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School of Materials Science and Engineering

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End date: 2009 × Start date: 2003 × Item Type: Publication × search.filters.applied.f.resourcesubtype: Thesis ×

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Now showing 1 - 10 of 57
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Electrochemical characterization of ordered mesoporous carbide-derived carbons

2009-07-08 , Korenblit, Yair

Porous carbon derived from an inorganic silicon carbide (SiC) precursor, termed SiC-derived carbon, is an attractive material for electrochemical energy storage applications, including electrodes for electrical double layer capacitors (EDLCs). The objective of this thesis is to investigate the effects that the carbide-derived carbon (CDC) microstructure and pore structure have on the energy and power characteristics of the EDLC electrodes. Conventional SiC CDC is produced from non-porous crystalline SiC powder at temperatures above 800 °C. Here we studied the performance of SiC CDCs produced by chlorination at 700-900 °C of an ordered mesoporous SiC precursor, which was synthesized via a 1000 °C pyrolysis of polycarbosilane infiltrated into an SBA-15 silica template having ordered mesopores. The SiC CDC was purified from chlorine impurities by annealing in ammonia. The surface area and pore size of the purified SiC CDC was characterized via N2 and CO2 sorption using density functional theory (DFT) and Brunnauer, Emmet, and Teller (BET) theory. The specific capacitance, power and energy densities were characterized via electrochemical measurements of the SiC CDC electrodes in 1 M tetraethylammonium tetrafluoroborate (TEABF4) acetonitrile solution. The SiC CDC exhibited a specific surface area (SSA) in excess of 2400 m2/g and gravimetric capacitance values of up to ~ 150 F/g, among the highest ever reported for any electrodes in this electrolyte. The ordered mesopores allowed for fast ion transport within each particle, resulting in excellent capacity retention under high current rates and ultra-fast frequency response, thus allowing for extremely high power and energy densities. The best overall performance was achieved in SiC CDC samples chlorinated at the lowest temperature of 700 °C.

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High density and high reliability thin film embedded capacitors on organic and silicon substrates

2008-11-20 , Kumar, Manish

With the digital systems moving towards higher frequencies, lower operating voltages and higher power, supplying the required current at the right voltage and at the right time to facilitate timely switching of the CMOS circuits becomes increasingly challenging. The board level power supply cannot meet these requirements directly due to the high inductance of the package interconnections. To overcome this problem, several thin film decoupling capacitors have to be placed on the IC or close to the IC in the package. Two approaches were pursued for high-k thin film decoupling capacitors. 1) Low cost sol-gel based thin film capacitors on organic board compatible Cu-foils 2) RF-sputtered thin film capacitors on silicon substrate for silicon compatible processes While sol-gel provides cost effective technology, sputtered ferroelectric devices are more compatible from manufacturing stand point with the existing technology. Nano-crystalline barium titanate and barium strontium titanate film capacitor devices were fabricated and characterized for organic and silicon substrates respectively. Sol-gel barium titanate films were fabricated first on a bare Cu-foil and then transferred to organic board through a standard lamination process. With process optimization and film doping, a capacitance density of 3 µF/cm2 was demonstrated with breakdown voltage greater than 12V. Leakage current characteristics, breakdown voltages, and electrical reliability of the devices were significantly improved through doping of the barium titanate films and modified film chemistry. Films and interfaces were characterized with high resolution electron microscopy, SEM, XRD, and DC leakage measurements. RF sputtering was selected for ferroelectric thin film integration on silicon substrate. Barium strontium titanate (BST) films were deposited on various electrodes sputtered on silicon substrates. The main focus was to improve interface stabilities for high-k thin films on Si to yield large-area defect-free devices. Effect of bottom electrode selection and barrier layers on device yield and performance were investigated carefully. High yield and high device performance was observed for certain electrode and barrier layer combination. A capacitance density up to 1 µF/cm2 was demonstrated with a breakdown voltage above 15 V on large area, 7 mm2, devices. These two techniques can potentially meet mid-high frequency future decoupling requirements.

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Effect of carbon filler characteristics on the electrical properties of conductive polymer composites possessing segregated network microstructures

2008-07-31 , Prystaj, Laurissa Alia

This thesis focused on making composites consisting of a polymethylmethacrylate matrix, with various carbon fillers. The fillers that were examined were 3 different carbon blacks: N-550, N-772 and pureblack, and short multi-wall carbon nano-tubes. The carbon fillers were coated onto the polymethylmethacrylate, and compression molded in order to form a segregated microstructure. The goal of this thesis is to compare the electrical and optical properties of the composites consisting of a segregated microstructure, containing various carbon fillers. Scanning electron microscopy was used to investigate the fracture surface of the composites. Impedance Spectroscopy measured the electrical response of the material, and was used to determine the conductivity and dielectric properties of the composites and estimate the percolation threshold. The multi-wall carbon nano-tubes were found to have the lowest percolation threshold, due to their rod like structure. All of the carbon black fillers displayed similar characteristics in their conductivity and dielectric properties. As the filler content increased, the conductivity and the dielectric constant of the composites increased. Optical absorption measurements determined the amount of light that travel through the specimen. These measurements, showed that the absorbance for the carbon black sample N-550 were lower than the multi-wall carbon nano-tubes at filler contents below a phr of 0.1 The absorption of the carbon black samples was then higher than multi-wall carbon nano-tubes at phrs higher than 0.1. This was found to be related to the nano-tubes starting to form a segregated microstructure at lower filler contents than the sphere-like carbon black nano-particles.

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Ultra thin ultrafine-pitch chip-package interconnections for embedded chip last approach

2008-03-18 , Mehrotra, Gaurav

Ever growing demands for portability and functionality have always governed the electronic technology innovations. IC downscaling with Moore s law and system miniaturization with System-On-Package (SOP) paradigm has resulted and will continue to result in ultraminiaturized systems with unprecedented functionality at reduced cost. The trend towards 3D silicon system integration is expected to downscale IC I/O pad pitches from 40µm to 1- 5 µm in future. Device- to- system board interconnections are typically accomplished today with either wire bonding or solders. Both of these are incremental and run into either electrical or mechanical barriers as they are extended to higher density of interconnections. Alternate interconnection approaches such as compliant interconnects typically require lengthy connections and are therefore limited in terms of electrical properties, although expected to meet the mechanical requirements. As supply currents will increase upto 220 A by 2012, the current density will exceed the maximum allowable current density of solders. The intrinsic delay and electromigration in solders are other daunting issues that become critical at nanometer size technology nodes. In addition, formation of intermetallics is also a bottleneck that poses significant mechanical issues. Recently, many research groups have investigated various techniques for copper-copper direct bonding. Typically, bonding is carried out at 400oC for 30 min followed by annealing for 30 min. High thermal budget in such process makes it less attractive for integrated systems because of the associated process incompatibilities. In the present study, copper-copper bonding at ultra fine-pitch using advanced nano-conductive and non-conductive adhesives is evaluated. The proposed copper-copper based interconnects using advanced conductive and non-conductive adhesives will be a new fundamental and comprehensive paradigm to solve all the four barriers: 1) I/O pitch 2) Electrical performance 3) Reliability and 4) Cost. This thesis investigates the mechanical integrity and reliability of copper-copper bonding using advanced adhesives through test vehicle fabrication and reliability testing. Test vehicles were fabricated using low cost electro-deposition techniques and assembled onto glass carrier. Experimental results show that proposed copper-copper bonding using advanced adhesives could potentially meet all the system performance requirements for the emerging micro/nano-systems.

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Inductive activation of magnetite filled shape memory polymers

2009-04-09 , Vialle, Greg

Thermally activated shape memory polymers are a desirable material for use in dynamic structures due to their large strain recovery, light weight, and tunable activation. The addition of ferromagnetic susceptor particles to a polymer matrix provides the ability to heat volumetrically and remotely via induction. Here, remote induction heating of magnetite filler particles dispersed in a thermoset matrix is used to activate shape memory polymer as both solid and foam composites. Bulk material properties and performance are characterized and compared over a range of filler parameters, induction parameters, and packaging configurations. Magnetite filler particles are investigated over a range of power input, in order to understand the effects of particle size and shape on heat generation and flux into the matrix. This investigation successfully activates shape memory polymers in 10 to 20 seconds, with no significant impact of filler particles up to 10wt% on mechanical properties of shape memory foam. Performance of different particle materials is dependent upon the amplitude of the driving magnetic field. There is a general improvement in heating performance for increased content of filler particles. Characterization indicates that heat transfer between the filler nanoparticles and the foam is the primary constraint in improved heating performance. The use of smaller, acicular particles as one way to improve heat transfer, by increasing interfacial area between filler and matrix, is further examined.

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Thermo-mechanical reliability of ultra-thin low-loss system-on-package substrates

2008-11-19 , Krishnan, Ganesh

Miniaturization and functionality have always governed advances in electronic system technology. To truly achieve the goal of a multi mega-functional system, advances must be made not just at the IC level, but at the system level too. This concept of tighter integration at the system level is called System-on-Package (SOP). While SOP has a wide range of applications, this work targets the mobile application space. The main driver in the mobile application space is package profile. Reduction in thickness is very critical for enabling next-generation ultra-high density mobile products. In order to pack more functionality into a smaller volume, it is absolutely imperative that package profiles are reduced. The NEMI roadmap projects that the package profile should be reduced to 200µm from the current 500µm by 2014. This work attempts to demonstrate the feasibility of ultra-thin substrates (<200µm) using a new advanced material system tailored for high-frequency mobile applications. The main barriers to adoption of thin substrates include processing challenges, concerns about via and through hole reliability and warpage. Each of these factors is studied and a full-fledged test vehicle built to demonstrate the reliability of thin substrates using the advanced low-loss RXP-4/RXP-1 material system. Finite element models are developed to provide an understanding of the factors that affect the reliability of these substrates. Finally, IC assembly is demonstrated on these substrates.

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Biomineralization of inorganic nanostructures using protein surfaces

2008-04-01 , Bergman, Kathryn N.

In nature, organisms have long been able to create elaborate mineral structures at ambient temperatures. From a materials science and engineering perspective, favorable properties emerge when the synthesis process can be controlled at finer levels. New strategies in materials chemistry synthesis has been inspired by biomineralization: biomimetics. In this work, silk fibroin films were used to synthesize gold nanoparticles room temperature by soaking a free standing 15nm silk film in HAuCl4. Particles ranged in size and shape from 5nm spheres to 105nm hexagons. Secondly, a film of ZnO1 peptide (ZnO selectively binding peptide) was successfully formed by drop casting on both silk and polystyrene surfaces. Using a HMT + Zn(NO3)2 system for ZnO wet chemical deposition, rods were formed on the peptide surface. Changing solution concentration and growth time affected the density and size of the nanorods. Spin coating a 3nm peptide film reduced the roughness to <1nm, upon which an array of vertical ZnO rods with controllable density was synthesized.

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Densification of nano-sized boron carbide

2009-01-12 , Shupe, John

Boron carbide nano-powders, singly-doped over a range of compositions, were pressurelessly-sintered at identical temperature and atmospheric conditions in a dif- ferential dilatometer to investigate sintering behavior. Samples that achieved relative densities greater than 93% of theoretical density were post-HIPed. Post-HIPing re- sulted in an increase in relative density as well as an increase in Vicker's hardness. To optimize the sintering behavior, nano-powders with multiple dopants were prepared based on the results of single dopant experiments. These powders were studied using the same heating schedule as the single dopant samples. The powder with optimized composition was selected, and 44.45 mm diameter disks were pressed to determine the effects of sample size. Powder composition #166 with Al, Ti, W and Mg additions was processed using di¢çerent methods in order to create defect-free green bodies after uniaxial press- ing. The 44.45 mm diameter compacts were heat-treated to remove organics and B₂O₃coatings on particles and then encapsulated in an evacuated fused silica am- pule. Encapsulated samples were HIPed at temperatures below the coarsening region observed in the dilatometric traces of multiply-doped nano-powders. The E-HIPed sample showed a relative density of 96% with a limited extent of nano-sized grain microstructure.

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Nanopowder nickel aluminate for benzothiophene adsorption from dodecane

2008-11-10 , Berrigan, John Daniel

Nickel aluminate reduced in hydrogen for 3 h at 500ºC was studied for desulfurization of model fuel comprised of dodecane spiked with benzothiophene (300 ppmw S). The nanopowder adsorbent was synthesized using combustion chemical vapor condensation, which created nickel aluminate with a BET specific surface area of 57.8 m2/g and average particle size of 11.7 nm. The nickel aluminate adsorbent removed 23 µmol of sulfur gram at breakthrough (<15 ppmw S). Regeneration by further heat treatment in hydrogen or air recovered 25% and 40% of original capacity, respectively.

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Effect of chemical structure and crosslinking density on the thermo-mechanical properties and toughness of (meth)acrylate shape-memory polymer networks

2008-03-31 , Safranski, David L.

The objective of this work is to characterize and understand structure- mechanical property relationships in (meth)acrylate networks. The networks are synthesized from mono-functional (meth)acrylates with systematically varying sidegroup structure and multi-functional crosslinkers with varying mole fraction and functionality. Fundamental trends are established between the network chemical structure, crosslink density, glass transition temperature, rubbery modulus, failure strain, and toughness. The glass transition temperature of the networks ranged from -29 to 112 °C, and the rubbery modulus ranged from 2.8 to 129.5 MPa. At low crosslink density (Er < 10 MPa) network chemistry has a profound effect on network toughness. At high crosslink densities (Er > 10 MPa), network chemistry has little influence on material toughness. The characteristic ratio of the mono-functional (meth)acrylates components is unable to predict trends in thermoset toughness as a function of chemical structure, as is accomplished for thermoplastics. The cohesive energy density is a better tool for prediction of network mechanical properties. Due to superior mechanical properties, networks with phenyl ring sidegroups are further investigated to understand the effect of phenyl ring distance on toughness. This work provides a fundamental basis for designing (meth)acrylate shape memory polymer networks with specific failure strain, toughness, glass transition temperature, and rubbery modulus.

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