Piezoelectric actuators (PEA) hold the most promise for precision positioning applications due to their capability of producing extremely small displacements down to 10 pm (1 pm = 10-12 m) as well as their high stiffness and force output. The piezoelectric-driven stick-slip (PDSS) actuator, working on the friction-inertia concept, has the capacity of accomplishing an unlimited range of motion. It also holds the promises of simple configuration and low cost. On the other hand, the PDSS actuator has a relatively low efficiency and low loading capability, which greatly limits its applications. The purpose of this research is to improve the performance of the PDSS actuators by employing specially-designed working surfaces.<p> The working surfaces, referred as anisotropic friction (AF) surfaces in this study, can provide different friction forces depending on the direction of relative motion of the two surfaces, and are used in this research to accomplish the aforementioned purpose. To fabricate such surfaces, two nanostructure technologies are employed: hot filament chemical vapour deposition (HFCVD) and ion beam etching (IBE). The HFCVD is used to deposit diamond on silicon substrates; and the IBE is used to etch the diamond crystalloid with a certain angle with respect to the coating surface to obtain an unsymmetrical-triangle microstructure. <p> A PDSS actuator prototype containing the AF surfaces was developed in this study to verify the function of the AF surfaces and characterize the performance of PDSS actuators. The designed surfaces were mounted on the prototype; and the improvement in performance was characterized by conducting a set of experiments with both the normal isotropic friction (IF) surfaces and the AF surfaces, respectively. The results illustrate that the PDSS actuator with the AF surface has a higher efficiency and improved loading capability compared to the one with the IF surfaces.<p> A model was also developed to represent the displacement of the novel PDSS actuator. The dynamics of the PEA and the platform were approximated by using a second order dynamic system. The pre-sliding friction behaviour involved was investigated by modifying the LuGre friction model, in which six parameters (Note that three parameters are used in the LuGre model) were employed to represent the anisotropic friction. By combining the PEA mechanism model, the modified friction model, and the dynamics of end-effector, a model for the PDSS actuator with the AF surface was developed. The model with the identified parameters was simulated in MATLAB Simulink and the simulation results obtained were compared to the experimental results to verify the model. The comparison suggests that the model developed in this study is promising to represent the displacement of the novel PDSS actuators with AF surfaces.

Piezoelectric actuators (PEA) hold the most promise for precision positioning applications due to their capability of producing extremely small displacements down to 10 pm (1 pm = 10-12 m) as well as their high stiffness and force output. The piezoelectric-driven stick-slip (PDSS) actuator, working on the friction-inertia concept, has the capacity of accomplishing an unlimited range of motion. It also holds the promises of simple configuration and low cost. On the other hand, the PDSS actuator has a relatively low efficiency and low loading capability, which greatly limits its applications. The purpose of this research is to improve the performance of the PDSS actuators by employing specially-designed working surfaces.<p> The working surfaces, referred as anisotropic friction (AF) surfaces in this study, can provide different friction forces depending on the direction of relative motion of the two surfaces, and are used in this research to accomplish the aforementioned purpose. To fabricate such surfaces, two nanostructure technologies are employed: hot filament chemical vapour deposition (HFCVD) and ion beam etching (IBE). The HFCVD is used to deposit diamond on silicon substrates; and the IBE is used to etch the diamond crystalloid with a certain angle with respect to the coating surface to obtain an unsymmetrical-triangle microstructure. <p> A PDSS actuator prototype containing the AF surfaces was developed in this study to verify the function of the AF surfaces and characterize the performance of PDSS actuators. The designed surfaces were mounted on the prototype; and the improvement in performance was characterized by conducting a set of experiments with both the normal isotropic friction (IF) surfaces and the AF surfaces, respectively. The results illustrate that the PDSS actuator with the AF surface has a higher efficiency and improved loading capability compared to the one with the IF surfaces.<p> A model was also developed to represent the displacement of the novel PDSS actuator. The dynamics of the PEA and the platform were approximated by using a second order dynamic system. The pre-sliding friction behaviour involved was investigated by modifying the LuGre friction model, in which six parameters (Note that three parameters are used in the LuGre model) were employed to represent the anisotropic friction. By combining the PEA mechanism model, the modified friction model, and the dynamics of end-effector, a model for the PDSS actuator with the AF surface was developed. The model with the identified parameters was simulated in MATLAB Simulink and the simulation results obtained were compared to the experimental results to verify the model. The comparison suggests that the model developed in this study is promising to represent the displacement of the novel PDSS actuators with AF surfaces.

Dry etching is an important technique for pattern transferin fabrication of most opto-electronic devices, since it canprovide good control of both structure size and shape even on asub-micron scale. Unfortunately, this process step may causedamage to the material which is detrimental to deviceperformance. It is therefore an objective of this thesis todevelop and investigate low damage etching processes for InPbased devices. An ion beam system in combination with hydrocarbon (CH4) based chemistries is used for etching. At variousion energies and gas flows the etching is performed in twomodes, reactive ion beam etching (RIBE) and chemical assistedion beam etching (CAIBE). How these conditions affect both etchcharacteristics (e.g. etch rates and profiles, surfacemorphology and polymer formation) and etch induced damage (onoptical and electrical properties) is evaluated and discussed.Attention is also paid to the effects of typical post etchingtreatments such as annealing on the optical and electricalproperties. An important finding is the correlation betweenas-etched surface morphology and recovery/degradation inphotoluminescence upon annealing in PH3. Since this type of atmosphere is typical forcrystal regrowth (an important process step in III/Vprocessing) a positive result is imperative. A low ion energy N2/CH4/H2CAIBE process is developed which not onlysatisfies this criteria but also exhibits good etchcharacteristics. This process is used successfully in thefabrication of laser gratings. In addition to this, the abilityof the ion beam system to modify the surface morphology in acontrollable manner is exploited. By exposing such modifiedsurfaces to AsH3/PH3, a new way to vary size and density of InAs(P)islands formed on the InP surfaces by the As/P exchangereaction is presented. This thesis also proposes a new etch chemistry, namelytrimethylamine ((CH3)3N or TMA), which is a more efficient methyl sourcecompared to CH4because of the low energy required to break the H3C-N bond. Since methyl radicals are needed for theetching it is presumably a better etching chemistry. A similarinvestigation as for the CH4chemistry is performed, and it is found that bothin terms of etch characteristics and etch induced damage thisnew chemistry is superior. Extremely smooth morphologies, lowetch induced damage and an almost complete recovery uponannealing can be obtained with this process. Significantly,this is also so at relatively high ion energies which allowshigher etch rates. <b>Keywords:</b>InP, dry etching, ion beam etching, RIBE,CAIBE, hydrocarbon chemistry, trimethylamine, As/P exchangereaction, morpholoy, low damage, AFM, SCM, annealing

<p>Dry etching is an important technique for pattern transferin fabrication of most opto-electronic devices, since it canprovide good control of both structure size and shape even on asub-micron scale. Unfortunately, this process step may causedamage to the material which is detrimental to deviceperformance. It is therefore an objective of this thesis todevelop and investigate low damage etching processes for InPbased devices.</p><p>An ion beam system in combination with hydrocarbon (CH₄) based chemistries is used for etching. At variousion energies and gas flows the etching is performed in twomodes, reactive ion beam etching (RIBE) and chemical assistedion beam etching (CAIBE). How these conditions affect both etchcharacteristics (e.g. etch rates and profiles, surfacemorphology and polymer formation) and etch induced damage (onoptical and electrical properties) is evaluated and discussed.Attention is also paid to the effects of typical post etchingtreatments such as annealing on the optical and electricalproperties. An important finding is the correlation betweenas-etched surface morphology and recovery/degradation inphotoluminescence upon annealing in PH₃. Since this type of atmosphere is typical forcrystal regrowth (an important process step in III/Vprocessing) a positive result is imperative. A low ion energy N₂/CH₄/H₂CAIBE process is developed which not onlysatisfies this criteria but also exhibits good etchcharacteristics. This process is used successfully in thefabrication of laser gratings. In addition to this, the abilityof the ion beam system to modify the surface morphology in acontrollable manner is exploited. By exposing such modifiedsurfaces to AsH₃/PH₃, a new way to vary size and density of InAs(P)islands formed on the InP surfaces by the As/P exchangereaction is presented.</p><p>This thesis also proposes a new etch chemistry, namelytrimethylamine ((CH₃)₃N or TMA), which is a more efficient methyl sourcecompared to CH₄because of the low energy required to break the H₃C-N bond. Since methyl radicals are needed for theetching it is presumably a better etching chemistry. A similarinvestigation as for the CH₄chemistry is performed, and it is found that bothin terms of etch characteristics and etch induced damage thisnew chemistry is superior. Extremely smooth morphologies, lowetch induced damage and an almost complete recovery uponannealing can be obtained with this process. Significantly,this is also so at relatively high ion energies which allowshigher etch rates.</p><p><b>Keywords:</b>InP, dry etching, ion beam etching, RIBE,CAIBE, hydrocarbon chemistry, trimethylamine, As/P exchangereaction, morpholoy, low damage, AFM, SCM, annealing</p>

Das reaktiv gesteuerte Ionenstrahlätzen von optischen Aluminiumoberflächen bietet einen vielversprechenden Prozessansatz, um Formfehlerkorrektur, Glättung periodischer Drehstrukturen und die Reduzierung von Rauheitsmerkmalen im Ortsfrequenzbereich der Mikrorauheit in einer Technologie zu kombinieren. Diese Arbeit konzentriert sich auf die experimentelle Analyse der niederenergetischen Ionenbestrahlung von einkorn-diamantgedrehten, technischen Aluminiumlegierungen RSA Al6061 und RSA Al905. Die Ionenstrahlbearbeitung unter Verwendung der Prozessgase Sauerstoff und Stickstoff ermöglicht eine direkte Oberflächenformfehlerkorrektur bis zu 1 µm Bearbeitungstiefe unter Beibehaltung der Ausgangsrauheit. Die sich aus dem vorangegangenen Formgebungsverfahren, dem Einkorn-diamantdrehen, ergebende Drehmarkenstruktur schränkt allerdings häufig die Anwendbarkeit dieser Spiegeloberflächen im kurzwelligen Spektralbereich ein. Daher wurde im Rahmen dieser Arbeit ein zweistufiger Prozessablauf entwickelt, um eine weitere Verbesserung der Oberflächenrauheit zu erreichen. Durch die Ionenstrahl-Planarisierungstechnik unter Verwendung einer Opferschicht werden die im hohen Ortsfrequenzbereich liegenden Drehmarken erfolgreich um insgesamt 82 % reduziert. Eine Kombination mit anschließender, direkter Ionenstrahlglättung zur nachfolgenden Verbesserung der Mikrorauigkeit wird vorgestellt. Um die Prozessführung in einem industrietauglichen Rahmen zu etablieren, wurden die experimentellen Untersuchungen mit einer 13,56 MHz betriebenen Hochfrequenz-Ionenquelle durchgeführt, konnten aber auch erfolgreich auf eine Breitstrahl-Ionenquelle vom Typ Kaufman übertragen werden.:Bibliographische Beschreibung iv Danksagung vi Table of Contents viii 1 Introduction 1 2 Surface engineering with energetic ions 8 2.1 Ion target interactions during ion beam erosion 8 2.2 Ion beam finishing methods 10 2.2.1 Ion beam figuring 11 2.2.2 Ion beam planarization 12 2.2.3 Ion beam smoothing 14 3 Experimental set-up and analytical methods 15 3.1 Experimental set-up 15 3.2 Kaufman-type broad beam ion source 18 3.3 Materials 19 3.3.1 Aluminium alloy materials 19 3.3.2 Photoresist materials as planarization layer 21 3.4 Surface topography error regimes 22 3.5 Analytical Methods 23 3.5.1 Analysis of surface roughness 23 3.5.1.1 White light interferometry (WLI) 23 3.5.1.2 Atomic force microscopy (AFM) 25 3.5.1.3 Power spectral density (PSD) analysis 27 3.5.2 Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) 29 3.5.3 X-ray photoelectron spectroscopy (XPS) 31 3.5.4 Time of flight- secondary ion mass spectrometry (ToF-SIMS) 32 3.5.5 Reflectometry 34 3.5.6 Photoresist composition 35 3.5.6.1 Attenuated total reflection infrared spectroscopy (ATR-IR) 35 3.5.6.2 Thermogravimetric analysis (TGA) 36 3.5.6.3 Differential scanning calorimetry (DSC) 38 3.5.6.4 Gas chromatography coupled mass spectrometry (GC-MS) 39 4 Surface engineering by reactive ion beam etching 41 4.1 Reactive ion beam etching with nitrogen 41 4.1.1 Dependence of the aluminium alloy composition 42 4.1.2 Ion beam etching of Al905 44 4.2 Local smoothing by reactive ion beam etching 50 4.2.1 Local surface error slope dependent sputter erosion 51 4.2.2 RIBE O2 direct smoothing 56 4.2.2.1 Oxygen finishing at 1.5 keV 56 4.2.2.2 Oxygen finishing at 0.6 keV 62 4.3 Conclusions 66 5 Technological aspects on photoresist preparation for ion beam planarization 69 5.1 Selection of a suitable photoresist 69 5.2 Photoresist application steps 71 5.2.1 DUV exposure of the photoresist layer 72 5.2.2 Postbake: the influence of the amount of organic solvent 73 5.2.3 Postbake: the influence of the baking temperature 74 5.3 Influence of process gas composition 77 5.3.1 Influence on roughness evolution during ion beam irradiation of the photoresist layer 78 5.3.2 Dependency of the process gas on the selectivity 79 5.4 Influence of the ion energy on the selectivity 80 5.5 Ion beam irradiation of the photoresist layer with nitrogen at different material removal depths 81 5.6 Conclusions 82 6 Ion beam planarization of optical aluminium surfaces RSA Al6061 and RSA Al905 84 6.1 Photoresist application on SPDT aluminium alloys 84 6.2 Ion beam planarization 85 6.2.1 Iterative nitrogen processing of RSA Al905 86 6.2.2 Iterative nitrogen processing of RSA Al6061 90 6.3 Ion beam direct smoothing 93 6.3.1 RIBE O2 smoothing of RSA Al905 93 6.3.2 RIBE O2 smoothing of RSA Al6061 97 6.4 Conclusions 101 7 Process transfer to a Kaufman-type broad beam ion source 103 7.1 RIBE machining investigations on RSA Al905 103 7.2 Ion beam planarization of RSA Al6061 106 7.3 Ion beam incidence angle dependent sputtering 107 7.4 Conclusions 113 8 Summary 115 9 Conclusions and Outlook 123 A List of abbreviations 127 B Selected properties of photoresist materials 129 References 131 / Reactively driven ion beam etching of optical aluminium surfaces provides a promising process route to combine figure error correction, smoothing of periodically turning structures and roughness features situated in the microroughness regime within one technology. This thesis focuses on experimental analysis of low-energy ion beam irradiation on single-point diamond turned technical aluminium alloys RSA Al6061 and RSA Al905. Reactively driven ion beam machining using oxygen and nitrogen process gases enables the direct surface error correction up to 1 µm machining depth while preserving the initial roughness. However, the periodic turning mark structures, which result from preliminary device shaping by single-point diamond turning, often limit the applicability of mirror surfaces in the short-periodic spectral range. Hence, during this work a two-step process route was developed to attain further improvement of the surface roughness. Within the ion beam planarization technique with the aid of a sacrificial layer, the turning marks situated in the high spatial frequency range are successfully reduced by overall 82 %. A combination with subsequently applied direct ion beam smoothing procedure to perform a subsequent improvement of the microroughness is presented. In order to establish the process control in an industrial framework, the experimental investigations were performed using a 13.56 MHz radio frequency ion source, but the developed process routes are also successfully transferred to a broad-beam Kaufman-type ion source.:Bibliographische Beschreibung iv Danksagung vi Table of Contents viii 1 Introduction 1 2 Surface engineering with energetic ions 8 2.1 Ion target interactions during ion beam erosion 8 2.2 Ion beam finishing methods 10 2.2.1 Ion beam figuring 11 2.2.2 Ion beam planarization 12 2.2.3 Ion beam smoothing 14 3 Experimental set-up and analytical methods 15 3.1 Experimental set-up 15 3.2 Kaufman-type broad beam ion source 18 3.3 Materials 19 3.3.1 Aluminium alloy materials 19 3.3.2 Photoresist materials as planarization layer 21 3.4 Surface topography error regimes 22 3.5 Analytical Methods 23 3.5.1 Analysis of surface roughness 23 3.5.1.1 White light interferometry (WLI) 23 3.5.1.2 Atomic force microscopy (AFM) 25 3.5.1.3 Power spectral density (PSD) analysis 27 3.5.2 Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) 29 3.5.3 X-ray photoelectron spectroscopy (XPS) 31 3.5.4 Time of flight- secondary ion mass spectrometry (ToF-SIMS) 32 3.5.5 Reflectometry 34 3.5.6 Photoresist composition 35 3.5.6.1 Attenuated total reflection infrared spectroscopy (ATR-IR) 35 3.5.6.2 Thermogravimetric analysis (TGA) 36 3.5.6.3 Differential scanning calorimetry (DSC) 38 3.5.6.4 Gas chromatography coupled mass spectrometry (GC-MS) 39 4 Surface engineering by reactive ion beam etching 41 4.1 Reactive ion beam etching with nitrogen 41 4.1.1 Dependence of the aluminium alloy composition 42 4.1.2 Ion beam etching of Al905 44 4.2 Local smoothing by reactive ion beam etching 50 4.2.1 Local surface error slope dependent sputter erosion 51 4.2.2 RIBE O2 direct smoothing 56 4.2.2.1 Oxygen finishing at 1.5 keV 56 4.2.2.2 Oxygen finishing at 0.6 keV 62 4.3 Conclusions 66 5 Technological aspects on photoresist preparation for ion beam planarization 69 5.1 Selection of a suitable photoresist 69 5.2 Photoresist application steps 71 5.2.1 DUV exposure of the photoresist layer 72 5.2.2 Postbake: the influence of the amount of organic solvent 73 5.2.3 Postbake: the influence of the baking temperature 74 5.3 Influence of process gas composition 77 5.3.1 Influence on roughness evolution during ion beam irradiation of the photoresist layer 78 5.3.2 Dependency of the process gas on the selectivity 79 5.4 Influence of the ion energy on the selectivity 80 5.5 Ion beam irradiation of the photoresist layer with nitrogen at different material removal depths 81 5.6 Conclusions 82 6 Ion beam planarization of optical aluminium surfaces RSA Al6061 and RSA Al905 84 6.1 Photoresist application on SPDT aluminium alloys 84 6.2 Ion beam planarization 85 6.2.1 Iterative nitrogen processing of RSA Al905 86 6.2.2 Iterative nitrogen processing of RSA Al6061 90 6.3 Ion beam direct smoothing 93 6.3.1 RIBE O2 smoothing of RSA Al905 93 6.3.2 RIBE O2 smoothing of RSA Al6061 97 6.4 Conclusions 101 7 Process transfer to a Kaufman-type broad beam ion source 103 7.1 RIBE machining investigations on RSA Al905 103 7.2 Ion beam planarization of RSA Al6061 106 7.3 Ion beam incidence angle dependent sputtering 107 7.4 Conclusions 113 8 Summary 115 9 Conclusions and Outlook 123 A List of abbreviations 127 B Selected properties of photoresist materials 129 References 131

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.

Photonic crystals (PhCs) are periodic dielectric structures that exhibit a photonic bandgap, i.e., a range of wavelength for which light propagation is forbidden. The special band structure related dispersion properties offer a realm of novel functionalities and interesting physical phenomena. PhCs have been manufactured using semiconductors and other material technologies. However, InP-based materials are the main choice for active devices at optical communication wavelengths. This thesis focuses on two-dimensional PhCs in the InP/GaInAsP/InP material system and addresses their fabrication technology and their physical properties covering both material issues and light propagation aspects. Ar/Cl2 chemically assisted ion beam etching was used to etch the photonic crystals. The etching characteristics including feature size dependent etching phenomena were experimentally determined and the underlying etching mechanisms are explained. For the etched PhC holes, aspect ratios around 20 were achieved, with a maximum etch depth of 5 microns for a hole diameter of 300 nm. Optical losses in photonic crystal devices were addressed both in terms of vertical confinement and hole shape and depth. The work also demonstrated that dry etching has a major impact on the properties of the photonic crystal material. The surface Fermi level at the etched hole sidewalls was found to be pinned at 0.12 eV below the conduction band minimum. This is shown to have important consequences on carrier transport. It is also found that, for an InGaAsP quantum well, the surface recombination velocity increases (non-linearly) by more than one order of magnitude as the etch duration is increased, providing evidence for accumulation of sidewall damage. A model based on sputtering theory is developed to qualitatively explain the development of damage. The physics of dispersive phenomena in PhC structures is investigated experimentally and theoretically. Negative refraction was experimentally demonstrated at optical wavelengths, and applied for light focusing. Fourier optics was used to experimentally explore the issue of coupling to Bloch modes inside the PhC slab and to experimentally determine the curvature of the band structure. Finally, dispersive phenomena were used in coupled-cavity waveguides to achieve a slow light regime with a group index of more than 180 and a group velocity dispersion up to 10^7 times that of a conventional fiber. / QC 20100712

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>

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.:Einleitung I Grundlagen 1 Spinelektronik und Magnetowiderstand 1.1 Der Elektronenspin – Grundlage des Magnetismus 1.2 Magnetoresistive Effekte 1.2.1 AnisotroperMagnetowiderstand 1.2.2 Riesenmagnetowiderstand 1.2.3 Tunnelmagnetowiderstand 1.3 Spin-Transfer-Torque 1.4 Anwendungen 1.4.1 Festplattenleseköpfe 1.4.2 Magnetoresistive Random AccessMemory (MRAM) 1.4.3 Nanooszillatoren für drahtlose Kommunikation 2 Grundlagen der Mikro- und Nanostrukturierung 2.1 Belacken 2.2 Belichten 2.2.1 Optische Lithographie 2.2.2 Elektronenstrahllithographie 2.3 Entwickeln 2.4 Strukturübertragung 2.4.1 Die Lift-off Technik 2.4.2 Ätzen 2.5 Entfernen der Lackmaske 2.6 Reinigung 2.6.1 Quellen von Verunreinigungen 2.6.2 Auswirkungen von Verunreinigungen 2.6.3 Entfernung von Verunreinigungen 2.6.4 Spülen und Trocknen der Probenoberfläche 3 Ionenstrahlätzen 3.1 Physikalisches Ätzen – Sputterätzen 3.2 Reaktives Ionenstrahlätzen – RIBE 3.3 Anlagentechnik 3.3.1 Parameter 3.3.2 Homogenität 3.3.3 Endpunktdetektion II Ergebnisse und Diskussion 4 TMR-Schichtsysteme 4.1 Prinzipielle Schichtfolge 4.2 Verwendete TMR-Schichtsysteme 4.3 Rekristallisation von Kupfer 4.4 Formierung der TMR-Schichtsysteme 4.4.1 Antiferromagnetische Kopplung an PtMn 4.4.2 Rekristallisation an der MgO-Barriere 4.5 Anpassung der MgO-Schicht – TMR-Effekt und RA-Produkt 4.6 Magnetische Charakterisierung 5 Probendesign 5.1 Beschreibung der vier lithographischen Ebenen 5.2 Layout für statische und dynamischeMessungen 5.2.1 Geometrie 5.2.2 Anforderungen für die Hochfrequenzmessung 5.3 Layout für Zuverlässigkeitsmessungen 5.3.1 Geometrie 5.3.2 Voraussetzungen für die Funktion 5.4 Chiplayout 5.4.1 Zusatzstrukturen 5.4.2 Anordnung der Elemente 6 Fertigung eines Maskensatzes für die optische Lithographie 6.1 Vorbereitung desMaskenrohlings 6.2 Strukturierung mittels Elektronenstrahllithographie 6.3 Ätzen der Chromschicht 7 Ergebnisse und Diskussion der Probenpräparation 7.1 Definition der Grundelektrode 7.1.1 Freistellen der Grundelektrode 7.1.2 Gratfreiheit der Grundelektrode 7.1.3 Oberflächenqualität nach der Strukturierung 7.2 Präparation der magnetischen Nanosäulen 7.2.1 Aufbringen einer Ätzmaske 7.2.2 Ionenstrahlätzen der TMR-Nanosäule 7.2.3 Abmessungen der präparierten Nanosäulen 7.3 Vertikale Kontaktierung 7.3.1 Seitenwandisolation 7.3.2 Freilegen der Kontakte 7.3.3 Aufbringen der elektrischen Zuleitungen 7.4 Die komplette Prozesskette und Ausbeute 8 Magneto-elektrische Charakterisierung 8.1 Messung des Tunnelmagnetowiderstandes 8.2 Stabilität der magnetischen Konfiguration 8.3 Spin-Transfer-Torque an TMR-Nanosäulen 9 Zusammenfassung und Ausblick Literaturverzeichnis / 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.:Einleitung I Grundlagen 1 Spinelektronik und Magnetowiderstand 1.1 Der Elektronenspin – Grundlage des Magnetismus 1.2 Magnetoresistive Effekte 1.2.1 AnisotroperMagnetowiderstand 1.2.2 Riesenmagnetowiderstand 1.2.3 Tunnelmagnetowiderstand 1.3 Spin-Transfer-Torque 1.4 Anwendungen 1.4.1 Festplattenleseköpfe 1.4.2 Magnetoresistive Random AccessMemory (MRAM) 1.4.3 Nanooszillatoren für drahtlose Kommunikation 2 Grundlagen der Mikro- und Nanostrukturierung 2.1 Belacken 2.2 Belichten 2.2.1 Optische Lithographie 2.2.2 Elektronenstrahllithographie 2.3 Entwickeln 2.4 Strukturübertragung 2.4.1 Die Lift-off Technik 2.4.2 Ätzen 2.5 Entfernen der Lackmaske 2.6 Reinigung 2.6.1 Quellen von Verunreinigungen 2.6.2 Auswirkungen von Verunreinigungen 2.6.3 Entfernung von Verunreinigungen 2.6.4 Spülen und Trocknen der Probenoberfläche 3 Ionenstrahlätzen 3.1 Physikalisches Ätzen – Sputterätzen 3.2 Reaktives Ionenstrahlätzen – RIBE 3.3 Anlagentechnik 3.3.1 Parameter 3.3.2 Homogenität 3.3.3 Endpunktdetektion II Ergebnisse und Diskussion 4 TMR-Schichtsysteme 4.1 Prinzipielle Schichtfolge 4.2 Verwendete TMR-Schichtsysteme 4.3 Rekristallisation von Kupfer 4.4 Formierung der TMR-Schichtsysteme 4.4.1 Antiferromagnetische Kopplung an PtMn 4.4.2 Rekristallisation an der MgO-Barriere 4.5 Anpassung der MgO-Schicht – TMR-Effekt und RA-Produkt 4.6 Magnetische Charakterisierung 5 Probendesign 5.1 Beschreibung der vier lithographischen Ebenen 5.2 Layout für statische und dynamischeMessungen 5.2.1 Geometrie 5.2.2 Anforderungen für die Hochfrequenzmessung 5.3 Layout für Zuverlässigkeitsmessungen 5.3.1 Geometrie 5.3.2 Voraussetzungen für die Funktion 5.4 Chiplayout 5.4.1 Zusatzstrukturen 5.4.2 Anordnung der Elemente 6 Fertigung eines Maskensatzes für die optische Lithographie 6.1 Vorbereitung desMaskenrohlings 6.2 Strukturierung mittels Elektronenstrahllithographie 6.3 Ätzen der Chromschicht 7 Ergebnisse und Diskussion der Probenpräparation 7.1 Definition der Grundelektrode 7.1.1 Freistellen der Grundelektrode 7.1.2 Gratfreiheit der Grundelektrode 7.1.3 Oberflächenqualität nach der Strukturierung 7.2 Präparation der magnetischen Nanosäulen 7.2.1 Aufbringen einer Ätzmaske 7.2.2 Ionenstrahlätzen der TMR-Nanosäule 7.2.3 Abmessungen der präparierten Nanosäulen 7.3 Vertikale Kontaktierung 7.3.1 Seitenwandisolation 7.3.2 Freilegen der Kontakte 7.3.3 Aufbringen der elektrischen Zuleitungen 7.4 Die komplette Prozesskette und Ausbeute 8 Magneto-elektrische Charakterisierung 8.1 Messung des Tunnelmagnetowiderstandes 8.2 Stabilität der magnetischen Konfiguration 8.3 Spin-Transfer-Torque an TMR-Nanosäulen 9 Zusammenfassung und Ausblick Literaturverzeichnis