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Browsing by Subject "flexible electronics"

Now showing 1 - 3 of 3
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    New Approaches for Printed Electronics Manufacturing
    (2015-09) Mahajan, Ankit
    In printed electronics, electronic inks are patterned onto flexible substrates using roll-to-roll (R2R) compatible graphic printing methods. For applications where large-area, conformal electronics are necessary, printed electronics holds a competitive advantage over rigid, semiconductor circuitry, which does not scale efficiently to large areas. However, in order to fully realize the true potential of printed electronics, several manufacturing hurdles need to be overcome. Firstly, minimum feature sizes produced by graphic printing methods are typically greater than 25 µm, which is at least an order of magnitude higher for dense, high performing electronics. In this thesis, conductive features down to 1.5 µm are demonstrated using a novel inkjet printing-based process. Secondly, high-resolution printed conductors usually have poor current-carrying capacity, especially for longer wires in large-area applications. This thesis explores the fundamentals of aerosol-jet printing and reveals the regime for printing high-resolution lines with excellent current carrying capacity. Additionally, a novel manufacturing process is demonstrated, which can process 2.5 µm wide conductive wires with linear resistances as small as 5 Ω mm-1. Another challenge for printed electronics manufacturing is to deal with topography produced on the substrate surface by printed features. Besides complicating the subsequent use of contact-printing methods, surface topography is a source of poor device yields as well. This thesis describes two novel methodologies of creating topography-free printed surfaces. In the first method, nanometer-level smooth, planarized silver lines are obtained using a transfer printing approach. In the second method, open microchannels, imprinted in plastic substrates, are filled with a controlled amount of metal using liquid-based additive processes, to obtain conductive wires flush with the substrate surface. Finally, this thesis addresses the issue of overlay alignment, which is the most significant challenge of printed electronics manufacturing. Multi-layered electronic devices require alignment of multiple layers of different materials with micron-level tolerances, which is a daunting task to accomplish on deformable, moving substrates in R2R production formats. This thesis describes a novel, self-aligned manufacturing strategy for printed electronics that relies on capillary flow of inkjet-printed inks within open micro-channels. Multi-level trench networks, pre-engineered on the substrate surface, are sequentially filled with different inks which, upon drying, form stacked layers of electronic materials. Using this approach, fully self-aligned fabrication of all the major building blocks of an integrated circuit is demonstrated. Overall, this thesis presents several new manufacturing avenues for realizing high-performing and dense electronics on plastic by R2R processing.
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    Photonic Curing Solution-Processed Metal Oxide Semiconductor Thin-Film Transistors
    (2021) Weidling, Adam
    Metal oxide semiconductors such as InGaZnO and its derivatives are a promising group of materials with high mobility, low cost, and optical transparency. As the development of flexible electronics continues, these materials have several advantages for thin-film transistors over amorphous silicon such as high field effect mobility, and the ease of synthesis and deposition. The ability to create high-quality semiconductor materials compatible with low-temperature processing has been an emerging area of research over the past few decades. This research has included alternative synthesis routes, processing methods, and substrate materials. The ability to develop high-quality flexible devices has vast societal impact in leisure with applications such as next generation flexible displays, as well as in conformal medical devices for health monitoring. In this work, photonic curing is introduced as a method to rapidly and efficiently create high-quality thin-film transistors. This work addresses the importance of material parameters on the transient curing response and design guidelines for developing high-quality devices. Photonic cured metal oxide TFTs were compared with a thermally annealed baseline to study the TFT performance and chemical composition. Despite the short time scale in which the photonic curing process operates over, the photonic cured devices had a higher field effect mobility than the thermally annealed devices having mobilities of 21.8 cm^2V^-1s^-1 and 17.1 cm^2V^-1s^-1 respectively. A 3D model was developed to simulated the photonic curing process and to explore the impact of different materials and device layouts on the thermal profiles. The development of a robust fabrication platform for flexible electronics has been a challenge in the development of higher-complexity flexible circuits. To overcome this, a robust photonic lift-off process using a light absorber layer was developed using a low-CTE polymer. The large area and uniformity of the lamp energy allows for rapid and large area polymer delamination. In addition to providing a robust platform for fabrication, this process allows for fully-photonic processed fabrication including both semiconductor processing and substrate lift-off. The ability to use photonic curing for both semiconductor processing and polymer delamination allows for process times to be greatly reduced, and provides a new pathway towards fabricating next-generation high-performance flexible electronics.
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    Printed electrolyte-gated transistors and circuits for flexible electronics
    (2013-04) Ha, Mingjing
    Printed electronics has broad potential applications due to its low fabrication cost, compatibility with flexible substrates, and its suitability for applications where large footprints are required. However, the supply voltages of printed circuits are high in general due to limitations of both the electronic properties of printable materials and the coarse dimensions of printed transistors. This thesis aims to demonstrate low-voltage operation of printed circuits by employing a printable electrolyte, a so-called ion gel, with very large specific capacitance (on the order of μF/cm2) as the gate insulator. Ion gels are composites formed by the self-assembly of triblock copolymers, e.g. poly(styrene-b-methyl methacrylate-b-styrene) (PS-PMMA-PS), in an ionic liquid, e.g. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMI][TFSA]). These ion gels and other functional materials, such as semiconductors and conductive polymers were fabricated by aerosol jet printing to form electrolyte-gated transistors (EGTs) and circuits on plastic substrates. This thesis demonstrates that these printed devices can achieve low-voltage operation, fast switching speed, remarkable operational stability, and can realize electronic functions of logic gates, capacitor, electrochromic device, etc. To explore the trade-off between supply voltage and switching speed, this thesis studied EGTs consisted of high capacitance ion gel and high mobility carbon nanotubes (CNTs), which together enable the fast switching speed at low voltages. The CNT EGTs were ambipolar and could be used to make complimentary-like inverters and circuits. Five-stage ring oscillators printed on flexible substrate achieved above 2 kHz frequency, corresponding to less than 50 μs delay time. The impact of key parameters on delay times were studied, including the EGT channel length, ionic conductivity of the ion gel, parasitic capacitance and resistance. With these understandings, the architecture of EGT was optimized, and ring oscillators with stage delay as short as 1.2 μs time was successfully demonstrated at voltages < 3 V. These results represent a significant improvement in the performance of printed electronics. Fabrication and characterization of inverters and NAND gates, device operational stability and power consumption were also discussed. To demonstrate integration of EGTs, a flexible circuit with 23 EGTs, 12 capacitors, 20 resistors and an electrochromic (EC) display pixel operates at a voltage as low as 1 V was fabricated on plastic substrates. All of the key components were aerosol jet printed from liquid inks, such as the ion gel, poly (3-hexylthiophene) (P3HT), a semiconductor, and the conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Characteristics and operation mechanisms of each device were discussed respectively. The circuit operated continuously for 100 min with no degradation. Overall, this thesis demonstrates that high reproducibility of device fabrication is possible and that EGTs may be used to achieve conventional electronic function at low voltage on plastics.