This work investigates the crystallography and dielectric properties of Zirconium- and Hafnium-oxide based nano-scale thin film insulators for memory. Hafnium- and Zirconium-oxide are industry leading candidates for high-k dielectrics. Most application research has focused on the application of amorphous high-k due to formation of defects associated with the crystalline phase. However the application of crystalline dielectrics offers two advantages: Potentially high thermal stability, since no measures have to be taken to avoid crystallization, and the ability to manipulate crystalline phase composition to maximize dielectric constants. Pure ZrO2 crystallized at a lower temperature than HfO2 and always formed a metastable t’ higher-k phase. ZrO2 crystallized already during deposition, leading to leakage current degradation. It was shown that this problem could be solved by SiO2 addition to raise the crystallization temperature, allowing fabrication of low leakage, low effective oxide thickness (EOT) metal-insulator-metal (MIM) capacitors suitable for stack based DRAM down to the 4X nm node. HfO2, in contrast, formed a mixture of monoclinic and tetragonal phase which led to the formation of mechanical defects (microcracks). Addition of SiO2 allowed manipulating the phase composition of HfO2. When up to 7 mol% SiO2 was added, increased stabilization of the metastable t' phase with a dielectric constant of 34-36 was observed. It could be shown that the stabilization is due to a combination of a surface energy effect and solved SiO2 in the HfO2 lattice. Above 11 mol% SiO2 segregated from HfO2 and a tetragonal phase with higher c/a splitting and lower dielectric constant was stabilized instead. It was discovered that the behavior of HfSiO was fundamentally altered if it was crystallized under mechanical confinement in presence of a top electrode. Besides a significant increase in dielectric constant, the material exhibited ferroelectric and antiferroelectric polarization hysteresis, a characteristic not previously reported for HfO2 or ZrO2. This behavior originated from the formation of a new orthorhombic crystal phase. Utilizing the increased permittivity of the antiferroelectic phase, it was possible to demonstrate low EOT, highly temperature stable, MIM capacitors with potential application in sub 50 nm deep trench-DRAM generations. Novel ferroelectric HfSiO was used to fabricate ferroelectric field effect transistors which allowed long term nonvolatile data storage. The electrical characteristics of the devices meet or exceed that of the best published literature results. Full compatibility to silicon semiconductor technology with a gate stack thickness down to 5 nm was demonstrated for the first time, suggesting that HfSiO based FEFETs can potentially be scaled to below the 30 nm node. This goal could not be achieved with previously known materials.

In 2011, Böscke et al. reported the unexpected discovery of ferroelectric properties in hafnia based thin films, which has since initiated many further studies and revitalized research on the topic of ferroelectric memories. In spite of many efforts, the unveiling of the fundamentals behind this surprising discovery has proven rather challenging. In this work, the originally claimed Pca21 phase is experimentally proven to be the root of the ferroelectric properties and the nature of this ferroelectricity is classified in the frame of existing concepts of ferroelectric materials. Parameters to stabilize this polar phase are examined from a theoretical and fabrication point of view. With these very basic questions addressed, the application relevant electric field cycling behavior is studied. The results of first-order reversal curves, impedance spectroscopy, scanning transmission electron microscopy and piezoresponse force microscopy significantly advance the understanding of structural mechanisms underlying wake-up, fatigue and the novel phenomenon of split-up/merging of transient current peaks. The impact of field cycling behavior on applications like ferroelectric memories is highlighted and routes to optimize it are derived. These findings help to pave the road for a successful commercialization of hafnia based ferroelectrics.

Ferroelectric field effect transistor (FeFET) memories based on a new type of ferroelectric material (silicon doped hafnium oxide) were studied within the scope of the present work. Utilisation of silicon doped hafnium oxide (Si:HfO2 thin films instead of conventional perovskite ferroelectrics as a functional layer in FeFETs provides compatibility to the CMOS process as well as improved device scalability. The influence of different process parameters on the properties of Si:HfO2 thin films was analysed in order to gain better insight into the occurrence of ferroelectricity in this system. A subsequent examination of the potential of this material as well as its possible limitations with the respect to the application in non-volatile memories followed. The Si:HfO2-based ferroelectric transistors that were fully integrated into the state-of-the-art high-k metal gate CMOS technology were studied in this work for the first time. The memory performance of these devices scaled down to 28 nm gate length was investigated. Special attention was paid to the charge trapping phenomenon shown to significantly affect the device behaviour.

Not only conventional computer architectures, such as the von-Neumann architecture with its inevitable von-Neumann bottleneck, but likewise the emerging field of edge computing require to substantially decrease the spatial separation of logic and memory units to overcome power and latency shortages. The integration of logic operations into memory units (Logic-in-Memory), as well as memory elements into logic circuits (Nonvolatile Logic), promises to fulfill this request by combining high-speed with low-power operation. Ferroelectric field-effect transistors (FeFETs) based on hafnium oxide prove to be auspicious candidates for the memory elements in applications of that kind, as those nonvolatile memory elements are CMOS-compatible and likewise scalable. This work presents implementations that merge logic and memory by exploiting the natural capability of the FeFET to combine logic functionality (transistor) and memory ability (nonvolatility).

Ferroelectricity in Doped Hafnium Oxide: Materials, Properties and Devices covers all aspects relating to the structural and electrical properties of HfO2 and its implementation into semiconductor devices, including a comparison to standard ferroelectric materials. The ferroelectric and field-induced ferroelectric properties of HfO2-based films are considered promising for various applications, including non-volatile memories, negative capacitance field-effect-transistors, energy storage, harvesting, and solid-state cooling. Fundamentals of ferroelectric and piezoelectric properties, HfO2 processes, and the impact of dopants on ferroelectric properties are also extensively discussed in the book, along with phase transition, switching kinetics, epitaxial growth, thickness scaling, and more. Additional chapters consider the modeling of ferroelectric phase transformation, structural characterization, and the differences and similarities between HFO2 and standard ferroelectric materials. Finally, HfO2 based devices are summarized. Explores all aspects of the structural and electrical properties of HfO2, including processes, modelling and implementation into semiconductor devices Considers potential applications including FeCaps, FeFETs, NCFETs, FTJs and more Provides comparison of an emerging ferroelectric material to conventional ferroelectric materials with insights to the problems of downscaling that conventional ferroelectrics face

In recent years, both hafnia and zirconia have been looked at closely in the quest for a high permittivity gate dielectric to replace silicon dioxide in advanced metal oxide semiconductor field effect transistors (MOSFET). Hafnium dioxide or HfO2 is chosen for its high dielectric constant (five times that of SiO2) and compatibility with stringent requirements of the Si process. As deposited, thin hafnia films are typically amorphous but turn polycrystalline after a post-deposition anneal. To control the phase composition in hafnia films understanding of structural phase transitions is a first step. In this dissertation using first principles methods we consider three phase transitions of hafnia and zirconia: monoclinic to tetragonal, tetragonal to cubic and amorphous to crystalline. Because the high surface to volume ratio in hafnia films and powders plays an important role in phase transitions, we also study the surface properties of hafnia. We discuss the mechanisms of various phase transitions and theoretically estimate the transition temperatures. We find two types of amorphous hafnia and show that they have different structural and electronic properties. The small energy barrier between the amorphous and crystalline structures is found to cause the low crystallization temperature. Moreover, we calculate work functions and surface energies for hafnia surfaces and show the surface suppression of the phase transitions.

A state-of-the-art overview of high-k dielectric materials for advanced field-effect transistors, from both a fundamental and a technological viewpoint, summarizing the latest research results and development solutions. As such, the book clearly discusses the advantages of these materials over conventional materials and also addresses the issues that accompany their integration into existing production technologies. Aimed at academia and industry alike, this monograph combines introductory parts for newcomers to the field as well as advanced sections with directly applicable solutions for experienced researchers and developers in materials science, physics and electrical engineering.