In den kommenden Jahren ist eine deutliche Erhöhung des digitalen Speicherbedarfs zu erwarten, was neue Anforderungen an künftige Speichertechnologien und –architekturen bringt. Hafniumoxid ist aktuell das Standard-Gatedielektrikum für Transistoren in der Halbleitertechnologie und wird in resistiven und ferroelektrischen Speichern eingesetzt, die für kommende Speichergenerationen geeignet sind. In dieser Arbeit wird die Kombination aus resistiven und ferroelektrischen Speichermechanismen untersucht. Zunächst konnte gezeigt werden, dass sich beide Schaltvorgänge in einer Zelle realisieren lassen. Dazu wurde eine polykristalline, ferroelektrische Hafniumoxidschicht in eine Kondensatorstruktur mit unterschiedlichen Elektroden gebracht. Der reversible resistive und ferroelektrische Schaltvorgang beruht auf einer Zurücksetz-Operation in einen sehr hochohmigen Zustand, wodurch die Oxidschicht für weiteres ferroelektrisches Schalten genutzt werden konnte. Zusätzlich wurde der Einfluss von Sauerstofffehlstellen auf die resistiven Formier- und Schreibspannungen nachgewiesen. Im zweiten Teil dieser Arbeit wurden ferroelektrische Tunnelkontakte (engl. FTJ) hergestellt und systematisch auf ihre Schalt- und Speichereigenschaften untersucht. Diese beruhen auf der Informationsspeicherung in der ferroelektrischen Hafniumzirkoniumoxid-Schicht (HZO) und auf einem resistiven Auslesemechanismus, bei dem der Tunnelstrom für den jeweiligen Polarisationszustand gemessen wird. Dieser Lesevorgang ist nichtdestruktiv. Für den quantenmechanischen Tunnelvorgang sind dünne Oxidschicht notwendig, um einen ausreichend hohen Tunnelstrom zu erreichen. HZO-basierte Schichten verlieren ihre ferroelektrischen Eigenschaften unter einer kritischen Schichtdicke, die für einen klassischen Metall-Ferroelektrikum-Metall-Tunnelkontakt zu hoch ist. Dazu wurde in dieser Arbeit der Ansatz gewählt, zusätzlich eine dielektrische Aluminiumoxid-Tunnelbarriere in die Struktur einzubringen. Dadurch können die ferroelektrische und dielektrische Schicht unabhängig voneinander optimiert werden (2-lagiger ferroelektrischer Tunnelkontakt). Es konnte gezeigt werden, dass nur in einem bestimmten Dielektrikums-Schichtdickenbereich zwischen etwa 2-2,5nm das gewünschte Tunnelverhalten der Struktur hervortritt. Beim Setzen der jeweiligen Polarisationszustände tritt in der Schaltkinetik der bekannte Zeit-Amplituden-Kompromiss auf. Dieser wurde mithilfe des nukleationslimierten Schaltmodells untersucht. Über eine geeignete Wahl von Pulsdauer und –amplitude können durch Teilpolarisation Zwischenzustände gespeichert werden. Die Zyklenfestigkeit zeigt ein stärkeres Aufwachverhalten als die reine HZO-Schicht. Es konnte gezeigt werden, dass der Auslesetunnelstroms direkt mit dem Anstieg der remanenten Polarisation korreliert und somit das Speicherfenster mit einem An/Aus-Verhältnis von 10 erst nach etwa 10^2 Schaltzyklen vollständig geöffnet ist. Die Datenhaltung zeigte nur ein marginales Speicherfenster bei Extrapolation auf 10 Jahre. Die Datenhaltung konnte durch Abscheidung von Titannitrid- und Platin-Metallelektroden mit unterschiedlichen Austrittsarbeiten stabilisiert werden. Damit ließ sich das Speicherfenster deutlich erhöhen. Die Möglichkeit, Zwischenzustände speichern und graduell einzustellen zu können, erlaubt die Nutzung der zweilagigen FTJs als künstliche Synapsen. Dazu wurde über verschiedene Pulsfolgen der veränderliche Tunnelwiderstand als synaptisches Gewicht interpretiert. Damit konnte Potenzierung- und Depressionsverhalten der künstlichen Synapse emuliert werden.:Danksagung I Kurzzusammenfassung II Abstract III Symbolverzeichnis VI Abkürzungsverzeichnis IX 1 Einführung und Motivation 1 2 Grundlagen 4 2.1 Dielektrizität und Ferroelektrizität 4 2.2 Ferroelektrizität in HfO2 9 2.3 Arten ferroelektrischer Speicher 13 2.3.1 Ferroelektrischer Kondensator 13 2.3.2 Ferroelektrischer Feldeffekttransistor 15 2.3.3 Ferroelektrischer Tunnelkontakt 16 2.4 Überblick über resistive Speicher 24 3 Experimentelle Methoden 28 3.1 Physikalische Charakterisierung 28 3.1.1 Röntgendiffraktometrie unter streifendem Einfall 28 3.1.2 Röntgenreflektometrie 28 3.1.3 Transmissionselektronenmikroskopie 29 3.2 Elektrische Untersuchungsmethoden 29 3.2.1 Elektrische Messung resistiver Schaltkurven 29 3.2.2 Dynamische Hysteresekurven und Messung der Zyklenfestigkeit 29 3.2.3 Elektrische Messung der ferroelektrischen Tunnelkontakte 30 3.3 Abscheideverfahren zur Herstellung der Kondensatorstrukturen 31 3.3.1 Reaktives Magnetronsputtern 32 3.3.2 Elektronenstrahlverdampfung und Thermisches Verdampfen 32 3.3.3 Atomlagenabscheidung 33 4 Resistives und ferroelektrisches Schalten in einer Zelle 34 4.1 Resistives Schalten in amorphem und kristallinem HfO2 34 4.2 Kombination von resistivem und ferroelektrischem Schalten in einer Struktur 38 5 Ferroelektrische Tunnelkontakte 46 5.1 Charakterisierung der ferroelektrischen Hafniumzirkoniumoxid-Schicht 46 5.2 Übersicht und Aufbau der untersuchten Proben 50 5.3 (Ferro-)Elektrische Eigenschaften und Schichtdickenoptimierung der FE/DE-FTJs 53 5.3.1 Einfluss der Al2O3-Schichtdicke 60 5.3.2 Skalierbarkeit 64 5.4 Schaltkinetik 67 5.5 Zyklenfestigkeit 78 5.6 Datenhaltung 87 5.6.1 Einfluss von Depolarisationsfeldern in zweilagigen FTJs 87 5.6.2 Optimierung durch Elektroden mit unterschiedlichen Austrittsarbeiten 93 5.7 Anwendung von FTJs als künstliche Synapse in gepulsten neuronalen Netzen 97 5.8 Vergleich, Ausblick und weiterführende Verbesserung des Bauelements 105 6 Zusammenfassung und Ausblick 109 Literaturverzeichnis XI Curriculum Vitae XXXVIII Publikationsliste XL Selbstständigkeitserklärung XLIII

Structural Health Monitoring (SHM) of automobile tires has been an active area of research in the last few years. Within this area, the monitoring of strain on tires using wireless devices and networks is gaining prominence because these techniques do not require any wired connections. Various tire manufacturers are looking into SHM of automobile tires due to the Transportation Recall Enhancement, Accountability and Documentation (TREAD) act which demands installation of tire pressure monitoring devices within the tire. Besides measuring tire pressures, tire manufactures are also examining ways to measure strain and temperature as well to enhance overall safety of an automobile. A sensor system that can measure the overall strain of a tire is known as a centralized strain sensing system. However, a centralized strain sensing system cannot find the location and severity of the damage on the tire, which is a basic requirement. Various sensors such as acceleration and optical sensors have also been proposed to be used together to get more local damage information on the tire. In this thesis we have developed a strain sensing system that performs local strain measurements on the tire and transmits them to a console inside the vehicle wirelessly. Our sensing system utilizes a new sensing material called Metal RubberTM which is shown to be conductive like metal, and flexible as rubber. Also, we have also developed a reliable and an energy efficient geographic routing protocol for transporting strain data wirelessly from a tire surface to the driver of the automobile. / Master of Science

Measuring low electrical currents with high precision is critical across various fields, particularly in applications like microfluidic biosensing. Traditional digital multimeters (DMMs) are inadequate for low current measurements due to their high input burden and limited resolution. Therefore, more sensitive instruments like electrometers and picoammeters are often required but are typically expensive. This thesis explores the design and construction of a cost-effective, portable, and user-friendly picoammeter based on a transimpedance amplifier (TIA), capable of measuring currents in the picoampere (pA) range with a resolution of 1-5 pA and minimal noise. The constructed picoammeter has a maximum input current range of ±1.5 nA.  A prototype was built on a soldering board to validate the design, which was then translated into a practical printed circuit board (PCB) layout. The device is powered by batteries to ensure low noise levels and enable isolated operation. An Arduino microcontroller was used to interface with the circuit, manage data acquisition, and enable real-time visualisation of the measured current data on a computer.  Simulation results confirmed the theoretical performance of the circuit, and experimental validation showed RMS noise levels of less than 0.3 pA under controlled conditions and up to 3 pA when measuring streaming currents from a microchip. Despite a slight underestimation of input currents due to resistor tolerances, calibration adjustments successfully corrected these discrepancies.  The total cost of the materials used in constructing the picoammeter was significantly less than the cost of commercially available devices. While commercial devices offer higher precision and additional functionalities, the developed picoammeter demonstrates how application-focused solutions can provide comparable accuracy and noise characteristics to commercial devices for a fraction of the price.

Memristor, defined as a two-terminal device which exhibits a pinched hysteresis loop in the current-voltage characteristics, is a main component of the resistive random access memory. Both memristor and memristive phenomena, known also as resistive switching (RS), have been thoroughly investigated in the past nearly two decades. This dissertation investigates YMnO3 thin films and explores a new concept concerning utilization of multiferroic properties for activation and/or enhancement of RS. It is hypothesized that the charged domain walls and/or vortex cores in YMnO3 thin films can act as an effective nanoscale features which support formation of the conductive filaments and, in consequence, enable development of an electroforming-free memristive structure. Results of the electrical characterization of YMnO3-based metal-insulator-metal structures indicate that hexagonal YMnO3 films deposited on metal-coated oxide substrate exhibit electroforming-free unipolar resistive switching (URS) while orthorhombic YMnO3 films grown on the doped oxide substrate show bipolar resistive switching (BRS). Observed URS is assigned to the formation and rupture of conductive, metallic-like filaments induced by the thermo-chemical phenomena. Results of polarity-dependent studies reveal that formation of conductive filaments proceeds in the electrostatic discharge event which is followed by their irreversible rupture during the reset process. Main properties of the observed URS include very good retention of programmed states, large memory window (between 10E+2 and 10E+4), high voltage and current required for set and reset, respectively, and low endurance. BRS is attributed to the complementary electronic and ionic processes within the p-n junction formed at the interface between p-YMnO3 and n-type oxide substrate. Results of ferroelectric characterization reveal that resistively switching YMnO3 films do not exhibit ferroelectric properties. Therefore, observed RS in YMnO3-based structures can not be directly related to the presence of charged domain walls and/or multiferroic vortex cores. Prospective functionality extension of YMnO3-based memristive devices is developed and presented on the example of photodetecting properties of metal-YMnO3-insulator-semiconductor stacks. Studies conducted within the framework of this doctoral dissertation investigate the resistive switching behaviour of YMnO3-based junctions. Obtained results contribute to the better understanding of the resistive switching and failure mechanisms in ternary oxides, and provide hints toward device engineering. / Der Memristor ist definiert als eine Zweipol-Vorrichtung, die eine hysteretische Strom-Spannungs-Charakteristik aufweist. Memristoren sind nichtflüchtige Widerstandsspeicher, deren elektrischer Widerstand mittels elektrischer Spannungspulse verändert werden kann. Sowohl Memristoren als auch memristive Widerstandsschalter (RS) werden seit mehr als zwei Jahrzehnten intensiv untersucht. Diese Dissertation untersucht YMnO3-Dünnschichten mit zirkularen Vorderseiten-Elektroden und unstrukturierten Rückseiten-Elektroden und erforscht ein neues Konzept über die Nutzung der multiferroischen Eigenschaften für die Aktivierung und/oder Verbesserung des memristiven Verhaltens. Es wird angenommen, dass die geladenen Domänenwände und/oder Vortices in YMnO3-Dünnschichten die Bildung leitfähiger Filamente wirksam unterstützt und folglich die Entwicklung eines neuartigen, formierungs-freiem Widerstandsspeichersermöglicht. Die Ergebnisse der elektrischen Charakterisierung von YMnO3-basierten Widerstandsschalter zeigen unipolares RS (URS), wenn eine metallische Rückseitenelektrode verwendet wird und bipolares RS (BRS), wenn als Rückseitenelektrode ein metallisch leitendes Oxid-Substrat verwendet werden. Das URS wird als thermochemisches RS klassifiziert und mit der Bildung und Auflösung metallisch leitender Filamente korreliert. Das BRS wird auf das Einfangen/Freigeben von Defekten in der Raumladungszone des YMnO3 im pn-Übergang von p-YMnO3/n-Nb:SrTiO3-Strukturen zurückgeführt. Die wichtigsten Eigenschaften des formierungsfreien URS sind die sehr gute Retention der programmiertenWiderstandszustände, große Speicherfenster (zwischen 10E+2 und 10E+4), die hohe Schreibspannung für den Set-Prozess und der hohe Schreibstrom für den Reset-Prozess. Die Endurance ist aufgrund der Degradation des Vorderseiten-Elektrode gering. Die Ergebnisse des polaritätsabhängigen Widerstandsschaltens zeigen, dass der Set-Prozess mit elektrostatischer Entladung einhergeht. Die ferroelektrische Charakterisierung zeigt, dass die YMnO3–Dünnfilme keine ferroelektrischen Eigenschaften aufweisen. Daher kann das beobachtete URS nicht direkt auf die Anwesenheit von geladenen Domänenwände und Vortices zurückgeführt werden. Darüberhinaus wurden die photodetektierenden Eigenschaften von Metall-YMnO3-Isulator-Halbleiter-Stacks als potenzielle Erweiterung der Funktionalität von YMnO3-basierten memristiven Bauelementen vorgestellt und vorgeschlagen. Im Rahmen der vorliegenden Dissertation wurde das Widerstandsschalten von multiferroischen, YMnO3-basierten Widerstandsschaltern untersucht. Die erhaltenen Ergebnisse tragen zu einem besseren Verständnis des Widerstandsschaltens von multiferroischen Materialien bei.

Master of Science / Department of Electrical and Computer Engineering / Dwight D. Day / Micro-hydro turbines generate power for small villages and industries in Afghanistan. They usually produce less than 100 kW of power. Currently the flow into the turbine is controlled manually and the voltage is controlled automatically with an electronic load controller. Excess power not used by the village is dumped into a community water heater. For larger sites that have a reservoir and/or large variable load throughout the day and night, the turbine needs to be fitted with an automatic flow control system to conserve water in the reservoir or deal with the variable loads. Large turbines usually use hydraulic governors that automatically adjust the flow of water into the turbine. For micro-hydro sized plants this method would be too expensive and be difficult to build and maintain locally. For this reason, a 3 phase AC induction motor will be used to move the internal flow control valve of the turbine. Because a sudden change in load is possible (30 – 40%) for micro-hydro plants, the electronic load controller will also be needed to respond to quick changes in load so that the village voltage does not exceed 220V. This report documents the process of building a test system comprising of a dynamic resistive load, microcontroller controlled resistive load, a three phase AC generator and a DC Motor. Where the dynamic resistive load represents the load of the village, the computer controlled resistive load would represent the community water heater, the three phase AC generator represents the Generator on site and the DC Motor together with its DC input voltage would emulate the turbine and its water flow respectively. The DC input voltage would be also controlled with a PWM signal through a delay loop to represent the water gate delay effects on the turbine as close as possible. With this, it would be possible to completely build and test a control system that emulates the dynamics of a water turbine generator.

Much of recent progress in medical research and diagnostics has been enabled through the advances in molecular analysis technologies, which now permit the detection and analysis of single molecules with high sensitivity and specificity. Assay sensitivity is fundamentally limited by the efficiency of the detection method used for read-out. Inefficient detection systems are usually compensated for by molecular amplification at the cost of elevated assay complexity. This thesis presents microfluidic automation and digital quantification of targeted nucleic acid detection methods based on padlock and selector probes and rolling circle amplification (RCA). In paper I, the highly sensitive, yet complex circle-to-circle amplification assay was automated on a digital microfluidic chip. In paper II, a new RCA product (RCP) sensing principle was developed based on resistive pulse sensing that allows label free digital RCP quantification. In paper III, a microfluidic chip for spatial RCP enrichment was developed, which enables the detection of RCPs with an unprecedented efficiency and allows for deeper analysis of enriched RCPs through next generation sequencing chemistry. In paper IV, a smart phone was converted into a multiplex fluorescent imaging device that enables imaging and quantification of RCPs on slides as well as within cells and tissues. KRAS point mutations were detected (i) in situ, directly in tumor tissue, and (ii) by targeted sequencing of extracted tumor DNA, imaged with the smart phone RCP imager. This thesis describes the building blocks required for the development of highly sensitive low-cost RCA-based nucleic acid analysis devices for utilization in research and diagnostics.

A large area time of flight (TOF) detector based on multi-gap resistive plate chamber (MRPC) technology has been developed for the STAR (Solenoidal Tracker at RHIC) experiment at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory, New York. The TOF detector replaces STAR's Central Trigger Barrel detector with 120 trays, each with 32 MRPCs. Each MRPC has 6 channels. The TOF detector improves by a factor of about 2 STAR's particle identification reach in transverse momenta and enhances STARs physics research program.

<p align="justify">Many different active control techniques can be used to control the vibrations of a mechanical structure: they however require at least a sensitive signal amplifier (for the sensor), a power amplifier (for the actuator) and an analog or digital filter (for the controller). The use of all these electronic devices may be impractical in many applications and has motivated the use of the so-called shunt circuits, in which an electrical circuit is directly connected to a transducer embedded in the structure. The transducer acts as an energy converter: it transforms mechanical (vibrational) energy into electrical energy, which is in turn dissipated in the shunt circuit. No separate sensor is required, and only one, generally simple electronic circuit is used. The stability of the shunted structure is guaranteed if the electric circuit is passive, i.e., if it is made of passive components such as resistors and inductors.</p> <p align="justify">This thesis compares the performances of the electric shunt circuits with those of classical active control systems. It successively considers the use of piezoelectric transducers and that of electromagnetic (moving-coil) transducers.</p> <p align="justify">In a first part, the different damping techniques are applied on a benchmark truss structure equipped with a piezoelectric stack transducer. A unified formulation is found and experimentally verified for an active control law, the Integral Force Feedback (IFF), and for various passive shunt circuits (resistive and resistive-inductive). The use of an active shunt, namely the negative capacitance, is also investigated in detail. Two different implementations are discussed: they are shown to have very different stability limits and performances.</p> <p align="justify">In a second part, vibration isolation with electromagnetic (moving-coil) transducers is introduced. The effects of an inductive-resistive shunt circuit are studied in detail; an equivalent mechanical representation is found. The performances are compared with that of resonant shunts and with that of active isolation with IFF. Next, the construction of a six-axis isolator based on a Stewart Platform is presented: the key parameters and the main limitations of the system are highlighted.</p>

Alors que les mémoires non-volatiles conventionnelles, telles que les mémoires flash à grille flottante, deviennent de plus en plus complexes à intégrer et souffrent de performances et d’une fiabilité de plus en plus réduite, les mémoires à variation de résistance (RRAM) telles que les OxRAM, CBRAM, MRAM ou PCM sont vues dans la communauté scientifique comme une alternative crédible. Cependant, les architectures de RRAM standard (telles que la 1Transistor-1RRAM) ne sont pas compétitives avec les mémoires flash sur le terrain de la densité. Ainsi, cette thèse se propose d’explorer le potentiel des architectures RRAM sans transistor que sont l’architecture Crosspoint et l’architecture VRRAM.Dans un premier temps, le positionnement des architectures Crosspoint et VRRAM dans la hiérarchie mémoire est étudié. De nouvelles problématiques, telles que les courant de sneakpath, la chute de tension dans les métaux ou la surface des circuits périphériques sont identifiées et modélisées. Dans un second temps, des solutions circuit répondant aux problématiques évoquées précédemment sont proposées. Finalement, cette thèse se propose d’explorer les opportunités ouvertes par l’utilisation de transistors innovants pour améliorer la densité ou les performances des architectures mémoires utilisant des RRAM. / While conventional non-volatiles memories, such as floating gate Flash memories, are becoming more and more difficult and costly to integrate and suffer of reduced performances and reliability, emerging resistive switching memories (RRAM), such as OxRAM, CBRAM, MRAM or PCM, are seen in the scientific community as a good way for tomorrow’s high-density memories. However, standard RRAM architectures (such as 1 Transistor-1 RRAM) are not competitive with flash technology in terms of density. Thereby, this thesis proposes to explore the opportunities opened by transistor-less RRAM architectures: Crosspoint and Vertical RRAM (VRRAM) architectures.First, the positioning of Crosspoint and VRRAM architectures in the memory hierarchy is studied. New constraints such as the sneakpath currents, the voltage drop through the metal lines or the periphery area overhead are identified and modeled. In a second time, circuit solutions answering to previously mentioned effects are proposed. Finally, this thesis proposes to explore new opportunities opened by the use of innovative transistors to improve the density or the performances of RRAM-based memory architectures.

The cosmic rays are the most energetic particles in the universe. Their production, propagation, and detection are objects of studies. Surface detectors aim to identify particles from extensive air showers (EAS) which the result from the cosmic-ray interactions with the atmosphere. Resistive Plate Chambers (RPCs) have shown to be a suitable muon detector to be integrated into the Pierre Auger Observatory. An instrumentation was developed to assembly RPCs in São Carlos (BRA). Data from RPCs already built by our collaborators in Coimbra (POR) were analyzed. The detector efficiency to muons was calculated and is approximately 88%, which is in good agreement with the values quoted in the literature. Direction maps were built to investigate the muon incoming direction and the quantity of matter traversed by the muons. The dependence of the muon flux on the zenith angle was calculated and compared with results from the simulation. A square cosine dependence is expected, though it is seen that the building structure has enough matter to block some of the incident muons and alter the dependence curve. The total muon flux was estimated based on the detector efficiencies and solid angle as 1.6.10&minus;5. mm&minus;2.sr&minus;1. s&minus;1 compared with the literature value of 7.1.10&minus;5 mm&minus;2.sr&minus;1.s&minus;1, which gives an absorption by the building of approximately 77%. / Os raios cósmicos são as partículas mais energéticas do universo. Sua produção, propagação e detecção são objetos de estudos. Os detectores de superfície têm como objetivo identificar partículas dos chuveiros atmosféricos extensos (EAS), o qual é o resultado das interações do raio cósmico com a atmosfera. A Câmaras de Placas Resistivas (RPCs) demonstra ser um detector de múons adequado para ser integrado ao Observatório Pierre Auger. Foi desenvolvida em São Carlos (BRA) uma instrumentação para montagem de RPCs. Dados de RPCs já construídas por nossos colaboradores em Coimbra (POR) foram analisados. A eficiência dos detectores para múons foi calculada como sendo de aproximadamente 88%, o que está de acordo com os valores citados na literatura. Mapas de direção foram construídos para investigar a direção de chegada e a quantidade de matéria atravessada pelos múons. A dependência do fluxo de múons com o ângulo zenital foi comparada com os resultados da simulação. Embora uma dependência com o quadrado do cosseno é esperada, foi constatado que a estrutura do prédio tem matéria suficiente para bloquear parte dos múons incidentes e alterar a curva da dependência. O fluxo total de múons foi estimado baseado nas eficiências do detector e no ângulo sólido é de 1.6.10&minus;5 mm&minus;2.sr&minus;1.s&minus;1. Comparado com o valor da literatura de 7.1.10&minus;5 mm&minus;2.sr&minus;1.s&minus;1 resulta em uma absorção pelo prédio de aproximadamente 77% do fluxo de múons.