Matching Items (6)
Filtering by
- All Subjects: Electrical Engineering
- All Subjects: Nanoparticles
- Status: Published
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
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
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
Description
In recent years, the field of nanomedicine has progressed at an astonishing rate, particularly with respect to applications in cancer treatment and molecular imaging. Although organic systems have been the frontrunners, inorganic systems have also begun to show promise, especially those based upon silica and magnetic nanoparticles (NPs). Many of these systems are being designed for simultaneous therapeutic and diagnostic capabilities, thus coining the term, theranostics. A unique class of inorganic systems that shows great promise as theranostics is that of layered double hydroxides (LDH). By synthesis of a core/shell structures, e.g. a gold nanoparticle (NP) core and LDH shell, the multifunctional theranostic may be developed without a drastic increase in the structural complexity. To demonstrate initial proof-of-concept of a potential (inorganic) theranostic platform, a Au-core/LDH-shell nanovector has been synthesized and characterized. The LDH shell was heterogeneously nucleated and grown on the surface of silica coated gold NPs via a coprecipitation method. Polyethylene glycol (PEG) was introduced in the initial synthesis steps to improve crystallinity and colloidal stability. Additionally, during synthesis, fluorescein isothiocyanate (FITC) was intercalated into the interlayer spacing of the LDH. In contrast to the PEG stabilization, a post synthesis citric acid treatment was used as a method to control the size and short-term stability. The heterogeneous core-shell system was characterized with scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), dynamic light scattering (DLS), and powder x-ray diffraction (PXRD). A preliminary in vitro study carried out with the assistance of Dr. Kaushal Rege's group at Arizona State University was to demonstrate the endocytosis capability of homogeneously-grown LDH NPs. The DLS measurements of the core-shell NPs indicated an average particle size of 212nm. The PXRD analysis showed that PEG greatly improved the crystallinity of the system while simultaneously preventing aggregation of the NPs. The preliminary in vitro fluorescence microscopy revealed a moderate uptake of homogeneous LDH NPs into the cells.
ContributorsRearick, Colton (Author) / Dey, Sandwip K (Thesis advisor) / Krause, Stephen (Committee member) / Ramakrishna, B (Committee member) / Arizona State University (Publisher)
Created2011
Description
The optical valley of water, where water is transparent only in the visible range, is a fascinating phenomenon and cannot be modeled by conventional dielectric material modeling. While dielectric properties of materials can be modeled as a sum of Lorentz or Debye simple harmonic oscillators, water is the exception. In 1992 Diaz and Alexopoulos published a causal and passive circuit model that predicted the window of water by adding a “zero shunt” circuit in parallel with every Debye and Lorentz circuit branch. Other than the Diaz model, extensive literature survey yielded no universal dielectric material model that included water or offered an explanation for this window phenomenon. A hybrid phenomenological model of water, proposed by Shubitidze and Osterberg, was the only model other than the Diaz-Alexopoulos model that tried to predict and match the optical valley of water. However, we show that when we apply the requirement that the permittivity function must be a complex analytic function, it fails our test of causality and the model terms lack physical meaning, exhibiting various mathematical and physical contradictions. Left with only the Diaz proposed fundamental model as the only casual model, this dissertation explores its physical implications. Specifically, the theoretical prescription of Kyriazidou et al for creating artificial dielectric materials with a narrow band transparency is experimentally demonstrated for the first time at radiofrequencies. It is proposed that the most general component of the model of the frequency dependent permittivity of materials is not the simple harmonic oscillator but rather the harmonic oscillator augmented by the presence of a zero shunt circuit. The experimental demonstration illustrates the synthesis and design of a new generation of window materials based on that model. Physically realizable Lorentz coatings and RF Debye “molecules” for creating the desired windows material are designed using the full physics computational electromagnetic code. The prescribed material is then implemented in printed circuit board technology combined with composite manufacturing to successfully fabricate a lab demonstrator that exhibits a narrow RF window at a preselected frequency of interest. Demonstrator test data shows good agreement with HFSS predictions.
ContributorsAlam, Shahriar (Author) / Diaz, Rodolfo E (Thesis advisor) / Krause, Stephen (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2017
Description
In this work a newly fabricated organic solar cell based on a composite of fullerene derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) and regioregular poly (3-hexylthiophene) (P3HT) with an added interfacial layer of AgOx in between the PEDOT:PSS layer and the ITO layer is investigated. Previous equivalent circuit models are discussed and an equivalent circuit model is proposed for the fabricated device. Incorporation of the AgOx interfacial layer shows an increase in fill factor (by 33%) and power conversion efficiency (by 28%). Moreover proper correlation has been achieved between the experimental and simulated I-V plots. The simulation shows that device characteristics can be explained with accuracy by the proposed model.
ContributorsHossain, Nazmul (Author) / Alford, Terry L. (Thesis advisor) / Theodore, David (Committee member) / Krause, Stephen (Committee member) / Arizona State University (Publisher)
Created2015