curvas de histerese a partir de 25 até 100 °C, a 0,2 T com o objetivo de avaliar o efeito da temperatura nas duas parcelas da perda histerética. Amostras sinterizadas a 1290 °C com a menor pressão de oxigênio apresentaram menor temperatura de mínimo de perda. As técnicas de análise química do teor de Fe2+ não foram capazes de estabelecer, inequivocamente, a esperada relação entre essa variável e o teor de oxigênio da atmosfera de sinterização. / The use of manganese zinc ferrite in power sources of battery chargers is growing, due to its low magnetic power losses at inductions around 0.2 T. These ferrites belong to the soft magnetic materials group, they are polycrystalline ferromagnetic oxides with face centered cubic structure. Powders of this material were compacted in uniaxial press and in automatic press of production, by ring and toroidal form, respectively. Two firing cycles, varying the atmosphere oxygen content between 5 and 15%, were applied to evaluate its effect on microstructure, density, magnetic losses in high induction and permeability. Samples sintered in warmer positions inside the furnace resulted in higher density and larger grain size, as expected, but higher losses at 25 °C were achieved. Increasing the atmosphere oxygen content from 5 to 15% did not alter density significantly, but resulted in a slight increase in grain size. On the other hand, the correlation between oxygen content and losses was complex. There are lower losses, at 60 °C. Similar behavior was observed with hysteresis loss, which is compatible with the change in magnetocrystalline magnetic anisotropy (K1). Measurements were performed from 25 to 100 °C, at 0.2 T, aiming at the evaluation of the effect of temperature on the two parcels of hysteresis loss. Samples sintered at 1290 °C with low atmosphere oxygen content showing a minimum on the losses versus temperature curve. The available techniques to analyze Fe2+ content were not capable of establishing, unequivocally, the expected relation between this variable and the oxygen content of the sintering atmosphere.

Im Rahmen dieser Arbeit wurde der Einfluss von Defekten auf die Eigenschaften von Ferrit-Dünnfilmen untersucht. Die Dünnfilme wurden mit Hilfe von gepulster Laserabscheidung bei verschiedenen Züchtungsparametern hergestellt. Durch Variation der Substrattemperatur und des Sauerstoffpartialdrucks wurden Dünnfilme verschiedener kristalliner Qualität gezüchtet. Diese wurden hinsichtlich ihrer chemischen Komposition mit Hilfe von energie-dispersiver Röntgenspektroskopie und Röntgenphotoelektronenspektroskopie untersucht. Durch Korrelation der Ergebnisse mit Messungen zum zirkularen magnetischen Röntgendichroismus, konnte eine partielle Inversion der Spinellstruktur nachgewiesen werden. Der Grad der Inversion ist höher für geringe Abscheidetemperaturen. Für diese defektreichen Dünnfilme zeigen Röntgenbeugungsuntersuchungen eine geringere kristalline Ordnung der Dünnfilme. Die strukturellen Defekte haben einen maßgeblichen Einfluss auf die elektrischen und magnetischen Eigenschaften der Ferrit-Dünnfilme. So zeigen die Ferrit-Dünnfilme für geringe Züchtungstemperaturen eine erhöhte elektrische Leitfähigkeit, während Dünnfilme, die bei hohen Substrattemperaturen gezüchtet wurden, isolierend sind. Die Temperaturabhängigkeit der elektrischen Leitfähigkeit kann auf thermisch aktivierte Hopping-Leitung oder die Leitung zwischen Clustern, die in einer Matrix eingebettet sind, zurückgeführt werden. Die magnetischen Eigenschaften von Zinkferrit-Dünnfilmen werden maßgeblich durch Defekte in der Spinellstruktur bestimmt, da es nominell in der normalen Spinellstruktur kristallisiert und daher antiferromagnetisch ist. Die partielle Inversion der Eisen- und Zinkionen führt zu Ferrimagnetismus in den Zinkferrit-Dünnfilmen, der mit Hilfe von SQUID-Messungen in dieser Arbeit eingehend untersucht wurde. Durch Korrelation der Ergebnisse der verschiedenen Untersuchungsmethoden konnten Rückschlüsse auf die dominierenden Defekte in den Ferrit-Dünnfilmen geschlossen werden. So sind zum einen Defekte auf atomarer Skala, wie Antisite-Defekte und divalenten Fe-Ionen für die erhöhte elektrische Leitfähigkeit und die größere Magnetisierung der defektreichen Dünnfilme verantwortlich. Zum anderen können ausgedehnte Defekte, im Speziellen Cluster, die in einer amorphen Matrix eingebettet sind, nicht ausgeschlossen werden.