Matching Items (91)
Description
Recently, the use of zinc oxide (ZnO) nanowires as an interphase in composite materials has been demonstrated to increase the interfacial shear strength between carbon fiber and an epoxy matrix. In this research work, the strong adhesion between ZnO and carbon fiber is investigated to elucidate the interactions at the interface that result in high interfacial strength. First, molecular dynamics (MD) simulations are performed to calculate the adhesive energy between bare carbon and ZnO. Since the carbon fiber surface has oxygen functional groups, these were modeled and MD simulations showed the preference of ketones to strongly interact with ZnO, however, this was not observed in the case of hydroxyls and carboxylic acid. It was also found that the ketone molecules ability to change orientation facilitated the interactions with the ZnO surface. Experimentally, the atomic force microscope (AFM) was used to measure the adhesive energy between ZnO and carbon through a liftoff test by employing highly oriented pyrolytic graphite (HOPG) substrate and a ZnO covered AFM tip. Oxygen functionalization of the HOPG surface shows the increase of adhesive energy. Additionally, the surface of ZnO was modified to hold a negative charge, which demonstrated an increase in the adhesive energy. This increase in adhesion resulted from increased induction forces given the relatively high polarizability of HOPG and the preservation of the charge on ZnO surface. It was found that the additional negative charge can be preserved on the ZnO surface because there is an energy barrier since carbon and ZnO form a Schottky contact. Other materials with the same ionic properties of ZnO but with higher polarizability also demonstrated good adhesion to carbon. This result substantiates that their induced interaction can be facilitated not only by the polarizability of carbon but by any of the materials at the interface. The versatility to modify the magnitude of the induced interaction between carbon and an ionic material provides a new route to create interfaces with controlled interfacial strength.
ContributorsGalan Vera, Magdian Ulises (Author) / Sodano, Henry A (Thesis advisor) / Jiang, Hanqing (Committee member) / Solanki, Kiran (Committee member) / Oswald, Jay (Committee member) / Speyer, Gil (Committee member) / Arizona State University (Publisher)
Created2013
Description
Microelectronic industry is continuously moving in a trend requiring smaller and smaller devices and reduced form factors with time, resulting in new challenges. Reduction in device and interconnect solder bump sizes has led to increased current density in these small solders. Higher level of electromigration occurring due to increased current density is of great concern affecting the reliability of the entire microelectronics systems. This paper reviews electromigration in Pb- free solders, focusing specifically on Sn0.7wt.% Cu solder joints. Effect of texture, grain orientation, and grain-boundary misorientation angle on electromigration and intermetallic compound (IMC) formation is studied through EBSD analysis performed on actual C4 bumps.
ContributorsLara, Leticia (Author) / Tasooji, Amaneh (Thesis advisor) / Lee, Kyuoh (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2013
Description
Rapid processing and reduced end-of-range diffusion effects demonstrate that susceptor-assisted microwave annealing is an efficient processing alternative for electrically activating dopants and removing ion-implantation damage in ion-implanted semiconductors. Sheet resistance and Hall measurements provide evidence of electrical activation. Raman spectroscopy and ion channeling analysis monitor the extent of ion implantation damage and recrystallization. The presence of damage and defects in ion implanted silicon, and the reduction of the defects as a result of annealing, is observed by Rutherford backscattering spectrometry, moreover, the boron implanted silicon is further investigated by cross-section transmission electron microscopy. When annealing B+ implanted silicon, the dissolution of small extended defects and growth of large extended defects result in reduced crystalline quality that hinders the electrical activation process. Compared to B+ implanted silicon, phosphorus implanted samples experience more effective activation and achieve better crystalline quality. Comparison of end-of-range dopants diffusion resulting from microwave annealing and rapid thermal annealing (RTA) is done using secondary ion mass spectroscopy. Results from microwave annealed P+ implanted samples show that almost no diffusion occurs during time periods required for complete dopant activation and silicon recrystallization. The relative contributions to heating of the sample, by a SiC susceptor, and by Si self-heating in the microwave anneal, were also investigated. At first 20s, the main contributor to the sample's temperature rise is Si self-heating by microwave absorption.
ContributorsZhao, Zhao (Author) / Alford, Terry Lynn (Thesis advisor) / Theodore, David (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2013
Description
This thesis work mainly examined the stability and reliability issues of amorphous Indium Gallium Zinc Oxide (a-IGZO) thin film transistors under bias-illumination stress. Amorphous hydrogenated silicon has been the dominating material used in thin film transistors as a channel layer. However with the advent of modern high performance display technologies, it is required to have devices with better current carrying capability and better reproducibility. This brings the idea of new material for channel layer of these devices. Researchers have tried poly silicon materials, organic materials and amorphous mixed oxide materials as a replacement to conventional amorphous silicon layer. Due to its low price and easy manufacturing process, amorphous mixed oxide thin film transistors have become a viable option to replace the conventional ones in order to achieve high performance display circuits. But with new materials emerging, comes the challenge of reliability and stability issues associated with it. Performance measurement under bias stress and bias-illumination stress have been reported previously. This work proposes novel post processing low temperature long time annealing in optimum ambient in order to annihilate or reduce the defects and vacancies associated with amorphous material which lead to the instability or even the failure of the devices. Thin film transistors of a-IGZO has been tested for standalone illumination stress and bias-illumination stress before and after annealing. HP 4155B semiconductor parameter analyzer has been used to stress the devices and measure the output characteristics and transfer characteristics of the devices. Extra attention has been given about the effect of forming gas annealing on a-IGZO thin film. a-IGZO thin film deposited on silicon substrate has been tested for resistivity, mobility and carrier concentration before and after annealing in various ambient. Elastic Recoil Detection has been performed on the films to measure the amount of hydrogen atoms present in the film. Moreover, the circuit parameters of the thin film transistors has been extracted to verify the physical phenomenon responsible for the instability and failure of the devices. Parameters like channel resistance, carrier mobility, power factor has been extracted and variation of these parameters has been observed before and after the stress.
ContributorsRuhul Hasin, Muhammad (Author) / Alford, Terry L. (Thesis advisor) / Krause, Stephen (Committee member) / Kitchen, Jennifer (Committee member) / Arizona State University (Publisher)
Created2013
Description
III-Nitride nanostructures have been an active area of research recently due to their ability to tune their optoelectronic properties. Thus far work has been done on InGaN quantum dots, nanowires, nanopillars, amongst other structures, but this research reports the creation of a new type of InGaN nanostructure, nanorings. Hexagonal InGaN nanorings were formed using Metal Organic Chemical Vapor Deposition through droplet epitaxy. The nanorings were thoroughly analyzed using x-ray diffraction, photoluminescence, electron microscopy, electron diffraction, and atomic force microscopy. Nanorings with high indium incorporation were achieved with indium content up to 50% that was then controlled using the growth time, temperature, In/Ga ratio and III/N ratio. The analysis showed that the nanoring shape is able to incorporate more indium than other nanostructures, due to the relaxing mechanism involved in the formation of the nanoring. The ideal conditions were determined to be growth of 30 second droplets with a growth time of 1 minute 30 seconds at 770 C to achieve the most well developed rings with the highest indium concentration.
ContributorsZaidi, Zohair (Author) / Mahajan, Subhash (Thesis advisor) / O'Connell, Michael J (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2012
Description
Zinc oxide (ZnO) has attracted much interest during last decades as a functional material. Furthermore, ZnO is a potential material for transparent conducting oxide material competing with indium tin oxide (ITO), graphene, and carbon nanotube film. It has been known as a conductive material when doped with elements such as indium, gallium and aluminum. The solubility of those dopant elements in ZnO is still debatable; but, it is necessary to find alternative conducting materials when their form is film or nanostructure for display devices. This is a consequence of the ever increasing price of indium. In addition, a new generation solar cell (nanostructured or hybrid photovoltaics) requires compatible materials which are capable of free standing on substrates without seed or buffer layers and have the ability introduce electrons or holes pathway without blocking towards electrodes. The nanostructures for solar cells using inorganic materials such as silicon (Si), titanium oxide (TiO2), and ZnO have been an interesting topic for research in solar cell community in order to overcome the limitation of efficiency for organic solar cells. This dissertation is a study of the rational solution-based synthesis of 1-dimentional ZnO nanomaterial and its solar cell applications. These results have implications in cost effective and uniform nanomanufacturing for the next generation solar cells application by controlling growth condition and by doping transition metal element in solution.
ContributorsChoi, Hyung Woo (Author) / Alford, Terry L. (Thesis advisor) / Krause, Stephen (Committee member) / Theodore, N. David (Committee member) / Arizona State University (Publisher)
Created2012
Description
Ball Grid Array (BGA) using lead-free or lead-rich solder materials are widely used as Second Level Interconnects (SLI) in mounting packaged components to the printed circuit board (PCB). The reliability of these solder joints is of significant importance to the performance of microelectronics components and systems. Product design/form-factor, solder material, manufacturing process, use condition, as well as, the inherent variabilities present in the system, greatly influence product reliability. Accurate reliability analysis requires an integrated approach to concurrently account for all these factors and their synergistic effects. Such an integrated and robust methodology can be used in design and development of new and advanced microelectronics systems and can provide significant improvement in cycle-time, cost, and reliability. IMPRPK approach is based on a probabilistic methodology, focusing on three major tasks of (1) Characterization of BGA solder joints to identify failure mechanisms and obtain statistical data, (2) Finite Element analysis (FEM) to predict system response needed for life prediction, and (3) development of a probabilistic methodology to predict the reliability, as well as, the sensitivity of the system to various parameters and the variabilities. These tasks and the predictive capabilities of IMPRPK in microelectronic reliability analysis are discussed.
ContributorsFallah-Adl, Ali (Author) / Tasooji, Amaneh (Thesis advisor) / Krause, Stephen (Committee member) / Alford, Terry (Committee member) / Jiang, Hanqing (Committee member) / Mahajan, Ravi (Committee member) / Arizona State University (Publisher)
Created2013
Description
Electromigration in metal interconnects is the most pernicious failure mechanism in semiconductor integrated circuits (ICs). Early electromigration investigations were primarily focused on aluminum interconnects for silicon-based ICs. An alternative metallization compatible with gallium arsenide (GaAs) was required in the development of high-powered radio frequency (RF) compound semiconductor devices operating at higher current densities and elevated temperatures. Gold-based metallization was implemented on GaAs devices because it uniquely forms a very low resistance ohmic contact and gold interconnects have superior electrical and thermal conductivity properties. Gold (Au) was also believed to have improved resistance to electromigration due to its higher melting temperature, yet electromigration reliability data on passivated Au interconnects is scarce and inadequate in the literature. Therefore, the objective of this research was to characterize the electromigration lifetimes of passivated Au interconnects under precisely controlled stress conditions with statistically relevant quantities to obtain accurate model parameters essential for extrapolation to normal operational conditions. This research objective was accomplished through measurement of electromigration lifetimes of large quantities of passivated electroplated Au interconnects utilizing high-resolution in-situ resistance monitoring equipment. Application of moderate accelerated stress conditions with a current density limited to 2 MA/cm2 and oven temperatures in the range of 300°C to 375°C avoided electrical overstress and severe Joule-heated temperature gradients. Temperature coefficients of resistance (TCRs) were measured to determine accurate Joule-heated Au interconnect film temperatures. A failure criterion of 50% resistance degradation was selected to prevent thermal runaway and catastrophic metal ruptures that are problematic of open circuit failure tests. Test structure design was optimized to reduce resistance variation and facilitate failure analysis. Characterization of the Au microstructure yielded a median grain size of 0.91 ìm. All Au lifetime distributions followed log-normal distributions and Black's model was found to be applicable. An activation energy of 0.80 ± 0.05 eV was measured from constant current electromigration tests at multiple temperatures. A current density exponent of 1.91 was extracted from multiple current densities at a constant temperature. Electromigration-induced void morphology along with these model parameters indicated grain boundary diffusion is dominant and the void nucleation mechanism controlled the failure time.
ContributorsKilgore, Stephen (Author) / Adams, James (Thesis advisor) / Schroder, Dieter (Thesis advisor) / Krause, Stephen (Committee member) / Gaw, Craig (Committee member) / Arizona State University (Publisher)
Created2013
Description
Aluminum alloys and their composites are attractive materials for applications requiring high strength-to-weight ratios and reasonable cost. Many of these applications, such as those in the aerospace industry, undergo fatigue loading. An understanding of the microstructural damage that occurs in these materials is critical in assessing their fatigue resistance. Two distinct experimental studies were performed to further the understanding of fatigue damage mechanisms in aluminum alloys and their composites, specifically fracture and plasticity. Fatigue resistance of metal matrix composites (MMCs) depends on many aspects of composite microstructure. Fatigue crack growth behavior is particularly dependent on the reinforcement characteristics and matrix microstructure. The goal of this work was to obtain a fundamental understanding of fatigue crack growth behavior in SiC particle-reinforced 2080 Al alloy composites. In situ X-ray synchrotron tomography was performed on two samples at low (R=0.1) and at high (R=0.6) R-ratios. The resulting reconstructed images were used to obtain three-dimensional (3D) rendering of the particles and fatigue crack. Behaviors of the particles and crack, as well as their interaction, were analyzed and quantified. Four-dimensional (4D) visual representations were constructed to aid in the overall understanding of damage evolution. During fatigue crack growth in ductile materials, a plastic zone is created in the region surrounding the crack tip. Knowledge of the plastic zone is important for the understanding of fatigue crack formation as well as subsequent growth behavior. The goal of this work was to quantify the 3D size and shape of the plastic zone in 7075 Al alloys. X-ray synchrotron tomography and Laue microdiffraction were used to non-destructively characterize the volume surrounding a fatigue crack tip. The precise 3D crack profile was segmented from the reconstructed tomography data. Depth-resolved Laue patterns were obtained using differential-aperture X-ray structural microscopy (DAXM), from which peak-broadening characteristics were quantified. Plasticity, as determined by the broadening of diffracted peaks, was mapped in 3D. Two-dimensional (2D) maps of plasticity were directly compared to the corresponding tomography slices. A 3D representation of the plastic zone surrounding the fatigue crack was generated by superimposing the mapped plasticity on the 3D crack profile.
ContributorsHruby, Peter (Author) / Chawla, Nikhilesh (Thesis advisor) / Solanki, Kiran (Committee member) / Liu, Yongming (Committee member) / Arizona State University (Publisher)
Created2014
Description
The central theme of this dissertation is to understand the chemical processing science of advanced ceramic materials for biomedicine, including therapy and imaging. The secondary component focuses on the chemical processing of energy materials.
Recently, layered double hydroxide (LDH) nanoparticles (NPs) with various intercalated compounds (e.g. fluorescent molecules, radio-labeled ATP, vitamins, DNA, and drugs) have exhibited versatility and promise as a combined therapeutic and diagnostic (i.e. theranostic) vector. However, its eventual acceptance in biomedicine will be contingent on understanding the processing science, reproducibly synthesizing monodispersed NPs with controlled mean particle size (MPS), and ascertaining the efficacy of the NPs for drug delivery and imaging. First, statistical design of experiments were used to optimize the wet chemistry synthesis of (Zn, Al)-LDH NPs. A synthesis model, which allows the synthesis of nearly monodispersed NPs with controlled MPS, was developed and experimentally verified. Also, the evolution of the nanostructure was characterized, from coprecipitation to hydrothermal treatment, to identify the formation mechanisms. Next, the biocompatibility, cellular uptake and drug delivery capability of LDH NPs were studied. In an in vitro study, using cultured pancreatic adenocarcinoma BXPC3 cells, valproate-intercalated LDH NPs showed an improved efficacy (~50 fold) over the sodium valproate alone. Finally, Gd(DTPA)-intercalated LDH NPs were synthesized and characterized by proton (1H) nuclear magnetic resonance. The longitudinal relaxivity (r1) of 28.38 s-1 mM-1, which is over 6 times higher than the clinically approved contrast agent, Gd(DTPA), demonstrated the potential of this vector for use in magnetic resonance imaging.
Visible light-transparent single metal-semiconductor junction devices, which convert ultraviolet photon energy into high open circuit voltage (Voc>1.5-2 V), are highly desirable for transparent photovoltaics that can potentially power an electrochromic stack for smart windows. A Schottky junction solar cell, comprised of sputtered ZnO/ZnS heterojunction with Cr/Au contacts, was fabricated and an Voc of fî1.35 V was measured. Also, a low-cost route to form ZnO/ZnS heterojunctions by partial sulfurization of solution-grown ZnO thin films (350 nm-5 fÝm thick; conductivity comparable to phosphorus-doped Si) was demonstrated. A final study was on a cathode material for Li-ion batteries. Phase-pure LiFePO4 powders were synthesized by microwave-assisted sol-gel method and characterized.
Recently, layered double hydroxide (LDH) nanoparticles (NPs) with various intercalated compounds (e.g. fluorescent molecules, radio-labeled ATP, vitamins, DNA, and drugs) have exhibited versatility and promise as a combined therapeutic and diagnostic (i.e. theranostic) vector. However, its eventual acceptance in biomedicine will be contingent on understanding the processing science, reproducibly synthesizing monodispersed NPs with controlled mean particle size (MPS), and ascertaining the efficacy of the NPs for drug delivery and imaging. First, statistical design of experiments were used to optimize the wet chemistry synthesis of (Zn, Al)-LDH NPs. A synthesis model, which allows the synthesis of nearly monodispersed NPs with controlled MPS, was developed and experimentally verified. Also, the evolution of the nanostructure was characterized, from coprecipitation to hydrothermal treatment, to identify the formation mechanisms. Next, the biocompatibility, cellular uptake and drug delivery capability of LDH NPs were studied. In an in vitro study, using cultured pancreatic adenocarcinoma BXPC3 cells, valproate-intercalated LDH NPs showed an improved efficacy (~50 fold) over the sodium valproate alone. Finally, Gd(DTPA)-intercalated LDH NPs were synthesized and characterized by proton (1H) nuclear magnetic resonance. The longitudinal relaxivity (r1) of 28.38 s-1 mM-1, which is over 6 times higher than the clinically approved contrast agent, Gd(DTPA), demonstrated the potential of this vector for use in magnetic resonance imaging.
Visible light-transparent single metal-semiconductor junction devices, which convert ultraviolet photon energy into high open circuit voltage (Voc>1.5-2 V), are highly desirable for transparent photovoltaics that can potentially power an electrochromic stack for smart windows. A Schottky junction solar cell, comprised of sputtered ZnO/ZnS heterojunction with Cr/Au contacts, was fabricated and an Voc of fî1.35 V was measured. Also, a low-cost route to form ZnO/ZnS heterojunctions by partial sulfurization of solution-grown ZnO thin films (350 nm-5 fÝm thick; conductivity comparable to phosphorus-doped Si) was demonstrated. A final study was on a cathode material for Li-ion batteries. Phase-pure LiFePO4 powders were synthesized by microwave-assisted sol-gel method and characterized.
ContributorsSun Zhou, Xiao Di (Author) / Dey, Sandwip K (Thesis advisor) / Krause, Stephen (Committee member) / Nagaraj, Vinay J (Committee member) / Marzke, Robert (Committee member) / Arizona State University (Publisher)
Created2014