In hybrid pixel detector fabrication, high-density interconnection between focal plane array and the read-out integrated circuit is important. Bump bonding is the preferable assembly method, it is small in size, low cost, high performance and flexible I/O. Flip-chip bonding is a vertical connection technique of focal plane array and top substrate with solder bumps. In this paper, Flip-chip bonding by electroplated indium bumps is described. There are advantages of using indium as the solder material. It is relatively inexpensive, it has good thermal and electrical conductivity, it is ductile, and it is cryogenically stable. Indium bumps with a diameter of 30 µm are successfully prepared by an electroplating method, however removing indium conductive layer after electrodeposition is challenging. The corresponding electroplating indium bump process is also discussed. Electrical measurement was applied to detect the connection integrity of the flip-chip assemblies.

abstract: In order to meet climate targets, the solar photovoltaic industry must increase photovoltaic (PV) deployment and cost competitiveness over its business-as-usual trajectory. This requires more efficient PV modules that use less expensive materials, and longer operational lifetime. The work presented here approaches this challenge with a novel metallization method for solar PV and electronic devices. This document outlines work completed to this end. Chapter 1 introduces the areas for cost reductions and improvements in efficiency to drive down the cost per watt of solar modules. Next, in Chapter 2, conventional and advanced metallization methods are reviewed, and our proposed solution of dispense printed reactive inks is introduced. Chapter 3 details a proof of concept study for reactive silver ink as front metallization for solar cells. Furthermore, Chapter 3 details characterization of the optical and electrical properties of reactive silver ink metallization, which is important to understanding the origins of problems related to metallization, enabling approaches to minimize power losses in full devices. Chapter 4 describes adhesion and specific contact resistance of reactive ink metallizations on silicon heterojunction solar cells. Chapter 5 compares performance of silicon heterojunction solar cells with front grids formed from reactive ink metallization and conventional, commercially available metallization. Performance and degradation throughout 1000 h of accelerated environmental exposure are described before detailing an isolated corrosion experiment for different silver-based metallizations. Finally, Chapter 6 summarizes the main contributions of this work. The major goal of this project is to evaluate potential of a new metallization technique –high-precision dispense printing of reactive inks–to become a high efficiency replacement for solar cell metallization through optical and electrical characterization, evaluation of durability and reliability, and commercialization research. Although this work primarily describes the application of reactive silver inks as front-metallization for silicon heterojunction solar cells, the work presented here provides a framework for evaluation of reactive inks as metallization for various solar cell architectures and electronic devices. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2019

In this work we proposed and demonstrated a novel and very cost effective method to fabricate bifacial solar cells with conventional structure. Bifacial cells collect sunlight from both faces, and hence have an obvious advantage over monofacial cells by occupying the same physical area and converting solar energy to electricity more efficiently. Despite this fact, bifacial cells are not that popular simply because of the costs associated with them. These costs are related to both manufacturing of the actual cells and integration of modules/solar panels. The cost of manufacturing is higher than regular commodity cells because the number of processing steps for fabrication is higher than their monofacial counterparts. The main reasons for that is a necessity of some kind of lithography step and/or alignment to make the grid pattern on both sides separately. Also metallization has to be done on both sides separately, one at a time. The method proposed in this work gets rid of both of those limitations by use of a lithography/alignment-less method for patterning contact holes, and a low temperature metallization scheme used for both the front and rear surfaces to grow metal simultaneously. This technique is simple and cost effective enough to be potentially incorporated in a batch process in industry, thereby reducing the cost of manufacturing. In this thesis we have presented preliminary results from the cells (bifacial and monofacial) fabricated using the above technique with proposals for further improvements. The measurement data underscores the clear advantage in using bifacial cells over monofacial cells fabricated using this method, in terms of efficiency. This also demonstrates that this proposed method is a viable way to manufacture bifacial cells with lower cost and relative ease. We also fabricated and measured monofacial solar cells in order to study the beneficial effects of including buried contacts as a possible part of device structure. The study shows significant improvement in efficiency due to incorporation of deep trenches for metal contacts in device design. / text

abstract: There is an ever growing need for larger memories which are reliable and fast. New technologies to implement non-volatile memories which are large, fast, compact and cost-efficient are being studied extensively. One of the most promising technologies being developed is the resistive RAM (ReRAM). In ReRAM the resistance of the device varies with the voltage applied across it. Programmable metallization cells (PMC) is one of the devices belonging to this category of non-volatile memories. In order to advance the development of these devices, there is a need to develop simulation models which replicate the behavior of these devices in circuits. In this thesis, a verilogA model for the PMC has been developed. The behavior of the model has been tested using DC and transient simulations. Experimental data obtained from testing PMC devices fabricated at Arizona State University have been compared to results obtained from simulation. A basic memory cell known as the 1T 1R cell built using the PMC has also been simulated and verified. These memory cells have the potential to be building blocks of large scale memories. I believe that the verilogA model developed in this thesis will prove to be a powerful tool for researchers and circuit developers looking to develop non-volatile memories using alternative technologies. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2014

High-temperature electrical- and morphological-stability of interconnect is critical for electronic systems based on wide band gap (WBG) semiconductors. In this context, the thermal stability of both Ag and Cu films with Ta and TaN films as diffusion barriers and/or surface-capping layers at high temperatures up to 800 oC is investigated in this thesis. The investigation of un-capped Ag films with either Ta or TaN diffusion barrier layers shows electrical stability upon annealing up to 600 °C. Degradation occurs above 600 °C mainly as a result of void formation and Ag agglomeration. Sandwiching Ag films between Ta and/or TaN layers is found to electrically and morphologically stabilize the Ag metallization up to 800 °C. The barrier layer plays a key role; the β-to-α phase transition in the underlying Ta barrier layer is identified as the major cause for the morphological instability of the film above 600 °C. This phase transition can be avoided using a stacked Ta/TaN barrier. Furthermore, no observable Ta diffusion in Ag films is found. Copper films with a Ta diffusion barrier show clearly different behaviors. In the Cu/Ta sample, Ta starts to diffuse up to the surface via fast-diffusing grain boundaries (GBs) after annealing at 500 °C. The activation energy for the GB diffusion is 1.0+0.3 eV. Un-capped Cu is electrically stable up to 800 °C. An appreciable increase in sheet resistance occurs above 600 °C for the asymmetric combinations Ta/Cu/TaN and TaN/Cu/Ta. This degradation is closely related to a substantial diffusion of Ta across the Cu film and on to the TaN layer, where Ta1+xN forms. The symmetrical combinations Ta/Cu/Ta and TaN/Cu/TaN show only small changes in sheet resistance even after annealing at 800 °C. No Ta diffusion can be found in the Ta/Cu/Ta and TaN/Cu/TaN stacks. Finally, the influence of barrier and cap, their interfaces to Cu and Ta diffusion and segregation in the Cu GBs on electromigration is studied. Our preliminary results with the TaN/Cu/Ta and TaN/Cu/TaN structures report a 2-fold higher activation energy and a 10-fold longer lifetime for the former, thus confirming an important role of the interface between Cu and the cap and/or barrier.

Ces travaux décrivent la réalisation et l'étude d'un procédé original permettant la métallisation de surface de substrats à matrice polymère chargés fibres de carbone (CFRP) par l'intermédiaire d'un revêtement polymère conducteur pour des applications de blindage électromagnétique. Ce revêtement conducteur est constitué d'une matrice polyuréthane (PU) contenant des fils submicroniques d'argent (AgNWs) obtenus par un procédé polyol. L'étude de la mobilité moléculaire de la matrice PU et de l'influence des AgNWs sur les propriétés physiques de la matrice ont été effectuées. Le revêtement PU/AgNWs présente un très faible seuil de percolation volumique et surfacique inférieur à 1 % en volume. Au-delà de ce seuil de percolation, la conductivité de surface est suffisante pour permettre l'électrodéposition. Les paramètres optimaux de l'électrodéposition ont été déterminés. Un dépôt homogène et uniforme est obtenu pour des revêtements faiblement chargés (4 %vol). La couche métallique conserve son adhérence, malgré les grandes variations thermiques, en adaptant les contraintes de dilatation. L'efficacité de blindage a été mesurée de 1 à 26 gigahertz. / This work describes the achievement and the study of an original process to permit the surface metallization of carbon fiber reinforced polymer (CFRP) substrates filled with carbon fibers through a conductive polymer coating for electromagnetic shielding applications. This conductive coating consists of a polyurethane (PU) matrix containing silver nanowires (AgNWs) obtained by a polyol process. The study of the molecular mobility of PU matrix and the influence of AgNWs on the physical properties of the matrix were carried out. The PU/AgNWs coating exhibits a very low volume and surface percolation threshold less than 1 % by volume. Above this percolation threshold, the surface conductivity allows metal electroplating. Optimal electrodeposition parameters were determined. A homogeneous and uniform deposition is obtained on the low-filled coatings (4 %vol). The metallic layer adheres to substrate for large thermal variations, by adapting the stresses of the thermal expansion. The EM shielding efficiency was measured from 1 to 26 gigahertz.

An investigation has been carried out to determine the fundamental reliability unit of copper dual-damascene metallization. Electromigration experiments have been carried out on straight via-to-via interconnects in the lower metal (M1) and the upper metal (M2), and in a simple interconnect tree structure consisting of straight via-to-via line with an extra via in the middle of the line (a "dotted-I"). Multiple failure mechanisms have been observed during electromigration testing of via-to-via Cu interconnects. The failure times of the M2 test structures are significantly longer than that of identical M1 structures. It is proposed that this asymmetry is the result of a difference in the location of void formation and growth, which is believed to be related to the ease of electromigration-induced void nucleation and growth at the Cu/Si₃N₄ interface. However, voids were also detected in the vias instead of in the Cu lines for some cases of early failure of the test lines. These early failures are suspected to be related to the integrity and reliability of the Cu via. Different magnitudes and directions of electrical current were applied independently in two segments of the interconnect tree structure. As with Al-based interconnects, the reliability of a segment in this tree strongly depends on the stress conditions of the connected segment. Beyond this, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are thought to be associated with variations in the architectural schemes of the two metallizations. The absence of a conducting electromigration-resistant overlayer in Cu technology allows smaller voids to cause failure in Cu compared to Al. Moreover, the Si₃N₄ overlayer that serves as an interlevel diffusion barrier provides sites for easy nucleation of voids and also provides a high diffusivity path for electromigration. The results reported here suggest that while segments are not the fundamental reliability unit for circuit-level reliability assessments for Al or Cu, vias, rather than trees, might be the appropriate fundamental units for the assessment of Cu reliability. / Singapore-MIT Alliance (SMA)

The aim of this master thesis has been to design, and partly manufacture and evaluate, a highly miniaturized, on-chip conductivity-temperature-depth (CTD) sensor system for deepwater analysis also including electrodes for pH and chloride ion concentration measurements. The microtechnology-based sensor system will be a vital instrument onboard the Deeper Access, Deeper Understanding submersible, which will be small enough for deployment through bore holes into the subglacial lakes of Antarctica. Design of the complete 15 x 30 mm chip, including variations of each sensor type (in total 39 sensors), is presented. Salinity (through conductivity), temperature, chloride ion concentration and pH sensors have been manufactured using conventional lithography, evaporation, wet etching and lift off techniques. Simulations of the pressure sensors (not manufactured) show how the set of four bossed membranes with integrated strain gauges combine to cover, yet withstand, pressures of 1-100 atm. Salinity is measured conductively with gold electrodes. The temperature sensor is a platinum thermoresistor. Chloride ion concentration and pH are measured potentiometrically with ion-selective microelectrodes of silver/silver chloride and iridium oxide, respectively. Tests of the conductivity sensor gave good results also on sea water samples of known salinity. The temperature sensor showed good linearity to a reference sensor in the tested range of 5-35 C. Issues with evaporation and lift off are discussed, and a process identification document is attached. / DADU

abstract: Miedema's plot is used to select the Cu/metal barrier for Cu metallization.The Cu/metal barrier system selected should have positive heat of formation (Hf) so that there is no intermixing between the two layers. In this case, Ru is chosen as a potential candidate, and then the barrier properties of sputtered Cu/Ru thin films on thermally grown SiO2 substrates are investigated by Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and electrical resistivity measurement. The Cu/Ru/SiO2 samples are analyzed prior to and after vacuum annealing at various temperatures of 400, 500, and 600 oC and at different interval of times of 0.5, 1 and 2 hrs for each temperature. Backscattering analysis indicate that both the copper and ruthenium thin films are thermally stable at high temperature of 600 oC, without any interdiffusion and chemical reaction between Cu and Ru thin films. No new phase formation is observed in any of the Cu/Ru/SiO2 samples. The XRD data indicate no new phase formation in any of the annealed Cu/Ru/SiO2 samples and confirmed excellent thermal stability of Cu on Ru layer. The electrical resistivity measurement indicated that the electrical resistivity value of the copper thin films annealed at 400, 500, and 600 oC is essentially constant and the copper films are thermally stable on Ru, no reaction occurs between copper films and Ru the layer. Cu/Ru/SiO2 multilayered thin film samples have been shown to possess good mechanical strength and adhesion between the Cu and Ru layers compared to the Cu/SiO2 thin film samples. The strength evaluation is carried out under static loading conditions such as nanoindentation testing. In this study, evaluation and comparison is donebased on the dynamic deformation behavior of Cu/Ru/SiO2 and Cu/SiO2 samples under scratch loading condition as a measure of tribological properties. Finally, the deformation behavior under static and dynamic loading conditions is understood using the scanning electron microscope (SEM) and the focused ionbeam imaging microscope (FIB) for topographical and cross-sectional imaging respectively. / Dissertation/Thesis / M.S. Materials Science and Engineering 2010

abstract: Advances in software and applications continue to demand advances in memory. The ideal memory would be non-volatile and have maximal capacity, speed, retention time, endurance, and radiation hardness while also having minimal physical size, energy usage, and cost. The programmable metallization cell (PMC) is an emerging memory technology that is likely to surpass flash memory in all the listed ideal memory characteristics. A comprehensive physics-based model is needed to fully understand PMC operation and aid in design optimization. With the intent of advancing the PMC modeling effort, this thesis presents two simulation models for the PMC. The first model is a finite element model based on Silvaco Atlas finite element analysis software. Limitations of the software are identified that make this model inconsistent with the operating mechanism of the PMC. The second model is a physics-based numerical model developed for the PMC. This model is successful in matching data measured from a chalcogenide glass PMC designed and manufactured at ASU. Matched operating characteristics observable in the current and resistance vs. voltage data include the OFF/ON resistances and write/erase and electrodeposition voltage thresholds. Multilevel programming is also explained and demonstrated with the numerical model. The numerical model has already proven useful by revealing some information presented about the operation and characteristics of the PMC. / Dissertation/Thesis / PMC numerical model written in M for Octave/MATLAB / M.S. Electrical Engineering 2013