Thin-film transistors (TFTs) capable of low-voltage and high-frequency operation will be required to reduce the power consumption of next generation electronic devices driven by microelectronic components such as inverters, ring oscillators, and backplane circuits for mobile displays. To produce high performance TFTs, transparent oxide-semiconductors are becoming an attractive alternative to hydrogenated amorphous silicon (a-Si:H)- and organic-based materials because of their high electron mobility vlaues and low processing temperatures, making them compatible with flexible substrates and opening the potential for low production costs. Practical electronic devices are expected to use p- and n-channel TFT-based complementary inverters to operate with low power consumption, high gain values, and high and balanced noise margins. The p- and n-channel TFTs should yield comparable output characteristics despite differences in the materials used to achieve such performance. However, most oxide semiconductors are n-type, and the only high performance, oxide-based TFTs demonstrated so far are all n-channel, which prevents the realization of complementary metal-oxide-semiconductor (CMOS) technologies. On the other hand, ambipolar TFTs are very attractive microelectronic devices because, unlike unipolar transistors, they operate independently of the polarity of the gate voltage. This intrinsic property of ambipolar TFTs has the potential to lead to new paradigms in the design of analog and digital circuits. To date, ambipolar TFTs and their circuits, such as inverters, have shown very limited performance when compared with that obtained in unipolar TFTs. For instance, the electron and hole mobilities typically found in ambipolar TFTs (ATFTs) are, typically, at least an order of magnitude smaller than those found in unipolar TFTs. Furthermore, for a variety of circuits, ATFTs should provide balanced currents during p- and n-channel operations. Regardless of the selection of materials, achieving these basic transistor properties is a very challenging task with the use of current device geometries. This dissertation presents research work performed on oxide TFTs, oxide TFT-based electronic circuits, organic-inorganic hybrid complementary inverters, organic-inorganic hybrid ambipolar TFTs, and ambipolar TFT-based complementary-like inverters in an attempt to overcome some of the current issues. The research performed first was to develop low-voltage and high-performance oxide TFTs, with an emphasis on n-channel oxide TFTs, using high-k and/or thin dielectrics as gate insulators. A high mobility electron transporting semiconductor, amorphous indium gallium zinc oxide (a-IGZO), was used as the n-channel active material. Such oxide TFTs were employed to demonstrate active matrix organic light emitting diode (AMOLED) display backplane circuits operating at low voltage. Then, high-performance hybrid complementary inverters were developed using unipolar TFTs employing organic and inorganic semiconductors as p- and n-channel layers, respectively. An inorganic a-IGZO and pentacene, a widely used organic semiconductor, were used as the n- and p-channel semiconductors, respectively. By the integration of the p-channel organic and n-channel inorganic TFTs, high-gain complementary inverters with high and balanced noise margins were developed. A new approach to find the switching threshold voltage and the optimum value of the supply voltage to operate a complementary inverter was also proposed. Furthermore, we proposed a co-planar channel geometry for the realization of high-performance ambipolar TFTs. Using non-overlapping horizontal channels of pentacene and a-IGZO, we demonstrate hybrid organic-inorganic ambipolar TFTs with channels that show electrical properties comparable to those found in unipolar TFTs with the same channel aspect ratios. A key characteristic of this co-planar channel ambipolar TFT geometry is that the onset of ambipolar operation is mediated by a new operating regime where one of the channels can reach saturation while the other channel remains off. This allows these ambipolar TFTs to reach high on-off current ratios approaching 104. With the new design flexibility we demonstrated organic-inorganic hybrid ambipolar TFT-based complementary-like inverters, on rigid and flexible substrates, that show a significant improvement over the performance found in previously reported complementary-like inverters. From a materials perspective, this work shows that future breakthroughs in the performance of unipolar n-channel and p-channel semiconductors could be directly transposed into ambipolar transistors and circuits. Hence, we expect that this geometry will provide new strategies for the realization of high-performance ambipolar TFTs and novel ambipolar microelectronic circuits.

The goal of the research in this dissertation is to develop techniques for 1) system-on-package integration of passive circuits using ultra-thin advanced polymers called RXP (Rogers experimental polymer), 2) extraction of frequency-dependent material properties up to millimeter-wave frequency, 3) development and synthesis of high-rejection filter topologies, 4) design and characterization of high performance miniaturized embedded passive circuits for microwave and millimeter-wave applications, and 5) development of via and through-silicon via (TSV) enhanced filter design method for integration in high-loss substrate. The RXP material is developed to reduce the layer-count for multi-layer configuration and adoption of advanced fabrication technologies. Frequency-dependent material properties of RXP, ceramic, and other materials have been extracted up to millimeter-wave frequency using parallel-plate resonator method. An automated extraction algorithm has been proposed to handle a large number of frequency samples efficiently. The accuracy of the extraction result has been improved by including the surface roughness effect for conductor operating at high frequency. Using extracted RXP material properties, 2.4/5 GHz WLAN bandpass filters have been designed and characterized. High-rejection bandpass filter topologies for narrow 2.4 GHz and wide 5 GHz have been proposed. The proposed topologies have been synthesized to provide design equations as well as graphical design methodologies using Z-parameters. A new capacitor design called 3D stitched capacitor has been proposed to achieve more symmetric layout by providing balanced shunt parasitics. The proposed topologies and design methodologies have been verified through the measurement of high-rejection RXP bandpass filters. Good correlation between the simulation and measurement was observed demonstrating an effective design methodology and embedding bandpass filters with good performance. Dual-band bandpass filters for WLAN applications have been implemented and measured. Instead of connecting two bandpass filter circuits, a new single bandpass filter topology has been developed with a compact size as well as high isolation between passbands. High-rejection duplexer has been designed in RXP substrate for chip-last embedded IC technology, and a novel matching circuit has been applied for the miniaturization as well. The 60 GHz V-band has special interest for wireless applications because of its high attenuation characteristics because of atmospheric oxygen. Millimeter-wave passive circuits such as bandpass filter, dual-band filter, and duplexer have been designed, and self-resonant frequency of passive components has been carefully avoided using the proposed method. For low-cost system integration, silicon interposer with through-silicon-via (TSV) technology has been studied. The filter design method for high-loss substrate has been proposed. The coupling characteristic of TSV has been investigated for obtaining good insertion loss in lossy substrates such as silicon, and TSV characteristics has been used to design bandpass and highpass filters. To demonstration of concept, bandpass filters with good insertion loss have been realized on high-loss FR4 substrate.

The continuous trend towards mega-functional, high-performance and ultra-miniaturized system has been driving the need for advances in novel materials with superior properties leading to thin components, high-density interconnect substrates and interconnections. Power supply and management is becoming a critical bottleneck for the advances in such mega-functional systems because power components do not scale down with the rest of the system resulting in bulky and stand-alone power modules. Amongst the power components, thin film capacitors are considered the most challenging to integrate because of several manufacturability concerns. The challenges are related to process compatibility of high permittivity dielectrics with substrates and high surface area electrodes, yield, leakage and losses. This thesis focuses on novel thin film capacitor technologies that address some of these critical challenges. / Thesis advisor has approved the addition of errata to this item. The abstract text in the metadata record has been modified to match the document text.

Recognising that the characterisation of actual interfaces in magnetic multilayer systems will provide valuable insight for the integration of spintronics in practical devices, a study of interface effects in various structures is presented. Magnetometry measurements are performed for a range of Fe thicknesses (0.4 - 23 nm) grown by molecular beam epitaxy on GaAs and InAs substrates in order to determine the factors governing the evolution of the magnetic moment of epitaxial Fe grown on a zinc-blende semiconductor. A greater reduction of the Fe magnetic moment is observed for films grown on InAs as compared to GaAs, as the Fe films reach a bulk-like moment (within 10% deviation) at a thickness of ~5.2 nm and ~2.2 nm, respectively. From this direct comparative study it is concluded that interface and interdiffusion effects are the dominant mechanisms influencing the value of the magnetic moment for ultra-thin Fe films on GaAs and InAs. Spin injection at this interface is performed, by detecting optical polarisation in the oblique Hanle geometry from a Fe/AlGaAs/GaAs spin-light emitting diode structure. The electrical and magnetic properties of the system are presented, and a ~1% injection polarisation at room temperature, rising to ~4% at 77 K is reported. A study of the deposition and growth of MgO thin (3 - 39 nm) films in conjunction with magnetic layers is also performed. Crystallinity of MgO grown on GaAs is obtained, and epitaxial growth of Fe and Co on MgO is demonstrated. Polarised neutron reflectivity results again indicate a slight decrease in Fe and Co magnetic moments due to interfacial oxide layers. MgO is also incorporated in a pseudo-spin-valve structure which demonstrates epitaxy-induced magneto-crystalline anisotropy. It is concluded that the interface quality is a critical parameter for spintronic devices. Atomic-scale defects and intermixing in real samples mean that current theoretical estimates of ~100% injection efficiency in perfect systems remain unattainable. However by increasing atomic-level structural control of interfaces, a substantial increase in efficiency might be achieved, similarly to the recent breakthrough in tunnelling magneto-resistance ratios which have reached 1000%.

The paper treats the question of feasibility of measuring intrinsic thin film stresses due to nanoindentation. A variety of different methods is proposed and analysed with respect to their applicability. As this accuracy-estimation results in boundary conditions for the measurements which can not be fulfilled yet, the whole topic is considered from a purely academic point of few. With the help of a special software package [25] the following methods are considered: 1. Taking the moment of beginning plastic flow within the substrate as indictor, 2. Taking the moment of beginning plastic flow within the film as indictor, 3. Applying mixed loads (normal and lateral forces), 4. Applying the concept of the effectively shaped indenter. While the methods 2 to 4 appear to be in principle feasible, method 1 can completely be ruled out as being of no practical use. The mentioned software package (FilmDoctor prototype) is part of the supplemental material of this study.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 101-108). Available also in a digital version from Dissertation Abstracts.

Indentation is used as a technique for mechanical characterization of materials for a long time. In the last few decades, new techniques of mechanical characterization at micro and nano level using indentation have been developed. Mechanical character-ization of thin films has become an important area of research because of their crucial role in modern technological applications. Theoretical and computational models of indentation are less time consuming,cost effective, and flexible. Many researchers have investigated mechanical properties of thin films using theoretical and computational models. In this study, an indentation model for a thin layer-substrate geometry with the possibility of nonhomogeneous or homogeneous interface of finite thickness between layer and substrate has been developed. The layer and substrate can be nonhomogeneous or homogeneous. Three types of indenters are modeled: 1) Uniform pressure indenter 2) Flat indenter 3) Smooth indenter. Contact depth, maximum interfacial normal stress and maximum interfacial shear stress play an important role in design and mechanical characterization of thin films using indentation and the effect of modeling the interface as homogeneous and nonhomogeneous on these parameters is studied. A sensitivity analysis is also conducted to find the effect of indentation area, substrate to layer Young's modulus ratio, layer to interface thickness ratio on contact depth and critical interfacial stresses.

The aim of this thesis is to provide an in-depth investigation of zinc tin oxide, Zn1-xSnxOy or ZTO, grown by atomic layer deposition (ALD) as a buffer layer in Cu(In,Ga)Se2 (CIGS) solar cells. The thesis analyzes how changes in the ALD process influence the material properties of ZTO, and how these in turn affect the performance of CIGS solar cells. It is shown that ZTO grows uniformly and conformably on CIGS and that the interface between ZTO and CIGS is sharp with little or no interdiffusion between the layers. The band gap and conduction band energy level of ZTO are dependent both on the [Sn]/([Zn]+[Sn]) composition and on the deposition temperature. The influence by changes in composition is non-trivial, and the highest band gap and conduction band energy level are obtained at a [Sn]/([Zn]+[Sn]) composition of 0.2 at 120  °C. An increase in optical band gap is observed at decreasing deposition temperatures and is associated with quantum confinement effects caused by a decrease in crystallite size. The ability to change the conduction band energy level of ZTO enables the formation of suitable conduction band offsets between ZTO and CIGS with varying Ga-content. It is found that 15 nm thin ZTO buffer layers are sufficient to fabricate CIGS solar cells with conversion efficiencies up to 18.2 %. The JSC is in general 2 mA/cm2 higher, and the VOC 30 mV lower, for cells with the ZTO buffer layer as compared to cells with the traditional CdS buffer layer. In the end comparable efficiencies are obtained for the two different buffer layers. The gain in JSC for the ZTO buffer layer is associated with lower parasitic absorption in the UV-blue region of the solar spectrum and it is shown that the JSC can be increased further by making changes to the other layers in the traditional CdS/i-ZnO/ZnO:Al window layer structure. The ZTO is highly resistive, and it is found that the shunt preventing i-ZnO layer can be omitted, which further increases the JSC. Moreover, an additional increase in JSC is obtained by replacing the sputtered ZnO:Al front contact with In2O3 deposited by ALD. The large gain in JSC for the ZTO/In2O3 window layer stack compensates for the lower VOC related to the ZTO buffer layer, and it is demonstrated that the ZTO/In2O3 window layer structure yields 0.6 % (absolute) higher conversion efficiency than the CdS/i-ZnO/ZnO:Al window layer structure.

The current reverse osmosis desalination membrane market is dominated by aromatic polyamide thin film composite (TFC) membranes. However, these polyamide membranes suffer from poor resistance to continual exposure to oxidizing agents such as chlorine in desalination applications. To overcome these problems, we have synthesized and characterized a new generation of materials, disulfonated poly(arylene ether sulfone) (BPS) random copolymer, for desalination membranes. A key technical feature of these new materials is their high tolerance to chlorine in feed water and their excellent reproducibility in synthesis. In this study, water and sodium chloride solubility, diffusivity and permeability in BPS copolymers were measured for both acid and salt form samples at sulfonation levels from 20 to 40 mol percent. The hydrophilicity of these materials, based on water uptake, increased significantly as sulfonation level increased. The water and salt diffusivity and permeability were correlated with water uptake, consistent with expectations from free volume theory. In addition, a tradeoff was observed between water/salt solubility, diffusivity, and permeability selectivity and water solubility, diffusivity and permeability, respectively. The influence of cation form and degree of sulfonation on free volume, as probed via positron annihilation lifetime spectroscopy (PALS), was determined in BPS random copolymers in both the dry and hydrated states. PALS-based free volume data for hydrated polymers were correlated with water and salt transport properties. The influence of processing history on transport properties of BPS films was also studied. Potassium form BPS films having a 32 mol% sulfonation level were acidified using solid state and solution routes. Additionally, several films were subjected to various thermal treatments in the solid state. The influence of acidification, thermal treatment, and counter-ion form on transport properties was investigated. Finally, the influence of synthesis methods of polyamide TFC membranes from m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization on transport properties is reported. Then, a disulfonated diamine monomer (S-BAPS) was used instead of MPD to prepare TFC membranes. The resulting membranes exhibited reduced chlorine tolerance than those prepared from MPD. However, introduction of S-BAPS to the MPD/TMC polymerization system increased the fouling resistance of the resulting polyamide TFC membranes. / text

Bulk imprinted polymers were synthesized using traditional small molecular weight imprinting techniques for the recognition of bovine serum albumin (BSA). Reproducibility and capacity concerns prompted the use of circular dichroism to investigate the potential effects that conditions commonly employed have on the structure of the protein prior to polymerization. These studies clearly showed a substantial change in the secondary structure of three common model protein templates when in the presence of various monomers and crosslinkers. Molecular docking was used to further examine the interactions taking place at the molecular level. Docking simulations revealed that significant amounts of non-covalent interactions are occurring between the amino acid side chains and ligands; although, the interactions taking place amongst the analyte and polypeptide backbone are responsible for the experimentally observed conformational change. The computational studies also showed that several of the ligands preferentially ‘docked’ to the same amino acids in the protein, indicating that if multiple monomers are employed, this competition for similar binding sites will potentially result in non-specific recognition. These findings are important as they offer insight into the fundamental reasons why recognition of macromolecular templates has proven difficult as well as provide guidance for future success in the field. Using this information, novel surface imprinted polymers were synthesized via a facile technique for the specific recognition of BSA. Thin films based on 2-(dimethylamino)ethyl methacrylate (DMAEMA) as the functional monomer and varying amounts of either N,N’ methylenebisacrylamide (MBA) or poly(ethylene glycol) (400) dimethacrylate (PEG400DMA) as crosslinker were synthesized via UV free-radical polymerization. A clear and reproducible increase in recognition of the template was demonstrated for these systems as 1.6-2.5 times more BSA was recognized by the MIP sample relative to the control polymers. Additionally, these polymers exhibited specific recognition of the template relative to similar competitor proteins with up to 2.9 times more BSA adsorbed than either glucose oxidase or bovine hemoglobin. These synthetic antibody mimics hold significant promise as the next generation of robust recognition elements in a wide range of bioassay and biosensor applications. / text