Gestión de jerarquías de memoria híbridas a nivel de sistema

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Informática, Departamento de Arquitectura de Computadoras y Automática y de Ku Leuven, Arenberg Doctoral School, Faculty of Engineering Science, leída el 11/05/2017.In electronics and computer science, the term ‘memory’ generally refers to devices that are used to store information that we use in various appliances ranging from our PCs to all hand-held devices, smart appliances etc. Primary/main memory is used for storage systems that function at a high speed (i.e. RAM). The primary memory is often associated with addressable semiconductor memory, i.e. integrated circuits consisting of silicon-based transistors, used for example as primary memory but also other purposes in computers and other digital electronic devices. The secondary/auxiliary memory, in comparison provides program and data storage that is slower to access but offers larger capacity. Examples include external hard drives, portable flash drives, CDs, and DVDs. These devices and media must be either plugged in or inserted into a computer in order to be accessed by the system. Since secondary storage technology is not always connected to the computer, it is commonly used for backing up data. The term storage is often used to describe secondary memory. Secondary memory stores a large amount of data at lesser cost per byte than primary memory; this makes secondary storage about two orders of magnitude less expensive than primary storage. There are two main types of semiconductor memory: volatile and nonvolatile. Examples of non-volatile memory are ‘Flash’ memory (sometimes used as secondary, sometimes primary computer memory) and ROM/PROM/EPROM/EEPROM memory (used for firmware such as boot programs). Examples of volatile memory are primary memory (typically dynamic RAM, DRAM), and fast CPU cache memory (typically static RAM, SRAM, which is fast but energy-consuming and offer lower memory capacity per are a unit than DRAM). Non-volatile memory technologies in Si-based electronics date back to the 1990s. Flash memory is widely used in consumer electronic products such as cellphones and music players and NAND Flash-based solid-state disks (SSDs) are increasingly displacing hard disk drives as the primary storage device in laptops, desktops, and even data centers. The integration limit of Flash memories is approaching, and many new types of memory to replace conventional Flash memories have been proposed. The rapid increase of leakage currents in Silicon CMOS transistors with scaling poses a big challenge for the integration of SRAM memories. There is also the case of susceptibility to read/write failure with low power schemes. As a result of this, over the past decade, there has been an extensive pooling of time, resources and effort towards developing emerging memory technologies like Resistive RAM (ReRAM/RRAM), STT-MRAM, Domain Wall Memory and Phase Change Memory(PRAM). Emerging non-volatile memory technologies promise new memories to store more data at less cost than the expensive-to build silicon chips used by popular consumer gadgets including digital cameras, cell phones and portable music players. These new memory technologies combine the speed of static random-access memory (SRAM), the density of dynamic random-access memory (DRAM), and the non-volatility of Flash memory and so become very attractive as another possibility for future memory hierarchies. The research and information on these Non-Volatile Memory (NVM) technologies has matured over the last decade. These NVMs are now being explored thoroughly nowadays as viable replacements for conventional SRAM based memories even for the higher levels of the memory hierarchy. Many other new classes of emerging memory technologies such as transparent and plastic, three-dimensional(3-D), and quantum dot memory technologies have also gained tremendous popularity in recent years...En el campo de la informática, el término ‘memoria’ se refiere generalmente a dispositivos que son usados para almacenar información que posteriormente será usada en diversos dispositivos, desde computadoras personales (PC), móviles, dispositivos inteligentes, etc. La memoria principal del sistema se utiliza para almacenar los datos e instrucciones de los procesos que se encuentre en ejecución, por lo que se requiere que funcionen a alta velocidad (por ejemplo, DRAM). La memoria principal está implementada habitualmente mediante memorias semiconductoras direccionables, siendo DRAM y SRAM los principales exponentes. Por otro lado, la memoria auxiliar o secundaria proporciona almacenaje(para ficheros, por ejemplo); es más lenta pero ofrece una mayor capacidad. Ejemplos típicos de memoria secundaria son discos duros, memorias flash portables, CDs y DVDs. Debido a que estos dispositivos no necesitan estar conectados a la computadora de forma permanente, son muy utilizados para almacenar copias de seguridad. La memoria secundaria almacena una gran cantidad de datos aun coste menor por bit que la memoria principal, siendo habitualmente dos órdenes de magnitud más barata que la memoria primaria. Existen dos tipos de memorias de tipo semiconductor: volátiles y no volátiles. Ejemplos de memorias no volátiles son las memorias Flash (algunas veces usadas como memoria secundaria y otras veces como memoria principal) y memorias ROM/PROM/EPROM/EEPROM (usadas para firmware como programas de arranque). Ejemplos de memoria volátil son las memorias DRAM (RAM dinámica), actualmente la opción predominante a la hora de implementar la memoria principal, y las memorias SRAM (RAM estática) más rápida y costosa, utilizada para los diferentes niveles de cache. Las tecnologías de memorias no volátiles basadas en electrónica de silicio se remontan a la década de1990. Una variante de memoria de almacenaje por carga denominada como memoria Flash es mundialmente usada en productos electrónicos de consumo como telefonía móvil y reproductores de música mientras NAND Flash solid state disks(SSDs) están progresivamente desplazando a los dispositivos de disco duro como principal unidad de almacenamiento en computadoras portátiles, de escritorio e incluso en centros de datos. En la actualidad, hay varios factores que amenazan la actual predominancia de memorias semiconductoras basadas en cargas (capacitivas). Por un lado, se está alcanzando el límite de integración de las memorias Flash, lo que compromete su escalado en el medio plazo. Por otra parte, el fuerte incremento de las corrientes de fuga de los transistores de silicio CMOS actuales, supone un enorme desafío para la integración de memorias SRAM. Asimismo, estas memorias son cada vez más susceptibles a fallos de lectura/escritura en diseños de bajo consumo. Como resultado de estos problemas, que se agravan con cada nueva generación tecnológica, en los últimos años se han intensificado los esfuerzos para desarrollar nuevas tecnologías que reemplacen o al menos complementen a las actuales. Los transistores de efecto campo eléctrico ferroso (FeFET en sus siglas en inglés) se consideran una de las alternativas más prometedores para sustituir tanto a Flash (por su mayor densidad) como a DRAM (por su mayor velocidad), pero aún está en una fase muy inicial de su desarrollo. Hay otras tecnologías algo más maduras, en el ámbito de las memorias RAM resistivas, entre las que cabe destacar ReRAM (o RRAM), STT-RAM, Domain Wall Memory y Phase Change Memory (PRAM)...Depto. de Arquitectura de Computadores y AutomáticaFac. de InformáticaTRUEunpu

Treated HfO2 based rram devices with ru, tan, tin as top electrode for in-memory computing hardware

The scalability and power efficiency of the conventional CMOS technology is steadily coming to a halt due to increasing problems and challenges in fabrication technology. Many non-volatile memory devices have emerged recently to meet the scaling challenges. Memory devices such as RRAMs or ReRAM (Resistive Random-Access Memory) have proved to be a promising candidate for analog in memory computing applications related to inference and learning in artificial intelligence. A RRAM cell has a MIM (Metal insulator metal) structure that exhibits reversible resistive switching on application of positive or negative voltage. But detailed studies on the power consumption, repeatability and retention of during multi-level operation have not been undertaken previously. Transition metal oxide-based RRAMs, using HfO2, executes change in resistance (switching behavior) via electrochemical migration of oxygen vacancies. This thesis investigates the role of extra oxygen vacancies, introduced by plasma exposure (treated), in HfO2 to reduce the power consumption of RRAM. In addition to oxygen vacancy rich HfO2, various top metal electrodes including Ruthenium (Ru) are explored to enhance the switching behavior and power consumption. Use of Ru as a top metal reduced the switching energy of the treated HfO2 RRAM device

Solution-based IGZO nanoparticles memristor

This work aims to characterize Indium-Gallium-Zinc-Oxide nanoparticles (IGZOnp) as a resistive switching matrix in metal-insulator-metal (MIM) structures for memristor application. IGZOnp was produced by low cost solution-based process and deposited by spin-coating technique. Several top and bottom electrodes combinations, including IZO, Pt, Au, Ti, Ag were investigated to evaluate memory performance, yield and switching properties. The effect of ambient and annealing temperature using 350 ºC and 200 ºC was also analysed in order to get more insight into resistive switching mechanism. The Ag/IGZOnp/Ti memristor structure annealed at 200 ºC exhibits the best results with a large yield. The device shows a self-compliant bipolar resistive switching behavior. The switching event is achieved by the set/reset voltages of -1 V/+1 V respectively with an operating window of 10, and it can be programmed for more than 100 endurance cycles. The retention time of on and off-states is up to 104 s. The obtained results suggest that Ag/IGZOnp/Ti structure could be applied in system on a panel (SoP) as a viable device

Carrier transport engineering in wide bandgap semiconductors for photonic and memory device applications

Wide bandgap (WBG) semiconductors play a crucial role in the current solid-state lighting technology. The AlGaN compound semiconductor is widely used for ultraviolet (UV) light-emitting diodes (LEDs), however, the efficiency of these LEDs is largely in a single-digit percentage range due to several factors. Until recently, AlInN alloy has been relatively unexplored, though it holds potential for light-emitters operating in the visible and UV regions. In this dissertation, the first axial AlInN core-shell nanowire UV LEDs operating in the UV-A and UV-B regions with an internal quantum efficiency (IQE) of 52% are demonstrated. Moreover, the light extraction efficiency of this UV LED can be further improved by 63% by utilizing appropriate hexagonal photonic crystal structures. The carrier transport characteristics of the LEDs have been carefully engineered to enhance the carrier distributions and reduce the current leakage, leading to a significantly improved IQE of the LEDs. In this regard, the p-type AlGaN electron blocking layer (EBL) has been utilized to suppress electron leakage. Although the EBL can suppress the electron leakage to an extent, it also affects the hole injection due to the generation of positive polarization sheet charges at the hetero interface of EBL and the last quantum barrier (QB). Moreover, the Mg acceptor activation energy of the Al-rich AlGaN EBL layer is elevated, affecting the Mg doping efficiency. To mitigate this problem, in this dissertation, EBL-free UV LED designs are proposed where the epilayers are carefully band-engineered to notably improve the device performance by lowering the electron overflows. The proposed EBL-free strip-in-a-barrier UV LED records the maximum IQE of -61.5% which is -72% higher, and IQE droop is -12.4%, which is -333% less compared to the conventional AlGaN EBL LED structure at 284.5 nm wavelength. Moreover, it is shown that the EBL-free AlGaN deep UV LED structure with linearly graded polarization-controlled QBs instead of conventional QBs in the active region could drastically reduce the electrostatic field in the quantum well (QW) region due to the decreased lattice mismatch between the QW and the QB. The carrier transport in the EBL-free deep UV LEDs is significantly improved, attributed to the increased radiative recombination, quantum efficiency, and output power compared to the conventional EBL LEDs. Overall, the study of EBL-free UV LEDs offers important insights into designing novel, high-performance deep UV LEDs for practical applications. Further, it is demonstrated that novel WBG materials could be perfectly employed for emerging non-volatile memory (resistive random access memory, RRAM) applications. The resistive switching (RS) capability has been observed in Ga2O3 at low power operation. Importantly, for the first time, the multi-bit storage capability of this types of RRAM devices with a reasonably high Roff/Ron ratio is experimentally demonstrated. In addition, integrating a thin SiNx layer in the conventional SiO2 RRAM device could effectively facilitate the formation of a conducting filament. It is reported that the proposed RRAM device exhibits excellent RS characteristics, such as highly uniform current-voltage characteristics with concentrated SET and RESET voltages, excellent stability, and high Roff/Ron (\u3e 103) even at ultra-low current (10 nA) operation. The multi-bit RS behavior has been observed in these RRAM devices, which pave the way for low-power and high-density data storage applications

Energy/Reliability Trade-Offs in Low-Voltage ReRAM-Based Non-Volatile Flip-Flop Design

The total power budget of Ultra-Low Power (ULP) VLSI Systems-on-Chip (SoCs) is often dominated by the leakage power of embedded memories as well as status registers. On the one hand, supply voltage scaling down to the near-threshold (near-VT) or even to the subthreshold (sub-VT) domain is a commonly used, efficient technique to reduce both leakage power and active energy dissipation. On the other hand, emerging CMOS-compatible device technologies such as Resistive Memories (ReRAMs) enable non-volatile, on-chip data storage and zero-leakage sleep periods. For the first time, we present and compare ReRAM-based Non-Volatile Flip-Flop (NVFF) topologies which are optimized for low-voltage operation (including near-VT and sub-VT operation). Three low-voltage NVFF circuit topologies are proposed and evaluated in terms of energy dissipation and reliability. Using topologies with two complementary programmed ReRAM devices, Monte Carlo simulations accounting for parametric variations confirm reliable data restore operation from the ReRAM devices at a sub- voltage as low as 400 mV. A topology using a single ReRAM device exhibits lower write energy, but requires a near- voltage for robust read. Energy characterization is performed at nominal, near-VT , and sub-VT supply voltages. The minimum energy point is reached for near-VT read operation with a total read+write energy of 735 fJ

Nanoparticle Dynamics in Oxide-Based Memristive Devices

In microelectronics a device's functionality is shaped by its interfaces. While classical semiconductor research aimed for preparation of nearly ideal interfaces, the emerging paradigm is that new functionalities can arise from interfaces with less perfection. Memristive devices rely on the control of such less-perfect interfaces. They are the building blocks for a new range of applications, including new memory and logic architectures and neuromorphic computing. Research on memristive systems and applications demands an interdisciplinary approach across disciplines including solid-state physics, electrochemistry and biochemistry. Advanced metrology is the key for a better understanding and finally a better control of such interfaces and novel device technologies. In this featured article we highlight such recent advances in characterization and the understanding of electrochemical reactions on the (sub-) nanoscale and the dynamics of the nanoparticles and clusters involved during operation of memristive devices acting as a model system. We focus particularly on in operando real time monitoring of the memristive switching effect by transmission electron microscopy and a novel plasmon enhanced spectroscopy method

Evaluation des performances des mémoires CBRAM (Conductive bridge memory) afin d’optimiser les empilements technologiques et les solutions d’intégration

The constant evolution of the data storage needs over the last decades have led the technological landscape to completely change and reinvent itself. From the early stage of magnetic storage to the most recent solid state devices, the bit density keeps increasing toward what seems from a consumer point of view infinite storage capacity and performances. However, behind each storage technology transition stand density and performances limitations that required strong research work to overcome. This manuscript revolves around one of the promising emerging technology aiming to revolutionize data storage landscape: the Conductive Bridge Random Access Memory (CBRAM). This technology based on the reversible formation and dissolution of a conductive path in a solid electrolyte matrix offers great advantages in term of power consumption, performances, density and the possibility to be integrated in the back end of line. However, for this technology to be competitive some roadblocks still have to be overcome especially regarding the technology variability, reliability and thermal stability. This manuscript proposes a comprehensive understanding of the CBRAM operations based on experimental results and a specially developed Kinetic Monte Carlo model. This understanding creates bridges between the physical properties of the materials involved in the devices and the devices performances (Forming, SET and RESET time and voltage, retention, endurance, variability). A strong emphasis is placed on the current limitations of the technology previously stated and how to overcome these limitations. Improvement of the thermal stability and device reliability are demonstrated with optimized operating conditions and proper devices engineering.Ces dernières décennies, la constante évolution des besoins de stockage de données a mené à un bouleversement du paysage technologique qui s’est complètement métamorphosé et réinventé. Depuis les débuts du stockage magnétique jusqu’aux plus récents dispositifs fondés sur l’électronique dit d’état solide, la densité de bits stockés continue d’augmenter vers ce qui semble du point de vue du consommateur comme des capacités de stockage et des performances infinies. Cependant, derrière chaque transition et évolution des technologies de stockage se cachent des limitations en termes de densité et performances qui nécessitent de lourds travaux de recherche afin d’être surmontées et repoussées. Ce manuscrit s’articule autour d’une technologie émergeante prometteuse ayant pour vocation de révolutionner le paysage du stockage de données : la mémoire à pont conducteur ou Conductive Bridge Random Access Memory (CBRAM). Cette technologie est fondée sur la formation et dissolution réversible d’un chemin électriquement conducteur dans un électrolyte solide. Elle offre de nombreux avantages face aux technologies actuelles tels qu’une faible consommation électrique, de très bonnes performances d’écriture et de lecture et la capacité d’être intégré aux seins des interconnexions métalliques d’une puce afin d’augmenter la densité de stockage. Malgré tout, pour que cette technologie soit compétitive certaines limitations ont besoin d’être surmontées et particulièrement sa variabilité et sa stabilité thermique qui posent encore problème. Ce manuscrit propose une compréhension physique globale du fonctionnement de la technologie CBRAM fondée sur une étude expérimentale approfondie couplée à un modèle Monte Carlo cinétique spécialement développé. Cette compréhension fait le lien entre les propriétés physiques des matériaux composant la mémoire CBRAM et ses performances (Tension et temps d’écriture et d’effacement, rétention de donnée, endurance et variabilité). Un fort accent est mis la compréhension des limites actuelle de la technologie et comment les repousser. Grâce à une optimisation des conditions d’opérations ainsi qu’à un travail d’ingénierie des dispositifs mémoire, il est démontré dans ce manuscrit une forte amélioration de la stabilité thermique ainsi que de la variabilité des états écrits et effacés

Substoichiometric Phases of Hafnium Oxide with Semiconducting Properties

Since the dawn of the information age, all developments that provided a significant improvement in information processing and data transmission have been considered as key technologies. The impact of ever new data processing innovations on the economy and almost all areas of our daily lives is unprecedented and a departure from this trend is unimaginable in the near future. Even though the end of Moore's Law has been predicted all too often, the steady exponential growth of computing capacity remains unaffected to this day, due to tremendous commercial pressure. While the minimum physical size of the transistor architecture is a serious constraint, the steady evolution of computing effectiveness is not limited in the predictable future. However, the focus of development will have to expand more strongly to other technological aspects of information processing. For example, the development of new computer paradigms which mark a departure from the digitally dominated van Neumann architecture will play an increasingly significant role. The category of so-called next-generation non-volatile memory technologies, based on various physical principles such as phase transformation, magnetic or ferroelectric properties or ion diffusion, could play a central role here. These memory technologies promise in part strongly pronounced multi-bit properties up to quasi-analog switching behavior. These attributes are of fundamental importance especially for new promising concepts of information processing like in-memory computing and neuromorphic processing. In addition, many next-generation non-volatile memory technologies already show advantages over conventional media such as Flash memory. For example, their application promises significantly reduced energy consumption and their write and especially read speeds are in some cases far superior to conventional technology and could therefore already contribute significant technological improvements to the existing memory hierarchy. However, these alternative concepts are currently still limited in terms of their statistical reliability, among other things. Even though phase change memory in the form of the 3D XPoint, for example, has already been commercialized, the developments have not yet been able to compete due to the enormous commercial pressure in Flash memory research. Nevertheless, the further development of alternative concepts for the next and beyond memory generations is essential and the in-depth research on next-generation non-volatile memory technologies is therefore a hot and extremely important scientific topic. This work focuses on hafnium oxide, a key material in next-generation non-volatile memory research. Hafnium oxide is very well known in the semiconductor industry, as it generated a lot of attention in the course of high-k research due to its excellent dielectric properties and established CMOS compatibility. However, since the growing interest in so-called memristive memory, research efforts have primarily focused on the value of hafnium oxide in the form of resistive random-access memory (RRAM) and, with the discovery of ferroelectricity in HfO₂, ferroelectric resistive random-access memory (FeRAM). RRAM is a next-generation non-volatile memory technology that features a simple metal-insulator-metal (MIM) structure, excellent scalability, and potential 3D integration. In particular, the aforementioned gradual to quasi-continuous switching behavior has been demonstrated on a variety of RRAM systems. A significant change of the switching properties is achievable, for example, by the choice of top and bottom electrodes, the introduction of doping elements, or by designated oxygen deficiency. In particular, the last point is based on the basic physical principle of the hafnium oxide-based RRAM mechanism, in which local oxygen ions are stimulated to diffuse by applying an electrical potential, and a so-called conducting filament is formed by the remaining vacancies, which electrically connects the two electrode sides. The process is characterized by the reversibility of the conducting filament which can be dissolved by a suitable I-V programming (e.g., reversal of the voltage direction). In the literature there are some predictions of sub-stoichiometric hafnium oxide phases, such as Hf₂O₃, HfO or Hf₆O, which could be considered as conducting filament phases, but there is a lack of conclusive experimental results. While there are studies that assign supposed structures in oxygen-deficient hafnium oxide thin films, these assignments are mostly based on references from various stoichiometric hafnium oxide high-temperature phases such as tetragonal t-HfO₂ (P4₂/nmc) or cubic c-HfO₂ (Fm-3m), or high-pressure phases such as orthorhombic o-HfO₂ (Pbca). Furthermore, the structural identification of such thin films proves to be difficult, as they are susceptible to arbitrary texturing and reflection broadening in X-ray diffraction. In addition, such thin films are usually synthesized as phase mixtures with monoclinic hafnium oxide. A further challenge in property determination is given by their usual arrangement in MIM configuration, which is determined by the quality of top and bottom electrodes and their interfaces to the active material. It is therefore a non-trivial task to draw conclusions on individual material properties such as electrical conductivity in such (e.g., oxygen-deficient) RRAM devices. To answer these open questions, this work is primarily devoted to material properties of oxygen-deficient hafnium oxide phases. Therefore, in the first comprehensive study of this work, Molecular-Beam Epitaxy (MBE) was used to synthesize hafnium oxide phases over a wide oxidation range from monoclinic to hexagonal hafnium oxide. The hafnium oxide films were deposited on c-cut sapphire to achieve effective phase selection and identification by epitaxial growth, taking into account the position of relative lattice planes. In addition, the choice of a substrate with a high band gap and optical transparency enabled the direct investigation of both optical and electrical properties by means of UV/Vis transmission spectroscopy and Hall effect measurements. With additional measurements via X-ray diffraction (XRD), X-ray reflectometry (XRR), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM), the oxygen content-dependent changes in crystal as well as band structure could be correlated with electrical properties. Based on these results, a comprehensive band structure model over the entire oxidation range from insulating HfO₂ to metallic Hf was established, highlighting the discovered intermediate key structures of rhombohedral r-HfO₁.₇ and hexagonal hcp-HfO₀.₇. In the second topic of this work, the phase transition from stoichiometric monoclinic to oxygen-deficient rhombohedral hafnium oxide was complemented by DFT calculations in collaboration with the theory group of Prof. Valentí (Frankfurt am Main). A detailed comparison between experimental results and DFT calculations confirms previously assumed mechanisms for phase stabilization. In addition, the comparison shows a remarkable agreement between experimental and theoretical results on the crystal- and band stucture. The calculations allowed to predict the positions of oxygen ions in oxygen-deficient hafnium oxide as well as the associated space group. Also, the investigations provide information on the thermodynamic stability of the corresponding phases. Finally, the orbital-resolved hybridization of valence states influenced by oxygen vacancies is discussed. Another experimental study deals with the reproduction and investigation, of the aforementioned substoichiometric hafnium oxide phases in MIM configuration which is typical for RRAM devices. Special attention was given to the influence of surface oxidation effects. Here, it was found that the oxygen-deficient phases r-HfO₁.₇ and hcp-HfO₀.₇ exhibit high ohmic conductivity as expected, but stable bipolar switching behavior as a result of oxidation in air. Here, the mechanism of this behavior was discussed and the role of the r-HfO₁.₇ and hcp-HfO₀.₇ phases as novel electrode materials in hafnium oxide-based RRAM in particular. In collaboration with the electron microscopy group of Prof. Molina Luna, the studied phases, which have been characterized by rather macroscopic techniques so far, have been analyzed by wide-ranging TEM methodology. The strong oxygen deficiency in combination with the verified electrical conductivity of r-HfO₁.₇ and hcp-HfO₀.₇ shows the importance of the identification of these phases on the nanoscale. Such abilities are essential for the planned characterization of the "conducting-filament" mechanism. Here, the ability to distinguish m-HfO₂, r-HfO₁.₇, and hcp-HfO₀.₇ using high-resolution transmission electron microscopy (HRTEM), Automated Crystal Orientation and Phase Mapping (ACOM), and Electron Energy Loss Spectroscopy (EELS), is demonstrated and the necessity of combined measurements for reliable phase identification was discussed. Finally, a series of monoclinic to rhombohedral hafnium oxide was investigated in a cooperative study with FZ Jülich using scanning probe microscopy. Since recent studies in particular highlight the significance of the microstructure in stoichiometric hafnium oxide-based RRAM, the topological microstructure in the region of the phase transition to strongly oxygen deficient rhombohedral hafnium oxide was investigated. Special attention was given to the correlation of microstructure and conductivity. In particular, the influences of grain boundaries on electrical properties were discussed. In summary, this work provides comprehensive insights into the nature and properties of sub-stoichiometric hafnium oxide phases and their implications on the research of hafnium oxide-based RRAM technology. Taking into account a wide range of scientific perspectives, both, the validity of obtained results and the wide range of their application is demonstrated. Thus, this dissertation provides a detailed scientific base to the understanding of hafnium oxide-based electronics