The aim of this project was to produce an integrate-able free space optical transceiver for Specks. Specks are tiny computing units that together can form a powerful network called a SpeckNet. The SpeckNet platform is developed by the SpeckNet consortium, which consists of five Scottish Universities and combines computer science, electrical engineering and digital signal processing groups. The principal goal of creating an optical transceiver was achieved by integrating in-house fabricated VCSELs (with lasing thresholds below 400 uA) and custom designed detectors on the SpeckNet platform. The transceiver has a very low power consumption (approximately 100 uW), which removes the need for synchronous communication through the SpeckNet thus making the network more efficient. I describe both static and dynamic beam control techniques. For static control, I used micro-lenses. I fabricated the lenses by greyscale electron beam lithography and integrated them directly on VCSEL arrays. I achieved a steering angle of 10 degrees with this design. I also looked at integrated gratings etched straight into a VCSEL and observed beam steering with an efficiency of 60% For dynamic control, I implemented a liquid crystal (LC) design. I built a LC cell with 30 individually controlled pixels, but I only achieved a steering angle of 1 degree. Furthermore, I investigated two different techniques for achieving beam steering by interference, using coupled VCSELs (a phased array approach). Firstly, using photonic crystals etched into the surface of the VCSEL, I built coupled laser cavities. Secondly, I designed and built bow-tie type VCSELs that were optically coupled but electrically isolated. These designs work by differential current injection causing an interference effect in the VCSELs far field. This technique is the first stepping stone towards realising a phased optical array. Finally, I considered signal detection. Using the same VCSEL material, I built a resonant-cavity detector. This detector had a better background rejection ratio than commercially available silicon devices.

O presente trabalho tem como objetivo desenvolver um processo de fabricação de elementos micro-ópticos utilizando-se litografia por feixe de elétrons, empregando o resiste SU-8, negativo e amplificado quimicamente, sobre substrato de Si. Para tanto, é realizado o estudo dos parâmetros do efeito de proximidade a, b e h para se modelar e controlar os efeitos do espalhamento dos elétrons no resiste e no substrato, e se altera o processamento convencional do SU-8 para se obter um processo com baixo contraste. A determinação dos parâmetros do efeito de proximidade para o sistema de escrita direta e amostra SU-8 / Si é feita experimentalmente e por simulação de Monte Carlo. Particularmente, verifica-se a dependência dos mesmos com a profundidade do resiste. Primeiramente utilizando o software PROXY, obtêm-se a, b e h da observação de padrões de teste revelados. Chega-se a 4m para o parâmetro () que mede o retroespalhamento dos elétrons pelo substrato e 0,7 para a relação (h) entre a intensidade destes com aquela dos elétrons diretamente espalhados pelo resiste (alcance dado por a). Ainda, com esses dados, estima-se o diâmetro do feixe do microscópio eletrônico de varredura a partir da equação de aproximação de espalhamento direto para pequenos ângulos (a = 128nm na superfície do resiste) e se determina a resolução lateral do processo (a = 800nm na interface resiste/ substrato, para um filme de 2,4m). Em seguida, usa-se o software CASINO para se calcular os parâmetros de proximidade a partir da curva de densidade de energia dissipada no resiste obtida pela simulação da trajetória de espalhamento dos elétrons. Confrontam-se, finalmente, os valores obtidos pelos dois métodos. Em relação ao processamento do resiste SU-8, são determinadas as condições experimentais para a fabricação de estruturas tridimensionais por litografia de feixe de elétrons. Especificamente, busca-se desenvolver um processo com características (espessura, contraste, sensibilidade e rugosidade) adequadas para a fabricação de micro-dispositivos ópticos. Inicia-se com o levantamento das curvas de contraste e da sensibilidade do SU-8 para determinadas temperaturas de aquecimento pós-exposição. Obtém-se contraste abaixo de 1 para aquecimento pós-exposição abaixo da temperatura de transição vítrea do resiste, mantendo-se sensibilidade elevada (2C/cm2). Em seguida, mede-se a rugosidade da superfície do filme revelado para diferentes doses de exposição. Para finalizar, submete-se a amostra a um processo de cura e escoamento térmico, para melhorar a dureza e a rugosidade do resiste a ser utilizado como dispositivo final Consegue-se um valor de rugosidade (40nm) inferior a 20 vezes o comprimento de onda de diodo laser de eletrônica de consumo. Por fim, é produzido um dispositivo com perfil discretizado em 16 níveis como prova de conceito. / This work aims at developing an electron-beam lithography process for the fabrication of microoptical elements using the negative tone chemically amplified resist SU-8 on Si substrate. A study of the proximity effect parameters a, b and h is carried out to model and control the electron scattering both in the resist and in the substrate, and the SU-8 standard processing conditions are changed to achieve a low contrast process. The determination of the SU-8 / Si proximity effect parameters and its dependence with resist depth is done employing an experimental method and through Monte Carlo simulations. First, a, b and h are obtained comparing exposed patterns calculated by the software PROXY. b, the parameter which measures the backscattering of the electrons by the substrate, is equal to 4m and the value of h, the ratio of the dose contribution of backscattered electrons to that of the forward scattered (related to a), is 0.7. The extrapolation of exposed patterns data is used to estimate the scanning electron microscope beam diameter through the equation for low angle scattering (a = 128nm at the resist surface) and the lateral resolution of the process is determined (a = 800nm at the resist/ substrate interface, for a 2.4m film). With aid of the software CASINO, Monte Carlo simulations of the scattering trajectories of electrons in substrate and resist materials are calculated, recording the energy that they dissipate through collisions along their path. The results obtained representing the profile of the energy dissipated in the resist are used to determine the proximity effect parameters. The experimental method results are compared to that obtained by simulation. Regarding the SU-8 processing, the process parameters for the fabrication of three-dimensional structures by electron-beam lithography are determined. The process is designed to have specifications (thickness, contrast, sensitivity and surface roughness) suitable for microoptical elements fabrication. It begins with the determination of the SU-8 contrast curve and its sensitivity for specific post-exposure bake temperatures. A below the unit contrast process with high sensitivity (2C/cm2) is achieved postannealing the sample below the resist glass transition temperature. The film surface roughness is measured after resist development for different exposure doses, and a controlled hardbake (cure) and reflow is carried to enhance both the mechanical properties and the surface roughness of the structures that will remain as part of the final device. A RMS roughness of 40nm, lower than 20 times the wavelength of consumer electronics laser diode, is obtained. The electron-beam process designed is applied to the fabrication of a microelement with a 16-level profile discretization.

Eletrônica utilizando polímero em substituição ao silício é uma área de pesquisa recente com perspectivas econômicas promissoras. Compósitos de polímeros com partículas metálicas apresentam interessantes propriedades elétricas, magnéticas e ópticas e têm sido produzidos por uma grande variedade de técnicas. Implantação iônica de metais utilizando plasma é um dos métodos utilizados para obtenção desses compósitos condutores. Neste trabalho é realizada implantação de íons de ouro de baixa energia em PMMA utilizando plasma. O PMMA tem grande importância tecnológica sendo largamente utilizado como resiste em litografias por feixe de elétrons, raios-X, íons e deep-UV. Como resultado da implantação iônica de baixa energia em PMMA há formação de uma camada nanométrica de material condutor. Esse novo material, denominado compósito isolante-condutor, permite criar micro e nanodispositivos através de técnicas largamente utilizadas em microeletrônica. Medidas elétricas são realizadas in situ em função da dose de íons metálicos implantada, o que permite um estudo das propriedades de transporte desses novos materiais, que podem ser modeladas pela teoria da percolação. Simulações utilizando o programa TRIDYN permitem obter a profundidade e o perfil da implantação dos íons. São mostradas caracterizações importantes tais como Microscopia Eletrônica de Transmissão, Microscopia de Varredura por Tunelamento, Espalhamento de Raios-X a Baixos Ângulos, Difração de Raios-X e Espectroscopia UV-vis. Essas técnicas permitem visualizar e investigar o caráter nanoestruturado do compósito metal-polímero. Ainda como parte deste projeto, as camadas condutoras formadas no polímero são caracterizadas quanto à manutenção das suas características de elétron resiste. / Electronics using polymers instead of silicon is a recent research area with promising economic perspectives. Polymer with metallic particles composites presents interesting electrical, magnetic and optical properties and they have been produced by a broad variety of techniques. Metal ion implantation using plasma is one of the used methods to obtain conductor composites. In this work it is performed low energy gold ion implantation in PMMA by using plasma. PMMA has great technological importance once it is broadly used as resist in electron-beam, X-ray, ion and deep UV lithography. As a result of low energy ion implantation in PMMA, a nanometric conducting layer is formed. This new material, named insulator-conductor composite, can allow the creation of micro and nanodevices through well known microelectronics techniques. Electrical measurements are performed in situ as a function of metal ions implanted dose, which allows the investigation of electrical transport of these new materials, which can be modeled by the percolation theory. Simulations using TRIDYN computer code provide the prediction of depth profile of implanted ions. Important characterizations are showed such as Transmission Electron Microscopy, Scanning Tunneling Microscopy, Small Angle X-Ray Scattering, X-Ray Diffraction and UV-vis Spectroscopy. These techniques allow to visualize and to investigate the nanostructured character of the metal-polymer composite. Still as a part of this project, the conducting layers formed are characterized in relation to the maintenance of their characteristics as electron-beam resist.

Eletrônica utilizando polímero em substituição ao silício é uma área de pesquisa recente com perspectivas econômicas promissoras. Compósitos de polímeros com partículas metálicas apresentam interessantes propriedades elétricas, magnéticas e ópticas e têm sido produzidos por uma grande variedade de técnicas. Implantação iônica de metais utilizando plasma é um dos métodos utilizados para obtenção desses compósitos condutores. Neste trabalho é realizada implantação de íons de ouro de baixa energia em PMMA utilizando plasma. O PMMA tem grande importância tecnológica sendo largamente utilizado como resiste em litografias por feixe de elétrons, raios-X, íons e deep-UV. Como resultado da implantação iônica de baixa energia em PMMA há formação de uma camada nanométrica de material condutor. Esse novo material, denominado compósito isolante-condutor, permite criar micro e nanodispositivos através de técnicas largamente utilizadas em microeletrônica. Medidas elétricas são realizadas in situ em função da dose de íons metálicos implantada, o que permite um estudo das propriedades de transporte desses novos materiais, que podem ser modeladas pela teoria da percolação. Simulações utilizando o programa TRIDYN permitem obter a profundidade e o perfil da implantação dos íons. São mostradas caracterizações importantes tais como Microscopia Eletrônica de Transmissão, Microscopia de Varredura por Tunelamento, Espalhamento de Raios-X a Baixos Ângulos, Difração de Raios-X e Espectroscopia UV-vis. Essas técnicas permitem visualizar e investigar o caráter nanoestruturado do compósito metal-polímero. Ainda como parte deste projeto, as camadas condutoras formadas no polímero são caracterizadas quanto à manutenção das suas características de elétron resiste. / Electronics using polymers instead of silicon is a recent research area with promising economic perspectives. Polymer with metallic particles composites presents interesting electrical, magnetic and optical properties and they have been produced by a broad variety of techniques. Metal ion implantation using plasma is one of the used methods to obtain conductor composites. In this work it is performed low energy gold ion implantation in PMMA by using plasma. PMMA has great technological importance once it is broadly used as resist in electron-beam, X-ray, ion and deep UV lithography. As a result of low energy ion implantation in PMMA, a nanometric conducting layer is formed. This new material, named insulator-conductor composite, can allow the creation of micro and nanodevices through well known microelectronics techniques. Electrical measurements are performed in situ as a function of metal ions implanted dose, which allows the investigation of electrical transport of these new materials, which can be modeled by the percolation theory. Simulations using TRIDYN computer code provide the prediction of depth profile of implanted ions. Important characterizations are showed such as Transmission Electron Microscopy, Scanning Tunneling Microscopy, Small Angle X-Ray Scattering, X-Ray Diffraction and UV-vis Spectroscopy. These techniques allow to visualize and to investigate the nanostructured character of the metal-polymer composite. Still as a part of this project, the conducting layers formed are characterized in relation to the maintenance of their characteristics as electron-beam resist.

Photonic crystals (PhCs) are structures periodic in thedielectric constant. They exhibit a photonic bandgap, i.e., arange of wavelengths for which light propagation is forbidden.Engineering of defects in the PhC lattice offers new ways toconfine and guide light. PhCs have been manufactured usingsemiconductors and other material technologies. This thesisfocuses on two-dimensional PhCs etched in InP-based materials.Only recently, such structures were identified as promisingcandidates for the realization of novel and advanced functionsfor optical communication applications. The primary focus was on fabrication and characterization ofPhC structures in the InP/GaInAsP/InP material system. Thedemands on fabrication are very high: holes as small as100-300nm in diameter have to be etched at least as deep as 2µm. Thus, different etch processes had to be explored andspecifically developed for InP. We have implemented an etchingprocess based on Ar/Cl2chemically assisted ion beam etching (CAIBE), thatrepresents the state of the art PhC etching in InP. Different building blocks were manufactured using thisprocess. A transmission loss of 10dB/mm for a PhC waveguide, areflection of 96.5% for a 4-row mirror and a record qualityfactor of 310 for a 1D cavity were achieved for this materialsystem. With an etch depth of 4.5 µm, optical loss wasfound to be close to the intrinsic limit. PhC-based opticalfilters were demonstrated using (a) a Fabry-Pérot cavityinserted in a PhC waveguide and (b) a contra-directionalcoupler. Lag effect in CAIBE was utilized positively to realizehigh quality PhC taper sections. Using a PhC taper, a couplingefficiency of 70% was demonstrated from a standard ridgewaveguide to a single line defect PhC waveguide. During the course of this work, InP membrane technology wasdeveloped and a Fabry-Pérot cavity with a quality factorof 3200 was demonstrated. Keywords:photonic crystals, photonic bandgap materials,indium phosphide, dry etching, chemically assisted ion beametching, reactive ion etching, electron beam lithography,photonic integrated circuits, optical waveguides, resonantcavities, optical filtering, finite difference time domain,plane wave expansion.

Diese Arbeit befasst sich mit der Nanostrukturierung von magnetischen Schichtsystemen mit Tunnelmagnetowiderstandseffekt (TMR-Effekt), welche in der Form von Nanosäulen in magnetoresistiven Speichern (MRAM) eingesetzt werden. Solche Nanosäulen können zukünftig ebenfalls als Nanoemitter von Mikrowellensignalen eine Rolle spielen. Dabei wird von der Auswahl eines geeigneten TMR-Schichtsystems mit einer MgO-Tunnelbarriere über die Präparation der Nanosäulen mit Seitenisolierung bis hin zum Aufbringen der elektrischen Zuleitungen eine komplette Prozesskette entwickelt und optimiert. Die Strukturen werden mittels optischer Lithographie und Elektronenstrahllithographie definiert, die anschließende Strukturübertragung erfolgt durch Ionenstrahlätzen (teilweise reaktiv) sowie durch Lift-off. Rückmeldung über Erfolg oder Probleme bei der Strukturierung geben Transmissionselektronenmikroskopie (teilweise mit Zielpräparation per Ionenfeinstrahl, FIB), Rasterelektronenmikroskopie sowie die Lichtmikroskopie. Es können so TMR-Nanosäulen mit minimalen Abmessungen von bis zu 69 nm x 71 nm hergestellt werden, von denen Nanosäulen mit Abmessungen von 65 nm x 87 nm grundlegend magneto-elektrisch charakterisiert worden sind. Dies umfasst die Bestimmung des TMR-Effektes und des Widerstandes der Tunnelbarriere (RA-Produkt). Weiterhin wurde das Verhalten der magnetischen Schichten bei größeren Magnetfeldern bis +-200mT sowie das Umschaltverhalten der magnetisch freien Schicht bei verändertem Winkel zwischen magnetischer Vorzugsachse des TMR-Elementes und dem äußeren Magnetfeld untersucht. Der Nachweis des Spin-Transfer-Torque Effektes an den präparierten TMR-Nanosäulen ist im Rahmen dieser Arbeit nicht gelungen, was mit dem zu hohen elektrischen Widerstand der verwendeten Tunnelbarriere erklärt werden kann. Mit dünneren Barrieren konnte der Widerstand gesenkt werden, allerdings führt ein Stromfluss durch diese Barrieren schnell zur Degradation der Barrieren. Weiterführende Arbeiten sollten das Ziel haben, niederohmige und gleichzeitig elektrisch belastbare Tunnelbarrieren in einem entsprechenden TMR-Schichtsystem abzuscheiden. Eine erste Auswahl an Ansatzpunkten dafür aus der Literatur wird im Ausblick gegeben. / This thesis deals with the fabrication of nanopillars with tunnel magnetoresistance effect (TMR-effect), which are used in magnetoresistive memory (MRAM) and may be used as nanooscillators for future near field communication devices. Starting with the selection of a suitable TMR-layer stack with MgO-tunnel barrier, the whole process chain covering the fabrication of the nanopillars, sidewall isolation and preparation of the supply lines on top is developed and optimised. The structures are defined by optical and electron beam lithography, the subsequent patterning is done by ion beam etching (partially reactive) and lift-off. Techniques providing feedback on the nanofabrication are transmission electron microscopy (partially with target preparation by focused ion beam, FIB), scanning electron microscopy and optical microscopy. In this way nanopillars with minimal dimensions reaching 69 nm x 71 nm could be fabricated, of which nanopillars with a size of 65 nm x 87 nm were characterized fundamentally with respect to their magnetic and electric properties. This covers the determination of the TMR-effect and the resistance of the tunnel barrier (RA-product). In addition, the behaviour of the magnetic layers under higher magnetic fields (up to +-200mT) and the switching behaviour of the free layer at different angles between the easy axis of the TMR-element and the external magnetic field were investigated. The spin transfer torque effect could not be detected in the fabricated nanopillars due to the high electrical resistance of the tunnel barriers which were used. The resistance could be lowered by using thinner barriers, but this led to a quick degradation of the barrier when a current was applied. Continuative work should focus on the preparation of tunnel barriers in an appropriate TMR-stack being low resistive and electrically robust at the same time. A first selection of concepts and ideas from the literature for this task is given in the outlook.

<p>Photonic crystals (PhCs) are structures periodic in thedielectric constant. They exhibit a photonic bandgap, i.e., arange of wavelengths for which light propagation is forbidden.Engineering of defects in the PhC lattice offers new ways toconfine and guide light. PhCs have been manufactured usingsemiconductors and other material technologies. This thesisfocuses on two-dimensional PhCs etched in InP-based materials.Only recently, such structures were identified as promisingcandidates for the realization of novel and advanced functionsfor optical communication applications.</p><p>The primary focus was on fabrication and characterization ofPhC structures in the InP/GaInAsP/InP material system. Thedemands on fabrication are very high: holes as small as100-300nm in diameter have to be etched at least as deep as 2µm. Thus, different etch processes had to be explored andspecifically developed for InP. We have implemented an etchingprocess based on Ar/Cl₂chemically assisted ion beam etching (CAIBE), thatrepresents the state of the art PhC etching in InP.</p><p>Different building blocks were manufactured using thisprocess. A transmission loss of 10dB/mm for a PhC waveguide, areflection of 96.5% for a 4-row mirror and a record qualityfactor of 310 for a 1D cavity were achieved for this materialsystem. With an etch depth of 4.5 µm, optical loss wasfound to be close to the intrinsic limit. PhC-based opticalfilters were demonstrated using (a) a Fabry-Pérot cavityinserted in a PhC waveguide and (b) a contra-directionalcoupler. Lag effect in CAIBE was utilized positively to realizehigh quality PhC taper sections. Using a PhC taper, a couplingefficiency of 70% was demonstrated from a standard ridgewaveguide to a single line defect PhC waveguide.</p><p>During the course of this work, InP membrane technology wasdeveloped and a Fabry-Pérot cavity with a quality factorof 3200 was demonstrated.</p><p><b>Keywords:</b>photonic crystals, photonic bandgap materials,indium phosphide, dry etching, chemically assisted ion beametching, reactive ion etching, electron beam lithography,photonic integrated circuits, optical waveguides, resonantcavities, optical filtering, finite difference time domain,plane wave expansion.</p>

O presente trabalho tem como objetivo desenvolver um processo de fabricação de elementos micro-ópticos utilizando-se litografia por feixe de elétrons, empregando o resiste SU-8, negativo e amplificado quimicamente, sobre substrato de Si. Para tanto, é realizado o estudo dos parâmetros do efeito de proximidade a, b e h para se modelar e controlar os efeitos do espalhamento dos elétrons no resiste e no substrato, e se altera o processamento convencional do SU-8 para se obter um processo com baixo contraste. A determinação dos parâmetros do efeito de proximidade para o sistema de escrita direta e amostra SU-8 / Si é feita experimentalmente e por simulação de Monte Carlo. Particularmente, verifica-se a dependência dos mesmos com a profundidade do resiste. Primeiramente utilizando o software PROXY, obtêm-se a, b e h da observação de padrões de teste revelados. Chega-se a 4m para o parâmetro () que mede o retroespalhamento dos elétrons pelo substrato e 0,7 para a relação (h) entre a intensidade destes com aquela dos elétrons diretamente espalhados pelo resiste (alcance dado por a). Ainda, com esses dados, estima-se o diâmetro do feixe do microscópio eletrônico de varredura a partir da equação de aproximação de espalhamento direto para pequenos ângulos (a = 128nm na superfície do resiste) e se determina a resolução lateral do processo (a = 800nm na interface resiste/ substrato, para um filme de 2,4m). Em seguida, usa-se o software CASINO para se calcular os parâmetros de proximidade a partir da curva de densidade de energia dissipada no resiste obtida pela simulação da trajetória de espalhamento dos elétrons. Confrontam-se, finalmente, os valores obtidos pelos dois métodos. Em relação ao processamento do resiste SU-8, são determinadas as condições experimentais para a fabricação de estruturas tridimensionais por litografia de feixe de elétrons. Especificamente, busca-se desenvolver um processo com características (espessura, contraste, sensibilidade e rugosidade) adequadas para a fabricação de micro-dispositivos ópticos. Inicia-se com o levantamento das curvas de contraste e da sensibilidade do SU-8 para determinadas temperaturas de aquecimento pós-exposição. Obtém-se contraste abaixo de 1 para aquecimento pós-exposição abaixo da temperatura de transição vítrea do resiste, mantendo-se sensibilidade elevada (2C/cm2). Em seguida, mede-se a rugosidade da superfície do filme revelado para diferentes doses de exposição. Para finalizar, submete-se a amostra a um processo de cura e escoamento térmico, para melhorar a dureza e a rugosidade do resiste a ser utilizado como dispositivo final Consegue-se um valor de rugosidade (40nm) inferior a 20 vezes o comprimento de onda de diodo laser de eletrônica de consumo. Por fim, é produzido um dispositivo com perfil discretizado em 16 níveis como prova de conceito. / This work aims at developing an electron-beam lithography process for the fabrication of microoptical elements using the negative tone chemically amplified resist SU-8 on Si substrate. A study of the proximity effect parameters a, b and h is carried out to model and control the electron scattering both in the resist and in the substrate, and the SU-8 standard processing conditions are changed to achieve a low contrast process. The determination of the SU-8 / Si proximity effect parameters and its dependence with resist depth is done employing an experimental method and through Monte Carlo simulations. First, a, b and h are obtained comparing exposed patterns calculated by the software PROXY. b, the parameter which measures the backscattering of the electrons by the substrate, is equal to 4m and the value of h, the ratio of the dose contribution of backscattered electrons to that of the forward scattered (related to a), is 0.7. The extrapolation of exposed patterns data is used to estimate the scanning electron microscope beam diameter through the equation for low angle scattering (a = 128nm at the resist surface) and the lateral resolution of the process is determined (a = 800nm at the resist/ substrate interface, for a 2.4m film). With aid of the software CASINO, Monte Carlo simulations of the scattering trajectories of electrons in substrate and resist materials are calculated, recording the energy that they dissipate through collisions along their path. The results obtained representing the profile of the energy dissipated in the resist are used to determine the proximity effect parameters. The experimental method results are compared to that obtained by simulation. Regarding the SU-8 processing, the process parameters for the fabrication of three-dimensional structures by electron-beam lithography are determined. The process is designed to have specifications (thickness, contrast, sensitivity and surface roughness) suitable for microoptical elements fabrication. It begins with the determination of the SU-8 contrast curve and its sensitivity for specific post-exposure bake temperatures. A below the unit contrast process with high sensitivity (2C/cm2) is achieved postannealing the sample below the resist glass transition temperature. The film surface roughness is measured after resist development for different exposure doses, and a controlled hardbake (cure) and reflow is carried to enhance both the mechanical properties and the surface roughness of the structures that will remain as part of the final device. A RMS roughness of 40nm, lower than 20 times the wavelength of consumer electronics laser diode, is obtained. The electron-beam process designed is applied to the fabrication of a microelement with a 16-level profile discretization.

To investigate quantum confinement effects on silicon (Si) light source electroluminescence (EL) properties like quantum efficiency, external power efficiency and spectral emission, thin Si finger junctions with nanometre-scale dimensions were designed and manufactured in a fully customized silicon-on-insulator (SOI) semiconductor production technology. Since commonly available photolithography is unusable to consistently define and align nanometre-scale line-widths accurately and electron-beam lithography (EBL) by itself is too time-expensive to expose complete wafers, the wafer manufacturing process employed a selective combination of photolithography and EBL. The SOI wafers were manufactured in the clean-rooms of both the Carl and Emily Fuchs Institute for Microelectronics (CEFIM) at the University of Pretoria (UP) and the Georgia Institute of Technology’s Microelectronic Research Centre (MiRC), which made a JEOL JBX-9300FS electron-beam pattern generator (EPG) available. As far as is known this was the first project in South Africa (and possibly at the MiRC) that employed EBL to define functional nanometre-scale semiconductor devices. Since no standard process recipe could be employed, the complete design and manufacturing process was based on self-obtained equipment characterization data and material properties. The manufacturing process was unprecedented in both the CEFIM and MiRC clean-rooms. The manufacture of nanometre-scale Si finger junctions not only approached the manufacturing limits of the employed processing machinery, but also had to overcome undesirable physical effects that in larger-scale semiconductor manufacture usually are negligible. The device design, mask layout and manufacturing process therefore had to incorporate various material, equipment limitation and physical phenomena like impurity redistribution occurring during the physical manufacturing process. Although the complicated manufacturing process allowed many unexpected problems to occur, it was expected that at least the simple junction breakdown devices be functional and capable of delivering data regarding quantum confinement effects. Although due to design and processing oversights only 29 out of 505 measured SOI light sources were useful light emitters, the design and manufacture of the SOI light sources was successful in the sense that enough SOI light sources were available to conduct useful optical characterization measurements. In spite of the fact that the functional light sources did not achieve the desired horizontal (width) confinement, measured optical spectra of certain devices indicate that vertical (thickness) confinement had been achieved. All spectrometer-measured thickness-confined SOI light sources displayed a pronounced optical power for 600 nm < λ < 1 μm. The SOI light source with the highest optical power output emitted about 8 times more optical power around λ = 850 nm than a 0.35 μm bulk-CMOS avalanche light-source operating at the same current. Possible explanations for this effect are given. It was shown that the buried oxide (BOX) layer in a SOI process could be used to reflect about 25 % of the light that would usually be lost to downward radiation back up, thereby increasing the external power efficiency of SOI light sources. This document elaborates on the technical objectives, approach, chip and process design, physical wafer manufacture, production process control and measurement of the nanometre-scale SOI light sources. Copyright / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

Magnetické vortexy jsou charakterizovány směrem stáčení magnetizace a polarizací vortexového jádra, přičemž každá z těchto veličin nabývá dvojice stavů. Ve výsledku jsou tak k dispozici čtyři možné stabilní konfigurace, čehož může být využito v multibitových paměťových zařízeních. Tato dizertační práce se zabývá selektivním zápisem stavů magnetického vortexu v magnetickém disku pulzem elektrického proudu stejně jako jejich následným elektrickým čtením. Před samotnou realizací elektrických měření byla provedena statická měření přepínání stavů vortexu pomocí různých proudových pulzů v kombinaci s technikami MFM a následně MTXM. Následně byl realizován dynamický odečet stavu vortexu kompletně založený na elektrických měřeních. Ovládání cirkulace vortexu je založeno na geometrické asymetrii vytvořené oříznutím magnetického disku a vytvořením fazety. Plochý okraj disku definuje preferenční smysl stáčení cirkulace během procesu nukleace vortexu. Řízení polarity se obvykle provádí ve dvou krocích. V prvním kroku, homogenně magnetizovaná vrstva s kolmou magnetickou anizotropií umístěná na dně disku definuje výchozí polaritu vortexu v době nukleace. V druhém kroku, je-li to nutné, je polarita vortexu přepnuta pomocí rychlého proudového pulzu. Proto je možné nastavit požadovaný stav cirkulace vysláním nanosekundového pulsu s nízkou amplitudou, následované nastavením polarity pikosekundovým pulsem s vysokou amplitudou. Stavy vortexů jsou pak detekovány elektrickou spektroskopií prostřednictvím anizotropní magnetorezistence. Vzorky pro všechna statická a dynamická měření byly připraveny pomocí elektronové litografie v kombinaci s lift-off procesem.