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<p>With the emergence of 5G/mm-Wave communication, there is a growing need for novel front-end electromechanical devices in filtering and carrier generation applications. CMOS-MEMS resonators fabricated using state-of-the-art Integrated Circuit (IC) manufacturing processes provide a significant advantage for power, area and cost savings. In this work, a comprehensive physics-based compact model capable of capturing the non-linear behaviour and other non-idealities has been developed for MEMS resonators seamlessly integrated in CMOS. As the first large signal model for CMOS-embedded resonators, it enables holistic design of MEMS components with advanced CMOS circuits as well as system-level performance evaluation within the framework of modern IC design tools. Global Foundries 14nm FinFET (GF14LPP) Resonant Body Transistors (fRBT) operating at 11.8 GHz are demonstrated and benchmarked against this large-signal electromechanical model. </p> <p><br></p> <p>Additionally, there is a growing interest in CMOS-integrable ferroelectric materials such as Hafnium Dioxide (HfO2) and Aluminum Scandium Nitride (AlScN) for next-generation memory and computation, as well as electromechanical transduction in CMOS-MEMS devices. This work also explores the performance of 700 MHz Ferroelectric Capacitor-based resonators in the Texas Instruments HPE035 process under high-power operating conditions. Identification of previously unreported characteristics, together with the first nonlinear large signal model for integrated ferroelectric resonators, provides insights on the design of frequency references and acoustic filters using ferroelectric transducers. </p> <p><br></p> <p>Extending the range of unreleased CMOS-MEMS resonators to lower frequency using novel design, we also investigate embedded transducers in chip-scale devices for physical sensing. We have simulated and modeled the transducer coupling for low-frequency propagating modes and benchmarked their projected performance against state-of-the-art conventional MEMS sensors. A new approach to phononic crystal (PnC) Interdigitated Transducers (IDTs) is presented emulating the acoustic dispersion in conventional ICs. Unloaded quality factors up to 15,000 have been measured in $\sim$80 MHz resonators, demonstrating their capacity for resonant rotation sensing. We present a unique methodology to amplify and collimate acoustic waves using CMOS-design-rule-compliant Graded Index (GRIN) Phononic IDTs. Ultimately, the CMOS-MEMS techniques presented in this work for both RF applications and physical sensing can facilitate additional functionality in standard CMOS and emerging 3D heterogeneously integrated (3DHI) ICs with minor or no modifications to manufacturing and packaging. This enables new paradigms in next-generation communications, internet of things (IoT), and hardware security.</p>

Ferroelectric-reinforced metal matrix composites (FR-MMCs) offer the potential to improve damping characteristics of structural materials. Many structural materials are valued based on their stiffness and strength; however, stiff materials typically have limited inherent ability to dampen mechanical or acoustic vibrations. The addition of ferroelectric ceramic particles may also augment the strength of the matrix, creating a multifunctional composite. The damping behavior of two FR-MMC systems has been examined. One involved the incorporation of barium titanate (BaTiO3) particles into a Cu- 10w%Sn (bearing bronze) matrix and the other incorporating them into an electroformed Ni matrix. Here the damping properties of the resulting ferroelectric reinforced metal matrix composites (FR-MMCs) have been investigated versus frequency, temperature (above and below the Curie temperature of the reinforcement), and number of strain cycles. FR-MMCs currently represent a material system capable of exhibiting increased damping ability, as compared to the structural metal matrix alone. Dynamic mechanical analysis and neutron diffraction have shown that much of this added damping ability can be attributed to the ferroelectric/ferroelastic nature of the reinforcement. / Ph. D.

Ferroelectric (piezoelectric) and ferromagnetic materials have extensively permeated in modern industry. (Na1/2Bi1/2)TiO3-BaTiO3 (NBT-x%BT) single crystals and K1/2Na1/2NbO3 (KNN) textured ceramics are top environment-friendly candidates which have potential to replace the commercial lead zirconate titanate or PZT. High magnetostrictive strain (up to 400 ppm) of Fe-xat.%Ga makes this alloys promising alternatives to existing magnetostrictive materials, which commonly either contain costly rare-earth elements or have undesirable mechanical properties for device applications. These systems have common characteristics: compositional/thermal/ electrical dependent structural heterogeneity and chemical disorder on sub-micron or nano scale, resulting in diverse local structures and different physical properties. In this work, I have investigated domain and local structures of NBT-x%BT crystals, KNN ceramics and Fe-xat.%Ga alloys under various conditions, mainly by scanning probe and electron transmission techniques. In NBT-x%BT single crystals, polarized light, piezo-response force (PFM) and transmission electron (TEM) microscopies were used to study domain structures and oxygen octahedral tiltings. Hierarchical domain structures were found in NBT: a high-temperature tetragonal ferroelastic domain structure is elastically inherited into a lower temperature rhombohedral ferroelectric phase. Nanoscale domain engineering mechanism was found to still work in NBT-x%BT system and a modified phase diagram was proposed based on domain observations. An increased intensity of octahedral in-phase tilted reflections and a decrease in the anti-phase ones was observed, with increasing x as the morphotropic phase boundary (MPB) is approached. It was also found that Mn substituents favor the formation of long range ordered micro-sized ferroelectric domains and octahedral in-phase tilted regions near the MPB. Nano-size heterogeneous regions were observed within submicron domain structure, indicating that the nanoscale polarization dynamics are not confined by domain boundaries, and the high piezoelectricity of NBT-x%BT is due to a polarization dynamics with high sensitivity to electric field and a broadened relaxation time distribution. In KNN textured ceramics, an aging effect was found to exist in the orthorhombic single phase field, not only in the orthorhombic and tetragonal two-phase field as previously reported. No variation of phase structure was revealed between before and after aging states. However, pronounced changes in domain morphology were observed by both PFM and TEM: more uniform and finer domain structures were then found with aging. These changes were even more pronounced after poling the aged state. A large number of sub-micron lamellar domains within micron-domains were observed: suggesting a domain origin for improved piezoelectric properties. In Fe-xat.%Ga alloys, an underlying inhomogeneity from Ga atoms embedded into the α-Fe matrix was believed to be the origin of giant magneostrictive properties. I have systematically investigated the phase structure and nano-size heterogeneity of Fe-xat.%Ga alloys subjected to different thermal treatments using standard TEM and high resolution TEM for 10<x<30. Nano-precipitates were observed in all specimens studied: A2, D03 and B2 phases were found depending on x. Nano-precipitates of D03 were observed to be dominant for compositions near the magnetostriction peaks in the phase diagram. Quenching was found to increase the volume fraction of nanoprecipitates for x=19, near the first magnetostriction peak. With increasing x to 22.5, nanoprecipitates were observed to undergo a D03 – B2 transformation. A high density of D03 precipitates of nanoscale size was found to be the critical factor for the first maximum in the magnetostriction. / Ph. D.

Multiferroics have attracted lots of research interest due to their potential in numerous multifunctional applications. The multiferroic materials could simultaneously exhibit two or more ferroic order parameters, and the coupling effects between ferroelectricity and ferromagnetism are named as magnetoelectric (ME) effect. Recently, with the development of thin film growth techniques, the multiferroics magnetoelectric composite heterostructures exhibit a very promising future prospects. This dissertation focused on the design, fabrication and characterization of new multiferroics magnetoelectric composite heterostructures. First, based on the specific phase architectures in BFO-CFO self-assembled thin films grown on variously oriented STO substrates and the epitaxial film growth knowledge, I designed two kinds of new film heterostructures: (i) I utilized self-assembled BFO nanopillars in a BFO-CFO two phase layer on (111) STO as a seed layer on which to deposit a secondary top BiFeO3 layer. The growth mechanism and multiferroic properties of these new heterostructures were investigated. (ii) I demonstrated the formation of a new quasi-(0-3) heterostructure by alternately growing (2-2) and (1-3) layers within the film. I proposed a new concept to overcome limitations of both the (2-2) and (1-3) phase connectivities and identified an indirect ME effect by the switching the characteristics of the piezoresponse for the new heterostructure. Second, for the option for candidates thin film materials with a high piezoelectric coefficient, which is a critical factor for ME composite films, I utilized the simple compositional BaSn0.11Ti0.89O3 bulk ceramic material as a target to grow films with the large piezoelectric properties. The grown high qualify lead-free epitaxial thin films had a chemical constituent similar to the reported giant piezoelectric ceramics near the MPB and with the QP. Both coherent and incoherent regions were observed in the interface and a larger piezoelectric coefficient d33 was achieved in this film. Finally, with respect to their characteristics and potential, I redirected from two-dimensional thin film materials to one-dimensional nanowire materials. By utilizing vertically aligned templates, I fabricated a new type of coaxial two-phase composite nanowires. Multiferroic properties of these new one-dimensional materials have been investigated. All these multiferroics magnetoelectric composite herterostructures would provide lots of potential in applications. / PHD

Piezoelectric materials find applications in multitude of devices such as sensors, actuators and energy harvesters. However, most of these piezoelectric materials utilize lead-based systems which are becoming serious problem owing to the restrictions imposed by regulatory agencies across the globe. In the functional ceramics community, currently there is no problem more important than to find a replacement for lead-based piezoelectrics used for actuators. The electromechanical properties required for actuators (high piezoelectric constant, high coupling factor, low loss, and high transition temperatures) for known lead-free compositions are, however, far inferior to those of lead-based systems. There are three lines of research for addressing this fundamental problem "C (i) search for new systems through a combination of theory-based prediction followed by experimental effort (doping, solid solutions having a morphotropic (M) or polymorphic (P) phase boundary (PB), (iii) stabilization of metastable phases or finding the high temperature triclinic systems, and (iii) improving the properties of known compositions through microstructure optimization, domain engineering and multilayering. All these approaches are challenging and require innovation to make a significant impact on the current state-of-the-art. In this thesis, the later line of research was focused which is promising for near future applications, as it builds upon the known material systems with high depoling temperatures that have demonstrated the potential to be practical. In the first chapter, a novel method for the synthesis of lead-free (1-x)(Na0.5Bi0.5)TiO₃ "C xBaTiO3 piezoelectric ceramics was investigated. Initially, multiple compositions around morphotrpic phase boundary (MPB) were synthesized to identify the optimum composition 0.93Na0.5Bi0.5TiO3-0.07BaTiO3 (NBT-BT) for electromechanical effect. The new synthesis method starts with the synthesis of Na2Ti6O13 (NTO) whiskers which are then transformed into lead-free NBT-BT ceramics. Synthesis of NTO whiskers was performed using molten salt synthesis (MSS) method. Tape casting method was used to align the whiskers in base matrix powder and subjected to various processing temperatures to elucidate the microstructure and texture evolution. For this, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis were used as principal tools. The sintering process can be understood by dividing it into three stages, namely (i) transformation of monoclinic whiskers in to NBT-BT perovskite phase through topochemical reaction (<800°C), (ii) localized sintering confined on single whisker (800-1050°C), and (iii) liquid phase sintering as densification and grain growth occurs in the whole matrix (>1050°C). The concentric growth ledges observed on grain surfaces were found to be preferably confined on the corners of cubical grains indicating <111> growth direction. The Lotgering factor (f100) for the sintered matrix was found to decrease with increase in sintering temperature. The longitudinal piezoelectric constant (d33) of samples sintered for 20h at 1175°C, 1200°C and 1225°C was measured to be ~153 pC/N, ~216 pC/N and ~180 pC/N, respectively. Next, a novel method was developed for the synthesis of nanostructured lead-free ferroelectric NBT-BT whiskers with high aspect ratio using NTO as a host structure. High energy x-ray diffraction coupled with atomic pair distribution function (PDF) and Raman scattering analyses were used to confirm the average structure of lead-free NBT-BT whiskers as rhombohedral, i.e. a ferroelectricity enabling type. The HRTEM analysis revealed local monoclinic-type structural distortions indicating a modulated structure at the nanoscale in the MPB composition of lead-free NBT-BT whiskers. The structural rearrangement during the synthesis of lead-free NBT-BT whiskers was found to occur via translation of edge shared octahedra of NTO into a corner sharing coordination. The high temperature morphological changes depicting disintegration of isolated whiskers into individual grains due to higher grain boundary energy have been found to occur in a close analogy with Rayleigh-type instability. In lead-based ABO3 compounds, with B-site disorder, the origin of enhancement of piezoelectric properties near MPB has been associated with the presence of an intermediate monoclinic/orthorhombic state that bridges the adjacent ferroelectric rhombohedral and tetragonal phases. However, the origin of high piezoelectric response in lead-free ABO3 compounds with A-site disorder has not been conclusively established. In this thesis, a microscopic model derived from comparative analyses of HR-TEM and neutron diffraction was developed that explains the origin of high piezoelectric response in lead "C free MPB compositions of NBT-BT. Direct observation of nanotwins with monoclinic symmetry confirmed the presence of an intermediate bridging phase that facilitates a pathway for polarization reorientation. Monoclinic distortions of an average rhombohedral phase were attributed to localized displacements of atoms along the non-polar directions. These results provide new insight towards design of high performance lead "C free piezoelectric materials. Microstructure and domain structure play dominant role towards controlling the magnitude of piezoelectric coefficient and hysteretic losses in perovskites. Brick-wall like microstructure with large grain size and small domain size can provide significant enhancement in the magnitude of piezoelectric coefficient. A synthesis technique for lead-free piezoelectric NBT-BT system that can provide [001]pc/[012]Rh grain oriented ceramics with large grain size and an electrical poling technique that results in smaller domain size will have significant impact on the electromechanical response. In this research, a synthesis technique was developed and the processing variables that play deterministic role in achieving the large grain brick-wall like microstructure were explained. Interfaces in the microstructure were found to be coherent at the atomic scale facilitating the domain wall motion with applied electric field. The piezoelectric response was found to increase monotonously with the incease in the degree of texturing and optimized microstructure was found to provide 200% enhancement in the magnitude of piezoelectric coefficient as compared to its random form. In order to understand the mechanism of enhanced piezoelectric response in textured NBT-BT, in-situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly-oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nano regions and internal stresses induced by domain switching. In conjunction to focus on NBT-BT, new lead-free piezoelectric materials with enhanced piezoelectric response were synthesized. This study provides fundamental understanding of the enhanced piezoelectric instability in lead-free piezoelectric (1-x) BaTiO₃-xA(Cu1/3Nb2/3)O3₃ (A: Sr, Ba and Ca and x = 0.0-0.03) solid solutions. These compositions were found to exhibit large d33 of ~330 pC/N and electromechanical planar coupling constant (kp)~ 46% at room temperature. The piezoelectric instability in these compositions was found to increase with x despite monotonous decrease in the long range polar ordering. High energy X-ray diffraction coupled with PDFs indicated increase in local polarization. Raman scattering analysis revealed that substitutions on A and B-site both substantially perturbed the local octahedral dynamics and resulted in localized nano polar regions with lower symmetry. These localized polar distortions were found to persist much above the Curie temperature (Tc). Polarization "C electric field (P-E) hysteresis loop analysis indicated presence of the internal bias that was found to be correlated with the formation of polar defects. This defect structure was found to modulate the domain structure resulting in nano domains and broad domain walls with higher mobility as revealed through analysis from HR-TEM and piezoresponse force microscopy (PFM). The presence of nano domains and local structural distortions smears the Curie peak resulting in diffuse order-disorder type phase transitions. The electron paramagnetic resonance (EPR) investigations revealed that substitution of Cu²⁺ takes place on octahedral sites that are distorted due to Jahn-Teller effect. The A-sites were distorted by substitution of Sr and Ca on Ba-site possessing different ionic radii and electronegativity. The effect of these distortions on the variations in physical property was modeled and analyzed within the context of nanodomains and phase transitions. As an application, the solid solution with nominal composition of (1-x)BaTiO₃-xBa(Cu1/3Nb2/3)O₃ (BCN) (x = 0, 0.025) was synthesized by conventional mixed oxide route, followed by compositional modification with varying concentration of Sn, as given by the formulation: 0.975 BaTi1-ySnyO₃ "C 0.025 Ba(Cu1/3Nb2/3)O₃ (y = 0.05, 0.06, 0.075, 0.1). Room temperature XRD patterns showed decrease in tetragonality of BT after modifying with BCN (BT-BCN). Modifications with Sn lead to further decrement in tetragonality and the room temperature structure became cubic at 6.0 at% doping level. The decrement in tetragonality was accompanied by lowering of Tc.  BT-BCN doped with 6 and 7.5 at% Sn were found to exhibit diffuse phase transition accompanied by high dielectric constant "Ý 7000, low loss tangent "Ü 1% and grain size in the submicron regime ("Ü 1 "Ìm). These compositions were found to be promising for Y5V type multilayer ceramic capacitors (MLCCs). Lastly, the dielectric and ferroelectric responses of compositionally graded bilayer and trilayer composites consisting of BT and 0.975BaTiO₃-0.025Ba(Cu1/3Nb2/3)O₃ (BT-BCN) were investigated. Two types of graded bilayer samples were synthesized, one with same thickness of BT and BT-BCN while other with different layer thicknesses. The graded trilayer sample consisted of BT layer sandwiched between two BT-BCN layers of equal thickness. SEM and TEM images showed a sharp interface with needle-shape domains across the interface. The domain size on BT-side was found to be larger than that on BT-BCN-side. The temperature dependence of dielectric response for all composite systems was found to exhibit shifting of characteristic Curie peak compared to constituent material which was associated to coupling between layers. Moreover, the differences in grain size, tetragonality, domain mobility of each layer was found to perturb the electrical response of composite. The polarization mismatch between uncoupled BT and BT-BCN established internal electric field in composite specimen and defined new polarization states in each layer by perturbing free energy functional of the composite specimen. Dynamic hysteresis behaviors and power-law scaling relations of all specimens were determined from P"CE field hysteresis loop measurements as a function of frequency. All systems were found to exhibit similar dynamic scaling relationships. Hysteresis area, Pr and EC decreased with increasing frequency due to delayed response, but increased with increasing applied electric field due to enhancement of driving force. Trilayer system was found to exhibit strong internal-bias field and double hysteresis behavior. The coupling effect resulting due to polarization mismatch between layers had substantial influence on the dynamic hysteresis behavior and power-law scaling relations. / Ph. D.

In the last decades, ferroelectric properties have been observed in thin films based on hafnia and zirconia. These fluorite-structured thin films have attracted significant interest due to their excellent compatibility with complementary metal-oxide-semiconductor technology. Undoped zirconia has a lower crystallization temperature compared to hafnia-based or HfxZr1-xO2 thin films, making it more attractive for back-end-of-line processes. However, it is commonly reported that undoped zirconia thin films exhibit antiferroelectric properties. When ferroelectric properties are observed in undoped zirconia thin films, they are not as remarkable as those of hafnia-based or HfxZr1-xO2 thin films. In this work, in order to better understand the crucial factors that stabilize the ferroelectric properties in zirconia-based thin films, various process parameters were varied, and physical and electrical characterizations were carried out. The results indicate that the in-plane tensile strain is a crucial factor in stabilizing the ferroelectric orthorhombic phase of these films. The ferroelectric properties of zirconia films are lost when a non-polar monoclinic or tetragonal phase is stabilized due to an in-plane strain that is too small or too large, respectively. The best ferroelectric behavior is achieved when the polar orthorhombic phase can be stabilized with an in-plane tensile strain of 0.4-0.6%. After optimizing the interfaces between the ZrO2 and electrodes, the ferroelectric properties can be further improved in the ZrO2 thin films to be comparable to the HfO2-based ferroelectric thin films.:1 Motivation 2 Fundamentals 3 Experimental Setup 4 Effect of Process Parameters 5 Crucial Factors for Ferroelectric Zirconia 6 Conclusion

The discovery of ferroelectricity in the CMOS-compatible material HfO2 at nanometer scales has enabled the realization of low power, high speed, and dense nonvolatile memories. Even though this discovery can be exploited for memory applications, the reliability needs to be thoroughly examined and improved to meet the standard requirements. HfO2 has an intrinsic coercive field of ≈ 1 MV/cm, field-cycling with such a high field leads to defect generation and, subsequently, hard-breakdown of the material. The defect generation with field cycling is evident from the leakage current increase. Prior to the discovery of ferroelectricity, HfO2 was used for high-k applications, where it was experimentally proven that doping it with La suppresses the leakage current through the dielectric. Motivated by this experiment, this thesis was initiated through the additional doping of La into a mixed oxide of Hf0.5Zr0.5O2 to subsequently improve endurance. The experiment was successful but at the cost of non-polar t-phase stabilization, which induced a decrease in pristine Pr, a strengthening of the undesired wake-up effect, and a degradation of data retention. As shown in the literature, the Hf/Zr ratio can potentially change the phase composition of Hf1−xZrxO2. As a next step, the concentration of Hf/Zr in the ternary oxide of La: Hf1−xZrxO2 is altered to roll back the degradation while maintaining the benefits of La. The experimental results deviated a bit from the expectation, derived by the different origins of structural changes caused by the La and Hf/Zr ratio. After understanding the origin of La-induced structural changes, a different strategy was employed instead of doping La into Hf0.5Zr0.5O2. Here, films comprising a non-mixed La mono-layer and an in-series ferroelectric Hf0.5Zr0.5O2 are fabricated and measured, improving field-cycling endurance while successfully rolling back the cons of La doping. Hence, this thesis concludes with an overall improvement in material properties while avoiding any degradation.:Declaration of Authorship iii Abstract vii Acknowledgements ix 1 Introduction 1 2 Fundamentals 5 2.1 Models explaining ferroelectricity . . . . . . . . . . . . . . . . . . . . . . 6 2.1.1 Thermodynamic model . . . . . . . . . . . . . . . . . . . . . . . 6 2.1.2 Preisach model of hysteresis . . . . . . . . . . . . . . . . . . . . 8 2.1.3 Switching kinetic models . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Ferroelectric materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Prior to ferroelectric H fO2: Perovskite structure ferroelectric materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 Ferroelectricity in H fO2 : A scalable fluorite structure ferroelectric material . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 Ferroelectric Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.3.1 One transistor one capacitor FeRAM . . . . . . . . . . . . . . . . 22 2.3.2 Ferroelectric Tunnel Junction . . . . . . . . . . . . . . . . . . . . 23 2.3.3 Ferroelectric Field Effect Transistor . . . . . . . . . . . . . . . . . 24 2.4 Dielectric leakage current mechanisms . . . . . . . . . . . . . . . . . . . 26 2.4.1 Direct tunneling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.4.2 Schottky emission . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.4.3 Fowler-Nordheim tunneling . . . . . . . . . . . . . . . . . . . . 29 2.4.4 Poole-Frenkel conduction . . . . . . . . . . . . . . . . . . . . . . 29 2.4.5 Trap assisted tunneling (hopping) . . . . . . . . . . . . . . . . . 29 3 Experimental 31 3.1 Processes for device fabrication . . . . . . . . . . . . . . . . . . . . . . . 31 3.1.1 Atomic layer deposition . . . . . . . . . . . . . . . . . . . . . . . 31 3.1.2 Physical vapor deposition . . . . . . . . . . . . . . . . . . . . . . 32 3.1.3 Rapid thermal annealing . . . . . . . . . . . . . . . . . . . . . . . 34 3.1.4 Chemical patterning of electrodes . . . . . . . . . . . . . . . . . 34 3.2 Test structure fabrication process . . . . . . . . . . . . . . . . . . . . . . 34 3.3 Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.3.1 Structural characterization . . . . . . . . . . . . . . . . . . . . . 37 3.3.2 Electrical characterization . . . . . . . . . . . . . . . . . . . . . . 37 4 Results and Analysis 43 4.1 Doping Hf0.5Zr0.5O2 with La2O3 . . . . . . . . . . . . . . . . . . . . . . . 43 4.1.1 Structural characterization . . . . . . . . . . . . . . . . . . . . . 45 4.1.2 Electrical characterization . . . . . . . . . . . . . . . . . . . . . . 46 4.1.3 Summary and conclusion . . . . . . . . . . . . . . . . . . . . . . 55 4.2 Doping of Hf1−xZrxO2 with 2.3 mol% La2O3 . . . . . . . . . . . . . . . 57 4.2.1 Structural characterization . . . . . . . . . . . . . . . . . . . . . 57 4.2.2 Electrical characterization . . . . . . . . . . . . . . . . . . . . . . 59 4.2.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 4.3 The strong wake-up effect in La-doped films . . . . . . . . . . . . . . . 61 4.3.1 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.3.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 4.3.3 Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . 68 4.4 Metal-ferroelectric interface engineering through La2O3 and Al2O3 . . 68 4.4.1 Structural characterization . . . . . . . . . . . . . . . . . . . . . 70 4.4.2 Electrical characterization . . . . . . . . . . . . . . . . . . . . . . 71 4.4.3 Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . 79 5 Summary and outlook 85 A The strong wake-up effect in La doped films 89 A.1 Switching current peaks assignment . . . . . . . . . . . . . . . . . . . . 89 A.2 Derivation of depolarization field equation . . . . . . . . . . . . . . . . 90 A.3 Impact of polarization on leakage current measurements . . . . . . . . 90 Bibliography

Nonlinear optics and ferroelectrics have been recognized for several decades as promising fields with important applications in the area of opto-electronics, photonics, memory devices, etc. High performance electro-optical switching elements for telecommunications and optical information processing are based on the material properties. Hence, there is always a continuous search for new and better materials. In this thesis we have investigated the growth and physical properties of four crystals viz. two NLO and two ferroelectric crystals. This thesis consists of eight chapters. The first chapter gives an overview of historical perspectives of nonlinear optical phenomenon, ferroelectricity and materials developed therein. The second chapter gives a brief description of the underlying theories of crystal growth, nonlinear optics and ferroelectricity. A major portion of this chapter consists of gist of the earlier work carried out on compounds of our interest viz. urea L-malic acid, sodium p-nitrophenolate dihydrate, glycine phosphite and lithium niobate. Synthesis, growth, crystal structure details and some physical properties of these materials are briefed. The third chapter describes the experimental techniques needed to grow as well as characterize these crystals. The experiments are performed on single crystals grown in the laboratory using the solution growth setup and Czochralski crystal puller. These growth units are described in detail. Preliminary characterization techniques like powder Xray diffraction, optical transmission, scanning electron microscopy, Vickers and Knoop hardness are described briefly. Various experimental methods viz. dielectric, polarization reversal, photoacoustic spectroscopy and laser induced damage for characterizing the grown crystals are explained. Urea L-malic acid (ULMA) is a new NLO organic material which is reported to exhibit second harmonic efficiency three times that of the widely used inorganic crystal, KDP. Hence, this material is selected for detailed investigation and the results obtained are discussed in chapter 4. This chapter contains details of single crystal growth and characterization of ULMA. The crystals are grown by slow cooling technique. The complete morphology of the crystal is evaluated using optical goniometry. The grown crystals are characterized for their optical and thermal properties. The defect content in the grown crystal is evaluated by chemical etching. As the surface damage of the crystal by high power lasers limits its performance in NLO applications, a detailed laser induced damage studies are performed on ULMA. Both single shot and multiple shot damage threshold values for 1064 nm and 532 nm laser radiation are determined and correlated with the mechanical hardness. In addition, the thermal diffusivity and thermal conductivity of ULMA along various crystallographic orientations are evaluated using laser induced photoacoustic spectroscopy and the results are interpreted in terms of crystal bonding environment. Another NLO crystal taken up for study is sodium p-nitrophenolate dihydrate (NPNa 2H2O), a semiorganic material. This crystal is a very efficient NLO material and has the advantages of both organics and inorganics. Earlier investigations on growth of NPNa.2H2O in various solvents have shown methanol as the most suitable solvent for growth. Growth from aqueous solution was discarded as it did not yield crystals which are stable. In the present investigation, stable, NLO active NPNa.2H2O crystals are obtained using aqueous solution itself by varying the crystallization conditions and exploring the suitable temperature range. The details of growth and characterization form the subject of fifth chapter. The grown crystals are characterized using optical transmission, XRD and thermo gravimetric analysis. Later, laser induced damage threshold is evaluated for both 1064 nm and 532 nm laser radiation and compared wit the methanol grown ones. A possible mechanism of damage is given. The sixth and seventh chapters deal with growth and characterization of ferroelectric materials namely glycine phosphite and lithium niobate respectively. Glycine phosphite is a low temperature ferroelectric crystal which is well studied in terms of its dielectric and ferroelectric properties. But very few radiation damage studies are reported. The effect of ionizing radiation on ferroelectrics is of considerable interest as it significantly modifies the physical properties of these materials. In the present investigation, effects of X-ray irradiation (_ = 1.5418 °A) on the lattice parameters, dielectric constant, loss tangent, polarization switching characteristics and domain dynamics of glycine phosphite are investigated. X-ray irradiation is performed in the non-polar phase of the sample. The effect as a function of duration of exposure is studied. X-ray irradiation in GPI has resulted in drastic reduction in _ values and shift in transition temperature towards lower temperatures. X-ray irradiation on polarization switching properties of the crystal are also investigated. The activation energy and threshold field of switching increase with the irradiation time. The behaviour of domain wall mobility is quite different from that exhibited by other well known ferroelectrics. These results are discussed in chapter 6 and a possible explanation for the unusual behaviour of domain wall mobility is given. The defect generated is identified as PO32− radical by electron paramagnetic measurement. Lithium niobate (LiNbO3) is an extensively studied material in terms of its NLO and ferroelectric properties. This material has high piezoelectric coupling coefficients along certain directions which makes it suitable for wide band surface acoustic wave applications. Hence there is a demand for good quality, single domain YZ-LiNbO3 substrates. Chapter 7 describes the growth of Z-pulled congruent LiNbO3 using Czochralski technique. Large single crystals of diameter 30 mm and length 80 mm are grown from congruent composition employing Czochralski technique. The grown crystals are multidomain and hence electric field poling is performed to get single domain crystals. Their subsequent characterization for SAW devices upto 200 MHz was performed and compared with the imported substrate. The general conclusions are given in chapter 8 along with possible future work that could be performed on these crystals.