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The present research work mainly focuses on the fabrication of 0.85PMN-0.15PT thin film relaxor ferroelectrics for energy harvesting applications. Chapter 1 gives a brief review about why energy harvesting is required and the different ways it can be scavenged. An introduction to relaxor ferroelectrics and their characteristics structural features are discussed. A brief introduction is given about charge storage, electrocaloric effect , DC-EFM and integration over Si substrate is discussed. Finally, the specific objectives of the current research are outlined. Chapter 2 deals with the various experimental studies carried out in this research work. It gives the details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. A brief explanation of material fabrication, Microstructural and physical property measurements is discussed. Chapter3 involves the optimization process carried out to contain a phase pure PMN-PT structure without any pyrochlore phase. The optimization process is an important step in the fabrication of a thin film as the quality of any device is determined by their structural and Microstructural features. XRD, SEM, AFM were used to characterize the observed phase formation in these films. The optimizing domain images of polycrystalline 0.85PMN-0.15PT thin films on La0.5Sr0.5CoO3/ (111) Pt/TiO2/SiO2/Si substrates deposited at different oxygen partial pressures are presented. The oxygen pressure has a drastic influence on the film growth and grain morphology which are revealed through XRD and SEM characterization techniques. The presence of oxygen vacancies have found to influence the distribution of polar nanoregions and their dynamics which are visualized using domain images acquired by DC-EFM In Chapter 7 the piezoelectric response of 0.85PMN-0.15PT thin films are studied due to the electric field induced bias. From this the d33 value is calculated. d33 value is an important parameter which determines whether a material is suitable for device application (PZT). But, for a device fabrication it is important to integrate them with Si wafer which is not a straightforward work .Hence, buffer layers are used to obtain a pure perovskite PMN-PT film. We have deposited 0.85PMN-0.15PT thin films of 500 nm on a SOI wafer and tried to investigate their piezoelectric application. Chapter 8 summarizes the present study and discusses about the future work that could give more insight into the understanding of the0.85PMN-0.15 PT relaxor ferroelectric thin film.

Edge computing requires highly energy efficient microprocessor units with embedded non-volatile memories to process data at IoT sensor nodes. Ferroelectric non-volatile memory devices are fast, low power and high endurance, and could greatly enhance energy-efficiency and allow flexibility for finer grain logic and memory. This paper will describe the basics of ferroelectric devices for both hysteretic (non-volatile memory) and negative capacitance (steep slope switch) devices, and then project how these can be used in low-power logic cell architectures and fine-grain logic-in-memory (LiM) circuits.

Ferroelectricity is a material property were a remanent polarization exists under zero electrical field that can be reversed by applying an electrical field [1]. As consequence, two nonvolatile states exist that can be switched by an electrical field. This feature makes ferroelectrics ideally suited for nonvolatile memories with low write energy. Therefore, already in the 1950s first attempts have been made to realize ferroelectric nonvolatile memories based on ferroelectric barium titanate (BTO) crystals having evaporated electrodes on both sides [2]. The success of this approach was hindered by disturb issues that could be solved in the early 1990s by adding a transistor device as a selector [3]. Such a memory is referred to as a ferroelectric random access memory (FeRAM). Since reading of the ferroelectric polarization from a capacitor requires switching of the ferroelectric [1], the information will be destroyed and a write back is necessary. This can be avoided if the ferroelectric is placed inside of the gate stack of a MOS transistor resulting in a ferroelectric field effect transistor (FeFET) [1]. Conventional ferroelectric materials like BTO or lead- zirconium titanate (PZT) cannot be placed directly on silicon since unwanted interface reactions will occur. The necessary interface layer together with the space charge region of the transistor device leads to a rather low capacitance in series with the ferroelectric dielectric and consequently results in a strong depolarization field that has destroyed the nonvolatility of the FeFET device for many years and hinters scaling as well [4]. Today FeRAM devices are established on the market [3,5], but are limited to niche application since scaling is hindered by many integration problems associated to materials like PZT.

Les mémoires non-volatiles (MNV) sont l'objet d'un effort de recherche croissant du fait de leur capacité à limiter la consommation statique, qui obère habituellement la réduction des dimensions dans la technologie CMOS. Dans ce contexte, cette thèse aborde plus spécifiquement deux technologies de mémoires non volatiles : d'une part les jonctions tunnel ferroélectriques (JTF), dispositif non volatil émergent, et d'autre part les dispositifs à transfert de spin (TS) assisté par effet Hall de spin (EHS), approche alternative proposée récemment pour écrire les jonctions tunnel magnétiques (JTM). Mon objectif est de développer des modèles compacts pour ces deux technologies et d'explorer, par simulation, leur intégration dans les circuits non-volatiles.J'ai d'abord étudié les modèles physiques qui décrivent les comportements électriques des JTF : la résistance tunnel, la dynamique de la commutation ferroélectrique et leur comportement memristif. La précision de ces modèles physiques est validée par leur bonne adéquation avec les résultats expérimentaux. Afin de proposer un modèle compatible avec les simulateurs électriques standards, nous j'ai développé les modèles physiques mentionnés ci-dessus en langue Verilog-A, puis je les ai intégrés ensemble. Le modèle électrique que j'ai conçu peut être exploité sur la plate-forme Cadence (un outil standard pour la simulation de circuit). Il reproduit fidèlement les comportements de JTF. Ensuite, en utilisant ce modèle de JTF et le design-kit CMOS de STMicroelectronics, j'ai conçu et simulé trois types de circuits: i) une mémoire vive (RAM) basée sur les JTF, ii) deux systèmes neuromorphiques basés sur les JTF, l'un qui émule la règle d'apprentissage de la plasticité synaptique basée sur le décalage temporel des impulsions neuronale (STDP), l'autre mettant en œuvre l'apprentissage supervisé de fonctions logiques, iii) un bloc logique booléen basé sur les JTF, y compris la démonstration des fonctions logiques NAND et NOR. L'influence des paramètres de la JTF sur les performances de ces circuits a été analysée par simulation. Finalement, nous avons modélisé la dynamique de renversement de l'aimantation dans les dispositifs à anisotropie perpendiculaire à transfert de spin assisté par effet Hall de spin dans un JTM à trois terminaux. Dans ce schéma, deux courants d'écriture sont appliqués pour générer l'EHS et le TS. La simulation numérique basée sur l'équation de Landau-Lifshitz-Gilbert (LLG) démontre que le délai d'incubation de TS peut être éliminé par un fort EHS, conduisant à la commutation ultra-rapide de l'aimantation, sans pour autant requérir une augmentation excessive du TS. Nous avons appliqué cette nouvelle méthode d'écriture à la conception d'une bascule magnétique et d'un additionneur 1 bit magnétique. Les performances des circuits magnétiques assistés par l'EHS ont été comparés à ceux écrits par transfert de spin, par simulation et par une analyse fondée sur le modèle théorique. / Non-volatile memory (NVM) devices have been attracting intensive research interest since they promise to solve the increasing static power issue caused by CMOS technology scaling. This thesis focuses on two fields related to NVM: the one is the ferroelectric tunnel junction (FTJ), which is a recent emerging NVM device. The other is the spin-Hall-assisted spin-transfer torque (STT), which is a recent proposed write approach for the magnetic tunnel junction (MTJ). Our objective is to develop the compact models for these two technologies and to explore their application in the non-volatile circuits through simulation.First, we investigated physical models describing the electrical behaviors of the FTJ such as tunneling resistance, dynamic ferroelectric switching and memristive response. The accuracy of these physical models is validated by a good agreement with experimental results. In order to develop an electrical model available for the circuit simulation, we programmed the aforementioned physical models with Verilog-A language and integrated them together. The developed electrical model can run on Cadence platform (a standard circuit simulation tool) and faithfully reproduce the behaviors of the FTJ.Then, using the developed FTJ model and STMicroelectronics CMOS design kit, we designed and simulated three types of circuits: i) FTJ-based random access memory (FTRAM), ii) two FTJ-based neuromorphic systems, one of which emulates spike-timing dependent plasticity (STDP) learning rule, the other implements supervised learning of logic functions, iii) FTJ-based Boolean logic block, by which NAND and NOR logic are demonstrated. The influences of the FTJ parameters on the performance of these circuits were analyzed based on simulation results.Finally, we focused on the reversal of the perpendicular magnetization driven by spin-Hall-assisted STT in a three-terminal MTJ. In this scheme, two write currents are applied to generate spin-Hall effect (SHE) and STT. Numerical simulation based on Landau-Lifshitz-Gilbert (LLG) equation demonstrates that the incubation delay of the STT can be eliminated by the strong SHE, resulting in ultrafast magnetization switching without the need to strengthen the STT. We applied this novel write approach to the design of the magnetic flip-flop and full-adder. Performance comparison between the spin-Hall-assisted and the conventional STT magnetic circuits were discussed based on simulation results and theoretical models.

Polarization entangled photon pairs on demand are considered to be an important building block of quantum communication technology. It has been demonstrated that semiconductor quantum dots (QDs), which exhibit a certain spatial symmetry, can be used as a triggered, on-chip source of polarization entangled photon pairs. Due to limitations of the growth, the as-grown QDs usually do not exhibit the required symmetry, making the availability of post-growth tuning techniques essential. In this work first the QD-morphology of hundreds of QDs is correlated with the optical emission of neutral excitons confined in GaAs/AlGaAs QDs. It is presented how elastic anisotropic stress can be used to partially restore the symmetry of self-assembled GaAs/AlGaAs and InGaAs/GaAs QDs, making them as candidate sources of entangled photon pairs. As a consequence of the tuning of the QD-anisotropy we observe a rotation of the polarization of the emitted light. The joint modification of polarization orientation and QD anisotropy can be described by an anticrossing of the so-called bright excitonic states. Furthermore, it is demonstrated that anisotropic stress can be used to tune the purity of the hole states of the QDs by modifying the degree of heavy and light hole mixing. This ability might be interesting for applications using the hole spin as a so-called quantum bit.

Thin-film organic field effect transistors (OFETs) have attracted growing interest in recent years due to their promising electrical, optical and mechanical properties. Especially, oligothiophenes and their derivates are candidates with good prospects for application as the organic semiconducting material in such devices. They possess an extended, polarisable aromatic π-electron system that promotes a high structural arrangement of the molecules. The charge transport in the organic film is realised in the direction perpendicular to the plane of the thiophene rings via a hopping transport mechanism. Thus, a good π-π-overlap and a consequent stacking of the thiophene molecules in the film perpendicular to the gate substrate is essential to achieve excellent electric properties such as high charge carrier mobilities and low resistive losses. The highly polarisable thiophene-based molecules are also very attractive materials that are potentially applicable as the field-sensitive organic semiconducting component of a ferroelectric OFET device. In such a device, the dielectric gate element of a conventional OFET setup is substituted by a ferroelectric substrate. The electric field that is induced by the polarisation of the ferroelectric material serves as gate field and controlls the charge injection and charge density inside the device. In this thesis, thiophene-based molecules are investigated in detail with respect to their application as field-sensitive organic semiconducting component in a ferroelectric OFET device employing quantum-chemical ab initio and DFT-based methods. We demonstrate that the phosphonic acids can bind the organic molecules to the dielectric or ferroelectric material and well-anchored, robust self-assembled monolayers are formed. Furthermore, special focus is put on the influence of the intermolecular interactions among the organic molecules on the technologically relevant structural and electronic properties. It is found that the CN···HC hydrogen bond link the molecules into extended ribbons, but the π-π-stacking-stacking interaction is the main driving force in the self-assembly of the molecules. We also establish in detail the influence of the electric field on the phosphonic acid anchoring molecule and some quarterthiophene derivates. For the latter, the strongest field-sensitivity is obtained for an external electric field aligned parallel to the extension of the thiophene framework. Hence, they are suitable to act as the field-sensitive organic components in devices that take advantage of a band-gap engineering. Moreover, the present results emphasise the importance of the adsorption morphology of the molecules in the film in a π-stacked fashion with their longitudinal axis oriented parallel to the (orthonormal) electric field induced by the ferroelectric substrate.

In dieser Arbeit werden ferroelektrische Phasenübergänge in verspannten (K,Na)NbO3-Schichten erstmals mit Hilfe temperaturabhängiger dreidimensionaler Röntgenbeugung untersucht. Der Fokus liegt auf stark anisotrop verspannten Dünnschichten, die bei Raumtemperatur ein geordnetes Fischgräten-Domänenmuster mit einer periodischen Anordnung von monoklinen a1a2/MC-Phasen aufweisen. Bei Erhöhung der Temperatur durchlaufen die (K,Na)NbO3-Dünnschichten einen ferroelektrischen Phasenübergang in die orthorhombische Hochtemperaturphase, die sich durch regelmäßige, alternierenden a1/a2-Streifendomänen mit ausschließlich lateraler Polarisation auszeichnet. In-plane Röntgenmessungen zeigen, dass die Filmeinheitszellen eine kleine Verzerrung in der Ebene erfahren, was zur Bildung von vier verschiedenen Einheitszellvarianten und damit vier verschiedenen (Super-)Domänenvarianten führt. Durch den Vergleich von Röntgenbeugungsmessungen verschiedener Bragg-Reflexe an Filmen mit unterschiedlicher Schichtdicke ist es möglich, die spezifischen Beugungsmerkmale zu unterscheiden und sie den einzelnen Phasen zuzuordnen. Mit Hilfe von in situ temperaturabhängiger Röntgenbeugung ist es daher möglich, die Details des Phasenübergangs vom Fischgräten in das Streifen-Domänenmuster aufzudecken. Es zeigt sich, dass dieser sich über einen großen Temperaturbereich erstreckt und in mehreren Schritten vollzieht. Die Beobachtung von Phasenkoexistenz innerhalb des Übergangs und einer thermischen Hysterese in der Phasenübergangstemperatur lassen auf einen Phasenübergang erster Art schließen. Zudem hängt die Phasenübergangstemperatur stark von der Kaliumkonzentration x in der KxNa1-xNbO3-Dünnschicht ab und kann durch eine Änderung von x=0,95 (stärker kompressiv verspannt) auf x=0,8 (stärker tensil verspannt) um etwa 60 K erhöht werden. Darüber hinaus ist dies die erste Studie, die experimentell beobachtete dreidimensionale Domänenanordnungen direkt mit Berechnungen aus Phasenfeldsimulationen vergleicht. / In this work, ferroelectric phase transitions in strained (K,Na)NbO3 films are studied for the first time using in situ temperature-dependent three-dimensional X-ray diffraction. The focus lies on strongly anisotropically strained thin films, which exhibit a well-ordered herringbone domain pattern with a periodic arrangement of monoclinic a1a2/MC phases at room temperature. Upon increasing temperatures, the (K,Na)NbO3 thin films undergo a ferroelectric phase transition to the orthorhombic high-temperature phase, which is characterized by a regular pattern of alternating a1/a2 stripe domains with pure lateral polarization. In-plane X-ray measurements show that the film unit cells undergo a small in-plane distortion, leading to the formation of four different unit cell variants and thus four different (super)domain variants. By comparing X-ray diffraction measurements of different Bragg reflections of films with different film thicknesses, it is possible to distinguish the specific diffraction features and assign them to the individual phases observed at the different temperatures. Using in situ temperature-dependent X-ray diffraction, it is therefore possible to reveal the details of the phase transition from the a1a2/MC herringbone to the a1/a2 stripe domain pattern. It is shown to extend over a wide temperature range and to occur in several steps. The observation of phase coexistence within the transition and a thermal hysteresis in the phase transition temperature suggests a first-order type phase transition. Moreover, the phase transition temperature strongly depends on the molar concentration of potassium x in the KxNa1-xNbO3 thin film and can be increased by about 60 K by changing x=0.95 (more compressively strained) to x=0.8 (more tensile strained). Furthermore, this is the first study to directly compare experimentally observed three-dimensional domain arrangements with calculations from phase field simulations.

So far, only CMOS compatible and scalable hafnia-zirconia (HZO) based ferroelectric (FE) n-FeFETs have been reported. To enable the full ferroelectric hierarchy [1] both p- and n-type devices should be available. Here we report a p-FeFET with a large memory window (MW) for the first time. Moreover, we propose different integration schemes comprising structures with and without internal gate resulting in metal-FE-insulator-Si (MFIS) and metal-FE-metal-insulator-Si (MFMIS) devices which could be used to tackle the problem of interface (IF) degradation and possibly decrease the power consumption of the devices.

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