In dieser Dissertation wird das viskoplastische Schubverhalten eines magnetorheologischen Fluids (MRF) modelliert. Mithilfe eines phänomenologischen Modellierungsansatzes auf Basis nichtlinearer rheologischer Elemente können die gemessenen Fließkurven sowie Speicher- und Verlustmoduli abgebildet werden. Ein MRF ist ein Material mit fest-flüssig Übergang. Es besitzt von einem Magnetfeld abhängige Materialeigenschaften. Um diese beschreiben zu können, wird zunächst eine phänomenologische Stoffklassifizierung eingeführt. Auf deren Grundlage teilen sich Stoffe allgemein in Flüssigkeiten, Festkörper und Materialien mit fest-flüssig Übergang auf. Zur Beschreibung des Materialverhaltens von MRF werden drei viskoplastische Modelle formuliert und gegenübergestellt. Zur Identifikation der Materialparameter wird eine Identifikationsstrategie auf der Grundlage charakteristischer Punkte entwickelt. Charakteristische Punkte sind exklusive Punkte von Materialfunktionen, die analytisch beschrieben und ohne Weiteres experimentell ermittelt werden können. Analytische Ausdrücke für charakteristische Punkte der Speicher- und Verlustmoduli werden über das Analogieprinzip unter Verwendung von Lissajous Diagrammen abgeleitet. Infolgedessen können die Materialparameter durch das Auswerten algebraischer Zusammenhänge identifiziert werden, ohne nichtlineare Optimierungsverfahren anwenden zu müssen. Hierbei stellt die Fließspannung einen signifikanten Materialparameter dar. Deswegen werden die Standardverfahren zur Bestimmung der Fließspannung auf rheologische Modelle angewendet und bewertet.

In an era in which the amount of produced and stored data continues to exponentially grow, standard memory concepts start showing size, power consumption and costs limitation which make the search for alternative device concepts essential. Within a context where new technologies such as DRAM, magnetic RAM, resistive RAM, phase change memories and eFlash are explored and optimized, ferroelectric memory devices like FeRAM seem to showcase a whole range of properties which could satisfy market needs, offering the possibility of creating a non-volatile RAM. In fact, hafnia and zirconia-based ferroelectric materials opened up a new scenario in the memory technology scene, overcoming the dimension scaling limitations and the integration difficulties presented by their predecessors perovskite ferroelectrics. In particular, HfₓZr₁₋ₓO₂ stands out because of high processing flexibility and ease of integration in the standard semiconductor industry process flows for CMOS fabrication. Nonetheless, further understanding is necessary in order tocorrelate device performance and reliability to the establishment of ferroelectricity itself. The aim of this work is to investigate how the composition of the ferroelectric oxide, together with the one of the electrode materials influence the behavior of a ferroelectric RAM. With this goal, different process parameters and reliability properties are considered and an analysis of the polarization reversal is performed. Starting from undoped hafnia and zirconia and subsequently examining their intermixed system, it is shown how surface/volume energy contributions, mechanical stress and oxygen-related defects all concur in the formation of the ferroelectric phase. Based on the process optimization of an HfₓZr₁₋ₓO₂-based capacitor performed within these pages, a 64 kbit 1T1C FeRAM array is demonstrated by Sony Semiconductor Solutions Corporation which shows write voltage and latency as low as 2.0 V and 16 ns, respectively. Outstanding retention and endurance performances are also predicted, which make the addressed device an extremely strong competitor in the semiconductor scene.

The advent of Storage Class Memory (SCM) is driving a rethink of storage systems towards a single-level architecture where memory and storage are merged. In this context, several works have investigated how to design persistent trees in SCM as a fundamental building block for these novel systems. However, these trees are significantly slower than DRAM-based counterparts since trees are latency-sensitive and SCM exhibits higher latencies than DRAM. In this paper we propose a novel hybrid SCM-DRAM persistent and concurrent B-Tree, named Fingerprinting Persistent Tree (FPTree) that achieves similar performance to DRAM-based counterparts. In this novel design, leaf nodes are persisted in SCM while inner nodes are placed in DRAM and rebuilt upon recovery. The FPTree uses Fingerprinting, a technique that limits the expected number of in-leaf probed keys to one. In addition, we propose a hybrid concurrency scheme for the FPTree that is partially based on Hardware Transactional Memory. We conduct a thorough performance evaluation and show that the FPTree outperforms state-of-the-art persistent trees with different SCM latencies by up to a factor of 8.2. Moreover, we show that the FPTree scales very well on a machine with 88 logical cores. Finally, we integrate the evaluated trees in memcached and a prototype database. We show that the FPTree incurs an almost negligible performance overhead over using fully transient data structures, while significantly outperforming other persistent trees.

Reconfigurable transistors merge unipolar p- and n-type characteristics of field-effect transistors into a single programmable device. Combinational circuits have shown benefits in area and power consumption by fine-grain reconfiguration of complete logic blocks at runtime. To complement this volatile programming technology, a proof of concept for individually addressable reconfigurable nonvolatile transistors is presented. A charge-trapping stack is incorporated, and four distinct and stable states in a single device are demonstrated.

The electric-field-driven and reversible polarization switching in ferroelectric materials provides a promising approach for nonvolatile information storage. With the advent of ferroelectricity in hafnium oxide, it has become possible to fabricate ultrathin ferroelectric films suitable for nanoscale electronic devices. Among them, ferroelectric field-effect transistors (FeFETs) emerge as attractive memory elements. While the binary switching between the two logic states, accomplished through a single voltage pulse, is mainly being investigated in FeFETs, additional and unusual switching mechanisms remain largely unexplored. In this work, we report the natural property of ferroelectric hafnium oxide, embedded within a nanoscale FeFET, to accumulate electrical excitation, followed by a sudden and complete switching. The accumulation is attributed to the progressive polarization reversal through localized ferroelectric nucleation. The electrical experiments reveal a strong field and time dependence of the phenomenon. These results not only offer novel insights that could prove critical for memory applications but also might inspire to exploit FeFETs for unconventional computing.

Ferroelectrics are promising for nonvolatile memories. However, the difficulty of fabricating ferroelectric layers and integrating them into complementary metal oxide semiconductor (CMOS) devices has hindered rapid scaling. Hafnium oxide is a standard material available in CMOS processes. Ferroelectricity in Si-doped hafnia was first reported in 2011, and this has revived interest in using ferroelectric memories for various applications. Ferroelectric hafnia with matured atomic layer deposition techniques is compatible with three-dimensional capacitors and can solve the scaling limitations in 1-transistor-1-capacitor (1T-1C) ferroelectric random-access memories (FeRAMs). For ferroelectric field-effect-transistors (FeFETs), the low permittivity and high coercive field Ec of hafnia ferroelectrics are beneficial. The much higher Ec of ferroelectric hafnia, however, makes high endurance a challenge. This article summarizes the current status of ferroelectricity in hafnia and explains how major issues of 1T-1C FeRAMs and FeFETs can be solved using this material system.

Diese Dissertation befasst sich mit quantenchemischen Untersuchungen der CO2-Insertion in Si-N-Bindungen von Aminosilanen und der Zuverlässigkeit quantenchemischer Berechnungsmethoden. Es wurden verschiedene Verbindungsklassen, wie Piperazinderivate, Di- und Monoethanolaminderivate, einfache und spirozyklische Aminosilane verwendet. Zunächst wurde ein Benchmarking der verwendeten Berechnungsmethoden durchgeführt, um die für diese Forschung am besten geeigneten Methoden herauszufinden. Quantenchemische Berechnungen wurden genutzt, um die Reaktionen und die möglichen Prozesse aus der Sicht der Thermodynamik zu bewerten. Desweiteren wurde der Mechanismus der CO2-Insertion untersucht. Zu diesem Zweck wurden Geometrieoptimierungen der Übergangszustände durchgeführt, wobei die Aminosilan-CO2-Komplexe mit unterschiedlichem C-N-Abstand berücksichtigt wurden, um den Weg der Reaktanten zum Übergangszustand zu finden. Zusätzlich wurden NBO-Berechnungen durchgeführt, um den Reaktionsmechanismus zu entschlüsseln. Die berechneten IR- und NMR-Spektren wurden mit gemessenen Spektren verglichen und ihre Zuverlässigkeit wurde in der Arbeit bewertet.

The new class of fully silicon-compatible hafnia-based ferroelectrics with high switchable polarization and good endurance and thickness scalability shows a strong promise for new generations of logic and memory devices. Among other factors, their competitiveness depends on the power efficiency that requires reliable low-voltage operation. Here, we show genuine ferroelectric switching in HfₓZr₍₁₋ₓ₎ O₂ (HZO) layers in the application-relevant capacitor geometry, for driving signals as low as 800 mV and coercive voltage below 500 mV. Enhanced piezoresponse force microscopy with sub-picometer sensitivity allowed for probing individual polarization domains under the top electrode and performing a detailed analysis of hysteretic switching. The authentic local piezoelectric loops and domain wall movement under bias attest to the true ferroelectric nature of the detected nanodomains. The systematic analysis of local piezoresponse loop arrays reveals a totally unexpected thickness dependence of the coercive fields in HZO capacitors. The thickness decrease from 10 to 7 nm is associated with a remarkably strong decrease of the coercive field, with about 50% of the capacitor area switched at coercive voltages ≤0.5 V. Our explanation consistent with the experimental data involves a change of mechanism of nuclei-assisted switching when the thickness decreases below 10 nm. The practical implication of this effect is a robust ferroelectric switching under the millivolt-range driving signal, which is not expected for the standard coercive voltage scaling law. These results demonstrate a strong potential for further aggressive thickness reduction of HZO layers for low-power electronics.

Im Mittelpunkt der Arbeit stehen Alanate und Aluminiumhydride der Übergangs- und Erdalkalimetalle in Bezug auf ihre Synthese, ihre thermodynamischen Eigenschaften, ihre Zersetzungsreaktionen und ihre potentielle Eignung für reversible Wasserstoffspeicheranwendungen. Es konnten für CeAlH6, Mg(AlH4)2, Ca(AlH4)2, Sr(AlH4)2, CaAlH5 und SrAlH5 die Wärmekapazitätsfunktionen sowie die absoluten Entropien und Bildungsenthalpien bei 298,15 K bestimmt werden. Weiterhin wurden Methoden zur Näherung der genannten thermodynamischen Daten evaluiert und mit den ermittelten Werten aktualisiert und erweitert. Außerdem wurde die im Bereich der komplexen Hydride übliche Annahme, dass sich die bei der Synthese gebildeten Nebenprodukte LiCl und NaCl gegenüber den Hydriden inert verhalten, überprüft. Es konnte gezeigt werden, dass die Annahme hinsichtlich der Eigenschaften und Zersetzungsreaktionen von Mg(AlH4)2, Ca(AlH4)2 und Sr(AlH4)2 Bestand hat. In Bezug auf die Dehydrierung von CaAlH5 und SrAlH5 ist sie jedoch ungültig, wenn die Probe LiCl enthält.

2D transition metal carbides and/or nitrides, so-called MXenes, are noted as ideal fast-charging cation-intercalation electrode materials, which nevertheless suffer from limited specific capacities. Herein, it is reported that constructing redox-active phosphorus−oxygen terminals can be an attractive strategy for Nb4C3 MXenes to remarkably boost their specific capacities for ultrafast Na+ storage. As revealed, redox-active terminals with a stoichiometric formula of PO2- display a metaphosphate-like configuration with each P atom sustaining three P-O bonds and one P=O dangling bond. Compared with conventional O-terminals, metaphosphate-like terminals empower Nb4C3 (denoted PO2-Nb4C3) with considerably enriched carrier density (fourfold), improved conductivity (12.3-fold at 300 K), additional redox-active sites, boosted Nb redox depth, nondeclined Na+-diffusion capability, and buffered internal stress during Na+ intercalation/de-intercalation. Consequently, compared with O-terminated Nb4C3, PO2-Nb4C3 exhibits a doubled Na+-storage capacity (221.0 mAh g-1), well-retained fast-charging capability (4.9 min at 80% capacity retention), significantly promoted cycle life (nondegraded capacity over 2000 cycles), and justified feasibility for assembling energy−power-balanced Na-ion capacitors. This study unveils that the molecular-level design of MXene terminals provides opportunities for developing simultaneously high-capacity and fast-charging electrodes, alleviating the energy−power tradeoff typical for energy-storage devices.