Design and fabrication of silver microelectrodes for biomedical applications

Tese de doutoramento em Engenharia BiomédicaO cancro é uma das maiores causas de mortalidade e morbilidade em países desenvolvidos em todo o mundo. É geralmente precedido por alterações pré-cancerígenas e a sua deteção precoce, especialmente numa fase de displasia, é um dos grandes objetivos da medicina moderna, visto que as probabilidades de tratamento aumentam consideravelmente nesta fase. Estudos in-vitro demonstraram que alterações no pH a nível do ambiente intra- e extracelular podem estar correlacionadas com a proliferação de células tumorais em diferentes estados. Contudo, medições in-situ das propriedades eletroquímicas das células podem ser desafiantes e requerer equipamento complexo ou dispendioso. A ambição desta tese consiste no desenvolvimento de ferramentas inovadoras para o diagnóstico celular in-vitro e in-situ, com base em elétrodos micrométricos “solid-state” com capacidade de leitura de pH. Este sistema deverá, preferencialmente, ser compatível e permitir a integração de componentes “lab-on-chip” subsequentes, maioritariamente de processos óticos para posterior análise química e biológica. O protótipo proposto consiste numa matriz de 9600 microelétrodos “solid-state” com pontas nanométricas. O processo de fabricação consiste na padronização de um molde negativo para as pontas individuais de cada microelétrodo, seguido de um aumento na altura do perfil (para um maior “aspect-ratio” e capacidade de penetração) através da adição de um Photoresist, preenchimento do molde com Prata através de um processo inovador de Eletrodeposição “Through-Silicon”, e finalmente a transferência do perfil para um substrato de vidro com compatibilidade com processos óticos. Os resultados finais demonstram a prova de conceito da viabilidade do processo e dos múltiplos desenvolvimentos em engenharia de processos, apesar de estudos e otimizações subsequentes serem necessárias em diversas áreas do projeto de forma a melhor compreender os princípios e mecânicas por detrás de alguns aspetos dos processos inovadores.Cancer is one of the major causes of mortality and morbidity in developed countries worldwide. It is usually preceded by precancerous changes and its early detection, especially at the dysplasia stage, is one of the major goals in modern medicine, as the chances of a successful treatment are increased at this stage. In-vitro studies have demonstrated that pH changes in both the intracellular and extracellular environment of a tissue can be correlated with tumor cell proliferation at different stages. However, in-situ measurements of the electrochemical properties of cells can be challenging and require complex or costly equipment. In this thesis, the ambition is to develop a novel tool for in-vitro and in-situ cell diagnosis, based on solid-state micrometric electrodes with pH sensing capabilities. This system should, optimally, be compatible and allow integration with subsequent lab-on-chip components, mainly optical processes for further biological and chemical analysis. The proposed prototype consists in an array of 9600 solid-state microelectrodes with nanometric tips. The fabrication process includes the patterning of a negative mold for the individual microelectrode tips, followed by an increase in height (for higher aspect-ratio and deeper penetration capability) through the addition of a Photoresist, filling of the mold with Silver through a novel Through-Silicon Electrodeposition process, and finally transferring the pattern to a Glass substrate with optical processing compatibility. The end results demonstrates a proof-of-concept of the process feasibility and the multiple achievements in process engineering, although further studies and optimization are required in different areas of the project as to better understand the mechanics and principles behind some of the novel aspects of the processes.This thesis had the support of Fundação para a Ciência e Tecnologia under a Doctoral Scholarship -SFRH/BD/90121/201

Self-Aligned 3D Chip Integration Technology and Through-Silicon Serial Data Transmission

The emerging three-dimensional (3D) integration technology is expected to lead to an industry paradigm shift due to its tremendous benefits. Intense research activities are going on about technology, simulation, design, and product prototypes. This thesis work aims at fabricating through-silicon vias (TSVs) on diced processor chips, and later bonding them into a 3D-stacked chip. How to handle and process delicate processor chips with high alignment precision is a key issue. The TSV process to be developed also needs to adapt to this constraint. Four TSV processes have been studied. Among them, the ring-trench TSV process demonstrates the feasibility of fabricating TSVs with the prevailing dimensions, and the whole-through TSV process achieves the first dummy chip post-processed with TSVs in EPFL although the dimension is rather large to keep a reasonable aspect ratio (AR). Four self-alignment (SA) techniques have been investigated, among which the gravitational SA and the hydrophobic SA are found to be quite promising. Using gravitational SA, we come to the conclusion that cavities in silicon carrier wafer with a profile angle of 60° can align the chips with less than 20 µm inaccuracies. The alignment precision can be improved after adopting more advanced dicing tools instead of using the traditional dicing saws and larger cavity profile angle. Such inaccuracy will be sufficient to align the relatively large TSVs for general products such as 3D image sensors. By fabricating bottom TSVs in the carrier wafer, a 3D silicon interposer idea has been proposed to stack another chip, e.g. a processor chip, on the other side of the carrier wafer. But stacking microprocessor chips fabricated with TSVs will require higher alignment precision. A hydrophobic SA technique using the surface tension force generated by the water-to-air interfaces around the pads can greatly reduce the alignment inaccuracy to less than 1 µm. This low-cost and high throughput SA procedure is processed in air, fully-compatible with current fabrication technologies, and highly stable and repeatable. We present a theoretical meniscus model to predict SA results and to provide the design rules. This technique is quite promising for advanced 3D applications involving logic and heterogeneous stacking. As TSVs' dimensions in the chip-level 3D integration are constrained by the chip-level processes, such as bonding, the smallest TSVs might still be about 5 µm. Thus, the area occupied by the TSVs cannot be neglected. Fortunately, TSVs can withstand very high bandwidths, meaning that data can be serialized and transmitted using less numbers of TSVs. With 20 µm TSVs, the 2-Gb/s 8:1 serial link implemented saves 75% of the area of its 8-bit parallel counterpart. The quasi-serial link proposed can effectively balance the inter-layer bandwidth and the serial links' area consumption. The area model of the serial or quasi-serial links working under higher frequencies provides some guidelines to choose the proper serial link design, and it also predicts that when TSV diameter shrinks to 5 µm, it will be difficult to keep this area benefit if without some novel circuit design techniques. As the serial links can be implemented with less area, the bandwidth per unit area is increased. Two scenarios are studied, single-port memory access and multi-port memory access. The expanded inter-layer bandwidth by serialization does not improve the system performance because of the bus-bottleneck problem. In the latter scenario, the inter-layer ultra-wide bandwidth can be exploited as each memory bank can be accessed randomly through the NoC. Thus further widening the inter-layer bandwidth through serialization, the system performance will be improved

Characterization of Nanomaterials: Selected Papers from 6th Dresden Nanoanalysis Symposiumc

This Special Issue “Characterization of Nanomaterials” collects nine selected papers presented at the 6th Dresden Nanoanalysis Symposium, held at Fraunhofer Institute for Ceramic Technologies and Systems in Dresden, Germany, on 31 August 2018. Following the specific motto of this annual symposium “Materials challenges—Micro- and nanoscale characterization”, it covered various topics of nanoscale materials characterization along the whole value and innovation chain, from fundamental research up to industrial applications. The scope of this Special Issue is to provide an overview of the current status, recent developments and research activities in the field of nanoscale materials characterization, with a particular emphasis on future scenarios. Primarily, analytical techniques for the characterization of thin films and nanostructures are discussed, including modeling and simulation. We anticipate that this Special Issue will be accessible to a wide audience, as it explores not only methodical aspects of nanoscale materials characterization, but also materials synthesis, fabrication of devices and applications

Piezoelectric thin films for bulk acoustic wave resonator applications:from processing to microwave filters

Bandpass filters for microwave frequencies realized with thin film bulk acoustic wave resonators (FBAR) are a promising alternative to current dielectric or surface acoustic wave filters for use in mobile telecommunication applications. With equivalent performance, FBAR filters are significantly smaller than dielectric filters and allow for a larger power operation than SAW filters. In addition, FBARs offer the possibility of on-chip integration, which will result in substantial volume and cost reduction. The first passive FBAR devices are now appearing on the market. They mainly cover needs in miniaturized RF-filters for the new bands around 2 GHz. A FBAR is essentially a thin piezoelectric plate sandwiched between two electrodes and acoustically isolated from the environment for energy trapping purposes. If the isolation is effectuated by an acoustic Bragg reflector, one speaks of solidly mounted resonators (SMR). Piezoelectric aluminum nitride (AlN) thin films are predominantly used in the emerging FBAR technology because AlN exhibits a sufficient electromechanical coupling coefficient kt2 , low acoustic losses at microwave frequencies, a low temperature coefficient of frequency, and its chemical composition is compatible with CMOS requirements. This thesis has two research directions. In the first part, FBAR structures based on AlN thin films were investigated for applications at X-band frequencies (7.2-8.5 GHz), i.e. operating at much higher frequencies than the ones used for present products. The goal was to identify property limitations related to such high frequencies, and to demonstrate to industry high performing SMR filters at 8 GHz. In the second part, a new material for FBAR devices was studied. The motivation is that AlN allows for a restricted filter bandwidth only, limited by its coupling factor of maximal 7%. Monocrystalline KNbO3 appears as an ideal alternative with its high coupling factor kt2 of 47%, and relatively large sound velocity of 8125m/s for longitudinal waves along the [101] direction. Piezoelectricity of KNbO3 films grown on electrodes has never been characterized. Single crystal results indicate that the optimal film texture would be (101). In this thesis, the growth of KNbO3 films on Pt electrodes was studied with the goal to achieve this texture uniformly, and to characterize piezoelectric properties. X-band FBAR's were first studied with numerical simulations based on a one-dimensional theory of the thickness-extensional bulk acoustic wave (BAW). Thickness, acoustic properties and electrical conductivity of the electrodes have a large impact on the resonator characteristics. There are conflicting requirements with respect to optimum acoustic and electrical properties of the electrode materials. An optimum thickness was calculated for 8GHz FBARs that use Pt bottom and Al top electrodes. The characteristics of ladder filters have been calculated based on the impedances of single resonators. The adjustable filter parameters, i.e. the areas of series and shunt resonators, frequency de-tuning between series and parallel resonators, and number of π-sections were screened for a process window offering maximum filter bandwidth with lowest ripple and low insertion loss for a given out-of-band rejection. An important result of the numerical simulations was that the bandwidth of ladder filters can be doubled by de-tuning the series and parallel resonators by more (1.3 times) than the difference of resonance and anti-resonance frequency. This also leads to a flatter passband while keeping the ripples below ±0.2dB. Solidly mounted resonators and filters were fabricated using an acoustic multilayer reflector consisting of AlN and SiO2 λ/4 layers. All films were sputter deposited in a high vacuum sputter cluster system with 4 process chambers. The films were patterned using standard photolithography and dry etching processes. The SMR exhibited a strong and spurious-free resonance at 8GHz with a high quality factor of 360 and electromechanical coupling coefficient of 6.0%. The temperature coefficient of frequency was -18ppm/K, and the voltage coefficient of frequency was -72ppm/V. Passband ladder filters with T- and π-topology consisting of 3 to 14 SMR were successfully demonstrated with a center frequency of 8GHz. These filters were optimized for maximum bandwidth and exhibited an insertion loss of 5.5dB, a rejection of 32dB, a 0.2dB bandwidth of 99MHz (1.3%), and a 3dB bandwidth of 224MHz (2.9%). There was good correspondence between measured and simulated filter and resonator characteristics. For perfect agreement, parasitic elements needed to be taken into account. These were a series resistance of 5Ω and a parallel conductance of 2mS in case of single resonators. The series resistance can be explained with resistive losses in the electrodes, whereas the parallel conduction was due to conduction along the surface. For π-filters, an additional series inductance of 100pH was needed to obtain a satisfactory fit. This inductance increased the out-of band rejection and insertion loss. Besides the group delay variation, all industrial specifications were met. KNbO3 was in-situ sputter deposited at 500 to 600°C using a rf magnetron source. A dedicated sputter chamber with load-lock and oxygen resistant substrate heater was built for this purpose. The high volatility of potassium oxide requires a potassium enrichment of the target. Targets with several excess concentrations (in the form of K2CO3) were studied. Stoichiometric KNbO3 films were obtained with targets containing 25 and 40% excess K. Zero and 10% excess yielded K deficient films, whereas 100% and 200% excess K led to highly unstable targets with K accumulation on the target surface, resulting in K rich second phases. The potassium-to-niobium ratio in the films depends strongly on sputter pressure and substrate temperature. Dense films, nucleated with cubic {100} texture, were obtained on platinized silicon substrates with a 10nm thick IrO2 seed layer at substrate temperatures of 520°C. At lower temperatures the films were amorphous, and at higher temperatures the films were composed of individual and facetted KNbO3 grains. The cubic high-temperature {100} texture results in a mixed (101)/(010) texture in the orthorhombic room temperature phase. The measured relative permitivity of 420 indicates that both orientations are equally present. Micro-Raman confirms the orthorhombic line splitting. Piezoelectrical and ferroelectrical activity were verified by means of a piezoelectric sensitive atomic force microscope. A very large piezoelectric activity was observed on some of the grains, and the polarization could be switched on most of the grains. However, the average d33,f = e33/c33, as measured by means of laser interferometry, showed a modest value of 24pm/V. The effective coupling factor is derived as kt2=2.8%, which is small relative to the theoretical value of 47%. The high dielectric constant and the absence of piezoelectric activity along the [010] direction are responsible for the reduction of the kt2 factor. Film roughness, complexity of deposition process and open poling issue make KNbO3 integration into BAW devices a difficult task

The Study of Ultra-thin Diffusion Barrier in Copper Interconnect System

Ph.DDOCTOR OF PHILOSOPH

Resistive-RAM for Data Storage Applications.

Mainstream non-volatile memory technology, dominated by the floating gate transistor, has historically improved in density, performance and cost primarily by means of process scaling. This simple geometrical scaling now faces significant challenges due to constraints of electrostatics and reliability. Thus, novel non-transistor based memory paradigms are being widely explored. Among the various contenders for next generation storage technology, RRAM devices have got immense attention due to their high-speed, multilevel capability, scalability, simple structure, low voltage operation and high endurance. In this thesis, electrical and material characterization is carried out on a MIM device system and formation / annihilation of nanoscale filaments is shown to be the reason behind the resistance switching. The MIM system is optimized to include an in-cell resistor which is shown to improve device endurance and reduce stuck-at-one faults. For highest density, the devices were arranged in a crossbar geometry and vertically integrated on CMOS decoders to demonstrate the feasibility of practical data storage applications. Next, we show that these binary RRAM devices exhibit native stochastic nature of resistive switching. Even for a fixed voltage on the same device, the wait time associated with programming is not fixed and is random and broadly distributed. However, the probability of switching can be predicted and controlled by the programming pulse. These binary devices have been used to generate random bit-streams with predicable bias ratios in time and space domains. The ability to produce random bit-streams using binary resistive switching devices based on the native stochastic switching principle may potentially lead to novel non-von-Neumann computing paradigms. Further, sub-1nA operating current devices have been developed. This ultra-low current provides energy savings by minimizing programming, erase and read currents. Despite having such low currents, excellent retention, on/off ratio and endurance have been demonstrated. Finally a scalable approach to simple 3D stacking is discussed. By implementation of a vertical sidewall-based architecture, the number of critical lithography steps can be reduced. A vertical device structure based on a W / WOx / Pd material system is developed. This scalable architecture is well suited for development of analog memory and neuromorphic systems.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/110461/1/sidgaba_1.pd

Nonlinear vibration energy harvesters for powering the internet of things

The ever decreasing power consumption in electronic devices and sensors have facilitated the development of autonomous wireless sensor nodes (WSNs), which ushered in the era of the Internet of Things (IoT). However, the problem of long-term power supply to the numerous WSNs pervasively dispersed to enable the IoT is yet to be resolved. This work focuses on the development of novel vibration energy harvesting (VEH) devices and technologies for effective transduction of mostly wide-band and noisy ambient mechanical vibrations to power WSNs. In this thesis meso-scale and MEMS-scale nonlinear and frequency tunable VEH devices have been designed, fabricated and characterized. The first meso-scale VEH prototype developed in this thesis combines a nonlinear bistable oscillator with mechanical impact induced nonlinearity, which exhibits upto 118% broadening in the frequency response over a standalone bistable system. The second meso-scale prototype combines magnetic repulsion induced bistable nonlinearity with stretching induced monostable cubic nonlinearity in a single device structure. The device effectively merged the beneficial features of the individual nonlinear bistable and monostable systems, and demonstrates upto 85% enhanced spectral performance compared to the bistable device. The third prototype is a MEMS-scale device fabricated using spiral silicon spring structure and double-layer planar micro-coils. A magnetic repulsion induced frequency tuning mechanism was incorporated in the prototype, and it was demonstrated that both linear and nonlinear hysteretic frequency responses could be tuned (by upto 18.6%) to match various ambient vibration frequencies. In order to enhance the power generating capability of MEMS-scale electromagnetic devices, an ultra-dense multi-layer micro-coil architecture has been developed. The proposed ultra-dense micro-coil is designed to incorporate double number of turns within the same volume as a conventional micro-coil, and significantly enhance the magnetic flux linkage gradient resulting in higher power output (~4 times). However, attempts to fabricate the ultra-dense coil have not been successful due to lack of proper insulation between the successive coil layers. Finally, a power management system combining diode equivalent low voltage drop (DELVD) circuit and a boost regulator module was developed. It was demonstrated that energy harvested from harmonic and bandlimited random vibrations using linear, nonlinear bistable, and combined nonlinear VEH devices could be conditioned into usable electricity by the power management system with 60% - 75% efficiency. In addition to developing new prototypes and techniques, this thesis recommends directions towards future research for further improvement in vibration energy harvesting devices and technologies

From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media —

Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities or magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest. The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation. In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements. Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics. Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetisation with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains. From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetisation aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived.Aufgrund des weltweiten, immer weiter steigenden Bedarfs an Speicherplatz von digitalen Information, sind neue Technologien für größere und schnellere Speichermedien im Fokus von Forschung und Entwicklung. Ein Schritt hin zu einer höheren Speicherdichte in der magnetischen Datenspeicherung ist dabei das sogenannte Konzept der ”Bit patterned media”, das definierte Informationseinheiten auf regelmäßig angeordneten Nanostrukturen beschreibt. Dieser Ansatz ist einer der derzeit vielversprechendsten Optionen die Speicherdichte zu erhöhen. Dabei ist die Herstellung der benötigten Nanostrukturen und deren Skalierung hin zu makroskopischen Dimensionen eines der Probleme an deren Lösung die Wissenschaft und Industrie derzeit arbeitet. Desweiteren ist die Antwort auf die noch offene Frage nach der Beeinflussung der nanoskaligen Strukturen auf die magnetischen Eigenschaften von großem Interesse. Das Hauptziel in dieser Arbeit ist es, einen Beitrag zur Beantwortung der Frage, welche magnetischen Eigenschaften sich durch eine Veränderung der Oberflächenstruktur im Nanometerbereich beeinflussen lassen, zu leisten. Hierzu wurden die folgenden Eigenschaften, wie zum Beispiel die Anisotropie, Remanenz,Koerzitivität, Schaltfeldverteilung, Sättigungsmagnetisierung, Gilbertdämpfung und inhomogene Linienverbreiterung von planaren zweidimensionalen dünnen ferromagnetische Schichten mit denen von dreidimensionalen magnetischen Strukturen verglichen. Zusätzlich wurde der Einfluss der angegpassten Morphologie auf die intergranularen- beziehungsweise auf die zwischen den Strukturen wirkende (interdot) Austauschkopplung untersucht. Der Hauptaugenmerk bei den ferromagnetisch dünnen Schichten lag dabei auf den granularen CoCrPt:SiO2 und [Co/Pd] Filmen, die heutzutage ein Standardmaterial für die magnetischen Speichermedien darstellen. Diese Materialien zeichnen sich durch eine hohe Koerzivität und senkrechte Anisotropie, mit geringer räumlicher Verteilung der Vorzugsrichtung der Magnetisierung, aus. Die hier vorgestellten vorstrukturierten GaSb(001) Substrate mit selbstordnenden periodischen Nanokegeln auf der Oberfläche, sind mittels Ionenstrahlerosion einfach, schnell und sehr gut reproduzierbar herzustellen. Deshalb ist diese Methode besonders für die Grundlagenforschung von Vorteil. Um einen Vergleich zwischen 2D Filmen und 3D Strukturen ziehen zu können, wurden neben den vorstrukturierten Substraten auch planare Proben beschichtet. Eine erste Versuchsreihe wurde mit einem dünnen Py Film präpariert. Da dessen magnetische Eigenschaften wohlbekannt sind, konnten neben den Untersuchungen mit VNA-FMR und MOKE auch einige OOMF Simulationen erstellt werden. Danach wurden zwei Proben mit planarem CoCrPt beziehungsweise CoCrPt:SiO2 untersucht. Bei den planaren CoCrPt:SiO2 Proben wurden außerdem noch Co+ Ionen implantiert, um deren Auswirkungen auf die intergranulare Austauschkopplung, Schaltfeldverteilung und besonders auf die Spindynamik zu bestimmen. Bei beiden Probensystemen konnte zusätzlich die Spindynamik mittels zeitaufgelöstem MOKE gemessen werden. Im Anschluss wurden die beiden senkrechten Speichermedien CoCrPt:SiO2 and [Co/Pd] auf Substraten mit Nanokegeln vorstrukturierten GaSb(001) Oberflächen abgeschieden. Diese Proben wurden mit MFM, MOKE, SQUID und Vektor-VSM vermessen. Aus den Messungen konnnten dann die Einflüsse auf die intergranulare- beziehungsweise interdot Austauschkopplung in Abhängigkeit von der Periodizität und Höhe der Nanokegel bestimmt werden, sowie die Umorientierung der Magnetisierung bezüglich der Substratkrümmung und den Morphologie induzierten Einfluss auf die magnetischen Domänen. Anhand der Vergleiche zwischen den Messungen der planaren und den vorstrukturierten Proben konnte eine Verringerung der Austauschkopplung zwischen den Strukturen gezeigt werden, die mit der Nanokegelstrukturperiodizität skaliert. Außerdem wurde in allen dünnen magnetischen Filmen auf Nanokegeln gezeigt, dass die Magnetisierung sich in Abhängigkeit der darunterliegenden Struktur ausrichtet. Bei den Py auf Nanokegeln, den planaren CoCrPt und dem planaren CoCrPt:SiO2 Proben konnten außerdem mit VNA-FMR und TRMOKE Informationen bezüglich der Spindynamik gemessen werden. Die erzielten Ergebnisse, der beiden planaren Proben, sind vergleichbar mit denen, aus der Literatur bekannten Werten, für die Gilbertdämpfung. Darüber hinaus wurde durch die Messungen an den Py Proben gezeigt, dass die Theorie, des bisher genutzten 2D Modells, nicht mehr gültig ist, da sich die Magnetisierung entlang der Substratstruktur ausrichtet, und deshalb ein neues Model aufgestellt werden muss

Through Silicon Via Field-Effect Transistor with Hafnia-based Ferroelectrics and the Doping of Silicon by Gallium Implantation Utilizing a Focused Ion Beam System

3-dimensional integration has become a standard to further increase the transistor density and to enhance the integrated functionality in microchips. Integrated circuits are stacked on top of each other and copper-filled through-silicon VIAs (TSVs) are the industry-accepted choice for their vertical electrical connection. The aim of this work is to functionalize the TSVs by implementing vertical field-effect transistors inside the via holes. The front and back sides of 200 ... 300 µm thin silicon wafers were doped to create the source/drain regions of n- and p-FETs. The TSVFETs showed very stable saturation currents and on/off current ratios of about 10^6 (n-TSVFET) and 10^3 (p-TSVFET) for a gate voltage magnitude of 4V. The use of hafnium zirconium oxide on a thin SiO_2 interface layer as gate dielectric material in a p-TSVFET, enabled the implementation of a charge trapping memory inside the TSVs, showing a memory window of about 1V. This allows the non-volatile storage of the transistor on/off state. In addition, the demonstration of the use of gallium as the source/drain dopant in planar p-FET test structures (ion implanted from a focused ion beam tool) paves the way for maskless doping and for a process flow with a low thermal budget. It was shown, that ion implanted gallium can be activated and annealed at relatively low temperatures of 500 °C ... 700 °C.:Abstract / Kurzzusammenfassung Danksagung Index I List of Figures III List of Tables X List of Symbols XI List of Abbreviations XV 1 Introduction 1 2 Fundamentals 5 2.1 Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) 5 2.1.1 Historical Development - Technological Advancements 7 2.1.2 Field-Effect Transistors in Semiconductor Memories 10 2.2 3D Integration and the Use of TSVs (Through Silicon VIAs) 16 2.3 Doping of Silicon 19 2.3.1 Doping by Thermal Diffusion 20 2.3.2 Doping by Ion Implantation 22 3 Electrical Characterization 24 3.1 Resistivity Measurements 24 3.1.1 Resistance Determination by Four-Point Probes Measurement 24 3.1.2 Contact Resistivity 27 3.1.3 Doping Concentration 32 3.2 C-V Measurements 35 3.2.1 Fundamentals of MIS C-V Measurements 35 3.2.2 Interpretation of C-V Measurements 37 3.3 Transistor Measurements 41 3.3.1 Output Characteristics (I_D-V_D) 41 3.3.2 Transfer Characteristics (I_D-V_G) 42 4 TSV Transistor 45 4.1 Idea and Motivation 45 4.2 Design and Layout of the TSV Transistor 47 4.2.1 Design of the TSV Transistor Structures 47 4.2.2 Test Structures for Planar FETs 48 5 Variations in the Integration Scheme of the TSV Transistor 51 5.1 Doping by Diffusion from Thin Films 51 5.1.1 Determination of Doping Profiles 52 5.1.2 n- and p- TSVFETs Doped Manufactures by the Use of the Diffusion Technique 59 5.2 Ferroelectric Hafnium-Zirconium-Oxide (HZO) in the Gate Stack 81 5.2.1 Planar ferroelectric p-MOSFETs Doped by Thermal Diffusion 82 5.2.2 p-TSVFETs with Hafnium-Zirconium-Oxide Metal Gate 90 5.3 Doping by Ion Implantation of Gallium with a Focused Ion Beam (FIB) Tool 96 5.3.1 Ga doped Si Diodes 97 5.3.2 Planar p-MOSFETs Doped by Ga Implantation 108 5.3.3 Proposal for a parallel integration of Cu TSVs and p-TSVFETs 117 6 Summary and Outlook 120 Bibliography XVIII A Appendix XXXVI A.1 Resistivity and Dopant Density XXXVI A.2 Mask set for the TSVFET XXXVII A.3 Mask Design of the Planar Test Structures XXXVIII Curriculum Vitae XXXIX List of Scientific Publications XL