Browsing by Subject "Flexure"
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Item Design of particle mitigating wafer chucks for yield enhancement(2014-08) Westfahl, Andrew Ian; Sreenivasan, S. V.; Crawford, Richard H.As the semiconductor industry drives down the minimum feature size on wafers to increase performance and device density, the necessary site flatness of a standard 26 x 33 mm field becomes much more stringent. A significant unresolved cause for non-planarity is particle contamination at the interface of the wafer substrate and the wafer chuck. The result is an out of plane distortion that can affect a significant portion of the wafer resulting in device yield loss. This research looks at two methods for mitigating the effects of particle contamination. The first method investigates using an in-situ cleaning approach in a wafer chuck to eliminate particles. This concept is called a Particle Eliminating Pin (PEP) chuck. The second method proposes enhancements to a wafer chuck design based on compliant mechanisms resulting in a chuck that is tolerant of particle contamination, referred to here as the enhanced compliant pin chuck (E-CPC). The PEP chuck was explored relative to well-established methods for removing back-side particles and demonstrated it could eliminate an additional 18.5% of particles that could not be removed via the well-established methods. Additional potential effectiveness of a PEP chuck is also discussed based on future improvements. A scaled prototype of the proposed new design of the E-CPC was fabricated and tested as well. The prototype validated most of the proposed improvements but failed to maintain the mechanism’s rotational requirement. With the understanding gained from this design and experimental research a future design of the E-CPC has been proposed in the future research section such that this new design can achieve all the proposed goals while still maintaining the required mechanism rotation.Item Retrofit of deficient lap splice with post-installed anchors(2015-12) Beiter, Katelyn Sean; Bayrak, Oguzhan, 1969-; Hrynyk, Trevor DAs concrete infrastructure ages or is re-purposed, there is an increasing need for efficient retrofit solutions, with deficient lap splices being one of many research areas. A possible method to increase the capacity of deficient lap splices is to use post-installed undercut anchors. These anchors function as active confinement in the splice region, potentially allowing members with inadequate lap splice lengths to reach the required design capacity. The solution presented in this thesis requires access to only one face of the reinforced concrete specimen, which could facilitate implementation on existing structures. However, limited research has been done on the use of post-installed anchors as a retrofit strategy for lap splices, and previous research on the retrofit of deficient lap splices has focused primarily on the use of either carbon fiber or metal jackets. To evaluate the capabilities of this retrofit solution, four large-scale tests on beam specimens have been completed at The University of Texas at Austin. The first specimen tested contained the full lap splice length as required by ACI 318-71 provisions, while in the other three, only half of that lap splice length was provided. The specimen with the full lap splice length was tested as a control specimen and one of the specimens with half the lap splice length was tested without a retrofit to determine baseline behavior. These tests formed the basis to evaluate the effectiveness of the retrofit techniques implemented on the other two specimens. Results from these tests indicated that post-installed anchors could enhance both the strength and ductility of members with deficient lap splices, but the enhanced members demonstrated limited ductility.Item Robust design of selectively compliant flexure-based precision mechanisms(2008-05) Patil, Chinmaya Baburao, 1978-; Sreenivasan, S. V.; Longoria, Raul G.Nano-scale positioning and metrology are at the cutting edge of motion control technology, driven by ever-increasing number of applications, including semiconductor fabrication, data storage, nano-fabrication, biotechnology among others. In this ‘very small range (few µm) and very high precision (few nm) domain’, flexure-based mechanisms are the preferred means for the motion guiding systems, because of several exceptional properties like selective compliance, monolithic design, absence of friction, hysteresis, and wear. However, despite their numerous advantages, their motion characteristics are extremely sensitive to thermal variations, material property variations, machining tolerances among others. The geometric errors induced by machining process variations interact with the mechanism geometry, and lead to parasitic motion in directions other than the mechanism degrees of freedom. These errors cannot be completely eliminated by calibration, as they are coupled with the desired mechanism motion. This thesis focuses on the problem of parasitic motion in flexure based precision compliant mechanisms in the presence of geometric errors induced by machining tolerances. A spatial kinematics approach based on screw systems is used to model the compliance of the flexure mechanisms. The geometric errors induced by machining tolerances are systematically included in the modeling. The model not only determines the complete spatial motion of flexure mechanisms, but also provides geometric insight into the parasitic motion problem, which leads to decoupling of error motions into intrinsic and extrinsic parasitic motion. The intrinsic error motion is shown to be tied to the mechanism motion, and cannot be corrected by calibration. A metric to quantify the intrinsic error motion is obtained for both rotational and translational degree of freedom systems, and is used to define the precision capability of the flexure mechanisms. The model is used to formulate an optimization problem that aims to minimize the intrinsic parasitic motion metric by optimal joint compliance design. The stochastic optimization problem is solved numerically for both rotational and translational flexure mechanisms with one degree of freedom. A test setup is developed to characterize the pitch of screw motion of a one degree of freedom rotational flexure mechanism. The experimental results validate the existence of intrinsic parasitic motion. The setup demonstrates the metrology capability required for parasitic motion characterization, and forms a preliminary prototype for a quality control station for evaluating precision capability of flexure mechanisms. Significant contributions from the proposed work include, (1) complete mathematical and geometric interpretation of parasitic motion of flexure mechanisms due to machining tolerances, (2) formulation and solution of the flexure mechanism joint compliance robust design problem applied to rotational and translational one degree of freedom mechanisms, (3) development of an experimental setup to characterize the spatial parasitic motion of one DOF rotational flexure mechanism, that forms the basis of a modular quality control station in a ‘test-and-select’ approach for precision flexure-based compliant mechanisms.Item The effects of lateral tectonics on a fluvio-deltaic system : an application to the Ganges Brahmaputra Delta(2013-05) Kopp, Jessica Ann; Kim, Wonsuck; Mohrig, David; Hickson, ThomasDeltaic systems have long been recognized for their socioeconomic impacts as well as their high potential to trap and store hydrocarbons. The Sediment Transport and Earth-surface Process (STEP) basin at the University of Texas at Austin has the ability to create large 3D physical experiments, designed for nurturing new understanding of these systems and the parameters that influence their evolution. We explored how a laterally tilting basin influenced a prograding fluvio-deltaic system. The tilting occurs along a rotational axis, bisecting the model’s basement and allowing the delta to experience uplift in one half of basin and subsidence in the opposite half. After six experiments with a range of tilting rates, we observed that varying rates of tilting changed progradation patterns as well as the resultant stratigraphy. The tectonic tilting forced a continuous change in topset slope, which accounts for the evolving behavior of the fluvial system with regards to channel occupation and thus shoreline asymmetry. When slow tilting was applied, the delta advanced faster in the direction of uplift due to the relative decline in basin water depth. This created truncated stratigraphic intervals dominated by active channel cut and fill with thin but laterally linked channel bodies depositing finer material. Behavior was significantly different on the subsidence side of the delta; shoreline migration was stunted while the delta became primarily aggradational, depositing thicker, alternating packages of sands. During higher rates of tilting, deposition at the uplift end was quickly abandoned and instead focused on stacking conformable sequences of delta lobes in the area of increased subsidence, resulting in a complete lack of progradation in any direction. Progressively greater rates of tilting yielded more dramatic steering of channelized flow toward the area of greatest subsidence. Comparing characteristic tectonic and channel timescales proves to be a good predictor of shoreline symmetry along with sediment distribution due to differential subsidence. In this study, we tested the hypothesis that differential subsidence acting on the Ganges-Brahmaputra (G-B) system is responsible for delta asymmetry. The asymmetry in planform shoreline geometry and subsurface stratigraphy of the G-B delta system are extensively similar to the experimental results.