Browsing by Subject "Printed Electronics"

Now showing 1 - 4 of 4
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    Enhancement of the Dynamic Performance of Electrolyte-Gated Transistors: Toward Fast-Switching, Low-Operating Voltage Printed Electronics
    (2019-06) Zare Bidoky, Fazel
    A transistor is an electrical circuit element which acts as a switch, can tune the current in an electrical circuit, and can amplify input signals. Fast switching with low-operating voltage and high amplification are desired characteristics for transistors but are not readily achieved by printed electronics. Electrolyte-gated transistors (EGTs) are a specific class of transistors with an electrolyte as the gate dielectric. Using electrolyte as the gate dielectric enables low-operating voltage, high amplification (gain), and relaxed fabrication requirements. Electrolytes have a huge capacitance which is thickness independent thanks to the formation of electrical double layers (EDL) at the interfaces of the electrolyte with the electrodes. Ion gel is a type of electrolyte consisting of an ionic liquid and a triblock copolymer. The polymer is responsible for providing mechanical integrity, whereas the ionic liquid is responsible for the gating mechanism with great electrical, physical, chemical, and electrochemical properties. Ion gels pave the way for miniaturizing EGTs and their use in printed electronics. Despite all the promising properties of printed EGTs including low-operating voltage, ease of printing, flexibility, and low-toxicity, fast EGTs have not yet been demonstrated. Similarly, higher EGT gain is also required to improve the sensitivity and computational power of devices. In this thesis, the EGT working principles have been investigated, as well as the effects of EGT architectures, materials, components, printing resolution, and precision on the EGT operating speed and gain. New architectures have been designed to produce fast and high-performance EGTs. Modification of EGT architectures and components enabled us to achieve 5 MHz operation with an order of magnitude increase in gain and amplification. In order to fabricate different architectures, a variety of techniques including inkjet, aerosol-jet, and screen printing have been employed. Screen-printed, UV-cured ion gels with a line width resolution of 10 µm have been demonstrated. In conclusion, in this thesis, the performance of printed ion gel-based electrolyte-gated transistors has been investigated and improved by relating the device dynamic and static characteristics to its material components and architecture.
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    Label-Free, Microfluidic Biosensors with Printed, Floating-Gate Transistors
    (2017-12) White, Scott
    Printed electronics and microfluidics are two emerging and developing technologies with the common attractive feature of scalability. Advancements in fabrication capabilities have evolved research questions from, “What can we build?” to, “What should we build?”. This work focuses on the combination of these two technologies and their application to biosensing. The motivating theme is to understand how integrated, functional materials interact, elucidate the underlying molecular phenomena, then utilize the emergent advantages to address the outstanding limitations of conventional biosensing strategies. Printed electronics have recently been applied to biological detection with a variety of techniques1 while microfluidics, since their inception, have been used to handle biological fluids.2 The work presented here outlines a patented sensing strategy based off Floating-Gate Transistors (FGTs). The FGT design physically separates the electronic materials and biological fluids and thus bypasses various compatibility obstacles limiting other next-generation sensor technologies.3 The specific changes in interfacial properties that lead to robust signal transduction are derived empirically.4 This is followed by a mechanistic investigation into the molecular origin of sensor operation when FGTs are used in biomolecular detection. Finally, the versatility and scalability engendered by facile prototyping of FGTs is exemplified by successful iterations to DNA,3 ricin,5 and gluten proteins. The first proof-of-principle experiments incorporated printed electronics with an elementary biological system of DNA oligonucleotides. The results successfully demonstrated the potential of FGTs but failed to solidify their concrete value. Systematic investigation into the complex dynamics at the interface of chemically functionalized electrodes and electrolytes uncovered the most attractive features of the FGT technology. The chemistry was tuned with molecules that range in complexity from simple, short-chain alkyl-thiols to reversible protein-protein interactions. The observed responses with well-controlled systems were generalized to real systems like protein capture in food matrices (e.g. ricin in milk, orange juice). The resulting versatility originated from the label-free, electronic sensing mechanism and opened a range of possibilities for FGTs’ impact. The fundamental insights into interfacial dynamics, device operation, and biomolecular interactions were made possible by the advancements in the materials science and fabrication techniques underlying the presented results. Future avenues of development are hypothesized along with the most promising strategies. The continued elucidation of the physical mechanism and engineering upgrades justify the proposed strategies and inspire the continued effort to fully realize the potential of FGT biosensors.
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    The Optimization and Development of Additive Manufacturing Strategies for High Performance Printed Electronics and Metal Interconnects
    (2021-11) Jochem, Krystopher
    Additive manufacturing strategies, including printing, provide tremendous potential to manufacture low-cost, high-performance electronic devices. While printed electronics have been prepared by a variety of traditional printing strategies including gravure and inkjet printing, these techniques face limitations including low lateral resolution and aspect ratio (feature height/feature width) and difficulty aligning multiple layers of functional materials to build complex electronic devices including diodes and transistors. Previous research in the Francis and Frisbie research groups at the University of Minnesota led to the development of the SCALE (Self-aligned Capillarity-Assisted Lithography for Electronics) process to address these limitations. This process combines high resolution UV micro imprinting of capillary channels and connected ink receiving reservoirs with inkjet printing of electrically functional inks into the reservoirs and spontaneous capillary flow which fills the connected capillary channels with the inks. By creating networks of carefully positioned capillary channels, the complex structures of electronic devices are deposited with higher resolution and layer-to-layer positioning accuracy than achieved with conventional printing methods. These strategies are fully compatible with roll-to-roll production, but this capability hadn’t been demonstrated prior to this work. In this dissertation, a process for roll-to-roll production of the plastic substrates patterned with SCALE capillary channels and reservoirs was developed using low-cost, roll-based imprinting stamps and common sources of air entrapment defects were identified and addressed. Low resistance, high precision metal interconnects were developed and optimized using these patterned plastic substrates. Variables affecting the conductor uniformity, flexibility, and reproducibility were identified and optimized to maximize the useful length and electrical performance of the conductors. This resulted in a fully roll-to-roll compatible manufacturing process for low resistance, flexible metal interconnects. A new, two level capillary channel geometry was developed for conductor fabrication to allow the production of solid metal conductors with flat tops, aspect ratios near 2, and precise feature edges, embedded in the plastic substrates. Finally, a roll-to-roll inkjet printing process was developed for full continuous manufacturing of SCALE devices, and silver SCALE conductors were prepared using this continuous process. This work develops strategies for full roll-to-roll production of SCALE devices and high-performance metal interconnects on patterned plastic substrates.
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    Polymer-Based Ion Gels as a Versatile Platform of Solid Electrolytes
    (2018-07) Tang, Boxin
    Ion gels are a versatile class of functional materials. Combining the excellent electrical properties such as high ionic conductivity and capacitance of the ionic liquid (IL) and the mechanical integrity of the polymer, the composite materials have led to a variety of applications such as electrolyte-gated transistors (EGTs), electroluminescent, and electrochromic soft materials. This thesis is built up from previous research on the electrical and mechanical properties of the ABA triblock polymer-based ion gels and continues to improve properties of the materials for electrochemical device applications. In the first part of the thesis work, the objective is to improve the existing ABA triblock polymer systems with poly(ethylene oxide) (PEO) or poly(methyl methacrylate) (PMMA) as the IL-solvating midblock by combining the merit of the low Tg from PEO and hydrophobicity from PMMA into one system. As a result, poly(styrene-b-ethyl acrylate-b-styrene) (SEAS) triblock polymer was developed. The ion gels made with SEAS demonstrate similarly high ionic conductivity as the PEO-based ion gels, which are significantly improved from those of the PMMA-based ion gels. By shortening the midblock size of the triblock polymer, a synergistic improvement of both the ionic conductivity and the modulus can be achieved. Additionally, the EGTs made by SEAS-based ion gels demonstrate superior stability under humidity compared with EGTs made by SOS-based ion gels. In the following two projects of the thesis work, the polymer platform changes from petroleum-based polymers with hydrocarbon backbones to renewable aliphatic polyesters with the potential aim of EGTs in biocompatible applications. To achieve the ion gels, both physical and chemical crosslinked-systems have been explored. The physically crosslinked ABA aliphatic polyester triblock ion gels demonstrate good mechanical integrity and can be successfully printed under similar conditions as the previous systems, and demonstrate improved ionic conductivity from the PMMA-based ion gels. In addition, the resulting ion gels also demonstrate efficient hydrolytic degradation under basic condition. In a different approach, chemically crosslinked poly(lactide) (PLA)-based ion gels can be synthesized from a facile one-pot method. Owing to a smaller volume fraction in ion-insulating domain, the ion gel demonstrates an excellent ionic conductivity at low polymer concentration. Meanwhile, the ion gel also possesses a high toughness owing to the chemical crosslinks. The thin chemically crosslinked PLA-ion gels can be laminated onto EGTs via a cut-and-stick method. On the other hand, the bulk ion gel demonstrates a good electromechanical response with high electromechanical sensitivity with the applied strain and a low hysteresis between stretching and unstretching.