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An effective way of providing complete sealing of glass using an 810 nm diode laser was investigated for longer lifetime of glass panel-based devices. Small amounts (

A nonconventional high k glass based on BaO·Nd2O3·TiO2·B2O3, which is combined with typical fillers of Al2O3 and BaTiO3, has been investigated for the purpose of generating potential k (dielectric constant) ~20 and k ~ 40 dielectric materials as a result of densification at 850°C. Crystallization, densification, and dielectric properties depended strongly on the type and content of the fillers. Glass itself was crystallized mainly with BaTi(BO3)2. The Al2O3 filler did not seem to be directly involved in the crystallization process as only non Al-containing crystalline phases, such as NdBO3, Nd2Ti4O11, and BaNd2Ti5O14, were observed. On the contrary, the BaTiO3 filler resulted in the crystallization of two phases, BaTi(BO3)2 and BaNd2Ti5O14. As an example of a promising dielectric candidate, a composite sample consisting of the glass and 30 wt% Al2O3 exhibited k ~ 22 and tan δ ~ 0.009 with nearly full densification at 850°C.

High dielectric constant (k) CaCu3Ti4O12 (CCTO) has been studied as a potential filler for low-temperature cofired ceramics (LTCC) based on typical calcium aluminoborosilicate glass. CCTO does not appear to be chemically reactive with the glass regardless of the firing temperature over the compositional range of 30–90 wt% CCTO. Dielectric constant and dielectric loss turned out to depend strongly on the relative content of CCTO and firing temperature. As an optimal composition, the glass with 60 wt% CCTO exhibited a k∼32 and tan δ∼0.01 as a result of firing at 850°C, which is preferably applicable for the medium k LTCC applications. The higher content of 90 wt% CCTO needed to be densified at 900°C for better densification with a higher dielectric constant of ∼150. However, the 900°C firing was not acceptable for the 30 and 60 wt% CCTO-containing samples due to the unexpected expansion of samples leading to significantly enlarged pores.

A dielectric system having an exceptionally high-quality factor of 1350 at 16.8 GHz is reported as a strong candidate for glass-based low-temperature cofireable materials. The dielectrics are based on unusual (16-27)ZnO · 16La 2 O 3 · (57-68)B 2 0 3 glass mixed with a fixed 50 wt% Al 2 O 3 filler. The ratio of ZnO/ B 2 0 3 was found to be critical in controlling the nature of glass and, consequently, performance of the dielectric mixture. For example, 27nO · 16La 2 O 3 · 57B 2 O 3 glass sample having the highest Zn content resulted in the lowest softening temperature of 647°C and the least porosity of ~6%. The enhanced densification and extensive crystallization of low loss phases, i.e., LaA) 2.03 (B 4 O 10 )O 0.54 and ZnAl 2 O 4 , are assumed to be responsible for better dielectric performance that resulted from the increase of Zn content in glass.

This work first reports a boron nitride-based dielectric system that is designed for MoSi2–based planar heating elements patterned on a regular 96% alumina substrate. The dielectric system is expected to function as an overcoat layer mainly to protect the printed heating elements from environments and to reduce thermal stress induced during thermal heating through improved heat dissipation. The boron nitride (BN) pastes mixed with a low softening glass of calcium barium aluminoborosilicate were screen printed onto MoSi2 thick films and then fired at a temperature of 900°C. The addition of BN was found to increase the thermal conductivity considerably without detrimental chemical reactions with glass constituents. For instance, the thick film containing 30 wt% BN was regarded as a promising composition from the supporting evidences of good adhesion with MoSi2, an increased thermal conductivity of ∼31 W·(m·K)−1, and a high electrical resistance of 4.7 × 1010Ω.

Fostered by the increasing use of AlN in highly thermally conductive electronic packages, it is attempted to grow ZnO thin films on polycrystalline AlN in the present work. Effects of the polycrystalline substrate on the structural and electrical properties of the ZnO films are highlighted. The ZnO films are synthesized by low-cost spin-coating technique from a precursor solution containing zinc acetate, 2-methoxyethanol, and monoethanolamine. Structural analysis was performed using X-ray diffraction, which showed all the films to be polycrystalline of hexagonal phase with no preferred orientation, in sharp contrast to numerous reports of strong c-axis orientation on glass substrates. The films, which were heat-treated at 700°C followed by firing in nitrogen containing 5% hydrogen at 500°C, exhibited better crystallinity and dense microstructure among all the samples and had the lowest resistivity (1.36 × 10−1Ω·cm). The minimum resistivity obtained in the present work is comparable to the values reported for the films grown using similar technique, thus indicating the negligible dependence of electrical properties on orientation of the films.

A low temperature co-fired ceramics system consisting of a typical calcium aluminoborosilicate glass and alumina filler was used to investigate the effects of four different sizes, 13 nm, 0.5, 3, and 39 μm, of a commercially available alumina filler on the resultant densification, crystallization, and dielectric properties. There was definitely a proper range of alumina particle size, which leads to desirable densification and enhanced dielectric properties. The onset temperatures of densification and crystallization depended strongly on the filler particle size. The 3 μm sample as an optimum filler size exhibited a promising performance of k∼8.1 and Q∼160 at a resonant frequency of 14.8 GHz, which results from early densification and intensive crystallization of the anorthite CaAl2Si2O8 phase. Particularly, the use of nano-sized alumina (13 nm) retarded both densification by ∼200°C and crystallization by ∼80°C compared with the results of the 3 μm alumina case. The dependence of the filler particle size was postulated as being related to the wetting and connectivity behavior of glass through consequent inter-reactions between glass and ceramic.

A uniform microstructure of Gd-substituted yttrium iron garnet (Y 2 Gd 1 Fe 5 O 12 ) was obtained with additives of Si and Mn using a sol-gel coating process. Tetraethyl orthosilicate (TEOS) and manganese acetate were used as Si and Mn sources for the sol-gel coating procedure, respectively. TEM/EDS analysis confirmed the presence of a relatively uniform nanoscale coating of Si and Mn around each particle. High density and uniform microstructure were obtained after sintering at 1400°C in O 2 atmosphere. The density and grain size of the specimens depended on Mn content. The results were compared with materials fabricated without additives incorporated by the sol-gel coating procedure.

Aluminum nitride thin films deposited on a low-temperature co-fired ceramics substrate by reactive magnetron sputtering were investigated with regard to their crystal orientation and microstructural characteristics. Strong c-axis orientations of AlN thin films were observed when either a higher deposition temperature or an RF bias was adopted. This orientation was believed to be responsible for the high thermal conductivity of 26 W/mK for the AlN films deposited at 700°C under 25-W bias. Photoluminescence spectrum in the wavelength range of 350–650 nm was analyzed to prove the involvement of potential oxygen-related defects in the thin films.

Microwave dielectric properties of (1-x)(Na 1/2 Nd 1/2 )Ti03 (NNT)-xLa(Mg 1/2 Ti 1/2 )03(LMT) system have been investigated with focus on structural ordering and far IR reflectivity spectra. A single perovskite phase was found to exist with various superlattice reflections over the entire compositional range. 1:1 ordering observed in the (111) reflection of X-ray diffraction patterns was found to progress significantly in the specimens above x = 0.8. The ordering characteristics that presumably related to B-site Mg/Ti ordering were assumed to affect favorably the quality factor at microwave frequencies. The increase of the quality factor also could be explained in terms of the decrease of lattice anharmonicity with LMT by analysis of far IR reflectivity spectra. As expected from the values of pure NNT and LMT, the dielectric constant and the temperature coefficient of frequency tended to gradually decrease with increasing LMT content.

The influences of processing parameters such as mineralizer, temperature, and nonstoichiometry on reaction product and morphology were investigated in the hydrothermal synthesis of yttrium iron garnet, Y 3 Fe 5 O 12 (YIG). A cubic YIG phase was synthesized successfully under hydrothermal conditions of 200°C and 6 h from yttrium and iron hydroxide coprecipitates obtained by adjusting the pH to 10.5 using NH 4 OH. The other mineralizer, NaOH, was not effective in forming the garnet phase. Nonstoichiometric compositions utilizing excess Y content tended to increase the yield of the garnet phase, but did not affect the morphology. Different morphology characteristics were observed by changing the synthesis temperature. Isometric YIG particles disappeared at a relatively high temperature of 250°C, resulting in irregular star-shaped particles of YIG due to the preferential orientation during particle growth.

Dielectric thick films based on a nonstoichiometric cordierite (2.4MgO·2Al2O3·5SiO2, containing 3 wt% B2O3, 3 wt% P2O5, and 3 wt% PbO) were investigated, in regard to their microstructure, crystallization kinetics, and properties. A stable glass-ceramic thick-film microstructure that was formed on a 96% alumina substrate was observed after firing at a temperature of 915°C for 30 min in a nitrogen atmosphere. No µ-cordierite was observed in the X-ray diffraction (XRD) patterns of the thick film. The crystallization kinetics were studied via quantitative XRD analysis using the Avrami equation, and the rate constant increased as the temperature increased. The decreasing tendency of the Avrami parameter, relative to temperature, suggested a change in growth directionality during crystallization. The activation energy for crystallization of the thick film was determined to be ~83 kcal/mol (~350 kJ/mol). The coefficient of thermal expansion (CTE) and the dielectric constant of the glass phase were evaluated using the bulk-sample data. For the case of a 3-wt%-PbO sample fired at 950°C for 30 min in a nitrogen atmosphere, the remaining glass was estimated, using the parallel mixing rule, to have a dielectric constant of 15.3 at 1 MHz. The dielectric constant of the remaining glass was dependent on the PbO content and the heat-treatment temperature. The estimated CTE of the remaining glass for the 3-wt%-PbO sample was 19 × 10-6/°C.

A chemical synthesis technique that uses polyacrylic acid (PAA) to prepare nanocrystalline Li0.3Zn0.4Fe2.3O4 was investigated. Phase-pure spinel that had an average particle size of ∼13 nm was synthesized at a low temperature (450°C) for 30 min. The average particle size was dependent on the firing temperature and amounts of PAA and Bi2O3. The combustion reaction of PAA was believed to be the main reason for the low-temperature synthesis of nanocrystalline lithium zinc (LiZn) ferrites. In addition, a chelating tendency was observed, via infrared (IR) spectroscopy, in the dried gel precipitates that were prepared at a low pH (∼2). The initial densification behavior of the nanopowder compacts was studied using linear-shrinkage data. Densification of the nanopowder without Bi2O3 started at low temperatures (∼400°C). The addition of Bi2O3 to the nanopowder noticeably did not contribute to reducing the initial densification temperature. This result was supported by the activation-energy calculation for the initial densification. Compared to an activation energy of 280 kJ/mol for grain-boundary diffusion of the nanopowder without Bi2O3, a higher value (430 kJ/mol) was obtained in the case of the 3 wt% Bi2O3-containing nanopowder.

A particulate coating process incorporating small amounts of several additives such as titanium, zinc, barium, strontium and iron was used to modify the composition and resultant dielectric and electromechanical properties of a commercially available 0.96(0.91Pb(Mg1/3Nb2/3)O3·0.09PbTiO3)·0.04BaTiO3. This method led to intimate mixing of the additives at the nanoscale without an additional ball-mixing process. Low- and high-field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200°C for 4 h. All properties were found to depend on the chemical additives and temperature. Specifically, the addition of small quantities of titanium and barium tended to increase strain and Qeff while maintaining a low dielectric constant which is a promising result for room temperature transducer applications. The addition of titanium with zinc or iron raised dielectric constant, strain, and polarization with significant increases in the temperature of maximum permittivity. On the other hand, the electromechanical properties of the samples containing barium or zinc with titanium did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements.

A new approach of producing ~0% fired shrinkage of dielectric ceramics is introduced without using the known physically constraining interaction during firing. The combination of SiC and Al2O3 fillers with a typical calcium aluminoborosilicate glass demonstrated the potential of generating nearly zero shrinkage, presumably from the chemical reaction between the glass and SiC above a critical temperature. The sample with zero shrinkage, as exemplified with the composition of 25 wt% SiC, 25 wt% Al2O3, and 50 wt% glass, does not produce fully dense microstructure, but shows acceptable values of k (dielectric constant) ~7.4 and tanδ ~0.004 at 1 MHz. The achievement of the least shrinkage is found to be sensitive to the relative content of SiC and firing temperature.

Two dielectric materials consisting of a zinc calcium aluminoborosilicate glass with either an Al 2 O 3 or a CaTiO 3 filler were selected to investigate the sensitivity of refirings at a fixed temperature of 850°C to the final physical and dielectric performance. The property changes with refirings depended on the type of filler material and the number of refirings. For example, crystallization of the unexpected ZnAl 2 O 4 phase was found to progress further on increasing the number of refirings in the case of the Al 2 O 3 filler sample. The five refirings of the sample resulted in a decrease of the dielectric constant from 8.46 to 8.06 at 1 MHz. The case of the CaTiO 3 filler can be highlighted with the opposite increasing effect of the dielectric constant as the crystalline CaTiSiO 5 phase evolved further with refirings.

The compatibility and crystallization of dielectric thick films, consisting of a bismuth borosilicate glass and crystalline cordierite, on a LiZn ferrite substrate were investigated by focusing on phase development and microstructural changes. Significant diffusion of Li and Fe from the substrate to the dielectric was confirmed as unexpected crystalline phases such as Li 2 Al 2 Si 3 O 10 and Fe 2 O 3 were found in the thick films fired at 850°C. The crystallization was believed to be initiated from the film interface and developed further toward the film surface as evidenced from cross-sectional microstructures of the films with additional firings. The degree of crystallization and the relative contents of the observed phases were dependent on the ratio between the glass and cordierite and the number of refirings.

The compositional dependence of microwave dielectric properties has been investigated in the (1 - x)(Na 1/2 Nd 1/2 )TiO 3 -xNd(Mg 1/2 Ti 1/2 )O 3 (NNT-NMT) system. The addition of NMT results in significant improvement in the quality factor and the temperature coefficient of frequency, but gradually decreases the dielectric constant from ∼100 for pure NNT to ∼25 for pure NMT. The single perovskite phase is observed with various {hkl} superlattice reflections over the entire compositional range. The increasing tendency of peak splitting with increasing x at some perovskite reflections strongly suggests that the crystal structure of the system changes to lower symmetry structures. This is confirmed using infrared reflectivity spectra. The superlattice reflections related to structural deviation become more predominant as the composition reaches pure NMT. Particularly, {111} superlattice reflections are believed to be associated with the 1:1 cation ordering and responsible for the observed abrupt increase in quality factor at x > 0.7.

A bismuth borosilicate glass-based thick film having a low glass transition temperature of 445°C was investigated as a passivation layer for protecting Ag-grid against corrosive reactions with the common I–/I3− electrolyte for large area dye-sensitized solar cells (DSSC). Glass paste was carefully screen-printed and then fired in the temperature range of 480°–540°C to have a final thickness of ∼4 μm. The effectiveness of the glass passivation film was related to the degree of densification or porosity, which depended on firing temperature of the glass. A high optical transmittance of ∼70% and the chemical inertness of the well-densified glass film can be highlighted as promising characteristics for this passivation application. The low electrical resistance of ∼27 Ω of the fluorine-doped tin oxide-coated substrate, which was obtained by patterning Ag grid, remained stable over the exposure period of ∼10 days in the electrolyte only when the hermetic protection of Ag was secured by the glass overcoat film after densification at 540°C.

A new potential low-temperature co-fired ceramics (LTCC) system based on a simple lanthanum borate (La2O3–B2O3) glass was investigated with regard to phase development and microwave dielectric properties as functions of alumina filler content less than 50 wt% and firing temperature up to 1050°C. Unexpected crystalline phases, such as La(BO2)3, LaAl2.03(B4O10)O0.54, LaBO3, and Al20B4O36, developed during the firing process are likely responsible for substantial resultant changes in physical and microwave dielectric properties. As a specific example, a high-quality factor of 785 at 15.8 GHz obtained for a composition containing 30 wt% alumina supports the hypothesis that the phase-dielectric property relation exists in this LTCC system. On a practical basis, two phases of LaAl2.03(B4O10)O0.54 and LaBO3 must be important in determining the final dielectric performance by manipulating the ratios of glass and filler and by selecting a desirable temperature.