Optoelectronic devices for power conservation and generation

Energy conservation and generation have become increasingly important in society. Here, we pursue novel transistor technologies based on three-dimensional (3D) FinFETs and two-dimensional (2D) materials to make low power, high speed transistors. We also develop quasi-2D silicon thin film solar cells for power generation. First, a novel approach of doping III-V semiconductors is presented. Oxygen rich silicon oxide (SiO [subscript x], where x > 2) is found to behave as a solid dopant source when deposited on InGaAs, followed by thermal annealing. Oxygen, when diffused into InGaAs, act as n-type dopants where the active carrier concentration reaches up to 1.4 x 10¹⁸ cm³. Besides the simple, CMOS compatible doping technique of solid source doping, another interesting factor is the dopant concentration can be altered by the deposited dopant thickness, which adds an additional control knob therefore allowing enhanced control over the doping process. Thermally induced compressive stress within InGaAs due to the difference in coefficient of thermal expansion (CTE) between InGaAs and SiO [subscript x] is known to increase the number of vacancies within InGaAs therefore giving rise to active dopant concentration. This approach can be used to make high speed, low power transistors. Second, study of thin indium metal contacts on InGaAs is presented. Unlike silicon, III-V compound semiconductors such as InGaAs decomposes around 450 ˚C which result in out-diffusion of indium and gallium and decrease in metal-InGaAs contact resistance. By adding a thin layer of indium between the metal-InGaAs interface, the out-diffusion of gallium was minimized. Third, solar cells based on graphene-silicon (GS) heterojunction architecture are demonstrated on bendable crystalline silicon substrates. Flexible, thin silicon films are fabricated by using the thermal expansion difference between electroplated nickel and bulk silicon, which generates residual strain upon thermal cycling. By controlling the amount of thermal stress, silicon thicknesses between 8 and 35 µm are exfoliated through a kerf-less mechanical method. Together with multi-layer graphene (MLG) grown by chemical vapor deposition (CVD) and atomic layer deposition (ALD) of Al₂O₃ as a silicon passivation layer, power conversion efficiencies (PCE) of 7.4 % were achieved on bendable silicon substrates. Finally, Chapter 7 summarizes the all the chapters from this dissertation and some thoughts for future work.Electrical and Computer Engineerin

Split Catalytic Probes for the Detection of Monkeypox Virus

The COVID-19 outbreak highlighted the important role that diagnostic tests play in the healthcare system. To reduce the impact of infectious disease outbreaks, the development of rapid and cost-effective point-of-care-tests (POCTs) is crucial. With the dissemination of the Monkeypox (Mpox) virus, it became a necessity to produce POCTS that are inexpensive and easy to use. This work explored the construction of two colorimetric assays that aim to detect Mpox genetic signatures. One is based on the split-peroxidase-like deoxyribozyme probes (sPDz), while the other utilizes a cascade system of split RNA-cleaving deoxyribozyme (sDz) and peroxidase-like deoxyribozyme (PDz). Both rely on catalytic probes as well as a G-Quadruplex (G4) structure to facilitate the production of a color change in the presence of the genetic signatures of Mpox. The sPDz probes were initially tested with synthetic genomic fragments of Mpox and other Orthopoxviruses for selectivity purposes. The sPDz probes were then further optimized. The optimal sPDz probes and the sDz/PDz cascade system were tested with an amplified genome fragment of Mpox. The genome fragments were generated by using both symmetric and asymmetric polymerase chain reaction (PCR). With further optimization to increase the signal-to-background ratio, these probes may show promise as an assay that may have the potential to be incorporated to develop POCTs

Potential Applicability of Distributed Ledger to Wireless Networking Technologies

In recent years, the rise of cryptocurrency has received enormous attention around the world. Since a centralized entity (e.g., a bank) is no longer needed for transactions in this currency platform, its potential impact on the financial sector in the future has been examined closely. Apart from the transaction platform itself, the driving technology behind cryptocurrency, namely blockchain, has also kindled huge research interest across different disciplines.This work has been partially funded by the H2020 collaborative Europe/Taiwan research project 5G-CORAL (grant no. 761586)

A Study on Social Overload in SNS: A Perspective of Reactance Theory

After a sizeable growth and propagation of social networking sites (SNS), there has been a decline on its usage. Studies have shown that this decline caused by the overinfluence of SNS on people\u27s life. And people were reacting with a variety of discontinuous behaviors in the service. Prior studies termed this as the SNS fatigue phenomenon and clarified potential factors. However, these studies primarily approached the phenomenon with fatigue as the sole manifest factor. Less attention has been paid on the social features of SNS. In this paper, we view SNS as a social platform; emotion perceived from social features of SNS is an important factor for people to continuously use the service. Based on this view, we employed reactance theory and proposed a reactance model by following two variables; existence of persona non grata and a threat to freedom of usage. Our empirical study on Facebook users (n = 210) revealed that encounter to certain unwelcomed subjects (existence of persona non grata) in the service moderates a social overload. And the social overload acts as a potential antecedent to threat on freedom (trigger of reactance status) to the users of Facebook; ultimately harming the intention for continuation of usage. Implications of research and practice are discussed

Ultrahigh areal number density solid-state on-chip microsupercapacitors via electrohydrodynamic jet printing

Microsupercapacitors (MSCs) have garnered considerable attention as a promising power source for microelectronics and miniaturized portable/wearable devices. However, their practical application has been hindered by the manufacturing complexity and dimensional limits. Here, we develop a new class of ultrahigh areal number density solid-state MSCs (UHD SS-MSCs) on a chip via electrohydrodynamic (EHD) jet printing. This is, to the best of our knowledge, the first study to exploit EHD jet printing in the MSCs. The activated carbon-based electrode inks are EHD jet-printed, creating interdigitated electrodes with fine feature sizes. Subsequently, a drying-free, ultraviolet-cured solid-state gel electrolyte is introduced to ensure electrochemical isolation between the SS-MSCs, enabling dense SS-MSC integration with on-demand (in-series/in-parallel) cell connection on a chip. The resulting on-chip UHD SS-MSCs exhibit exceptional areal number density [36 unit cells integrated on a chip (area = 8.0 mm x 8.2 mm), 54.9 cells cm(-2)] and areal operating voltage (65.9 V cm(-2))

An Edge and Fog Computing Platform for Effective Deployment of 360 Video Applications

This paper has been presented at: Seventh International Workshop on Cloud Technologies and Energy Efficiency in Mobile Communication Networks (CLEEN 2019). How cloudy and green will mobile network and services be? 15 April 2019 - Marrakech, MoroccoIn press / En prensaImmersive video applications based on 360 video streaming require high-bandwidth, high-reliability and lowlatency 5G connectivity but also flexible, low-latency and costeffective computing deployment. This paper proposes a novel solution for decomposing and distributing the end-to-end 360 video streaming service across three computing tiers, namely cloud, edge and constrained fog, in order of proximity to the end user client. The streaming service is aided with an adaptive viewport technique. The proposed solution is based on the H2020 5G-CORAL system architecture using micro-services-based design and a unified orchestration and control across all three tiers based on Fog05. Performance evaluation of the proposed solution shows noticeable reduction in bandwidth consumption, energy consumption, and deployment costs, as compared to a solution where the streaming service is all delivered out of one computing location such as the Cloud.This work has been partially funded by the H2020 collaborative Europe/Taiwan research project 5G-CORAL (grant num. 761586)

X-ray: Discovering DRAM Internal Structure and Error Characteristics by Issuing Memory Commands

The demand for accurate information about the internal structure and characteristics of dynamic random-access memory (DRAM) has been on the rise. Recent studies have explored the structure and characteristics of DRAM to improve processing in memory, enhance reliability, and mitigate a vulnerability known as rowhammer. However, DRAM manufacturers only disclose limited information through official documents, making it difficult to find specific information about actual DRAM devices. This paper presents reliable findings on the internal structure and characteristics of DRAM using activate-induced bitflips (AIBs), retention time test, and row-copy operation. While previous studies have attempted to understand the internal behaviors of DRAM devices, they have only shown results without identifying the causes or have analyzed DRAM modules rather than individual chips. We first uncover the size, structure, and operation of DRAM subarrays and verify our findings on the characteristics of DRAM. Then, we correct misunderstood information related to AIBs and demonstrate experimental results supporting the cause of rowhammer. We expect that the information we uncover about the structure, behavior, and characteristics of DRAM will help future DRAM research.Comment: 4 pages, 7 figure

Exercise and the Risk of Dementia in Patients with Newly Diagnosed Atrial Fibrillation: A Nationwide Population-Based Study

Background: It is unclear whether exercise would reduce dementia in patients with a new diagnosis of atrial fibrillation (AF). Therefore, we aimed to evaluate the association between the change in physical activity (PA) before and after new-onset AF and the risk of incident dementia. Methods: Using the Korean National Health Insurance Service database, we enrolled a total of 126,555 patients with newly diagnosed AF between 2010 and 2016, who underwent health examinations within two years before and after their diagnosis of AF. The patients were divided into four groups: persistent non-exercisers, exercise starters, exercise quitters, and exercise maintainers. Results: Based on a total of 396,503 person-years of follow-up, 5943 patients were diagnosed with dementia. Compared to persistent non-exercisers, exercise starters (adjusted hazard ratio (aHR) 0.87; 95% confidence interval (CI) 0.81–0.94), and exercise maintainers (aHR 0.66; 95% CI 0.61–0.72) showed a lower risk of incident dementia; however, the risk was similar in exercise quitters (aHR 0.98; 95% CI 0.92–1.05) (p-trend < 0.001). There was a J-shaped relationship between the dose of exercise and the risk of dementia, with the risk reduction maximized at 5–6 times per week of moderate-to-vigorous PA among exercise starters. Conclusion: Patients who initiated or continued regular exercise after diagnosis of AF were associated with a lower risk of dementia than persistent non-exercisers, with no risk reduction associated with exercise cessation. Our findings may provide evidence for the benefit of exercise prescription to patients with new-onset AF to prevent incident dementia regardless of their current exercise status

High-performance and scalable metal-chalcogenide semiconductors and devices via chalco-gel routes

We report a general strategy for obtaining high-quality, large-areametal-chalcogenide semiconductor films from precursors combining chelated metal salts with chalcoureas or chalcoamides. Using conventional organic solvents, such precursors enable the expeditious formation of chalco-gels,which are easily transformed into the corresponding highperformance metal-chalcogenide thin films with large, uniform areas. Diverse metal chalcogenides and their alloys (MQx: M = Zn, Cd, In, Sb, Pb; Q = S, Se, Te) are successfully synthesized at relatively low processing temperatures (&amp;lt;400°C). The versatility of this scalable route is demonstrated by the fabrication of large-area thin-film transistors (TFTs), optoelectronic devices, and integrated circuits on a 4-inch Si wafer and 2.5-inch borosilicate glass substrates in ambient air using CdS, CdSe, and In2Se3 active layers. The CdSe TFTs exhibit a maximum field-effect mobility greater than 300 cm2 V-1 s-1 with an on/off current ratio of &amp;gt;107 and good operational stability (threshold voltage shift &amp;lt; 0.5 V at a positive gate bias stress of 10 ks). In addition,metal chalcogenide-based phototransistors with a photodetectivity of &amp;gt;1013 Jones and seven-stage ring oscillators operating at a speed of ∼2.6 MHz (propagation delay of &amp;lt; 27 ns per stage) are demonstrated. © 2018 The Authors.1