Zugl.: Konstanz, Univ., Diss., 2008

Zugl.: Hamburg, Univ., Diss., 2008

University, Diss.--Regensburg, 2007.

Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1929. / Reprinted from Journal of the Franklin Institute, vol. 213, no. 1 (Jan. 1932). Includes bibliographical references.

Zugl.: Regensburg, Univ., Diss., 2006

Made available in DSpace on 2014-12-17T15:15:04Z (GMT). No. of bitstreams: 1 AnnaCDM_DISSERT.pdf: 3464816 bytes, checksum: 8d617feb92fa3c439455f7c50d0cdd96 (MD5) Previous issue date: 2014-05-30 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The study and fabrication of nanostructured systems composed of magnetic materials has been an area of great scientific and technological interest. Soft magnetic materials, in particular, have had great importance in the development of magnetic devices. Among such materials we highlight the use of alloys of Ni and Fe, known as Permalloy. We present measurement results of structural characterization and magnetic films in Permalloy (Ni81Fe19), known to be a material with high magnetic permeability, low coercivity and small magneto- crystalline anisotropy, deposited on MgO (100) substrates. The Magnetron Sputtering technique was used to obtain the samples with thicknesses varying between 9 150 nm. The techniques of X- ray Diffraction at high and low angle were employed to confirm the crystallographic orientation and thickness of the films. In order to investigate the magnetic properties of the films the techniques of Vibrant Sample Magnetometry (VSM), Ferromagnetic Resonance (FMR) and Magnetoimpedance were used. The magnetization curves revealed the presence of anisotropy for the films of Py/MgO (100), where it was found that there are three distinct axis - an easy-axis for ?H = 0?, a hard-axis for ?H = 45? and an intermediate for ?H = 90?. The results of the FMR and Magnetoimpedance techniques confirm that there are three distinct axes, that is, there is a type C2 symmetry. Then we propose, for these results, the interpretation of the magnetic anisotropy of Py/MgO ( 100 ) is of type simple C2, ie a cubic magnetic anisotropy type ( 110 ) / O estudo e obten??o de sistemas nanoestruturados compostos por materiais magn?ticos tem se mostrado uma ?rea de grande interesse cient?fico e tecnol?gico. Materiais magn?ticos macios, em especial, tem tido grande import?ncia no desenvolvimento de dispositivos magn?ticos. Entre esses tipos de materiais cabe-nos destacar o uso de ligas de Ni e Fe, conhecidas como Permalloy. Neste trabalho apresentamos resultados de medidas de caracteriza??o estrutural e magn?tica em filmes nanom?tricos de Permalloy (Ni81Fe19), conhecido por ser um material com alta permeabilidade magn?tica, baixa coercividade e pequena anisotropia magneto-cristalina, depositado em substratos de MgO(100). A t?cnica de Magnetron Sputtering foi utilizada na obten??o das amostras com espessuras variando entre 9 150nm. As t?cnicas de Difratometria de Raios-X em alto e baixo ?ngulo foram empregadas para confirmar a orienta??o cristalogr?fica e a espessura dos filmes. Com o intuito de investigar as propriedades magn?ticas dos filmes foram usadas as t?cnicas de Magnetometria de Amostra Vibrante (VSM), Resson?ncia Ferromagn?tica (FMR) e Magnetoimped?ncia. As curvas de magnetiza??o revelaram a presen?a de anisotropia para os filmes de Py/MgO(100), verificando-se a ocorr?ncia de tr?s eixos distintos um eixo-f?cil para ?H=0?, um eixo-duro para ?H=45? e um eixo intermedi?rio para ?H=90?. Os resultados obtidos usando as t?cnicas de FMR e Magnetoimped?ncia confirmaram que h? tamb?m tr?s eixos distintos, isto ?, h? uma simetria tipo C2. Propomos ent?o, para esses resultados, a interpreta??o de que a anisotropia magn?tica do Py/MgO(100) seja do tipo C2 simples, isto ?, uma anisotropia magn?tica c?bica tipo (110)

Stress in electrochemically deposited (ECD) magnetic films is an important parameter that can have a critical effect on the performance of MEMS devices such as microinductors. This is especially the case when thick layers of materials are required and where it is important to monitor and hence control stress to prevent cracking and delamination. The reliability of devices, therefore, deeply depends on process parameters and conditions used in depositing these materials on silicon wafers. A MEMS technique for measuring stress spatially around such a wafer has been developed and used to characterise the materials involved in the fabrication of a microinductor. This thesis discusses the design and fabrication of test structures, along with a custom built automatic measurement technique to wafer map the spatial variation of strain, on any sized wafers. The effect of agitation on the grain structure of NiFe has been observed to affect strain which were spatially mapped and correlated with the film composition and thickness. Film uniformity were also shown to improve in the absence of agitation in the bath. To further understand the fundamentals of ECD small scale beaker level galvano-static experiments have been employed to use the same test structures fabricated on small Si chips. The effects of hydrogen evolution on film stress and efficiency with the inclusion of boric acid and saccharin, have been discussed. It was concluded that the tensile stress developed in Ni and NiFe films have an inversely proportional relationship with the plating efficiency. The characterisation of electrodeposited copper films is also of importance as copper films are integrated with magnetic materials in the form of windings for microinductors. The variations in recrystallization and evolution of grains of ECD copper, is for the first time demonstrated spatially using the test structures. The effect of additives in bath on film uniformity was investigated and it was observed that with carrier and additive together the three phases of self annealing were more pronounced. Finally the use of these strain test structures have been demonstrated on thick polymer SU-8 films, which is employed as a structural material in microinductors. The effect of UV exposure dose on the cross linking properties of SU-8 has also been studied. It was observed that non-uniformity in the coated film thickness over the wafer can cause variations in the UV exposure during photolithography that effects the cross linking of the polymer hence, inducing different levels of tensile stress in the material. This unique methodology has therefore opened up many possibilities and can be used for characterising newer materials employed in MEMS, fine-tuning the manufacturing processes to achieve set goals in terms of material properties as well as uniformity and gaining a better understanding of the influence of processing conditions on the produced films.

In this work the dynamics of permalloy circular magnetic islands of 225 nm radius and 10 nm thickness arranged into square lattices was investigated employing micromagnetic simulations.The simulations of the vortex magnetization loops and the ferromagnetic resonance (FMR) spectra were carried out using a free micromagnetics simulation software Mumax3. The obtained data was analyzed using Matlab. The simulations were carried out on a single vortex island as well as on two different lattices. The first lattice is comprised of interacting islands, while the second lattice - of non-interacting islands, separated by 25 nm and by 450 nm edge-to-edge distance, respectively. The magnetization loops were simulated by applying the static magnetic field in-plane of the single island or the lattice. The FMR simulations were carried out by applying the static magnetic field in-plane of the lattice and after the system reached the ground state in that field, the excitation as a sinc pulse was sent out along the out-of-plane direction of the lattice. The analysis of the obtained FMR spectra revealed that the several resonant modes are present for the single vortex island and the lattice, comprised of such islands. However, the physical explanation of the origin of those modes is a subject for further investigations.

The development of magnetic technologies employing microfabricated magnetic structures for the production of integrated electronic components is a driving topic in the electronic industry. Despite the large amount of work reported in the literature towards the production of magnetic devices that can be integrated into conventional silicon technology, the published research has only achieved moderate success. The research presented in this thesis was conducted with the aim to progress towards the production of a magnetic MEMS relay based on electro-deposited NiFe that combines magnetic and electrostatic actuation and that can be integrated in a standard IC processing chain. This work includes a comprehensive design study for the proposed MEMS device and presents the development of the manufacturing processes required for its fabrication. As the theoretical performance of the device is found to be crucially reliant on the mechanical and magnetic properties of the microformed structures, a series of novel test methodologies has been devised and implemented with the aim of acquiring knowledge on the behaviour of the NiFe films. Novel mechanical test routines employing microfabricated test structures are presented and applied to build a systematic and robust system for the characterisation of the electrodeposited films. The quantitative mapping of residual stress at the wafer level using microfabricated test structures has been demonstrated for the first time and applied to optimise processes and tools. A complete fabrication process flow for manufacturing the designed magnetic MEMS switch has been proposed and the fabrication of the actuated section of the switch has been demonstrated, comprising all the functional electric and magnetic components. The fabricated magnetic devices have been tested to monitor their response to an external magnetic force and prove their viability for use in MEMS actuators. Additional work was finally conducted towards the development of a reliable and robust process aimed at increasing the device yield and thus facilitating the eventual commercialisation of magnetic MEMS switches.

No description available.