<p>Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, and electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies.</p><p>Ferroelectric materials usually have high dielectric constants, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used in fabrication capacitors for electronic industry because of their high dielectric constants, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure, and electrically tunable microwave integrated circuits using ferroelectric thin films can be developed. Therefore, it is very important to characterize the dielectric constant and tunability of ferroelectric thin films.</p><p>This thesis shows experimental results for growth, crystalline properties and microwave characterization of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering of a stoichiometric, high density, ceramic NKN, ATN, BST target onto single crystal LaAlO3(LAO), Al2O3 (sapphire), and Nd:YAlO3, and amorphous glass substrates. By x-ray diffractometry, NKN, ATN, BST films on LAO substrates were found to grow epitaxially, whereas films on r-cut sapphire substrates were found to be preferentially (00l) oriented.</p><p>Coplanar waveguide interdigital capacitor (CPWIDC) structures were fabricated by standard photolithography processing and metal lift-off technique. Microwave properties of the NKN/Sapphire and ATN/Sapphire with CPW structures were characterized using on-wafer microwave measurement technique. Measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field through the connection between network analyzer and power supply was applied to measure voltage tunability. Measured S-parameter were used for the calculation of capacitance, loss tanδ, tunability and K-factor.</p><p>The NKN films interdigital capacitors with 2 μm finger gap on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor = tunability/tanδ from 152% @ 10GHz to 46% @ 40GHz.</p><p>The microwave performance of ATN film CPWIDC with 2 μm finger gap on sapphire substrate in the microwave range from 1 to 40 GHz showed that frequency dispersion is about 4.3%, voltage tunability was 4.7% @ 20GHz and 200 kV/cm, loss tangent ∼ 0.068 @ 20GHz, K-factor = tunability/tanδ is ranged from 124% @ 10GHz to 35% @ 40GHz.</p><p>The BST films CPWIDC with 2μmfinger gap on Al2O3 substrate showed frequency dispersion of capacitance in the microwave range from 1 to 40 GHz about 17%, voltage tunability = 1 - C(40V)/C(0) ∼ 22.2%, loss tangent ∼ 0.137 @ 20GHz, and K-factor = tunability/tanδ from 281% @ 10GHz to 95% @ 40GHz.</p>

Les couches minces dérivées du matériau ferroélectrique BaTiO3 présentent un grand intérêt en vue de l'élaboration de composants intégrés pour la microélectronique et les télécommunications. Ainsi, des films de Ba0.6Sr0.4TiO3 (BST) possèdent une forte permittivité dont la valeur peut être modulée sous champ électrique, ce qui permet d'envisager leur utilisation dans des condensateurs aux propriétés ajustables. Cependant, le principal frein à leur intégration est l'importance de leurs pertes diélectriques. Des couches de BST déposées par pulvérisation magnétron radiofréquence ont été caractérisées d'un point de vue structural, chimique et diélectrique afin d'établir une référence. De nouvelles compositions exemptes de plomb, comme le BTZ (BaTi1-xZrxO3) et le BST substitué avec de l'étain, ont été synthétisées en vue d'abaisser les pertes. Des mesures diélectriques en température ont mis en évidence le caractère relaxeur des couches minces de BTZ riches en zirconium, et la copulvérisation a permis d'étudier l'ensemble de la solution solide BaTiO3-BaZrO3. Enfin, un nouveau type d'hétérostructures alliant le BST à une barrière diélectrique de SiO2 a permis d'atteindre des pertes très inférieures à 0.5% tout en conservant une permittivité et une accordabilité satisfaisantes.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 87-88). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 87-88). Also available on the Internet.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 208-215).

Ferroelectric materials have received lots of attention thanks to their intriguing properties such as the piezoelectric and pyroelectric effects, as well as the large dielectric constants and the spontaneous polarization which can potentially be used for information storage. In particular, perovskite crystal has a very simple unit cell structure yet a very rich phase transition diagram, which makes it one of the most intensively studied ferroelectric materials. In this dissertation, we use effective Hamiltonian, a first-principles-based computational technique to study the finite-temperature properties of ferroelectric perovskites. We studied temperature-graded (BaxSr1-x )TiO3 (BST) bulk alloys as well as the dynamics of nanodomain walls (nanowalls) in Pb(ZrxTi1-x )O3 (PZT) ultra-thin films under the driving force of an AC field. Our computations suggest that, for the temperature-graded BST, the polarization responds to the temperature gradient (TG), with the "up" and "down" offset observed in polarization components along the direction of TG, in agreement with the findings from experiments. For the nanowalls in PZT, the dynamics can be described by the damped-harmonic-oscillator model, and we observed a size-driven transition from resonance to relaxational dynamics at a critical thickness of 7.2 nm. The transition originates from the change in the effective mass of a nanowall as a film thickness increases. Some of the findings may find potential applications in various devices, such as thermal sensors, energy converters, or novel memory units.

This dissertation shows a detailed investigation on reconfigurable low profile antennas using tunable high impedance surfaces (HIS). The specific class of HIS used in this dissertation is called a frequency selective surface (FSS). This type of periodic structure is fabricated to create artificial magnetic conductors (AMCs) that exhibit properties similar to perfect magnetic conductors (PMCs). The antennas are intended for radiometric sensing applications in the biomedical field. For the particular sensing application of interest in this dissertation, the performance of the antenna sub-system is the most critical aspect of the radiometer design where characteristics such as small size, light weight, conformability, simple integration, adjustment in response to adverse environmental loading, and the ability to block external radio frequency interference to maximize the detection sensitivity are desirable. The antenna designs in this dissertation are based on broadband dipole antennas over a tunable FSS to extend the usable frequency range. The main features of these antennas are the use of an FSS that does not include via connections to ground, their low profile and potentially conformal nature, high front-to-back radiation pattern ratio, and the ability to dynamically adjust the center frequency. The reduction of interlayer wiring on the tunable FSS minimizes the fabrication complexity and facilitates the use of flexible substrates. This dissertation aims to advance the state of the art in low profile tunable planar antennas. It shows a qualitative comparison between antennas backed with different unit cell geometries. It demonstrates the feasibility to use either semiconductor or ferroelectric thin film varactor-based tunable FSS to allow adjustment in the antenna frequency in response to environment loading in the near-field. Additionally, it illustrates how the coupling between antenna and HIS, and the impact of the varactor losses affect the antenna performance and it shows solutions to compensate these adverse effects. Novel hybrid manufacturing approaches to achieve flexibility on electrically thick antennas that could be transitioned to thin-film microelectronics are also presented. The semiconductor and ferroelectric varactor-based tunable low profile antennas demonstrated tunability from 2.2 GHz to 2.65 GHz with instantaneous bandwidths greater than 50 MHz within the tuning range. The antennas had maximum thicknesses of λ/45 at the central frequency and front to back-lobe radiation ratios of approximately 15dB. They also showed impedance match improvement in the presence of a Human Core Model (HCM) phantom at close proximity distances of the order of 10-20 mm. In addition, the use of thin film ferroelectric Barium Strontium Titanate (BST) varactors in the FSS layer enabled an antenna that had smaller size, lower cost and less weight compared to the commercially available options. The challenging problems of fabricating robust flexible antennas are also addressed and novel solutions are proposed. Two different types of flexible antennas were designed and built. A series of flexible microstrip antennas with slotted grounds which demonstrated to be robust and have 42% less mass than typically used technologies (e.g., microstrip antennas fabricated on Rogers® RT6010, RT/duroid® 5880, etc.); and flexible ferroelectric based tunable low profile antennas that showed tunability from 2.42 GHz to 2.66 GHz using overlapping metallic plates instead of a continuous ground plane. The bending test results demonstrated that, by placing cuts on the ground plane or using overlapping metallic layers that resemble fish scales, it was possible to create highly conductive surfaces that were extremely flexible even when attached to other solid materials. These new approaches were used to overcome limitations commonly encountered in the design of antennas that are intended for use on non-flat surfaces. The material presented in this dissertation represents the first investigation of reconfigurable low profile antennas using tunable high impedance surfaces where the desired electromagnetic performance as well as additional relevant features such as robustness, low weight, low cost and low complexity were demonstrated.

The research presented in this dissertation was performed in the Atomic, Molecular and Optical (AMO) physics laboratory at the University of Manitoba. Atomic beams of the two-valence-electron heavy atom systems, barium and ytterbium, were investigated with low energy electron scattering and optical emission studies. Both the ground states and laser excited states were investigated as a function of incident electron beam energy from 10 eV to 50 eV. Measurements of relative cross sections and polarization for 583 nm and 554 nm line emission from the (6s7p)1P1 and (6s6p)1P1 states of barium excited by electron impact from both the ground states and the optically pumped metastable (6s5d)1D2 are reported. Data are normalized to absolute cross sections for the ground state (6s2)1S0→(6s6p)1P1 state transition due to electron scattering, with corrections for branching ratios and cascading from higher states to deduce the total level excitation cross sections. Results are also presented for the first studies of the 399 nm line emission from laser-excited ytterbium, yielding an upper limit on the apparent cross section for the (6s6p)3P1→(6s6p)1P1 transition. Results are compared with the latest theoretical models and previous data, where available. / October 2015

High performance miniaturized passives are of great importance for advanced nanoelectronic packages for several applications including efficient power delivery. Low cost thin film capacitors fabricated directly on package (and/or on-chip) are an attractive approach towards realizing such devices. This thesis aims to explore fundamental frequency dependent dielectric and insulating properties of thin film high-k dielectric constant in the perovskite and perovskite-related complex oxides. Throughout this thesis, we have successfully observed the role of structure, strain and oxygen stoichiometry on the dielectric properties of thin film complex oxides, allowing a greater understanding of processing conditions and polarization mechanisms. In the first section of the thesis, we explore novel processing methods in the conventional ferroelectric, barium strontium titanate, \(Ba_{1-x}Sr_xTiO_3 (BST)\), using ultraviolet enhanced oxidation techniques in order to achieve improvements in the dielectric properties. Using this method, we also explore the growth of BST on inexpensive non-noble metals such as Ni which presents technical challenges due to the ability to oxidize at high temperatures. We observe a significant lowering of the dielectric loss while also lowering the process temperature which allows us to maintain an intimate interface between the dielectric layer and the metal electrode. The second section of this thesis explores the novel dielectric material, Lanthanum Strontium Nickelate, \(La_{2-x}Sr_xNiO_4 (LSNO)\), which exhibits a colossal dielectric response. For the first time, we report on the colossal dielectric properties of polycrystalline and epitaxial thin film LSNO. We observe a significant polarization dependence on the microstructure due to the grain/grain boundary interaction with charged carriers. We next grew epitaxial films on various insulating oxide substrates in order to decouple the grain boundary interaction. Here we observed substrate dependent dielectric properties associated with induced strain. We also observe, due to the p-type carriers in LSNO, pn junction formation when grown epitaxially on the conducting oxide degenerate n-type Nb-doped \(SrTiO_3\). Finally we explore the growth mechanism of epitaxial LSNO as a function of high oxygen content. Due to the ability for LSNO to take in interstitial oxygen, a reoriented growth is observed at a critical thickness, thereby allowing us to vary anisotropy as a function of deposition conditions. / Engineering and Applied Sciences

The stoichiometry of the Nd_1+xBa_2-xCu₃O_7-δ solid solution has been investigated using XRD and EPMA. At 980°C in air, an essentially continuous solid solution forms with limiting compositions x_min = 0.03(1) and x_max = 0.92(2). The solid solution limits are independent of temperature over the range 300 to 1050°C, i.e. stoichiometric Nd123 does not form. Preliminary studies show that annealing in an Ar atmosphere does not affect x_min. Three structurally distinct polymorphs of Nd123ss exist - tetragonal Nd123ss, orthorhombic Nd123ss and orthorhombic Nd123ss. The stability range of each in air has been determined. Quenched samples with 0.03 ≤ x ≤ 0.6 have the tetragonal Nd123ss structure. On oxygenation, samples with 0.03 ≤ x <˜0.2 are orthorhombic. The orthorhombic-tetragonal phase transition is second order, both with increasing temperature and increasing x. Samples with 0.7-0.9 have the orthorhombic Nd213ss structure at all oxygen contents. Tetragonal Nd123ss is isostructural with tetragonal Y123 and orthorhombic Nd123ss is isostructural with orthorhombic Y123. Orthorhombic Nd213ss has the ideal stoichiometry Nd₂BaCu₃O_7-δ and is based on a 2a x b x 2c superstructure of the Nd123ss structure. The supercell is due to ordering of the Nd and Ba atoms, which leads to ordering of the oxygen atoms. Melting temperatures decrease with x. Two distinct regions of melting behaviour are observed; the first for 0.03 ≤ x ≤ 0.6 with a thermal minimum at x˜0.4, and the second for 0.7 ≤ x ≤ 0.9. Oxygen contents increase with x. Samples with larger x values have a smaller range of oxygen contents. High pressure oxygen annealing results in a constant Cu valence state of ˜2.35 for all values of x. Average copper valence states <2 are only obtained readily for x ≤ 0.3. T_c decreases with x and samples become non-superconducting at x˜0.5. For samples annealed in 1 bar O₂, 'double plateau' behaviour is observed.