On-chip probe metrology

The semiconductor market was valued at over $270 billion in 2007, with projections to continue steady growth [7]. Any manufacturing process of this volume is tightly controlled to ensure high efficiency, and improvements are readily sought after. Despite semiconductor fabrication process advancements allowing circuits to contain larger numbers of transistors in smaller package sizes, there has not been any significant change in the way these circuits interface with test systems before packaging. This limitation causes the area overhead occupied by circuit contacts, known as bond pads, to become increasingly costly. To amend the situation, VLSI designers have attempted to reduce bond pads size and pitch as much as possible while retaining reliable probing accuracy [15]. Currently, there is no standard solution to assess the accuracy of probe stations inline with wafer testing. As such, a balance must be struck between overhead cost of large bond pads and operational cost spent analyzing probe performance off-line. A feedback loop on probe card performance during wafer fabrication sort could allow plants to recalibrate probe cards before a yield drop is detected, thus improving yield and saving operational costs [26]. This thesis demonstrates a proof of concept design that offers a viable solution to perform probe metrology in-line with wafer-level circuit testing. A versatile circuit was designed and laid out that promises fine accuracy resolution of 3.21 μm, and fast test time of 1.25 ms per probe

Modelling in vitro dissolution and release of sumatriptan succinate from polyvinylpyrrolidone-based microneedles aided by iontophoresis

A novel dissolving microneedle array system is developed to investigate permeation of a sumatriptan succinate formulations through the skin aided by iontophoresis. Three formulations consisting of hydrophilic, positively charged drug molecules encapsulated in a water-soluble biologically suitable polymer, polyvinylpyrrolidone (PVP), have been accepted by the U.S. Food and Drug Administration (FDA). The microneedle systems are fabricated with 600 pyramid-shaped needles, each 500 µm tall, on a 0.785-cm2 circular array. In vitro transdermal studies with minipig skin and vertical Franz diffusion cells show \u3e 68% permeation of sumatriptan over a 24-hour period. A combination of microneedle and electrical current density ranging from 100 to 500 µA/cm2 using Ag / AgCl electrodes displays increased flux with current density. At 500 µA/cm2, a dissolving array loaded with 4.3 mg sumatriptan leads to a steady-state delivery rate of 490 µg/cm2h with negligible lag time. In theory, a 9.58-cm2 microneedle-array patch loaded with 47.30 mg of sumatriptan succinate could provide the required plasma concentration, 72 ng/ml, for nearly six hours. In parallel, a mathematical model based on first principles is developed to predict the amount of drug delivered into the skin using software (e.g., Mathematica). A system of mass balance equations are derived to simulate the dissolution, diffusion, electromigration and transport of the active ingredient through the epidermis. The analytical approach allows for the evaluation and estimation of the effects of key parameters (i.e., loading dose, polymer concentration, needle height, needle pitch width and current density) on the release profile. The skin layer concentration increases significantly with either increased loading dose or elongated height of the microneedle. The percentage of sumatriptan permeating through skin increased favorably with increased electrical current applied to microneedle patch. An inverse correlation was observed between the pitch width (center to center distance of adjacent needles) and the cumulative amount of sumatriptan permeated into the dermis. Predicted cumulative release data from mathematical model simulations of each of the three formulations were successfully validated with in vitro permeation data administered with Franz cells and minipig skin

Adaptive optics wavefront compensation for solid immersion microscopy in backside imaging

Thesis (Ph.D.)--Boston UniversityThis dissertation concerns advances in high-resolution optical microscopy needed to detect faults in next generation semiconductor chips. In this application, images are made through the chips' back side to avoid opaque interconnect metal layers on the frontside. Near infrared wavelengths are required, since the silicon is relatively transparent at these wavelengths. A significant challenge in this technique is to resolve features as small as 200nm using wavelengths exceeding 1OOOnm. The highest imaging resolution achievable with refractive optics at infrared wavelengths is demonstrated in this dissertation using an aplanatic solid immersion lens (SIL). This is the only method that has been found to be of sufficient resolution to image the next generation of integrated circuits. While the use of an aplanatic solid immersion lens theoretically allows numerical aperture far in excess of conventional microscopy (NASIL ~ 3.5), it also makes the system performance particularly sensitive to aberrations, especially when the samples have thicknesses that are more than a few micrometers thicker or thinner than designed thickness, or when the refractive index of the SIL is slightly different than that of the sample. In the work described here, practical design considerations of the SILs are examined. A SIL-based confocal scanning microscope system is designed and constructed. The aberrations of the system due to thickness uncertainty and material mismatch are simulated using both analytical model and ray-tracing software, and are measured in the SIL experimental apparatus. The dominant aberration for samples with thickness mismatch is found to be spherical aberration. Wavefront errors are compensated by a microelectromechanical systems deformable mirror (MEMS DM) in the optical system's pupil. The controller is implemented either with closed-loop real time sensor feedback or with predictive open-loop estimation of optical aberrations. Different DM control algorithms and aberration compensation techniques are studied and compared. The experimental results agree well with simulation and it has been demonstrated through models and experiments in this work that the stringent sample thickness tolerances previously needed for high numerical aperture SIL microcopy can be relaxed considerably through aberration compensation. Near-diffraction-limited imaging performance has been achieved in most cases that correspond to practical implementation of the technique

Self-Assembling Peptide Nanomaterials: Molecular Dynamics Studies, Computational Designs And Crystal Structure Characterizations

Peptides present complicated three-dimensional folds encoded in primary amino acid sequences of no more than 50 residues, providing cost-effective routes to the development of self-assembling nanomaterials.� The complexity and subtlety of the molecular interactions in such systems make it interesting to study and to understand the fundamental principles that determine the self-assembly of nanostructures and morphologies in solution. Such principles can then be applied to design novel self-assembling nanomaterials of precisely defined local structures and to controllably engineer new advanced functions into the materials. We first report the rational engineering of complementary hydrophobic interactions to control β-fibril type peptide self-assemblies that form hydrogel networks. Complementary to the experimental observations of the two distinct branching morphologies present in the two β-fibril systems that share a similar sequence pattern, we investigated on network branching, hydrogel properties by molecular dynamics simulations to provide a molecular picture of the assemblies. Next, we present the theory-guided computational design of novel peptides that adopt predetermined local nanostructures and symmetries upon solution assembly. Using such an approach, we discovered a non-natural, single peptide tetra-helical motif that can be used as a common building block for distinct predefined material nanostructures. The crystal structure of one designed peptide assembly demonstrates the atomistic match of the motif structure to the prediction, as well as provides fundamental feedback to the methods used to design and evaluate the computationally designed peptide candidates. This study could potentially improve the success rate of future designs of peptide-based self-assembling nanomaterials

Simulation and fabrication of an interposer for electrical testing of fine-pitch wafer-level packages

Master'sMASTER OF ENGINEERIN

Vacuum jacketed umbilical lines technology advancement study. Task 3, sub-task 2 - Vacuum and CO2 jacketed line repair techniques Final technical report

Vacuum jacketed components on launch umbilical tower service arms at Launch Complex 39 - repair techniques for carbon dioxide and vacuum jacketed transfer line

Aerodynamics and interaction of single and multiple jets in rotation

The work contained within the body of this thesis is concerned with the isothermal aerodynamic study of multiple jet systems with special reference to flame interactions. The type of jets used were jets with or without recirculation (swirl) and simple flame interactions were shown to occur for the configurations studied. The main purpose of the study was to show the nature and degree of the aerodynamic interference and to relate these to the factors which govern flame length, stability and combustion intensity. The thesis also contains a study of the turbulence and mean flow characteristics of a swirling jet of variable swirl. The instrument used to measure the mean velocity and turbulence quantities was the hot wire anemometer, and since for the case of a strongly swirling jet each component of the mean velocity and the normal and shear stresses are significant, a technique was evolved capable of separating out each of the 9 individual terms associated with the above, namely ¯u,¯( v), ¯w, ¯(u'v'), ¯(u'w'), ¯(v'w'), ¯(〖u'〗^2 ), ¯(〖v'〗^2 ), ¯(〖w'〗^2 ). The method of analysis is based upon a new velocity voltage relationship which is accurate for all types of probe and/or flow velocity range. Previous methods of analysis were restricted to low turbulence levels where typically the local turbulence intensity (¯(〖u'〗^2 ) ½ / ¯u, ), is not more than 20%. The new method is shown to be valid until the onset of flow reversal which depends upon the type of waveform that the fluctuations in velocity take. The magnitude of the measured quantities are shown to be independent of the type of waveform and assuming that the fluctuations closely resemble a triangular waveform the maximum turbulence levels measurable are 57%