Browsing by Subject "Inkjet"
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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 Jet and coat of adaptive sustainable thin films(2012-08) Singhal, Shrawan; Sreenivasan, S. V.Deposition of nanoscale thickness films is ubiquitous in micro- and nano-scale device manufacturing. Current techniques such as spin-coating and chemical vapor deposition are designed to create only uniform thin films, and can be wasteful in material consumption. They lack the ability to adaptively prescribe desired film thickness profiles. This dissertation presents a novel inkjet-based zero-waste polymer deposition process referred to as Jet and Coat of Adaptive Sustainable Thin Films or J-CAST. The core of this process is built on an experimentally validated multi-scale fluid evolution model, based on extensions of lubrication theory. This model involves a nano-scale fluid film sandwiched between two flat plates: a compliant superstrate and a rigid substrate, with spatial topography on both surfaces. Accounting for the flexural elasticity of the compliant superstrate, and describing the temporal evolution of the fluid film in the presence of different boundary conditions reveals that instead of seeking process equilibrium, non-equilibrium transients should be exploited to guide film deposition. This forms the first core concept behind the process. This concept also enables robust full-wafer processes for creation of uniform films as well as nanoscale films with prescribed variation of thickness at mm-scale spatial wavelengths. The use of inkjets enables zero-waste adaptive material deposition with the preferred drop volumes and locations obtained from an inverse optimization formulation. This forms the second core concept behind the process. The optimization is based on the prescribed film thickness profile and typically involves >100,000 integer parameters. Using simplifying approximations for the same, three specific applications have been discussed - gradient surfaces in combinatorial materials science and research, elliptical profiles with ~10km radius of curvature for X-ray nanoscopy applications and polishing of starting wafer surfaces for mitigation of existing nanotopography. In addition, the potential of extending the demonstrated process to high throughput roll-roll systems has also been mentioned by modifying the model to incorporate the compliance of the substrate along with that of the superstrate.