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Description
The colossal global counterfeit market and advances in cryptography including quantum computing supremacy have led the drive for a class of anti-counterfeit tags that are physically unclonable. Dendrites, previously considered an undesirable side effect of battery operation, have promise as an extremely versatile version of such tags, with their fundamental nature ensuring that no two dendrites are alike and that they can be read at multiple magnification scales. In this work, we first pursue a simulation for electrochemical dendrites that elucidates fundamental information about their growth mechanism. We then translate these results into physical dendrites and demonstrate methods of producing a hash from these dendrites that is damage-tolerant for real-world verification. Finally, we explore theoretical curiosities that arise from the fractal nature of dendrites. We find that uniquely ramified dendrites, which rely on lower ion mobility and conductive deposition, are particularly amenable to wavelet hashing, and demonstrate that these dendrites have strong commercial potential for securing supply chains at the highest level while maintaining a low price point.
ContributorsSneh, Tal (Author) / Kozicki, Michael (Thesis director) / Gonzalez-Velo, Yago (Committee member) / School of Molecular Sciences (Contributor) / Department of Physics (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Carrier lifetime is one of the few parameters which can give information about the low defect densities in today's semiconductors. In principle there is no lower limit to the defect density determined by lifetime measurements. No other technique can easily detect defect densities as low as 10-9 - 10-10 cm-3 in a simple, contactless room temperature measurement. However in practice, recombination lifetime τr measurements such as photoconductance decay (PCD) and surface photovoltage (SPV) that are widely used for characterization of bulk wafers face serious limitations when applied to thin epitaxial layers, where the layer thickness is smaller than the minority carrier diffusion length Ln. Other methods such as microwave photoconductance decay (µ-PCD), photoluminescence (PL), and frequency-dependent SPV, where the generated excess carriers are confined to the epitaxial layer width by using short excitation wavelengths, require complicated configuration and extensive surface passivation processes that make them time-consuming and not suitable for process screening purposes. Generation lifetime τg, typically measured with pulsed MOS capacitors (MOS-C) as test structures, has been shown to be an eminently suitable technique for characterization of thin epitaxial layers. It is for these reasons that the IC community, largely concerned with unipolar MOS devices, uses lifetime measurements as a "process cleanliness monitor." However when dealing with ultraclean epitaxial wafers, the classic MOS-C technique measures an effective generation lifetime τg eff which is dominated by the surface generation and hence cannot be used for screening impurity densities. I have developed a modified pulsed MOS technique for measuring generation lifetime in ultraclean thin p/p+ epitaxial layers which can be used to detect metallic impurities with densities as low as 10-10 cm-3. The widely used classic version has been shown to be unable to effectively detect such low impurity densities due to the domination of surface generation; whereas, the modified version can be used suitably as a metallic impurity density monitoring tool for such cases.
ContributorsElhami Khorasani, Arash (Author) / Alford, Terry (Thesis advisor) / Goryll, Michael (Committee member) / Bertoni, Mariana (Committee member) / Arizona State University (Publisher)
Created2013
Description
As crystalline silicon solar cells continue to get thinner, the recombination of carriers at the surfaces of the cell plays an ever-important role in controlling the cell efficiency. One tool to minimize surface recombination is field effect passivation from the charges present in the thin films applied on the cell surfaces. The focus of this work is to understand the properties of charges present in the SiNx films and then to develop a mechanism to manipulate the polarity of charges to either negative or positive based on the end-application. Specific silicon-nitrogen dangling bonds (·Si-N), known as K center defects, are the primary charge trapping defects present in the SiNx films. A custom built corona charging tool was used to externally inject positive or negative charges in the SiNx film. Detailed Capacitance-Voltage (C-V) measurements taken on corona charged SiNx samples confirmed the presence of a net positive or negative charge density, as high as +/- 8 x 1012 cm-2, present in the SiNx film. High-energy (~ 4.9 eV) UV radiation was used to control and neutralize the charges in the SiNx films. Electron-Spin-Resonance (ESR) technique was used to detect and quantify the density of neutral K0 defects that are paramagnetically active. The density of the neutral K0 defects increased after UV treatment and decreased after high temperature annealing and charging treatments. Etch-back C-V measurements on SiNx films showed that the K centers are spread throughout the bulk of the SiNx film and not just near the SiNx-Si interface. It was also shown that the negative injected charges in the SiNx film were stable and present even after 1 year under indoor room-temperature conditions. Lastly, a stack of SiO2/SiNx dielectric layers applicable to standard commercial solar cells was developed using a low temperature (< 400 °C) PECVD process. Excellent surface passivation on FZ and CZ Si substrates for both n- and p-type samples was achieved by manipulating and controlling the charge in SiNx films.
ContributorsSharma, Vivek (Author) / Bowden, Stuart (Thesis advisor) / Schroder, Dieter (Committee member) / Honsberg, Christiana (Committee member) / Roedel, Ronald (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2013
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
Soft magnetic alloys play a significant role for magnetic recording applications and highly sensitivity magnetic field sensors. In order to sustain the magnetic areal density growth, development of new synthesis techniques and materials is necessary. In this work, the effect of oxygen incorporation during electrodeposition of CoFe alloys on magnetic properties, magnetoresistance and structural properties has been studied. Understanding the magnetic properties often required knowledge of oxygen distribution and structural properties of the grown films. Transmission electron microscopy (TEM) was a powerful tool in this study to correlate the oxygen-distribution nanostructure to the magnetic properties of deposited films. Off-axis electron holography in TEM was used to measure magnetic domain wall width in the deposited films. Elemental depth profiles of Fe, Co, O were investigated by secondary ion mass spectroscopy (SIMS). Magnetic properties have been determined by superconducting quantum interference device (SQUID) measurements. Oxygen content in the CoFe deposited films was controlled by electrolyte composition. Films were deposited on Si 100 substrates and on other substrates such as Cu and Al. However, a good film quality was achieved on Si substrate. Electron energy loss and x-ray spectroscopies showed that the low oxygen films contained intragranular Fe2+ oxide (FeO) particles and that the high oxygen films contained intergranular Fe3+ (Fe2O3) along grain boundaries. The films with oxide present at the grain boundary had significantly increased coercivity, magnetoresistance and reduced saturation magnetization relative to the lower oxygen content films with intragranular oxide. The differences in magnetic properties between low oxygen and high oxygen concentration films were attributed to stronger mobile domain wall interactions with the grain boundary oxide layers. The very high magnetoresistance values were achieved for magnetic devices with nanocontact dimension < 100 nm and oxide incorporation in this nanoconfined geometry. The content of oxide phase in nanocontact was controlled by concentration of the Fe3+ ions in the electrodeposition solution. Magnetic device integrity was improved by varying amount of additive into plating solution. These results indicated that electrodeposited CoFe nanocontact is a novel class of materials with large application for magnetic field sensors.
ContributorsElhalawaty, Shereen (Author) / Carpenter, Ray (Thesis advisor) / Chamberlin, Ralph (Committee member) / McCartney, Martha (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2012
Description
Proposed and tested were three different methods to deposit important layers of Silicon heterojunction solar cells (SHJs). If there were a shortage of Silver, Aluminum could be substituted for the contacts. If there were a shortage of Indium, Yttrium Zinc Oxide could be substituted. To improve the solar cell, the p and n type layers can be grown with hydrogenated nanocrystallline Silicon (nc-Si:H). 40% and 50% nc-Si:H has shown a maximum absorbance reduction of 5 times compared to hydrogenated amorphous Silicon (a-Si). The substitutions offer alternatives which increase the total possible amount of solar cell production, advancing toward completion of the Terrawatt challenge.
ContributorsCarpenter, Joe Victor (Author) / Alford, Terry (Thesis director) / Holman, Zachary (Committee member) / Barrett, The Honors College (Contributor) / Chemical Engineering Program (Contributor) / Materials Science and Engineering Program (Contributor)
Created2014-05
Description
Volume depletion can lead to migraines, dizziness, and significant decreases in a subject's ability to physically perform. A major cause of volume depletion is dehydration, or loss in fluids due to an imbalance in fluid intake to fluid excretion. Because proper levels of hydration are necessary in order to maintain both short and long term health, the ability to monitor hydration levels is growing in clinical demand. Although devices capable of monitoring hydration level exist, these devices are expensive, invasive, or inaccurate and do not offer a continuous mode of measurement. The ideal hydration monitor for consumer use needs to be characterized by its portability, affordability, and accuracy. Also, this device would need to be noninvasive and offer continuous hydration monitoring in order to accurately assess fluctuations in hydration data throughout a specified time period. One particular method for hydration monitoring that fits the majority of these criteria is known as bioelectric impedance analysis (BIA). Although current devices using BIA do not provide acceptable levels of accuracy, portability, or continuity in data collection, BIA could potentially be modified to fit many, if not all, desired customer specifications. The analysis presented here assesses the viability of using BIA as a new standard in hydration level measurement. The analysis uses data collected from 22 subjects using an existing device that employs BIA. A regression derived for estimating TBW based on the parameters of age, weight, height, sex, and impedance is presented. Using impedance data collected for each subject, a regression was also derived for estimating impedance based on the factors of age, weight, height, and sex. The derived regression was then used to calculate a new impedance value for each subject, and these new impedance values were used to estimate TBW. Through a paired-t test between the TBW values derived by using the direct measurements versus the calculated measurements of impedance, the two samples were found to be comparable. Considerations for BIA as a noninvasive measurement of hydration are discussed.
ContributorsTenorio, Jorge Antonio (Author) / LaBelle, Jeffrey (Thesis director) / Pizziconi, Vincent (Committee member) / Spano, Mark (Committee member) / Barrett, The Honors College (Contributor) / W. P. Carey School of Business (Contributor) / Harrington Bioengineering Program (Contributor)
Created2013-05
Description
Programmable Metallization Cell (PMC) is a resistance-switching device based on migration of nanoscale quantities of cations in a solid electrolyte and formation of a conducting electrodeposit by the reductions of these cations. This dissertation presents electrical characterization results on Cu-SiO2 based PMC devices, which due to the na- ture of materials can be easily integrated into the current Complimentary metal oxide semiconductor (CMOS) process line. Device structures representing individual mem- ory cells based on W bottom electrode and n-type Si bottom electrode were fabricated for characterization. For the W bottom electrode based devices, switching was ob- served for voltages in the range of 500mV and current value as low as 100 nA showing the electrochemical nature and low power potential. The ON state showed a direct de- pendence on the programming current, showing the possibility of multi-bit storage in a single cell. Room temperature retention was demonstrated in excess of 105 seconds and endurance to approximately 107 cycles. Switching was observed for microsecond duration 3 V amplitude pulses. Material characterization results from Raman, X-ray diffraction, Rutherford backscattering and Secondary-ion mass spectroscopy analysis shows the influence of processing conditions on the Cu concentration within the film and also the presence of Cu as free atoms. The results seemed to indicate stress-induced void formation in the SiO2 matrix as the driving mechanism for Cu diffusion into the SiO2 film. Cu/SiO2
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
Si based PMC devices were characterized and were shown to have inherent isolation characteristics, proving the feasibility of such a structure for a passive array. The inherent isolation property simplifies fabrication by avoiding the need for a separate diode element in an array. The isolation characteristics were studied mainly in terms of the leakage current. The nature of the diode interface was further studied by extracting a barrier potential which shows it can be approximated to a Cu-nSi metal semiconductor Schottky diode.
ContributorsPuthenthermadam, Sarath (Author) / Kozicki, Michael N (Thesis advisor) / Diaz, Rodolfo (Committee member) / Schroder, Dieter K. (Committee member) / Alford, Terry (Committee member) / Arizona State University (Publisher)
Created2011
Description
Silicon carbide (SiC), long touted as a material that can satisfy the specific property requirements for high temperature and high power applications, was studied quantitatively using various techniques. The electronic band structure of 4H SiC is examined in the first half of this dissertation. A brief introduction to band structure calculations, with particular emphasis on the empirical pseudopotential method, is given as a foundation for the subsequent work. Next, the crystal pseudopotential for 4H SiC is derived in detail, and a novel approach using a genetic algorithm search routine is employed to find the fitting parameters needed to generate the band structure. Using this technique, the band structure is fitted to experimentally measured energy band gaps giving an indirect band gap energy of 3.28 eV, and direct f¡, M, K and L energy transitions of 6.30, 4.42, 7.90 and 6.03 eV, respectively. The generated result is also shown to give effective mass values of mMf¡*=0.66m0, mMK*=0.31m0, mML*=0.34m0, in close agreement with experimental results. The second half of this dissertation discusses computational work in finding the electron Hall mobility and Hall scattering factor for 6H SiC. This disscussion begins with an introductory chapter that gives background on how scattering rates are dervied and the specific expressions for important mechanisms. The next chapter discusses mobility calculations for 6H SiC in particular, beginnning with Rode's method to solve the Boltzmann transport equation. Using this method and the transition rates of the previous chapter, an acoustic deformation potential DA value of 5.5 eV, an inter-valley phonon deformation potential Dif value of 1.25~1011 eV/m and inter-valley phonon energy ℏfÖif of 65 meV that simultaneously fit experimental data on electron Hall mobility and Hall scattering factor was found.
ContributorsNg, Garrick (Author) / Schroder, Dieter K. (Thesis advisor) / Vasileska, Dragica (Committee member) / Skromme, Brian (Committee member) / Alford, Terry (Committee member) / Marinella, Matthew (Committee member) / Arizona State University (Publisher)
Created2010
Description
Microstructure refinement and alloy additions are considered potential routes to increase high temperature performance of existing metallic superalloys used under extreme conditions. Nanocrystalline (NC) Cu-10at%Ta exhibits such improvements over microstructurally unstable NC metals, leading to enhanced creep behavior compared to its coarse-grained (CG) counterparts. However, the low melting point of Cu compared to other FCC metals, e.g., Ni, might lead to an early onset of diffusional creep mechanisms. Thus, this research seeks to study the thermo-mechanical behavior and stability of hierarchical (prepared using arc-melting) and NC (prepared by collaborators through powder pressing and annealing) Ni-Y-Zr alloys where Zr is expected to provide solid solution and grain boundary strengthening in hierarchical and NC alloys, respectively, while Ni-Y and Ni-Zr intermetallic precipitates (IMCs) would provide kinetic stability. Hierarchical alloys had microstructures stable up to 1100 °C with ultrafine eutectic of ~300 nm, dendritic arm spacing of ~10 μm, and grain size ~1-2 mm. Room temperature hardness tests along with uniaxial compression performed at 25 and 600 °C revealed that microhardness and yield strength of hierarchical alloys with small amounts of Y (0.5-1wt%) and Zr (1.5-3 wt%) were comparable to Ni-superalloys, due to the hierarchical microstructure and potential presence of nanoscale IMCs. In contrast, NC alloys of the same composition were found to be twice as hard as the hierarchical alloys. Creep tests at 0.5 homologous temperature showed active Coble creep mechanisms in hierarchical alloys at low stresses with creep rates slower than Fe-based superalloys and dislocation creep mechanisms at higher stresses. Creep in NC alloys at lower stresses was only 20 times faster than hierarchical alloys, with the difference in grain size ranging from 10^3 to 10^6 times at the same temperature. These NC alloys showed enhanced creep properties over other NC metals and are expected to have rates equal to or improved over the CG hierarchical alloys with ECAP processing techniques. Lastly, the in-situ wide-angle x-ray scattering (WAXS) measurements during quasi-static and creep tests implied stresses being carried mostly by the matrix before yielding and in the primary creep stage, respectively, while relaxation was observed in Ni5Zr for both hierarchical and NC alloys. Beyond yielding and in the secondary creep stage, lattice strains reached a steady state, thereby, an equilibrium between plastic strain rates was achieved across different phases, so that deformation reaches a saturation state where strain hardening effects are compensated by recovery mechanisms.
ContributorsSharma, Shruti (Author) / Peralta, Pedro (Thesis advisor) / Alford, Terry (Committee member) / Jiao, Yang (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2022