Rapid and reliable diagnostics of a disease represents one of the main focuses of today’s academic and industrial research in the development of new sensor prototypes and improvement of existing technologies. With respect to demographic changes and inhomogeneous distribution of the clinical facilities worldwide, especially in rural regions, a new generation of miniaturized biosensors is highly demanded offering an easy deliverability, low costs and sample preparation and simple usage. This work focuses on the integration of nanosized electronic structures for high-specific sensing applications into adequate microfluidic structures for sample delivery and liquid manipulation. Based on the conjunction of these two technologies, two novel sensor platforms were prototyped, both allowing label-free and optics-less electrochemical detection ranging from molecular species to eukaryotic micron-sized human cells.:Table of Figures List of Tables Abbreviations List of Symbols 1 Introduction 1.1 Motivation 1.2 State of the art 1.3 Scope of this thesis 2 Fundamentals 2.1 Sensors at the nanoscale 2.2 Transistors technology 2.2.1 p-n junction 2.2.3 The MOSFET 2.2.4 The ISFET and BioFET 2.3 Impedance measurements for biodetection 2.3.1 Electrical impedance spectroscopy 2.3.2 Electrical impedance cytometry 2.4 Microfluidics 2.4.1 Definition 2.4.2 Droplet-based microfluidics 2.5 Biomarkers for sensing applications 2.5.1 Peripheral blood mononuclear cells (PBMCs) 2.5.2 Physical parameters 3. Material and methods 3.1 General 3.1.1 Materials and chemicals 3.1.2 Surface cleaning 3.2 Lithography 3.2.1 Electron beam lithography 3.2.2 Laser lithography 3.2.3 UV lithography 3.2.4 Soft lithography 3.3 Thermal deposition of metals 3.4 APTES functionalization 3.4.1 Fluorescent labeling of APTES 3.5 Measurement devices 3.5.1 SiNW FET measurements 3.5.2 Electrical Impedance cytometry measurements 3.6 Bacteria and cell cultivation 3.6.1 PBMC purification and treatment 3.6.2 Bacteria cultivation 4. Compact nanosensors probe microdroplets 4.1 Overview 4.2 Fabrication 4.2.1 SiNW FET fabrication 4.2.2 SiNW FET modification for top-gate sensing 4.3 Electrical characterization 4.4 Flow-focusing droplet generation 4.4.1 Flow-focusing geometry 4.4.2 Flow-focusing droplet characterization 4.4.3 Microfluidic integration 4.5 Deionized water droplet sensing 4.6 Phosphate-buffered saline (PBS) droplet sensing 4.6.1 Influence of the droplet’s ionic concentration 4.6.2 Plateau formation in dependence of the droplet’s settling time 4.6.3 Droplet analysis by their ratio 4.6.4 Dependence on pH value 4.6.5 Long time pH sensing experiment 4.6.6 Dependence on ionic concentration 4.7 Tracking of reaction kinetics in droplets 4.7.1 Principle and setup of the glucose oxidase (GOx) enzymatic test 4.7.2 GOx enzymatic assay 4.8 Stable baseline by conductive carrier phase 5. Impedance-based flow cytometer on a chip 5.1 Overview 5.2 Overview of the fabrication of the sensor device 5.3 COMSOL simulation of sensing area 5.3.1 Prototyping of the sensing geometry 5.3.2 Optimization of the sensing geometry 5.3.3 Evaluation of the working potential 5.3.4. Scaling of the sensing area 5.4 Fabrication of the nanoelectronic sensing structure 5.4.1 Nanofabrication and analysis 5.4.2 Evaluation of the proximity effect 5.5 Microcontacting of nanostructured sensing structures 5.6 Electrical characterization of the sensing structure 5.6.1 Characterization in alternating current 5.6.2 Characterization in direct current (DC) 5.7 Scaling effect of nanostructures in static sensing conditions 5.8 Multi-analyte detection on the sensor 5.9 Microfluidic focusing system 5.9.1 1D focusing using FITC-probed deionized water 5.9.2 2D Focusing using fluorescent microparticles 5.10 Microfluidic integration of the two technologies 5.11 Dynamic SiO2 particle detection 5.11.1 Single particle detection 5.11.2 Scatter plot representation 5.11.3 Effect of the sensing area in dynamic particle detection 5.11.4 Dynamic detection of SiO2 particles with different diameters 5.12 Detection of peripheral blood mononuclear cells (PBMCs) 5.12.1 Overview 5.12.2 PBMC classification detected by impedance cytometry 5.12.3 PBMC Long-time detection 5.13 Detection of acute myeloid leukemia by impedance cytometry 5.13.1 Manual analysis of the output response 5.13.2 Learning algorithm for automatic cell classification 5.14 Exploring the detection limit of the device 6. Summary and outlook Scientific output References Acknowledgements / Rasche und zuverlässige biologische Krankheitsdiagnostik repräsentiert eines der Hauptfokusse heutiger akademischer und industrieller Forschung in der Entwicklung neuer Sensor-Prototypen und Verbesserung existierender Technologien. In bezug auf weltweite demographische Änderungen und hohe Distanzen zu Kliniken, besonders in ländlichen Gegenden, werden zusätzliche Anfordungen an neue miniaturisierte Biosensor-Generationen gestellt, wie zum Beispiel ihre Transportfähigkeit, geringe Kosten und Probenpräparation, sowie einfache Handhabung. Diese Dissertation beschäftigt sich mit der Integration nanoskalierter Strukturen zur Detektion chemischer und biologischer Spezies und mikrofluidischen Kanälen zu deren Transport und zur Manipulation der Ströme. Basierend auf der Verbindung dieser beiden Technologien wurden zwei Sensor-Plattformen entwickelt, die eine markierungsfreie und nicht-optische elektrische Detektion von Molekülen bis zu eukaryotischen menschlichen Zellen erlauben.:Table of Figures List of Tables Abbreviations List of Symbols 1 Introduction 1.1 Motivation 1.2 State of the art 1.3 Scope of this thesis 2 Fundamentals 2.1 Sensors at the nanoscale 2.2 Transistors technology 2.2.1 p-n junction 2.2.3 The MOSFET 2.2.4 The ISFET and BioFET 2.3 Impedance measurements for biodetection 2.3.1 Electrical impedance spectroscopy 2.3.2 Electrical impedance cytometry 2.4 Microfluidics 2.4.1 Definition 2.4.2 Droplet-based microfluidics 2.5 Biomarkers for sensing applications 2.5.1 Peripheral blood mononuclear cells (PBMCs) 2.5.2 Physical parameters 3. Material and methods 3.1 General 3.1.1 Materials and chemicals 3.1.2 Surface cleaning 3.2 Lithography 3.2.1 Electron beam lithography 3.2.2 Laser lithography 3.2.3 UV lithography 3.2.4 Soft lithography 3.3 Thermal deposition of metals 3.4 APTES functionalization 3.4.1 Fluorescent labeling of APTES 3.5 Measurement devices 3.5.1 SiNW FET measurements 3.5.2 Electrical Impedance cytometry measurements 3.6 Bacteria and cell cultivation 3.6.1 PBMC purification and treatment 3.6.2 Bacteria cultivation 4. Compact nanosensors probe microdroplets 4.1 Overview 4.2 Fabrication 4.2.1 SiNW FET fabrication 4.2.2 SiNW FET modification for top-gate sensing 4.3 Electrical characterization 4.4 Flow-focusing droplet generation 4.4.1 Flow-focusing geometry 4.4.2 Flow-focusing droplet characterization 4.4.3 Microfluidic integration 4.5 Deionized water droplet sensing 4.6 Phosphate-buffered saline (PBS) droplet sensing 4.6.1 Influence of the droplet’s ionic concentration 4.6.2 Plateau formation in dependence of the droplet’s settling time 4.6.3 Droplet analysis by their ratio 4.6.4 Dependence on pH value 4.6.5 Long time pH sensing experiment 4.6.6 Dependence on ionic concentration 4.7 Tracking of reaction kinetics in droplets 4.7.1 Principle and setup of the glucose oxidase (GOx) enzymatic test 4.7.2 GOx enzymatic assay 4.8 Stable baseline by conductive carrier phase 5. Impedance-based flow cytometer on a chip 5.1 Overview 5.2 Overview of the fabrication of the sensor device 5.3 COMSOL simulation of sensing area 5.3.1 Prototyping of the sensing geometry 5.3.2 Optimization of the sensing geometry 5.3.3 Evaluation of the working potential 5.3.4. Scaling of the sensing area 5.4 Fabrication of the nanoelectronic sensing structure 5.4.1 Nanofabrication and analysis 5.4.2 Evaluation of the proximity effect 5.5 Microcontacting of nanostructured sensing structures 5.6 Electrical characterization of the sensing structure 5.6.1 Characterization in alternating current 5.6.2 Characterization in direct current (DC) 5.7 Scaling effect of nanostructures in static sensing conditions 5.8 Multi-analyte detection on the sensor 5.9 Microfluidic focusing system 5.9.1 1D focusing using FITC-probed deionized water 5.9.2 2D Focusing using fluorescent microparticles 5.10 Microfluidic integration of the two technologies 5.11 Dynamic SiO2 particle detection 5.11.1 Single particle detection 5.11.2 Scatter plot representation 5.11.3 Effect of the sensing area in dynamic particle detection 5.11.4 Dynamic detection of SiO2 particles with different diameters 5.12 Detection of peripheral blood mononuclear cells (PBMCs) 5.12.1 Overview 5.12.2 PBMC classification detected by impedance cytometry 5.12.3 PBMC Long-time detection 5.13 Detection of acute myeloid leukemia by impedance cytometry 5.13.1 Manual analysis of the output response 5.13.2 Learning algorithm for automatic cell classification 5.14 Exploring the detection limit of the device 6. Summary and outlook Scientific output References Acknowledgements

Silicon Nanowire based Reconfigurable Field Effect Transistor (SiNW RFET) presents a solution to increase the system functionality beyond the limits of classical CMOS scaling in More-than-Moore era of semiconductor technology. They are not only spatially reconfigurable, i.e., the source and the drain can be interchangeable in design, but in such devices one can also control the primary charge carrier by controlling the voltage in the control gate. The two key morphological factors controlling reconfigurability are the structure and composition of the Schottky junctions, which serve as the location for Program and Control gates and radial strain induced by the self-limiting oxidation, which influences the carrier mobility resulting in symmetric p and n characteristic curves of an RFET. Despite its potential, in-depth nanoscale studies on the structural and compositional characterization of the key features controlling the reconfigurability are limited and thereby presents as a novel area of research. In this study, the composition and morphology of the Schottky junction and the radial strain profile due to self-limiting oxidation were studied using advanced imaging and sample preparation techniques like Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) imaging alongside with precise sample preparation methods like Focused Ion Beam (FIB) liftout techniques. For analysis of radial strain in nanowires that underwent self-limiting oxidation, a TEM lamella was taken of a cross-section of the NW. The lamella was kept at 200 nm thickness to preserve the strain state of the nanowire cross-section. It was observed that nanowires undergoing such oxidation have an omega (Ω) shaped oxide shell where the shell was discontinued at the spot where the nanowire was touching the substrate. Fast Fourier transform of the high-resolution image of such a NW crossection was used to calculate the strain profile. The strain is also found to be not radially uniform for such Ω shaped oxide shells. The strain profile shows a local maxima near the nanowire base where it touches the substrate then a minima approximately at the geometric center followed by the maximum strain at the area adjacent to the oxide shell thereby showing a sinusoidal profile. Theoretical simulations performed by Dr. Tim Baldauf further verified the nature of the sinusoidal strain that was observed experimentally. Similar simulations were done for different omega shell shapes, which yielded strain plots of similar sinusoidal strain plots, with the local maxima depending on the level of encapsulation of the NW by the shell. In the characterization of the Schottky junction, a TEM lamella was taken along the longitudinal direction of a nanowire, which was silicidized from both ends, similar to ones used in SiNW RFET devices. High resolution TEM micrographs and EDX (Energy dispersive X-Ray Spectroscopy) in the TEM along the Schottky junction showed a Ni rich phase and pure Si on either side of the junction. This participating phase was identified as NiSi2. However, the transition between the phases shows a gradient and in-situ experiments were designed to verify the sharpness of the junction. In in-situ silicidation experiments, Si nanowires with a thin native oxide shell were distributed on an electron transparent surface and were partially covered with Ni islands by shadow sputtering. The whole setup was then heated in a heating stage of a TEM and the Ni was allowed to disperse within the Si nanowires forming NiSi2. HRTEM (High Resolution TEM), EDX and EELS (Electron Energy Loss Spectroscopy) studies were performed on the silicidized samples for further ex-situ analysis. During the in-situ experiment, it was observed that Ni-phase interface is atomistically sharp and seldom progresses perpendicularly to the nanowire’s direction but through the closed packed planes of the NW. The interface velocity at different temperatures was used to calculate the activation energy of the silicidation process. The value of the activation energy indicates the Ni undergoing volume diffusion through the Ni-rich phase. The velocity of the interface was observed to be much higher in nanowires with smaller diameters than those with higher diameters, further proving the hypothesis. During the in-situ experiments, in around 10% of nanowires that underwent complete silicidation and held isothermally, the crystalline silicide phase was observed to partially or fully diffuse out of the nanowire core, leaving only a thin shell of Silicon oxide forming ultra-thin walled SiO2 nanotubes (NT). The onset and the time required for completion of the process varies in the nanowires depending on size of the nanowire, the distance and contact to the nearest Ni islands and presence of defects such as kinks and twists within the nanowire. In order to study the dynamics of the process, the velocity of the receding front was calculated for nanowires of two different diameters. They are found to be identical, indicating the volume flow rate of the process is directly proportional to the cross-sectional area. The voids were formed by the reduced diffusivity of Ni in Ni2Si phase in comparison to phases with lower percent of Ni. This indicates that the reason behind the phenomenon is coalition of Kirkendall voids and thus dependent on volume diffusion. From this study, it can be concluded that the extent of self-limiting oxidation and shape of the shell can influence the radial strain state. This can be used to manipulate the strain to tailor the electron and hole transfer characteristics within the RFET. A variety of factors including temperature, time, orientation and radius of the nanowires has been studied with respect to silicidation of a SiNW. The calculated activation energy can be used for precise process control over the location and morphology of Schottky junction. Although not directly related to SiNW RFET devices, the self-assembly of ultra-thin-walled SiO2 NT is a novel research area in itself, the findings of which can be applied in to design novel electronics and sensors.:TABLE OF CONTENTS Preface List of Abbreviations CHAPTER 1: Introduction and Motivation 1.1 Definition and History 1.2 Synthesis Routes 1.3 Properties and Applications 1.4 Nanoscale Electronics and Role of Si Nws 1.4.1 1.4.2 SiNW Reconfigurable Field Effect Transistor 1.5 Introduction to The Topic of The Thesis 1.6 Outline of The Thesis CHAPTER 2: Physical Basics and Previous Research: A Short Summary 2.1 Strain Measurement and Effects of Strain on on Nanoelectronics 2.1.1 Strain Analysis in Planar CMOS Structures 2.2 Silicidation and Schottky Junction 2.2.1 In-situ Silicidation 2.2.2 Silicon oxide nanotubes CHAPTER 3: Background of Instruments and Experimental Set-up 3.1 Scanning Electron Microscope 3.2 Transmission Electron Microscope 3.2.1 Imaging Techniques 3.2.2 TEM sample preparation 3.3 Focused Ion Beam CHAPTER 4: Strain in Nanowire 4.1 Goal of This Study 4.2 Strain in SiNW RFET Devices 4.3 Strain Analysis in SiNW Cross-section 4.3.1 Sample Preparation 4.3.2 Experimental Process 4.3.3 Results and Discussion 4.4 Conclusions CHAPTER 5: Schottky Junction 5.1 Crystallographic Data on Nickel Silicides 5.2 Formation of Silicides in 2-D Structures 5.2.1 Sample History 5.2.2 Sample Preparation 5.2.3 Results and Discussion 5.3 Formation of Silicides in 1-D Structures: Schottky Junction in NWs 5.3.1 Sample History 5.3.2 Sample Preparation 5.3.3 Results and Discussion 5.3.4 Shortcomings of The Lift-out Technique 5.4 In-situ Silicidation 5.4.1 Motivation 5.4.2 Sample Preparation 5.4.3 Experimental Procedure 5.4.4 Results and Discussions 5.4.5 Shortcoming of The Experiment 5.5 Self-assembling SiO2 Nanotubes 5.5.1 Sample Preparation 5.5.2 Experimental Process 5.5.3 Results and Discussion . 5.5.4 Post In-situ Experiment TEM Analysis 5.5.5 Conclusions CHAPTER 6: Conclusions and Outlook 6.1 Strain Analysis 6.2 Schottky Junction Studies Bibliography Acknowledgements

We report the self assembly of nanostructures via. the bottom-up approach by dielectrophoresis. Dielectrophoresis deals with the force on an electric dipole placed in an external in-homogenous field. The force depends on the geometry and volume of the dielectric material and on the frequency and gradient of the electric field. We report the self-assembly of metallic palladium nanowires from the aqueous solution by dielectrophoresis. The metal cations with the surrounding hydration shell and counter-ion cloud results in the formation of a dipole which responds to the local dielectrophoretic forces. Structural properties and morphology of the palladium nanowires are listed. Depending on the experimental conditions two different types of nanowires were grown. Some of them were extremely thin (5 nm diameter) and branched while the others were thick (25 nm diameter) and dendritic. The wire formation can be divided into the nucleation and growth process. For the particle assembly, a minimum threshold force is needed to overcome the random Brownian motion. The nucleation depends on the asperities on the electrode surface and the growth depends on the tip of the growing wires where exists extremely high field magnitude and in-homogeneties and so the force overcomes the threshold at these locations. We showed that wire growth depends a lot on the formation of the double layer at the electrode/solution interface and potential drop within the double layer. Carbon nanotubes (CNT) were also deposited between the electrodes leading to the formation of field-effect transistors (FETs). We produced CNTFETs having extremely high on/off ratio, in a single step without the requirement of any intermediate burning process of the metallic tubes. Besides these inorganic systems, we also investigated the dielectrophoretic experimental conditions required for self assembly of bio-molecules like microtubules between the electrodes. Hybrid structures were also formed by mixing these materials in combination of two. In conclusion, we report in this work the possibility to assemble a large variety of particles (ions, neutral particles and bio-molecules) between the electrodes leading to the device formation. The thesis was mainly devoted to the task for the synthesis and assembly of the nanostructures via. the bottom-up approach.

This contribution discusses scaling aspects of individually gated nanowire Schottky junctions which are essential parts of reconfigurable field effect transistors (RFETs). The applicability of the screening (or natural) length theory in relation to the carrier transport is discussed first. Various geometrical parameters of the device were investigated to find the optimal structure in terms of performance. For this purpose, electrostatic properties and the dynamic behavior of the RFET were studied. Finally the increase in performance due to an additional substitution of the silicon by germanium is analyzed.

As modern microelectronics advances, enormous challenges have to be overcome in order to further increase device performance, enabling highspeed and ultra-low-power applications. With progressive scaling of Silicon MOSFETs, charge carrier mobility has dropped significantly and became a critical device parameter over the last decade. Present technology nodes make use of strain engineering to partially recover this mobility loss. Even though carrier mobility is a crucial parameter for present technology nodes, it cannot be determined accurately by methods typically available in industrial environments. A major objective of this work is to study the magnetoresistance mobility μMR of strained VLSI devices based on a 28 nm ground rule. This technique allows for a more direct access to charge carrier mobility, compared to conventional current/ voltage and capacitance/ voltage mobility derivation methods like the effective mobility μeff, in which series resistance, inversion charge density and effective channel length are necessary to extract the mobility values of the short channel devices. Aside from providing an anchor for accurate μeff measurements in linear operation conditions, μMR opens the possibility to investigate the saturation region of the device, which cannot be accessed by μeff. Electron and hole mobility of nFET and pFET devices with various gate lengths are studied from linear to saturation region. In addition, the interplay between mobility enhancement due to strain improvement, and mobility degradation due to short channel effects with decreasing channel length is analyzed. As a concept device for future nanoelectronic building blocks, silicon nanowire Schottky field-effect transistors are investigated in the second part of this work. These devices exhibit an ambipolar behaviour, which gives the opportunity to measure both electron and hole transport on a single device. The temperature dependence of the source/drain current for specific gate and drain voltages is analyzed within the framework of voltage dependent effective barrier heights.:1. Einleitung 2. Theoretische Grundlagen 3. Charakterisierungsmethoden 4. Messaufbau 5. Ergebnisse der Untersuchungen an MOSFETs 6. Ergebnisse der Untersuchungen an SiNW Transistoren 7. Zusammenfassung Anhang Danksagungen

Single-crystalline nanostructures often exhibit gradients of surface (and/or interface) curvature that emerge from fabrication and growth processes or from thermal fluctuations. Thus, the system-inherent capillary force can initiate morphological transformations during further processing steps or during operation at elevated temperature. Therefore and because of the ongoing miniaturization of functional structures which causes a general rise in surface-to-volume ratios, solid-state capillary phenomena will become increasingly important: On the one hand diffusion-mediated capillary processes can be of practical use in view of non-conventional nanostructure fabrication methods based on self-organization mechanisms, on the other hand they can destroy the integrity of nanostructures which can go along with the failure of functionality. Additionally, capillarity-induced shape transformations are effected and can thereby be controlled by applied fields and forces (guided or driven evolution). With these prospects and challenges at hand, formation and shape transformation of single-crystalline nanostructures due to the system-inherent capillary force in combination with external fields or forces are investigated in the frame of this dissertation by means of atomistic computer simulations. For the exploration (search, description, and prediction) of reaction pathways of nanostructure shape transformations, kinetic Monte Carlo (KMC) simulations are the method of choice. Since the employed KMC code is founded on a cellular automaton principle, the spatio-temporal development of lattice-based N-particle systems (N up to several million) can be followed for time spans of several orders of magnitude, while considering local phenomena due to atomic-scale effects like diffusion, nucleation, dissociation, or ballistic displacements. In this work, the main emphasis is put on nanostructures which have a cylindrical geometry, for example, nanowires (NWs), nanorods, nanotubes etc.

Our society demands for increasingly powerful and efficient microprocessors. However, the conventional method to achieve this, i.e. by reducing the device dimensions and operation voltage of field-effect transistors (FETs), is approaching physical limits. This state of things is driving science and industry to consider new approaches for the generation of efficient logic devices. An emerging solution is the use of reconfigurable FETs (RFETs) that – unlike conventional CMOS transistors – do not need doping but can be toggled between p- and n-type behavior in runtime. For this to be possible, it is necessary to employ an intrinsic channel with Schottky junctions at source and drain. A program gate then toggles the polarity of the device at the Schottky junction on the drain side while one or more additional control gates switch the transistor on or off. This allows to create compact and delay-efficient logic gates that can switch their functionality dynamically, e.g. to save area or to prevent the disclosure of the circuit functionality. Additionally, the ability to include multiple gates in a single transistor to implement a wired-AND functionality allows to create power- and delay-efficient circuits. This thesis demonstrates that such devices can be created by means of a lithographic top-down technology based on commercial silicon-on-insulator (SOI) wafers. In order to ensure a compatibility with future CMOS process lines, the channels are created from silicon nanosheets and nanowires, which will most likely substitute the current FinFET and FD-SOI technology in the future. Nano-dimensional channels allow for ideal electrostatic control by the gates especially if the gates surround them. For this purpose, a process employing multiple oxide etching and oxidation steps, nickel silicide formation and the structuring of conformal metal gates is developed to create shrank and omega-gated nanosheets and nanowires with atomically sharp source and drain Schottky junctions. The resulting RFETs feature high on-current densities, high on/off current ratios and up to four individual gates that realize a wired-AND functionality. More importantly, in contrast to top-down fabricated RFETs in earlier works, these RFETs provide symmetrical electrical characteristics for p- and n-configuration but only need a single supply voltage. These properties will allow to create circuits of cascaded, static logic gates with polarity-independent signal delay times and no need for interposed buffers to refresh the signals. Additionally, the use of ferroelectric materials to create RFETs with nonvolatile programming has been tested at a Schottky-barrier MOSFET. Unfortunately, contact fabrication by self-aligned silicidation can lead to some difficulties: The silicide intrusion length varies widely even between similar nanowires on the same chip, which makes the fabrication of short channels and the application of narrow gates particularly challenging. Detailed analyses in this work show that the variation is mainly caused by the variable amount of nickel supplied. Several material-, temperature- and geometry-based methods to gain a more homogeneous silicidation length are tested. One of these methods employs the layout freedom of the top-down technology to create novel structures of nanowires with local volume extensions. When using a single nickel source, these structures allow to study the impact of wire geometry on silicidation dynamics independently from the nickel contact quality. The gained findings have implications well beyond the application in RFETs, as nickel silicidation is widely used in state-of-the-art semiconductor technology.:Abstract Kurzzusammenfassung 1 Introduction 2 Fundamentals and state-of-the-art of reconfigurable field-effect transistors 2.1 Schottky junction 2.2 Schottky-barrier field-effect transistor 2.3 Current control by the gate voltage 2.4 Reconfigurable FETs 2.4.1 Working principle 2.4.2 Architectures and channel materials of RFETs in prior works 2.4.3 Applications 2.4.4 Requirements for the use in circuits 3 Transistor fabrication 3.1 Electron-beam lithography 3.2 Top-down nanowire fabrication 3.3 Nanowire oxidation and underetch 3.3.1 Oxidation of nanowires 3.3.2 Oxidation processes 3.4 Top-gate fabrication 3.4.1 Basic process for tri-gate 3.4.2 Advanced process for omega-gate 3.4.3 Integration of ferroelectric hafnium-zirconium oxide 3.5 Contact formation by nickel silicidation 3.5.1 Contact metal selection 3.5.2 Nickel deposition and silicide formation 3.5.3 Influences on nickel silicidation in nanowires 3.5.3.1 General 3.5.3.2 Silicide and void formation in different nanowire orientations 3.5.3.3 Influence of nanowire width on silicidation length 3.5.3.4 Importance of an oxide shell 3.5.3.5 Titanium interlayer and exhaustible nickel source 3.5.3.6 Influence of the contact to the nickel supply 3.5.3.7 Effect of temperature on silicidation length homogeneity 3.6 Gate-first and gate-last approach 3.7 RFET circuit realization 3.7.1 Logic gate layout 3.7.2 Mix-and-match technology 4 Nickel silicidation in extended wire geometries 4.1 Silicidation into areas 4.2 Control of silicide growth regime by extensions to nanowires 4.3 Polder extensions for controlled silicidation lengths 4.3.1 Concept and model 4.3.2 Experimental verification 5 Transistor characteristics 5.1 Measurement setup 5.2 Single gate Schottky-barrier MOSFET 5.2.1 Back-gate control 5.2.2 Single top-gate control 5.3 Double top-gate RFET 5.3.1 Tri-gate architecture by gate-last fabrication 5.3.2 Omega-gate architecture by gate-first fabrication 5.4 Multiple independent top-gate RFET 5.4.1 Value of multiple independent gates 5.4.2 Single channel MIG-RFET 5.4.3 Multiple channel MIG-RFET 5.5 Towards nonvolatile RFETs using ferroelectric gate dielectric 5.5.1 Fundamentals and applications of ferroelectric materials in FETs 5.5.2 Schottky-barrier MOSFET with ferroelectric gate 5.6 Performance comparison to state-of-the-art RFETs 6 Conclusion 7 Outlook 7.1 Enhanced understanding, performance and yield of RFETs 7.2 RFETs with split channels 7.3 Silicidation control 8 Appendix 8.1 Analysis of unsuccessful silicidation on circuit chips Bibliography Own publications List of constants and symbols List of abbreviations Acknowledgments Curriculum Vitae / Unsere Gesellschaft verlangt nach immer leistungsfähigeren und effizienteren Mikroprozessoren. Die herkömmlichen Methoden, d.h. das Reduzieren der Bauelementabmessungen und der Betriebsspannung von Feldeffekttransistoren (FETs), nähern sich jedoch physikalischen Grenzen. Diese Tatsache veranlasst Forschung und Industrie dazu, neue Ansätze bei der Erzeugung von effizienten logischen Schaltkreisen zu verfolgen. Auf großes Interesse stößt dabei die Verwendung von rekonfigurierbaren Feldeffekttransistoren (RFETs), die im Gegensatz zu herkömmlichen FETs keine Dotierung benötigen, sondern jederzeit zwischen p- und n-Typ Verhalten umgeschaltet werden können. Dazu wird ein intrinsischer Kanal mit Schottky-Kontakten an den Drain- und Source-Anschlüssen benötigt. Außerdem wird ein Programmier-Gate verwendet um die Polarität des Bauelements festzulegen, und ein oder mehrere weitere Kontroll-Gates schalten den Transistor ein oder aus. Dies ermöglicht es kompakte und laufzeiteffiziente Logikgatter zu konstruieren, die ihrer Funktionalität dynamisch verändern können, zum Beispiel um den Flächenverbrauch zu reduzieren oder um eine Enthüllung der Schaltkreisfunktionalität zu verhindern. Außerdem können in einem einzelnen Transistor mehrere Gates angelegt werden. Die sich ergebende nicht-komplementäre UND-Verkettung kann dazu genutzt werden, um energie- und laufzeit-sparende Schaltkreise zu generieren. Diese Arbeit weist nach, dass solche Bauelemente mit einem lithographischen Top-Down-Ansatz auf Basis von kommerziellen Silizium-auf-Isolator Substraten (sog. SOI-Wafern) realisierbar sind. Um eine Kompatibilität mit zukünftigen CMOS-Prozesslinien sicherzustellen, wurden die Kanäle aus nanometer-dünnen Silizium-Drähten oder -Bändern gebildet. Es wird erwartet, dass solche Kanalgeometrien bald die heutigen FinFET und FD-SOI Technologien ablösen werden, weil sie insbesondere mit umschließendem Gate eine optimale elektrostatische Gate-Kontrolle über den Kanal aufweisen. Der in dieser Arbeit entwickelte Prozess umfasst daher mehrfache Oxid-Ätzungen und Oxidationen zur Schrumpfung und teilweisen Unterätzung der Kanäle, die Bildung von abrupten Schottky-Kontakten aus Nickel-Silizid und die Strukturierung umschließender Metall-Gates. Die erzeugten RFETs weisen besonders hohe Stromdichten im An-Zustand und sehr hohe Verhältnisse von An- zu Aus-Strom auf. Außerdem besitzen sie bis zu vier unabhängige Gates, deren Eingänge somit quasi UND-verknüpft sind. Vor allem aber weisen diese RFETs im Gegensatz zu vorangegangenen Arbeiten symmetrische elektrische Charakteristiken für p- und n-Konfiguration auf, wozu sie sogar nicht mehr als eine Betriebsspannung benötigen. Diese Eigenschaften ermöglichen die Erzeugung von Schaltkreisen aus verkoppelten Logikgattern, bei denen die Signal-Laufzeit nicht von der Polarität der Transistoren abhängt und bei denen die Signale nicht durch zwischengeschaltete Pufferschaltungen aufgefrischt werden müssen. Darüber hinaus wurde in einem Schottky-Barrieren FET die Verwendung ferroelektrischer Materialien erprobt, mit denen zukünftig RFETs mit nichtflüchtiger Programmierung erzeugt werden könnten. Leider bereitet die Kontaktbildung durch die selbst-ausgerichtete Silizidierung häufig Probleme: Die Silizid-Eindringlänge schwankt stark, selbst zwischen ähnlichen Nanodrähten auf demselben Chip, was die Herstellung kurzer Kanäle und die Verwendung schmaler Gates besonders erschwert. Detaillierte Analysen in dieser Arbeit zeigen, dass insbesondere der ungleiche Nachschub von Nickel diese Varianz verursacht. Verschiedene material-, temperatur- und geometrie-basierte Ansätze wurden getestet um homogenere Silizid-Eindringlängen zu erreichen. Einer dieser Ansätze macht sich zunutze, dass mit der Top-Down-Technologie beliebige Strukturen definiert werden können, sodass Nanodrähte lokal erweitert werden können. Wenn solche Strukturen mit nur einer einzelnen Nickelquelle verbunden sind, kann der Einfluss der Drahtgeometrie auf den Silizidierungsprozess unabhängig von der Güte des Nickel-Kontakts beobachtet werden. Die auf diese Weise gewonnenen Erkenntnisse sind über die Arbeit an RFETs hinaus von Relevanz, da die Nickel-Silizidierung in vielen modernen Halbleiterprozessen zum Einsatz kommt.:Abstract Kurzzusammenfassung 1 Introduction 2 Fundamentals and state-of-the-art of reconfigurable field-effect transistors 2.1 Schottky junction 2.2 Schottky-barrier field-effect transistor 2.3 Current control by the gate voltage 2.4 Reconfigurable FETs 2.4.1 Working principle 2.4.2 Architectures and channel materials of RFETs in prior works 2.4.3 Applications 2.4.4 Requirements for the use in circuits 3 Transistor fabrication 3.1 Electron-beam lithography 3.2 Top-down nanowire fabrication 3.3 Nanowire oxidation and underetch 3.3.1 Oxidation of nanowires 3.3.2 Oxidation processes 3.4 Top-gate fabrication 3.4.1 Basic process for tri-gate 3.4.2 Advanced process for omega-gate 3.4.3 Integration of ferroelectric hafnium-zirconium oxide 3.5 Contact formation by nickel silicidation 3.5.1 Contact metal selection 3.5.2 Nickel deposition and silicide formation 3.5.3 Influences on nickel silicidation in nanowires 3.5.3.1 General 3.5.3.2 Silicide and void formation in different nanowire orientations 3.5.3.3 Influence of nanowire width on silicidation length 3.5.3.4 Importance of an oxide shell 3.5.3.5 Titanium interlayer and exhaustible nickel source 3.5.3.6 Influence of the contact to the nickel supply 3.5.3.7 Effect of temperature on silicidation length homogeneity 3.6 Gate-first and gate-last approach 3.7 RFET circuit realization 3.7.1 Logic gate layout 3.7.2 Mix-and-match technology 4 Nickel silicidation in extended wire geometries 4.1 Silicidation into areas 4.2 Control of silicide growth regime by extensions to nanowires 4.3 Polder extensions for controlled silicidation lengths 4.3.1 Concept and model 4.3.2 Experimental verification 5 Transistor characteristics 5.1 Measurement setup 5.2 Single gate Schottky-barrier MOSFET 5.2.1 Back-gate control 5.2.2 Single top-gate control 5.3 Double top-gate RFET 5.3.1 Tri-gate architecture by gate-last fabrication 5.3.2 Omega-gate architecture by gate-first fabrication 5.4 Multiple independent top-gate RFET 5.4.1 Value of multiple independent gates 5.4.2 Single channel MIG-RFET 5.4.3 Multiple channel MIG-RFET 5.5 Towards nonvolatile RFETs using ferroelectric gate dielectric 5.5.1 Fundamentals and applications of ferroelectric materials in FETs 5.5.2 Schottky-barrier MOSFET with ferroelectric gate 5.6 Performance comparison to state-of-the-art RFETs 6 Conclusion 7 Outlook 7.1 Enhanced understanding, performance and yield of RFETs 7.2 RFETs with split channels 7.3 Silicidation control 8 Appendix 8.1 Analysis of unsuccessful silicidation on circuit chips Bibliography Own publications List of constants and symbols List of abbreviations Acknowledgments Curriculum Vitae

In dieser Arbeit werden das Wachstum und die optischen Eigenschaften von selbstorganisierten GaN Nanodrähten auf TiN und nanodrahtbasierten (In,Ga)N/GaN Heterostrukturen für LED Anwendungen untersucht. Zu diesem Zweck wird das selbstorganisierte Wachstum von langen, dünnen und nicht koaleszierten GaN Nanodrähten auf TiN mittels Molekularstrahlepitaxie demonstriert. In weiteren Untersuchungen werden diese gut separierten und nicht koaleszierten GaN Nanodrähte auf TiN als Basis für die Herstellung von axialen und radialen Heterostrukturen verwendet. Trotz der definierten Morphologie der aktiven Zonen ist die Lichtausbeute der axialen (In,Ga)N Quantentöpfen eher gering. Um das Potenzial der Molekularstrahlepitaxie für das Wachstum von Kern-Hüllen-Strukturen im Allgemeinen besser zu verstehen, wird der Aspekt, dass die Seitenfacetten der Nanodrähte nur sequentiell den verschiedenen Materialstrahlen ausgesetzt werden, durch Modellierung des Wachstums von GaN Hüllen auf GaN Nanodrähten untersucht. Es wird gezeigt, dass Ga Adatomdiffusionsprozesse zwischen verschiedenen Facetten das Wachstum auf den Seitenfacetten stark beeinflussen. Neben der Untersuchung von radialsymmetrischen (In,Ga)N Hüllen wird ein neuer Wachstumsansatz vorgestellt, der die kontrollierte Abscheidung von III-Nitridhüllen auf verschiedenen Seiten des Nanodrahtes ermöglicht. Unter Ausnutzung der Richtungsabhängigkeit der Materialstrahlen in einer Molekularstrahlepitaxieanlage ermöglicht der neuartige Ansatz die sequentielle Abscheidung verschiedener Verbundstoffmaterialien auf einer bestimmten Seite der Nanodrähte, um eine einseitige Schale zu wachsen. Diese sequentielle gerichtete Abscheidungsmethode ermöglicht prinzipiell die Kombination mehrerer aktiver Zonen mit unterschiedlichen Eigenschaften auf verschiedenen lateralen Seiten ein und derselben Nano- oder Mikrostruktur. Solche Architekturen könnten beispielsweise für die Realisierung von mehrfarbigen Pixeln für Mikro-LED-Displays interessant sein. / In this thesis, the growth and the optical characteristics of self-assembled GaN nanowires on TiN and nanowire-based (In,Ga)N/GaN heterostructures for LED applications is investigated. To this end, the self-assembled growth of long, thin and uncoalesced GaN nanowires on TiN by molecular beam epitaxy is demonstrated. Subsequently, these well-separated and uncoalesced GaN nanowires on TiN are used as a basis for the fabrication of axial and radial heterostructures. Despite the well-defined morphology of the active regions, the luminous efficiency of axial (In,Ga)N quantum wells is found to be rather low. To better understand the potential of molecular beam epitaxy for the growth of core-shell structures in general, the aspect of the side facets of the nanowires being only sequentially exposed to the different material beams is studied by modeling the shell growth of GaN shells on GaN nanowires. It is shown that Ga adatom diffusion processes between different facets strongly affect the growth on the side facets. Besides the fundamental investigation of the growth of radially symmetric (In,Ga)N shells, a new growth approach which allows the controlled deposition of III-nitride shells on different sides of the nanowire is presented. Using the directionality of the material beams in an molecular beam epitaxy system, the novel approach facilitates the sequential deposition of different compound materials on a specific side of the nanowires to grow a one-sided shell. This sequential directional deposition method may in principle allow the combination of multiple active regions with different properties on different lateral sides of one and the same nano- or microstructure. Such architectures, for instance, might be interesting for the realization of multi-color pixels for micro-LED displays.

Ziel dieser Arbeit war die Entwicklung neuer Methoden in der Rasterkraftmikroskopie, um die Qualität und Interpretierbarkeit von Oberflächenabbildungen auf der Nanometerskala, vor allem jener sehr weicher Proben, entscheidend zu verbessern. Der für polymere und biologische Materialien standardmäßig verwendete intermittierende Kontaktmodus führt auf weichen Oberflächen zu verfälschten Abbildungen der Topographie und der mechanischen Eigenschaften. In dieser Arbeit wurden Techniken entwickelt, die einerseits zerstörungsfreie, tiefenaufgelöste Rasterkraftmikroskopie und andererseits Einzelmessungen mit variabler Dämpfung im intermittierenden Kontaktmodus ermöglichen. Die laterale Auflösung beider Methoden liegt dabei im Rahmen herkömmlicher Techniken (< 10 nm). Die Tiefenauflösung konnte im Vergleich zu anderen Methoden um eine Größenordnung auf unter 1 nm verbessert werden. Die neuen Methoden wurden auf einer breiten Palette polymerer Materialien angewandt. Die räumliche Struktur oberflächennaher Bereiche eines Blockcopolymerfilms konnte im Vergleich zu herkömmlichen Methoden deutlich genauer abgebildet werden. Gleiches wurde auf elastomerem Polypropylen erreicht. Es konnten weiche, amorphe Deckschichten auf teilkristallinen Polymeren nachgewiesen und vermessen werden, was in der organischen Elektronik eine wichtige Rolle spielen kann. Die innere Struktur selbstangeordneter Nanodrähte aus Oligothiophen-Aggregaten konnte aufgelöst werden und es wurde die Selbstanordnung von Kollagenfibrillen im gequollenen Zustand beobachtet.

Ziel dieser Arbeit war die Entwicklung neuer Methoden in der Rasterkraftmikroskopie, um die Qualität und Interpretierbarkeit von Oberflächenabbildungen auf der Nanometerskala, vor allem jener sehr weicher Proben, entscheidend zu verbessern. Der für polymere und biologische Materialien standardmäßig verwendete intermittierende Kontaktmodus führt auf weichen Oberflächen zu verfälschten Abbildungen der Topographie und der mechanischen Eigenschaften. In dieser Arbeit wurden Techniken entwickelt, die einerseits zerstörungsfreie, tiefenaufgelöste Rasterkraftmikroskopie und andererseits Einzelmessungen mit variabler Dämpfung im intermittierenden Kontaktmodus ermöglichen. Die laterale Auflösung beider Methoden liegt dabei im Rahmen herkömmlicher Techniken (< 10 nm). Die Tiefenauflösung konnte im Vergleich zu anderen Methoden um eine Größenordnung auf unter 1 nm verbessert werden. Die neuen Methoden wurden auf einer breiten Palette polymerer Materialien angewandt. Die räumliche Struktur oberflächennaher Bereiche eines Blockcopolymerfilms konnte im Vergleich zu herkömmlichen Methoden deutlich genauer abgebildet werden. Gleiches wurde auf elastomerem Polypropylen erreicht. Es konnten weiche, amorphe Deckschichten auf teilkristallinen Polymeren nachgewiesen und vermessen werden, was in der organischen Elektronik eine wichtige Rolle spielen kann. Die innere Struktur selbstangeordneter Nanodrähte aus Oligothiophen-Aggregaten konnte aufgelöst werden und es wurde die Selbstanordnung von Kollagenfibrillen im gequollenen Zustand beobachtet.