arXiv subjects

Utkarsh Jain

Publications and source records attributed to Utkarsh Jain.

7 recordsLinked to original sources

arXiv2026

Low Distortion Fusion Bonding using Pneumatically Warped Wafers

Backside power-delivery-network (BSPDN) schemes require wafer-to-wafer bonding steps that do not leave high order shape changes or localized stresses in the bonded stack to ensure that these don't get transferred to the thinned wafer for further lithographic exposure. However, bonding mechanics involve strong adhesive forces which can inherently create localized distortions that lithography tools must eventually compensate. Some contributors to grid distortion of the target wafer are, method of bond initiation, bond front velocity variations, and lack of symmetry between the wafers. In this work, we evaluate a low-distortion bonding approach in the SUSS XBA tool, where some of these contributors are tackled at the source, namely by initiating the bond without a localized external force, and keeping the wafers compliant & symmetric during bonding. Wafers are bonded with a slight pre-stress due to controlled gas pressure applied over the whole backside of the wafers throughout bonding. Wafer-shape measurements of the bonded stacks are used to perform gradient-based in-plane-displacements (IPD) modelling to estimate bonding-induced grid distortion. Dense scanner metrology is used on patterned-bonded wafers to confirm the location and severity of distortion predictions from patterned wafer geometry (PWG) measurements. On the PWG distortion maps and scanner grid readouts, we perform alignment and CPE modelling with different field layouts. Sub-10 nm levels of residual grid distortion are achievable with relatively low-order correction models, and less than or equal to 3 nm by using advanced CPE models. These results demonstrate that pneumatically warped bonding yields low-distortion bonded stacks, and that simple process tuning can decouple the dominant distortion source from edge-related variability.

physics.app-ph↗

arXiv2022

Controlled and impulsive compression of an entrapped air bubble during impact

Wave slamming onto a structure is often accompanied by the entrapment of an air pocket. A large scale impact typically has a rapidly evolving and disturbed liquid-gas interface, such that several bubbles are entrapped upon impact. While it is largely understood how the peak pressure is created by liquid coming into contact with the solid structure, it is more challenging to ascertain how an isolated air pocket is pressurised by an impulsive impact, and how the maximum impact pressure inside this bubble evolves. We study such a Bagnold-type impulsive compression of an air bubble by performing well-controlled experiments, where we use an inverted, hollow cone as an impactor. The cone is kept immersed throughout in a water bath, such that it encloses an air bubble of known and controlled volume. A high-sensitivity sensor measures pressures at the vertex of the cone. Using high-speed imaging we show how incoming liquid deforms the air bubble enclosed in such a geometry, and how an impact peak is registered inside the bubble, which can be traced back to the impact of a liquid jet onto the pressure sensor. We compare the measured pressures to a Bagnold model, and discuss the dominant resonances in the bubble. From visualisations of the deforming bubble, we also discuss the air-pocket's deformations, resulting from the presence of surrounding rigid geometry (such as corrugations in an LNG containment membrane).

physics.flu-dyn↗

arXiv2021

Air-cushioning effect and Kelvin-Helmholtz instability before the slamming of a disk on water

The macroscopic dynamics of a droplet impacting a solid is crucially determined by the intricate air dynamics occurring at the vanishingly small length scale between droplet and substrate prior to direct contact. Here we investigate the inverse problem, namely the role of air for the impact of a horizontal flat disk onto a liquid surface, and find an equally significant effect. Using an in-house experimental technique, we measure the free surface deflections just before impact, with a precision of a few micrometers. Whereas stagnation pressure pushes down the surface in the center, we observe a lift-up under the edge of the disk, which sets in at a later stage, and which we show to be consistent with a Kelvin-Helmholtz instability of the water-air interface.

physics.flu-dyn↗

arXiv2020

Air Entrapment and its effect on Pressure Impulses in the slamming of a Flat Disc on Water

The presence of ambient air in liquid-slamming events plays a crucial role in influencing the shape of the liquid surface prior to the impact, and the distribution of loads created upon impact. We study the effect of trapped air on impact loads in a simplified geometry, by slamming a horizontal flat disc onto a stationary water bath at a well-controlled velocity. We show how air trapping influences pressure peaks at different radial locations on the disc, how the pressure impulses are affected, and how local pressure impulses differ from those obtained from area-integrated (force) impulses at impact. More specifically, we find that the air layer causes a gradual buildup of the load before the peak value is reached, and show that this buildup follows inertial scaling. Further, the same localised pressure impulse at the disc centre are found to be lower than the corresponding (area-integrated) force impulse on the entire disc. While the (area-integrated) force impulses are close to the classical result of Batchelor (1967, section 6.10) and Glasheen & McMahon (1996), the localised pressure impulses at disc center, where the trapped air layer is at its thickest, are found to lie closer to the theoretical estimation by Peters et al. (2013) for an air-cushioned impact.

physics.flu-dyn↗

arXiv2020

On wedge-slamming pressures

The water entry of a wedge has become a model test in marine and naval engineering research. Wagner theory, originating in 1932, predicts impact pressures, and accounts for contributions to the total pressure arising from various flow domains in the vicinity of the wetting region on the wedge. Here we study the slamming of a wedge and a cone at a constant, well-controlled velocity throughout the impact event using high fidelity sensors. Pressures at two locations on the impactor are measured during and after impact. Pressure time series from the two impactors are discussed using inertial pressure and time scales. The non-dimensionalised pressure time series are compared to sensor-integrated averaged composite Wagner solutions (Zhao & Faltinsen 1993), Logvinovich (1969, 4.7), modified Logvinovich (Korobkin & Malenica 2005) and generalised Wagner models (Korobkin 2004). In addition, we provide an independent experimental justification of approximations made in the literature in extending the Wagner model to three-dimensions. The second part of the paper deals with pre-impact air cushioning -- an important concern since it is responsible for determining the thickness of air layer trapped upon impact. Using a custom-made technique we measure the air-water interface dynamics as it responds to the build up of pressure in the air layer intervening in between the impactor and the free surface. We show both experimentally and using two-fluid boundary integral (BI) simulations, that the pre-impact deflection of the interface due to air-cushioning is fully described by potential flow.

physics.flu-dyn↗

arXiv2020

Total-internal-reflection deflectometry for measuring small deflections of a fluid surface

We describe a method that uses total internal reflection at the water-air interface inside a large, transparent tank, to measure the interface's deflections. Using this configuration, we obtain an optical set-up where the liquid surface acts as a deformable mirror. The set-up is shown to be extremely sensitive to very small disturbances of the reflecting water surface, which are detected by means of visualising the reflections of a reference pattern. When the water surface is deformed, it reflects a distorted image of the reference pattern, similar to a synthetic Schlieren set-up. The distortions of the pattern are analysed using a suitable image correlation method. The displacement fields thus obtained correlate to the local spatial gradients of the water surface. The gradient fields are integrated in a least-squares sense to obtain a full instantaneous reconstruction of the water surface. This method is particularly useful when a solid object is placed just above water surface, whose presence makes the liquid surface otherwise optically inaccessible.

physics.flu-dyn↗

arXiv2017

On curing silicone elastomers with a plasticising solvent

There is a growing interest in producing materials with mechanical behaviours similar to those of internal organs. An artificial tissue may be expected to experience several types of compressive and shear deformation in the course of normal usage. Thus research into mechanical modelling of these types of materials which behave similar to biological tissues, or can be used in making implants, is of importance to understand their usability and performance when subjected to different types of stresses. Here we study the behaviour of plasticised silicone elastomers and comment on the feasibility for modelling the behaviour of tissues. We perform compression tests on samples made of a silicone elastomer which is diluted with (plasticiser) silicone oil in the cross-linking stage. We show that the modification of material broadly follows a simple law of mixtures. Further, we use samples with a specific periodic structure which has neatly separated behavioural regimes under compression where it first extends outwards and then undergoes internal buckling. In terms of material behaviour, this results in two neatly separated regimes where the deformation is averaged throughout the length in the first regime, and highly localised in the later regime. This allows us to disentangle the two types of deformations (simple compression and shear of the same material) and study how the recovery of the material upon re-crosslinking, if any, affects its elastic properties.

physics.app-ph↗