The recent developments in Low Temperature Co-fired Ceramic (LTCC) as a substrate material enable it to be used in the micro and millimetre wave range providing low dissipation factors at high frequencies, good dielectric properties and a high degree of integration for further miniaturised devices. The most common metallisation method used in LTCC technology is screen printing with high cost noble metals such as silver and gold that are compatible with the high sintering temperatures (850°C). However, these techniques require high capital cost and maintenance cost. As the commercial world requires convenient and low cost process technologies for mass production, alternative metallisation methods should be considered. As a result, electroless copper plating of fired LTCC was mainly investigated in this research. The main goals of this project were to carry out electroless plating of fired LTCC with sufficient adhesion and to extend the process to metallise closed LTCC channel structures to manufacture Substrate Integrated Waveguide (SIW) components. The objectives were focused on electroless copper deposition on fired LTCC with improved adhesion. Electroless deposits on the Sn/Pd activated LTCC surface showed poor adhesion without any surface pre-treatments. Hence, chemical etching of fired LTCC was carried out using concentrated NaOH solution. NaOH pre-treatment of LTCC led to the formation of flake like structures on the LTCC surface. A number of surface and chemical analysis techniques and weight measurements were used to investigate the mechanism of the modification of the LTCC surface. The results showed that the flake like structures were dispersed in the LTCC material and a material model for the LTCC structure was proposed. SEM EDX elemental mapping showed that the flake like structure consisted of aluminium, calcium, boron and oxygen. Further experiments showed that both the concentration of NaOH and the immersion time affect the surface morphology and the roughness of fired LTCC. The measured Ra values were 0.6 μm for untreated LTCC and 1.1 μm for the LTCC sample treated with 4M NaOH for 270 minutes. Adhesion tests including peel test and scratch test were carried out to examine the adhesion strength of the deposited copper and both tests indicated that the NaOH pre-treatment led to an improvement, with the best results achieved for samples treated with 4M NaOH. A second aspect of the research focused on the selective metallisation of fired LTCC. Excimer laser machining was used to pattern a resist film laminated on the LTCC surface. This process also roughened the substrate and created channels that were characterised with respect to the laser operating parameters. After patterning the resist layer, samples were activated using Sn/Pd catalyst solution followed by the electroless copper deposition. Electroless copper was selectively deposited only on the patterned LTCC surface. Laser parameters clearly affected the copper plating rate. Even with a similar number of shots per area, the tracks machined with higher repetition rate showed relatively more machining depth as well as good plating conditions with low resistance values. The process was further implemented to realize a complete working circuit on fired LTCC. Passive components including a capacitor and an inductor were also fabricated on LTCC using the mask projection technique of the excimer laser system. This was successful for many designs, but when the separation between conductor lines dropped below 18 μm, electroless copper started to deposit on the areas between them. Finally, a method to deposit copper films on the internal walls of closed channel structures was developed. The method was first demonstrated by flowing electroless copper solutions through silane treated glass capillaries. A thin layer (approx. 60 nm) of electroless copper was deposited only on the internal walls of the glass capillaries. The flow rate of the electroless copper solution had to be maintained at a low level as the copper deposits tended to wash away with higher flow rates. The structures were tested for transmission losses and showed low (<10dB) transmission losses in the terahertz region of the electromagnetic spectrum. The process was further applied to deposit electroless copper on the internal walls of the LTCC closed channel structures to manufacture a LTCC Substrate Integrated Waveguide (SIW).

Systemic inflammation involves a complex array of cytokines that can result in organ dysfunction. Mortality remains high despite the vast amount of research conducted to find an effective biomarker. The cause of systemic inflammation can be broad and non-specific; therefore, this research investigates using transendothelial electrical resistance (TEER) measurements to better define systemic inflammatory response syndrome (SIRS)/sepsis within a patient. Results show a difference in TEER measurements between healthy individuals and SIRS-rated patients. This research also displays correlations between TEER measurements and biomarkers currently studied with systemic inflammation (tumor necrosis factor-α, C- reactive protein, procalcitonin). Furthermore, this research also presents the groundwork for developing a microfluidic cell-based biosensor using low temperature co-fired ceramic materials. An LTCC TEER-based microfluidic device has the potential to aid in a more effective treatment strategy for patients and potentially save lives.

In recent decades, advances in low NOₓ coal combustion and increasingly strict CO₂ reduction mandates have changed power plant boiler operations quite significantly. As a result of these necessary efforts, the characteristics of fly ash generated at many power plants have also changed. In particular, increases in unburned carbon content have been observed with detrimental implications on the utility of these fly ashes in concrete applications. Over the same time period, the combustion of biomass for energy generation has received increased attention due to the potential benefits of reducing CO₂ emissions and improved sustainability when compared to fossil fuel combustion. Biomass is directly burned, gasified, or co-fired with coal to achieve this goal. Currently, close to 120 million metric tons of coal combustion by products are produced in the U.S. annually. As with coal combustion, production of energy from biomass combustion/gasification results in significant by-product generation that must either be productively reused or geologically disposed. While much research effort has been devoted to understanding the properties and potential productive reuse alternatives for coal combustion residuals, relatively little work has been done on the by-products of biomass combustion. This study investigated the properties and engineering behavior of sixteen ash samples that were produced in eleven different power plants. Specifically, three high carbon content Class F fly ashes, eight coal and biomass co-fired ashes, three pure biomass ash samples, and two high quality, low carbon content ash samples, one of which is commercially marketed (for reference) were chosen. The various ash samples were characterized by means of: electron microscopy; laser diffraction and dry sieve particle size analysis; loss on ignition and total organic carbon analysis; specific surface area analysis; as well as x-ray fluorescence and x-ray diffraction. The ash samples were also investigated for their potential engineering application in the fired clay brick industry, as low-cost adsorptive agents, and in alkali activated geopolymer synthesis for geotechnical and geoenvironmental applications. Results from physical and chemical characterization of the ash samples show no significant differences between pure coal ash and coal co-fired with biomass ash samples from the same power plant. However, there are significant morphological, chemical, and mineralogical differences between coal ash and pure biomass ash. Unlike pure coal ash, biomass ash is not composed primarily of aluminosilicate glass cenospheres but rather consists mainly of charred, fibrous woody remnants with elevated calcite content as compared to coal ash. Bench scale fired bricks produced by partial replacement of clay material with high carbon coal ash, co-fired ash, and pure biomass ash, respectively, was successful. Physical properties of a number of the mix designs exceeded the highest ASTM weathering grade requirements. As sorptive agents, high carbon concentrates from coal and co-fired ash samples, along with all the biomass ash samples, showed significant uptake of lead. The unaltered as- received ash samples (i.e. no acid or steam activation) showed only moderate arsenic (V) and selenium (VI) sorption capacity. Finally, solidification/stabilization by geopolymerization of high carbon content, co-fired ash with as little as 3 molar NaOH in the activator solution was successful, possibly paving the way for various geotechnical and geoenvironmental applications in ground improvement and soil/ash-pond stabilization.

Abstract In the first part of the thesis, novel glass-ceramic compositions based on Al2O3 and BaTiO3 and bismuth-zinc borosilicate (BBSZ) glass, sintered at ultra-low temperatures, were researched. With adequate glass concentration, dense microstructures and useful dielectric properties were achieved. The composite of BaTiO3 with 70 wt % BBSZ sintered at 450 &#176;C exhibited the highest relative permittivity, &#949;r, of 132 and 207 at 100 kHz and 100 MHz, respectively. Thus, the dielectric properties of the composites were dominated by the characteristics of glass, BaTiO3, and Bi24Si2O40 phase, especially the contribution of Bi24Si2O40 for the samples with 70-90 wt % glass. Actually, the existence of the secondary phase Bi24Si2O40 may not hinder but enhance the dielectric properties. The Al2O3-BBSZ composition samples showed a similar situation, not only for densification but also for their microstructures and phases (Al2O3, BBSZ, Bi24Si2O40), explaining the achieved dielectric properties. The second part of the thesis mainly discusses the composite of BaTiO3 with 50 wt % BBSZ with different thermal treatments. After sintering at 720 &#176;C, dense microstructures and the existence of Bi4BaTi4O15, BaTiO3, Bi24Si2O40 phases were observed. The results also showed that the size of glass powder particles did not influence the dielectric properties (&#949;r = 263-267, tan &#948; = 0.013 at 100 kHz) of sintered samples, but the addition of LiF degraded the dielectric properties due to the features and amount of Bi4BaTi4O15. These results demonstrate the feasibility of the BBSZ based composites for higher sintering temperature technologies as well. At the end, a novel binder system, which enables low sintering temperatures close to 300 &#176;C, was developed. A dielectric multilayer module containing BaTiO3-BBSZ and Al2O3-BBSZ composites with silver electrodes was co-fired at 450 &#176;C without observable cracks and diffusions. These results indicate that these glass-ceramic composites provide a new horizon to fabricate environmentally friendly ULTCC materials, as well as multilayers for multimaterial 3D electronics packages and high frequency devices. / Tiivistelmä Väitöstyön ensimmäisessä osassa tutkittiin ja kehitettiin uudentyyppisiä, ultramatalissa sintrauslämpötiloissa (ULTCC) valmistettuja lasi-keraami komposiitteja käyttäen vismuttisinkkiborosilikaatti -pohjaista lasia (BBSZ). Täyteaineina olivat alumiinioksidi (Al2O3) ja bariumtitanaatti (BaTiO3). Materiaaleille saatiin riittävän suuren lasipitoisuuden avulla tiheät mikrorakenteet ja sovelluskelpoiset dielektriset ominaisuudet. BaTiO3:n komposiitti, joka sisälsi 70 p-% BBSZ lasia, saavutti 450 &#176;C lämpötilassa sintrattuna korkeimman suhteellisen permittiivisyyden: &#949;r=132 (@100 kHz) ja &#949;r=207 (@100 MHz). Komposiittien dielektrisiä ominaisuuksia määrittivät tällöin lasi-, BaTiO3- ja Bi24Si2O40- faasien ominaisuudet ja erityisesti Bi24Si2O40 -faasi näytteissä, joissa on 70-90 p-% lasia. Sekundäärinen faasi Bi24Si2O40 ei välttämättä heikentänyt, vaan jopa paransi dielektrisiä ominaisuuksia. Vastaavilla Al2O3-BBSZ –komposiiteilla saavutettiin samanlaisia tuloksia tihentymisen, mikrorakenteiden ja faasien (Al2O3, BBSZ, Bi24Si2O40) suhteen. Lisäksi tässä tapauksessa saavutetut dielektriset ominaisuudet voidaan selittää näiden kolmen faasin yhdistelmän olemassaololla. Väitöstyön toinen osa käsitteli pääasiassa eritavoin lämpökäsiteltyjä BaTiO3:n komposiitteja, joissa on 50 p-% BBSZ-lasia. Näillä saavutettiin tiheä mikrorakenne sintrattaessa 720 &#176;C lämpötilassa ja havaitiin Bi4BaTi4O15-, Bi24Si2O40-faasien muodostuminen BaTiO3 lähtöfaasin rinnalle. Tulokset osoittivat myös, että lasijauheen partikkelikoko ei vaikuttanut sintrattujen näytteiden dielektrisiin ominaisuuksiin (&#949;r = 263-267, tan &#948; = 0.013 (@100 kHz)). LiF -lisäys sen sijaan heikensi dielektrisiä ominaisuuksia ja vähensi Bi4BaTi4O15 faasin muodostumista. Tämä aiheutui Bi4BaTi4O15-faasin ominaisuuksista ja oli riippuvainen kyseisen faasin määrästä. Nämä tulokset osoittivat BBSZ -pohjaisten komposiittien käytettävyyden myös korkeampien sintrauslämpötilojen teknologioihin. Viimeisenä kehitettiin uudentyyppinen sideainesysteemi, joka mahdollistaa ultramatalien keraamien yhteissintraamisen jopa noin 300 &#176;C lämpötilassa. Hyödyntäen kehitettyä sideainesysteemiä monikerrosrakenne, jossa käytettiin dielektrisiä BaTiO3-BBSZ- ja Al2O3-BBSZ-komposiitteja ja hopeaelektrodeja, yhteissintrattiin 450 &#176;C lämpötilassa. Valmistetuissa rakenteissa ei havaittu murtumia eikä diffuusioita. Tulokset osoittavat, että kehitetyt lasi-keraami komposiitit mahdollistavat ympäristöystävällisten ULTCC -materiaalien valmistuksen. Lisäksi osoitettiin kehitettyjen materiaalien soveltuvuus monikerroksisten rakenteiden käyttöön monimateriaali-3D-elektroniikan pakkauksissa ja suurtaajuuskomponteissa.

The strength of materials such as glass and ceramics can be influenced by the environment (stress corrosion). Under applied stress defects (cracks) can grow sub-critically below fracture toughness K_Ic. The aim of this work was to develop a three-dimensional finite-element model to analyze the subcritical crack growth behavior of ceramic-based particulate composites. The maximum tangential stress criterion (MTS) was used to predict the direction of the crack propagation in the framework of linear elastic fracture mechanics. The modeled material was a Low Temperature Co-fired Ceramics (LTCC), containing alumina particles embedded in a glass matrix. The main aim of this work was to develop a 3D model describing the crack growth. Conclusions from this work can contribute to a better understanding of subcritical crack propagation in particle composites.

Subcritical crack growth in composite materials plays quite an important role in determination of the service life and leads to the defects growth below the fracture toughness. The thesis presents search of the several scientific works dealing with the determination of the crack growth direction in composite materials. The aim of this diploma thesis was to create 2D and 3D finite element models to analyse crack growth in Low Temperature Co-fired Ceramics (LTCC). These models were compared based on the time calculation of the crack propagation under the subcritical growth conditions.

This diploma thesis is divided into two parts - theoretical and practical. In its first, theoretical part, deals with the theory of fluid and gas flow, heat transfer and diversification of sensors for flow measurement working on the electrical principle. It also deals with thermodynamic principle, which can be used for measuring very small flow and low-temperature ceramics that is used to implement microcanals for sensing very low flows. The practical part of the thesis deals with the very simulation of the entire structure in the program “COMSOL Multiphysics” - both in 2D and 3D views. Then there is shown the implementation and measurement of the flow sensor in a low-temperature ceramics, working on a thermodynamic principle.