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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 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
The focus of education in the classroom traditionally is one of fact memorization and recall. The teaching process of linear knowledge progression is not always in tune with the way that the human brain actually processes, conceptualizes, and comprehends concepts and information. In an introductory engineering class, focused on materials engineering and its related concepts, a system of lecture interventions has been put in place to increase concept comprehension by supplementing lecture units with various activities, from additional worksheets, explicit concept discussions, and most recently, YouTube videos showcasing specific concepts and situations. In an attempt to correct the lack of actual concept comprehension, these interventions seek to interact with the human mind in a way that capitalizes on its ability to process and interpret non-linear knowledge and information.
Using a concept test given prior to the lecture unit, and after, the difference in scores is used to recognize if the concepts presented have actually been comprehended. Used specifically in a lecture unit on solubility and solutions, the concept test tested student’s knowledge of supersaturated, saturated, and unsaturated solutions. With a visual identification and a written explanation, the student’s ability to identify and explain the three solutions was tested.
In order to determine the cause of the change in score from pre- to post-test, an analysis of the change in scores and the effects of question type and solution type was conducted. The significant results are as follows:
The change in score from pre- to post-test was found to be significant, with the only difference between the two tests being the lecture unit and intervention
From pre- to post-test, solution type had a significant effect on the score, with the unsaturated solution being the most easily recognized and explained solution type
Students that felt that the YouTube videos greatly increased their concept comprehension, on average, performed better than their counterparts and also saw a greater increase their score from pre- to post-test
Using a concept test given prior to the lecture unit, and after, the difference in scores is used to recognize if the concepts presented have actually been comprehended. Used specifically in a lecture unit on solubility and solutions, the concept test tested student’s knowledge of supersaturated, saturated, and unsaturated solutions. With a visual identification and a written explanation, the student’s ability to identify and explain the three solutions was tested.
In order to determine the cause of the change in score from pre- to post-test, an analysis of the change in scores and the effects of question type and solution type was conducted. The significant results are as follows:
The change in score from pre- to post-test was found to be significant, with the only difference between the two tests being the lecture unit and intervention
From pre- to post-test, solution type had a significant effect on the score, with the unsaturated solution being the most easily recognized and explained solution type
Students that felt that the YouTube videos greatly increased their concept comprehension, on average, performed better than their counterparts and also saw a greater increase their score from pre- to post-test
ContributorsLinich, Christopher Graham (Author) / Krause, Stephen (Thesis director) / Middleton, James (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
Description
This study looked at college-age students' ability to comprehend and retain information learned from news articles depending on what platform they read from. Fifteen participants read three local New York Times articles on each of the platforms provided: iPad, laptop, and paper. They took one test immediately after to test comprehension and another two weeks later to test their retention. Participants were also asked if they found the articles interesting, enjoyable, clear, etc. Results showed that participants' views on each format had little, if any, affect on their number of correct responses. The most consistent results on the participants' perceptions of the formats came from the laptop and paper, whereas the iPad received a bimodal pattern of responses. Participants were also asked to share their news habits while taking the test by selecting how frequently they gain news from various sources such as social media or television. These habits also seemed to have very little effect on their scores.
ContributorsKillin, Jamie Faye (Author) / Gilpin, Dawn (Thesis director) / Russomanno, Joseph (Committee member) / Dodge, Nancie (Committee member) / Barrett, The Honors College (Contributor) / Walter Cronkite School of Journalism and Mass Communication (Contributor) / School of Art (Contributor)
Created2014-05
Description
This study looked at college-age students' ability to comprehend and retain information learned from news articles depending on what platform they read from. Fifteen participants read three local New York Times articles on each of the platforms provided: iPad, laptop, and paper. They took one test immediately after to test comprehension and another two weeks later to test their retention. Participants were also asked if they found the articles interesting, enjoyable, clear, etc. Results showed that participants' views on each format had little, if any, affect on their number of correct responses. The most consistent results on the participants' perceptions of the formats came from the laptop and paper, whereas the iPad received a bimodal pattern of responses. Participants were also asked to share their news habits while taking the test by selecting how frequently they gain news from various sources such as social media or television. These habits also seemed to have very little effect on their scores.
ContributorsKillin, Jamie Faye (Author) / Gilpin, Dawn (Thesis director) / Russomanno, Joseph (Committee member) / Dodge, Nancie (Committee member) / Barrett, The Honors College (Contributor) / Walter Cronkite School of Journalism and Mass Communication (Contributor) / School of Art (Contributor)
Created2014-05
Description
The premise of the embodied cognition hypothesis is that cognitive processes require emotion, sensory, and motor systems in the brain, rather than using arbitrary symbols divorced from sensorimotor systems. The hypothesis explains many of the mechanisms of mental simulation or imagination and how they facilitate comprehension of concepts. Some forms of embodied processing can be measured using electroencephalography (EEG), in a particular waveform known as the mu rhythm (8-13 Hz) in the sensorimotor cortex of the brain. Power in the mu band is suppressed (or de-synchronized) when an individual performs an action, as well as when the individual imagines performing the action, thus mu suppression measures embodied imagination. An important question however is whether the sensorimotor cortex involvement while reading, as measured by mu suppression, is part of the comprehension of what is read or if it is arises after comprehension has taken place. To answer this question, participants first took the Gates-MacGinitie reading comprehension test. Then, mu-suppression was measured while participants read experimental materials. The degree of mu-suppression while reading verbs correlated .45 with their score on the Gates-MacGinitie test. This correlation strongly suggests that the sensorimotor system involvement while reading action sentences is part of the comprehension process rather than being an aftereffect.
ContributorsMarino, Annette Webb (Author) / Glenberg, Arthur (Thesis director) / Presson, Clark (Committee member) / Blais, Chris (Committee member) / Department of Psychology (Contributor) / Barrett, The Honors College (Contributor)
Created2016-05
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