Browsing by Subject "Roll-to-roll"
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Item Investigation of a roll-to-roll nanoimprinting process utilizing inkjet based resist deposition(2011-12) Kincaid, Matthew Michael; Sreenivasan, S.V.A high-speed, large-area technique capable of nanopatterning flexible substrates is highly desirable in several applications such as; 1) thin film photovoltaics (TFPV's), 2) flexible electronics, 3) optoelectronics, 4) energy storage devices and 5) biological applications. Flexible substrates are attractive as they can be lower in cost than traditional substrates, and provide the ability to perform continuous processing both of which are valuable for cost sensitive applications such as TFPVs. Also, flexible substrates can conform to non-planar surfaces and therefore provide versatility in applications such as wearable electronics and biomedical devices. In this thesis, a patterning approach known as Jet and Flash Imprint Lithography (J-FIL) is explored for flexible substrates. J-FIL uses inkjets to deposit low-viscosity UV curable polymer materials (resists) that are molded by a template at room temperature and low pressures prior to UV cross-linking. There are inherent advantages to the J-FIL process that lends itself to patterning flexible substrates. The room temperature and low pressure process makes it more compatible with flexible substrates which tend to become dimensionally unstable at elevated temperatures and pressure. The extension of J-FIL to flexible substrates involves the following key challenges: (i) Understanding the level of precision required in roll-to-roll machine systems to ensure that these systems can facilitate imprint and separation of nano-scale features; (ii) The substrate surface should be controlled to initiate and maintain proper interface with the template and avoid formation of bubbles; (iii) The tension in the film should be controlled to ensure that the discrete resist drops are coerced to form a uniform contiguous residual film underneath the patterns; (iv) The fluid filling time - that is representative of the process throughput - should be low; and (v) After UV curing and separation, the nanoscale patterns should not be deformed or damaged. The above challenges were addressed by developing a roll-to-roll test bed to imprint flexible polycarbonate films using the J-FIL process. The test bed has the capability of controllably varying a number of web tension parameters as well as process variables in order to calibrate machine precision and establish control schemes for a robust process. Process metrics such as RLT uniformity, target RLT accuracy, feature filling and feature distortion were measured and quantified. A design of experiments was performed on the test bed for the purposes tuning the process variables as well as developing a model of process performance, with respect to critical process parameters. A two-level design, with three input variables, is utilized in this experimental process. The process yielded blank imprints with mean thickness of 70.5 nm, and a standard deviation of 3.9 nm. The sensitivity of the mean thickness and uniformity to process variables were quantified. The best performing set of input parameters were then used during patterned imprints, to determine if any pattern filling issues or pattern deformation would take place. The patterned imprints, made up of an array of hexagonal pillars (125nm tall, by 240 nm wide, by 450 nm pitch) showed no sign of fluid filling voids, or deformation due to separation. Given this result, the feasibility of implementing J-FIL on a roll-to-roll prototype system was established. A proposed next generation flexible substrate J-FIL tool is presented, along with the expected challenges associated with metrology and dynamic noise. Future work entails the design and qualification of a full scale roll-based imprint tool, capable of meeting throughput metrics established for industrial applications.Item Modeling, design, development, and control of a pilot-scale continuous coating line for proton exchange membrane fuel cell electrode assembly(2012-08) Devaraj, Vikram; Beaman, Joseph J.; Prudhomme, Serge M; Fahrenthold, Eric P; Longoria, Raul G; Meyers, Jeremy PFuel cells are electrochemical energy devices that convert the chemical energy in a fuel into electrical energy. Although they are more efficient, clean, and reliable than fossil fuel combustion systems, they have not been widely adopted because of manufacturing challenges and high production cost. The most expensive component of a fuel cell is the membrane electrode assembly (MEA), which consists of an ionomer membrane coated with catalyst material. Best performing MEAs are currently fabricated by depositing and drying liquid catalyst ink on the membrane, however, this process is limited to individual preparation by hand due to the membrane’s rapid water absorption that leads to shape deformation and coating defects. This work models the swelling and drying phenomena of the membrane and coating during manufacturing, and then applies the results to develop and control a continuous coating line for the production of defect free fuel cell MEAs. A continuous coating line can reduce the costs and time needed to fabricate the MEA, incentivizing the commercialization and widespread adoption of fuel cells. Membrane swelling is a three-dimensional, transient, coupled mass transfer, heat transfer, and solid mechanics problem. Existing models describe the membrane’s behavior in operating conditions, but none predict the behavior during manufacturing. This work develops a novel physics-based model that describes the behavior of the membrane and coating in a continuous manufacturing scenario and incorporates effects that are missing from existing models. A model that can predict wrinkles, the most commonly observed defect during manufacturing, is presented. Simulation results from the above models are used to design and develop an improved continuous MEA coating process that includes pre-swelling and two-stage drying of the coated membrane. A prototype pilot-scale coating line to implement and test the improved coating process is designed and constructed. Finally, a Linear-Quadratic-Gaussian type controller is developed using the physics-based model of the manufacturing process to optimally control the temperature and humidity of the drying zones, and its effectiveness when implemented on the coating line is discussed.Item Simulation of UV nanoimprint lithography on rigid and flexible substrates(2016-12) Jain, Akhilesh; Bonnecaze, R. T. (Roger T.); Sreenivasan, S.V.; Willson, C. Grant; Schunk, P. Randall; Ganesan, VenkatNanoimprint lithography (NIL) is a low cost, high throughput process used to replicate sub-20 nm feature from a patterned template to a rigid or flexible substrate. Various configurations for NIL are analyzed and classified based on type of template and substrate. The steps involved in pattern transfer using roller template based NIL are identified and models to study these steps are proposed. Important process parameters such as maximum web speed possible, required UV intensity, minimum droplet size and pitch and required force on the roller are calculated. The advantages, disadvantages and optimal process window for the different configurations are identified. Droplet spreading is simulated in NIL with rigid substrates in order to study the effect of droplet size, droplet placement error, gas diffusion and template pattern on throughput and defectivity. Square arrangement is found to be the optimum arrangement for achieving minimum throughput. Large droplet-free regions on the substrate edge and error in droplet placement error have significant impact on the throughput. A fluid flow model with average flow permeability is presented to account for flow in the template patterns. Optimum droplet dispensing for multi-patterned templates is achieved by distributing droplet volume according to local filling requirements. Non-fill defects in NIL are classified into pocket, edge and channel defects. A model to predict the size of non-fill defects based on imprint time and droplet size is presented. Defect characterization is presented for various pattern-types. A model is presented to determine the time required for the encapsulated gas to diffuse into the resist. The coupled fluid-structure interaction in NIL with flexible substrate is studied by simulating the web deformation as the droplet spreads on the substrate. It is found that the flexible substrate can be modeled as a membrane due to the lack of rigidity. RLT variation reduces as the number of droplets or the web tension increases. For the magnitude of RLT variation, thinner residual layers require higher web tension. The position of the template on the substrate is important and template positioned at the corner of the substrate is found to provide the least RLT variation.