Sn-based solder alloys are extensively used in electronic devices to form interconnects between different components to provide mechanical support and electrical path. The formation of a reliable solder interconnects fundamentally relies on the metallurgic reaction between the molten solder and solid pad metallization in reflowing. The resultant IMC layer at the solder/pad metallization interface can grow continuously during service or aging at an elevated temperature, uplifting the proportion of IMCs in the entire solder joint. However, the essential mechanical properties of interfacial IMC (i.e. Cu6Sn5, Cu3Sn) layers, such as Young s modulus and hardness, are drastically different in comparison with Sn-based solder and substrate. Therefore, the increasing fraction of interfacial IMCs in the solder joint can lead to significant deformation incompatibility under exterior load, which becomes an important reliability concern in the uses of solder joints for electronic interconnects. In the past decades, extensive research works were implemented and reported regarding the growth of interfacial IMC layers and its effect on the mechanical integrity of solder joints. But, the following fundamental issues in terms of mechanical and microstructural evolution in the uses of solder joints still remain unclear, demanding further research to elaborate: (1) The protrusion of IMCs: Though the growth of interfacial IMC layers along the diffusion direction in solder joints were studied extensively, the growth of IMCs perpendicular to the diffusion direction were reported in only a few papers without any further detailed investigation. This phenomena can crucially govern the long-term reliability of solder interconnects, in particular, in the applications that require a robust microstructural integrity from a solder joint. (2) Fracture behaviour of interfacial IMC layers: The fracture behaviour of interfacial IMC layers is a vital factor in determining the failure mechanism of solder joints, but this was scarcely investigated due to numerous challenges to enable a potential in-situ micro-scale tests. It is therefore highly imperative to carry out such study in order to reveal the fracture behaviour of interfacial IMC layers which can eventually provide better understanding of the influence of interfacial IMC layers on the mechanical integrity of solder joints. (3) Volume shrinkage: The volume shrinkage (or solder joint collapse) induced by the growth of interfacial IMC layers was frequently ascribed as one of the main causes of the degradation of mechanical reliability during aging due to the potentially resulted voids and residual stress at the solder/substrate interface. However, very few experimental works on the characterisation of such type of volume shrinkage can be found in literatures, primarily due to the difficulties of observing the small dimensional changes that can be encountered in the course of IMCs growth. (4) Residual stress: The residual stress within solder joints is another key factor that contributes to the failure of solder joints under external loads. However, the stress evolution in solder joints as aging progresses and the potential correlation between the residual stress and the growth of interfacial IMC layers is yet to be fully understood, as stress/strain status can fundamentally alter the course of total failure of a solder joint. (5) Crack initiation and propagation in solder joints: Modelling on the mechanical behaviour of solder joints is often undertaken primarily on the stress distribution within solder joints, for instance, under a given external loading. But there is lack of utilising numerical analysis to simulate the crack initiation and propagation within solder joints, thus the effect of interfacial IMC layers on the fracture behaviour of the solder joints can be elaborated in further details. In this thesis, the growth of interfacial IMCs in parallel and perpendicular to the interdiffusion direction in the Sn99Cu1/Cu solder joints after aging was investigated and followed by observation with SEM, with an intention of correlating the growth of IMCs along these two directions with aging durations based on the measured thickness of IMC layer and height of perpendicular IMCs. The mechanism of the protrusion of IMCs and the mutual effect between the growth of IMCs along these two directions was also discussed. The tensile fracture behaviour of interfacial Cu6Sn5 and Cu3Sn layers at the Sn99Cu1/Cu interface was characterised by implementing cantilever bending tests on micro Cu6Sn5 and Cu3Sn pillars prepared by focused ion beam (FIB). The fracture stress and strain were evaluated by finite element modelling using Abaqus. The tensile fracture mechanism of both Cu6Sn5 and Cu3Sn can then be proposed and discussed based on the observed fracture surface of the micro IMC pillars. The volume shrinkage of solder joints induced by the growth of interfacial IMC layers in parallel to the interdiffusion direction in solder joint was also studied by specifically designed specimens, to enable the collapse of the solder joint to be estimated by surface profiling with Zygo Newview after increased durations of aging. Finite element modelling was also carried out to understand the residual stress potentially induced due to the volume shrinkage. The volume shrinkage in solder joints is likely to be subjected to the constraint from both the attached solder and substrate, which can lead to the build-up of residual stress at the solder/Cu interface. Depth-controlled nanoindentation tests were therefore carried out in the Sn99Cu1 solder, interfacial Cu6Sn5 layer, Cu3Sn layer and Cu with Vickers indenter after aging. The residual stress was then evaluated in the correlation with aging durations, different interlayers and the locations in the solder joint. Finally, finite element models incorporated with factors that may contribute to the failure of solder joints, including microstructure of solder joints, residual stress and the fracture of interfacial IMC, were built using Abaqus to reveal the effect of these factors on the fracture behaviour of solder joints under applied load. The effect of growth of IMC layer during aging on the fracture behaviour was then discussed to provide a better understanding of the degradation of mechanical integrity of solder joints due to aging. The results from this thesis can facilitate the understanding of the influence of interfacial IMC layers on the mechanical behaviour of solder joints due to long-term exposure to high temperatures.

The work described in this thesis is aimed at developing a novel piezoelectric cantilever energy harvesting circuit, so that more energy can be obtained from a particular piezoelectric harvester than is possible using conventional circuits. The main focus of the work was to design, build and test a proof of principle system, and not a commercial version, so as to determine any limitations to the circuit. The circuit functions by cancelling the capacitive output reactance of the piezoelectric harvester with a simulated inductance, and is based on an idea proposed by Qi in 2011. Although Qi's approach demonstrated that the circuit could function, the system proved too lossy, and so a less lossy version is attempted here. Experimental and software simulations are provided to verify the theoretical predictions. A prototype amplified inductor circuit was simulated and tested. From the simulation results, although harmonic current losses were found in the circuit, it was found that the circuit should produce an amplified effective inductance and a maximum output power of 165mW. The effective inductance is derived from the voltage across the 2H inductor, and this voltage is amplified and applied to the circuit via an inverter, to provide an extra simulated inductance, so that the overall inductance can be resonated with the piezoelectric harvester output capacitance. Hence the capacitive impedance of the harvester is nearly cancelled. The study and analysis of the amplified inductor circuit was carried out for a single cantilever harvester. Both open loop and closed loop testing of the system were carried out. The open loop test showed that the concept should function as predicted. The purpose of the closed loop test was to make the system automatically adjust for different resonance frequencies. The circuit was tested at 52Vpp inverter output voltage, and demonstrated a harvested power of 145.5mW. Experimental results show that the harvester output power is boosted from 8.8mW as per the manufacturer data sheet to 145.5mW (16.5 times). This is approximately double the power available using circuits described in the literature.

In this work, a multi dimensional RF MEMS variable capacitor that utilizes electrostatic actuation is designed and fabricated on a 425um thick silicon substrate. Electrostatic actuation is preferred over other actuation mechanisms due to low power consumption. The RF MEMS variable capacitor is designed in a CPW topology, with multiple beams supported (1 - 7 beams) on a single pedestal. The varactors are fabricated using surface micromachining techniques. A 1um thick silicon monoxide (Er - 6) is used as a dielectric layer for the varactor. The movable membrane is suspended on a 2.5um thick electroplated gold pedestal. The capacitance between the membrane and the bottom electrode increases as the bias voltage between the membrane and the bottom electrode is increased, eventually causing the membrane to snap down at the actuation voltage. For the varactors designed herein, the actuation voltage is approximately 30 - 90V. Full-wave electromagnetic simulations are performed from 1 - 25GHz to accurately predict the frequency response of the varactors. The EM simulations and the measurement results compare favorably. A series RLC equivalent circuit is used to model the varactor and used to extract the parasitics associated with the capacitor by optimizing the model with the measurement results. The measured capacitance ratio is approximately 12:1 with a tuning range from 0.5 - 6pF. Furthermore, the measured S-parameter data is used to extract the unloaded Q of the varactor (at 1GHz) and is found to be 234 in the up state and 27 in the down state. An improved anodic bonding technique to bond high resistivity Si substrate and low alkali borax glass substrate that finds potential application towards packaging of MEMS varactors is investigated. To facilitate the packaging of the varactors the temperature is maintained at 400°C. The bonding time is approximately 7min at an applied voltage of 1KV.

The objective of the dissertation is to develop and describe kinematic models (Pseudo-Rigid-Body Models) for approximating large-deflection of spatial (3D) cantilever beams that undergo multiple bending motions thru end-moment loading. Those models enable efficient design of compliant mechanisms, because they simply and accurately represent the bending and stiffness of compliant beams. To accomplish this goal, the approach can be divided into three stages: development of the governing equations of a flexible cantilever beam, development of a PRBM for axisymmetric cantilever beams and the development of spatial PRBMs for rectangular cross-section beam with multiple end moments. The governing equations of a cantilever beam that undergoes large deflection due to force and moment loading, contains the curvature, location and rotation of the beam. The results where validated with Ansys, which showed to have a Pearson's correlation factor higher than 0.91. The resulting deflections, curvatures and angles were used to develop a spatial pseudo-rigid-body model for the cantilever beam. The spatial pseudo-rigid-body model consists of two links connected thru a spherical joint. For an axisymmetric beam, the PRB parameters are comparable with existing planar PRBMs. For the rectangular PRBM, the parameters depend on the aspect ratio of the beam (the ratio of the beam width over the height of the cross-section). Tables with the parameters as a function of the aspect ratio are included in this work.

[Truncated abstract] The feasibility of using interlocked light gauge sheet piles to form a deep cross-sectional wall embedded in a residual slope or with a berm support is explored. This thesis compares the performance of a large section modulus sheet pile wall as an alternative to a concrete diaphragm wall, acting as an embedded cantilever wall on a slope (ECWS) by means of experimental centrifuge tests, numerical models and analytical methods. Abaqus (Hibbitt, Karlsson and Sorensen Inc, 1997) was used to conduct extensive numerical trials on the structural performance of the sheet pile wall model prior to the actual physical testing. The Abaqus results showed that the integrity of the interlock and reduced modulus action (RMA) due to slippage along the interlocked joint did not cause premature buckling of the thin wall even at the ultimate load. Further, a comparative study using centrifuge tests on 1:30 scaled models and Plaxis analysis demonstrated that under the worst condition with high water table, the rigid sheet pile wall of 1.32 m cross-sectional width carried a higher ultimate surcharge load with a much lower top of wall deflection, compared to a more flexible 0.6 m thick cracked concrete diaphragm wall. The analysis of the wall/soil/slope interactions for an ECWS involves many inter-dependent variables in addition to the complications of considering an adjacent slope or a berm support. It is difficult for existing analytical approaches to take all these factors into account, and some form of numerical analysis, calibrated through field data and results from centrifuge model tests is necessary. From the observations of the centrifuge tests and finite element analysis, major assumptions about the failure of a stiff ECWS in a rotational mode were deduced and adopted in the proposed limiting equilibrium method (Leq). The plane strain Leq ECWS Abstract ii analysis is based on the framework of minimum upper bound limiting equilibrium with planar failure planes and a Mohr-Coulomb soil model. As compared to the traditional limit equilibrium analysis, the Leq method is a fully coupled analysis using the shear strength reduction technique (SSR). New formulations are proposed for the development of horizontal active and passive pressure distributions based on the experimental and FE models. The proposed active pressure profile used is derived by combining the Coulomb and Krey method, and empirically back-figured to curve-fit the centrifuge tests by Morris (2005). The proposed passive pressure profile of a rigid rotational wall in failure is adjusted to allow for an adjacent slope or berm support through a presumed elasto-plastic deformation instead of a linear rigid translation of the passive wedge. ... A parametric study was later undertaken using the Leq method to develop a series of non-dimensionalised graphs to study and draw summarised conclusions on the behaviour of the ECWS. The final conclusions on the comparative study of the centrifuge tests, Plaxis and Leq analyses demonstrated that the alternative light gauge steel sheet pile performed very well as an ECWS. A key factor in the performance of the sheet pile wall was attributed to the large 1.32 m cross-sectional width of the interlocked sections. This provided high bending stiffness and high moment stability from shear stresses acting on the back and front faces of the wall.

Minimum impact construction for bridge building is a growing demand in modern urban environments. Pre-cast segmental construction is one solution that offers low-impact, economical, and aesthetically pleasing bridges. The standardization of pre-cast concrete sections and segments has facilitated an improved level of economy in pre-cast construction. Through the development of high performance materials such as high strength fibre-reinforced concrete (FRC), further economy in pre-cast segmental construction may be realized. The design of pre-cast bridges using high-strength FRC and external unbonded tendons for cantilever construction may provide an economical, low-impact alternative to overpass bridge design. This thesis investigates the feasibility and possible savings that can be realized for a single cell box girder bridge with thin concrete sections post-tensioned exclusively with external unbonded tendons in the longitudinal direction. A cantilever-constructed single cell box girder with a curtailed arrangement of external unbonded tendons is examined.

Minimum impact construction for bridge building is a growing demand in modern urban environments. Pre-cast segmental construction is one solution that offers low-impact, economical, and aesthetically pleasing bridges. The standardization of pre-cast concrete sections and segments has facilitated an improved level of economy in pre-cast construction. Through the development of high performance materials such as high strength fibre-reinforced concrete (FRC), further economy in pre-cast segmental construction may be realized. The design of pre-cast bridges using high-strength FRC and external unbonded tendons for cantilever construction may provide an economical, low-impact alternative to overpass bridge design. This thesis investigates the feasibility and possible savings that can be realized for a single cell box girder bridge with thin concrete sections post-tensioned exclusively with external unbonded tendons in the longitudinal direction. A cantilever-constructed single cell box girder with a curtailed arrangement of external unbonded tendons is examined.

The dynamic characteristics of shroud blade group played a significant role in steam turbine design. However, the complex shape and periodical structure of shroud blades make it so hard to find its dynamic characteristics under high speed operation. The complicate shape, periodic structure, and tedious computation limit the application of finite element method in the design analysis of shroud group blades. In order to design the shroud blade group, the component mode synthesis method was employed to derive the system dynamic equation of the grouped periodical blades. For simplicity, a pre-twisted and tapered cantilever beam is used to derive the approximate analytic solution of a rotating turbo blade. Then the approximated eigen solution of single blade is synthesized in company with the constrain condition by using the component mode synthesis method. In order to confirm the feasibility of the proposed simulation method, a real size turbine blade is used to discuss in the study. Through a comparison between the results solved from the proposed method and finite element method of single blade and shroud blade group to prove the reliability of the proposed method. The effect of blade parameters on the dynamic characteristic of shroud blade group has investigated in this work. Numerical results indicate the proposed method is feasible and effective in dynamic design analyses of the shroud blade group.

This investigation examines a novel means of integrating high-performance AlN piezoelectric thin films with a flexible stainless steel substrate (SUS 304) to fabricate a double-sided piezoelectric transducer. Various sputtering parameters, such as sputtering pressure, substrate temperature, nitrogen concentration, and RF power, were investigated to improve the piezoelectric characteristics of AlN thin films. Scanning electron microscopy and X-ray diffraction of AlN piezoelectric film reveal a rigid surface structure and highly c-axis-preferring orientation. The maximum output power per unit thickness was discussed, and the optimal sputtering parameters were determined. The double-sided piezoelectric transducer is constructed by depositing AlN piezoelectric thin films on both the front and the back sides of SUS 304 substrate. The titanium (Ti) and platinum(Pt) layers were deposited using a dual-gun DC sputtering system between the AlN piezoelectric thin film and the SUS 304 substrate. The optimal deposition parameters for AlN thin films are sputtering pressure of 5 mTorr, substrate temperature of 300 ¢J, nitrogen concentration of 40 %, and RF power of 250 W. The maximum open circuit voltage of the transducer under the vibrational frequency of 80 Hz, vibration amplitude of 4mm, and mass loading of 0.5g, is approximately 20 V, or 5.3 V/£gm. After full-wave rectification and filtering through a 33 nF capacitor, a specific output power of 1.462 £gW/cm2 is obtained from the transducer with a load resistance of 7 M£[.

Atomic Force Microscopy (AFM) has become an indispensable metrology tool for nanoscale surface characterization. Today, research and industry demand faster and more accurate metrology and these demands must be met expediently. Traditional AFM cantilevers and associated actuators (i.e. piezoelectric) are limited in regards to actuation speed and resonance frequency presenting the user with an undesired trade-off of speed versus resolution. Based on a pre-existing technology known as the FIRAT (Force Sensing Integrated Readout and Active Tip) AFM probe, this work aims to remedy actuation and response issues by implementing a cantilever-on-cantilever probe as well as a novel seesaw probe. Both cases implement electrostatic actuation, eliminating the need for piezoelectrics while demonstrating large - micron scale - actuation and sensitive displacement detection. These new probe designs can potentially demonstrate a wide bandwidth frequency response (e.g. 100 kHz) ideal for high-speed video-rate imaging. Unlike traditional AFM cantilevers, this is realized by mechanically coupling two physically separate structures to provide a soft resonator sensor atop a stiff actuator structure. Common surface-micromachining techniques are utilized to solve the logistical challenge of fabricating these stacked structures. By manipulating the viscous damping and mechanical mode coupling it becomes feasible to attain the aforementioned desired dynamic characteristics.