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Cordierite ceramics were produced from alumina with 5 and 0.65 μm particle sizes or AlOOH and talc, clays and feldspar, to determine the influence of the alumina particle size on the microstructure, coefficient of thermal expansion (CTE) and flexural strength (FS) of the ceramics. After sintering at 1300 °C the ceramics made from 5-μm-sized alumina consisted of cordierite, glass, quartz, mullite and alumina, and had the highest density, FS and CTE. The alumina grains act as inclusions, from which the trajectories of the cracks were deflected or terminated, which increases the FS and CTE. The ceramics from sub-micrometre-sized alumina or AlOOH contained a negligable amount and no alumina, respectively, together with other phases. This is reflected in the low CTE and FS. The cordierite ceramic with the lowest CTE of ∼2.0 × 10 −6 K −1 and a high FS of 100 MPa was prepared from the 0.65-μm-sized alumina particles.

Purpose – The purpose of this paper is to present the research activity and results to research and development society on the field of ceramic microsystems. Design/methodology/approach – The chemical reactor was developed as a non-conventional application of low temperature co-fired ceramic (LTCC) and thick-film technologies. In the ceramic reactor with a large-volume, buried cavity, filled with a catalyst, the reaction between water and methanol produces hydrogen and carbon dioxide (together with traces of carbon monoxide). The LTCC ceramic three-dimensional (3D) structure consists of a reaction chamber, two inlet channels, an inlet mixing channel, an inlet distributor, an outlet collector and an outlet channel. The inlet and outlet fluidic barriers for the catalyst of the reaction chamber are made with two “grid lines”. Findings – A 3D ceramic structure made by LTCC technology was successfully designed and developed for chemical reactor – methanol decomposition. Research limitations/implications – Research activity includes the design and the capability of materials and technology (LTCC) to fabricate chemical reactor with large cavity. But further dimensions-scale-up is limited. Practical implications – The technology for the fabrication of LTCC-based chemical reactor was developed and implemented in system for methanol decomposition. Originality/value – The approach (large-volume cavity in ceramic structure), which has been developed, can be used for other type of reactors also.

A miniature methanol reformer system has been designed and built to technology readiness level exceeding a laboratory prototype. It is intended to feed fuel cells with electric power up to 100 W and contains a complete setup of the technological elements: catalytic reforming and PROX reactors, a combustor, evaporators, actuation and sensing elements, and a control unit. The system is engineered not only for performance and quality of the reformate, but also for its lightweight and compact design, seamless integration of elements, low internal electric consumption, and safety. In the paper, the design of the system is presented by focussing on its miniaturisation, integration, and process control.

PurposeIn this manuscript the purpose is to present and evaluate the developed non‐destructive method for analysing the phase composition of LTCC Du Pont “Green Tape 951” material fired in the temperature range from 800 to 1,000°C using X‐ray powder diffraction and Rietveld refinement.Design/methodology/approachThe method uses the crystalline Al2O3 which is already present in the material as an internal standard since its mass fraction was previously found to be constant in the described temperature range.FindingsThe results of the non‐destructive analyses and the classical destructive analyses are comparable and the estimated error of the destructive phase analyses and the calculated errors for the non‐destructive phase analyses are of the same order.Practical implicationsThe described method can be used also for analysing another type of LTCC material. In this case it is necessary to check whether the mass fraction of any crystalline phase present in the sample is constant in the given temperature range, because only in this case can it be used as an internal standard for a determination of the phase composition.Originality/valueThe non‐destructive method is a fast and easy approach for analysing the fired samples and is also suitable for controlling the phase composition of LTCC materials on 3D complex structures without destroying them, just by using the X‐ray diffraction patterns collected from their surface.

For the fabrication of complex, micro-electromechanical systems (MEMS) devices based on low-temperature co-fired ceramic (LTCC), higher firing temperatures and longer times than those proposed by the LTCC producer are needed. These changes to the thermal budget may influence the material properties and consequently its functional properties. The effect of the firing conditions on the LTCC DuPont 951 and thus on the phase composition, that is, the alumina/anorthite ratio and porosity, on the mechanical properties is presented. The samples fired at low temperatures (800°C) had a high porosity (7%), which significantly contributed to the low elastic modulus (100 GPa) and the low mechanical strength of the LTCC (140 MPa). The samples fired at 850°C, which had only 1% of porosity, resulted in an elastic modulus of 122 GPa and a flexural strength of 224 MPa. A further increase in the temperature contributed to a slight decrease in the elastic modulus, while no significant difference in the flexural strength could be observed. The enhancement of the flexural strength with an increasing firing temperature was mainly related to a decrease in the porosity and to a lesser extent to the different ratio of the alumina/anorthite phases. The effect of firing time on the phase composition at selected temperatures (i.e., 100 h at 700 and 800°C) is also discussed.

Graphical abstract: Display Omitted Highlights: ► Lead free thick film resistors based on ruthenium oxide were developed. ► The compatibility of resistors with different LTCC substrates was evaluated. ► The interactions between resistors and glassy LTCC substrates were not detected. ► Electrical characteristics were comparable with commercial thick film resistors. -- Abstract: Lead-free thick-film resistors were synthesised and investigated. The thick-film resistor materials with nominal sheet resistivities from 50 ohm/sq. to 50 kohm/sq. were prepared using combinations of two lead-free glasses with reflow temperatures at 940 °C and 1240 °C, respectively, and two RuO{sub 2} powders (fine-grained and coarse-grained RuO{sub 2}). The thick-film resistors were printed and fired on alumina and on low temperature co-fired ceramics substrates and fired at 850 °C and 950 °C. The fired resistors were investigated by X-ray powder diffraction, by scanning electron microscopy and by energy dispersive X-ray analysis. The sheet resistivities, temperature coefficients of resistivity, gauge factors and noise indices were measured.

Advanced micro- or macro-systems are in some cases made with multilayer ceramic technology. Low-Temperature Co-fired Ceramic (LTCC) technology is considered as one of the more suitable technologies for the fabrication of ceramic micro-systems that integrate screen-printed, thick-film electronic components as well as three-dimensional buried structures, for example, cavities and channels. One of the applications is a ceramic combustor. The chemical energy of the fuel is converted into thermal energy in a chemical micro-combustor through a burning process, while the accompanying high temperatures and, frequently, high pressures impose harsh conditions on the combustor structure. Therefore, the combustor must be carefully designed not only from the functional, thermal and chemical points of view, but also with respect to the mechanical strength. The combustor device was prepared by laminating of Du Pont 951PX LTCC green tapes. The fabricated 3D LTCC structures with buried cavities and channels including two inlets (for fuel and air), the evaporator for the fuel, the mixing system of the channels (for mixing the evaporated fuel and air), the distribution channels and eight microburners were realized. The main parts are eight micro-burners realized as buried cavities. In the burners a platinum-based catalyst was deposited to assist the oxidation, i.e., the burning, of the methanol with the air. Thickfilm, platinum-based heaters and temperature sensors are incorporated within the structure. The device was tested with different flow rates of liquid methanol (1 ml/h to 5 ml/h) and air (7 l/h to 15 l/h). The obtained temperatures were between 250°C and 450°C.

Low-temperature co-fired ceramic (LTCC) is an important material in the production of ceramic multilayer structures. Large and complex multilayer structures are usually fired at higher temperatures and/or longer firing times compared to the relatively thin LTCC tapes. The firing conditions of LTCC determine the phase composition and the microstructure, which both influence the physical characteristics, such as the mechanical and thermal properties. In this work the effect of the phase composition on the biaxial flexural strength and the temperature coefficient of expansion of the DuPont 951 LTCC is presented. The samples were fired at different temperatures and times to obtain different phase compositions. The phase composition, especially the mass fraction of anorthite, was correlated with the biaxial flexural strength and the thermal coefficient of expansion (TCE). A very long firing time, i.e., 100h at 800 °C, yields, apart from crystalline anorthite, the cristobalite phase. The anorthite that crystalizes from the glass phase in a dense LTCC material changes the crack-propagation mechanism and improves the biaxial flexural strength of the material. The major change in the biaxial flexural strength is observed when the anorthite phase appeared. The increasing mass fraction of anorthite does improve the biaxial flexural strength less drastically. With the increasing mass fraction of the anorthite, decreases of the TCE of the material and a small decrease of the density of the LTCC material occur.

In this work the effect of firing temperature and firing time on the phase composition, microstructure, biaxial flexural strength, and temperature coefficient of expansion (TCE) of low-temperature cofired ceramic (LTCC) material is presented. At temperatures around 700°C the Al2O3 starts to dissolve in a low viscosity glass phase and this takes place up to 800°C, when 10 wt% of Al2O3 ceramic filler is dissolved in the glass phase forming the alumina-enriched area. This area is suitable for the crystallization of anorthite, which nucleates on the Al2O3 particles. The crystallization starts at 875°C and the mass fraction of anorthite increases with increasing temperature until it reaches a plateau value of around 22 wt% at higher temperatures or longer firing times. The biaxial flexural strength of the LTCC increases with increasing firing temperature from 135 MPa (at 800°C) to around 300 MPa (at 900°C). The major effect on the biaxial flexural strength of LTCC is that of porosity. The effect of the amount of anorthite on the LTCC biaxial flexural strength is minor. The TCE of the LTCC decreases from 5.6 × 10−6 to 5.0 × 10−6 K−1 with increasing firing temperatures or times and it is correlated with the anorthite mass fraction, which crystallizes at the expense of a decreasing amount of glass phase in the LTCC.

During firing the conductive phase based on CaRuO3 in lead-free thick-film resistors decomposes, presumably due to interactions with the silica-rich glass phase. Subsolidus equilibria in the CaO-poor part of the RuO2–CaO–SiO2 diagram were studied with the aim of investigating possible interactions between the conductive phase and silica-rich glasses in thick-film resistors. The tie lines are between CaRuO3 and CaSiO3, and between RuO2 and CaSiO3. This indicates that the calcium ruthenate is not stable in the presence of the silica-rich glass phase.

The paper presents investigation of four lead free thick film resistor pastes, developed at ITME, denoted R-100, R-1k, R-10k and R-100k with sheet resistivities of 0.1, 1, 10 and 100 kΩ/□, respectively. The resistors were based on RuO2 as the conductive phase. The aim of the work was to evaluate the influence of firing conditions of the resistive pastes on a sintering process. The pastes were screen printed onto alumina substrate with prefired AgPd lead-free terminations. They were fired at several temperatures from 750 to 950 °C for 10 min at peak temperature, as well as fired at the highest temperature for 6 h, in order to bring the sintering process into the equilibrium. The properties of the resistors, i.e , sheet resistivity and temperature coefficient of resistance (TCR), microstructure changes, glass crystallization upon firing, etc., were examined. Dried and fired resistor samples were evaluated by X-Ray diffraction analysis and by the scanning electron microscopy. The RuO2 conductive phase maintained the same crystal structure regardless of the firing conditions. No devitrification was observed in lead-free resistors glasses. The lattice constants of RuO2 were uniform after firing at temperatures over 800 °C. The resistors matched the desired resistivity and the TCR was the least temperature dependent at the firing temperatures around 850 °C.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film NTC thermistors (4993, EMCA Remex) fired either on LTCC (low-temperature cofired ceramic) substrates or buried within LTCC structures were evaluated. The thermistors were fired at different temperatures to study the influence of firing temperature on the electrical characteristics. The results were compared with the characteristics obtained on alumina substrates. The sheet resistivities were higher than the resistivities of thick-film thermistors on alumina substrates. The increase of the sheet resistivities was attributed to the diffusion of the glass phase from the rather glassy LTCC substrates into the NTC thermistors. This was confirmed by EDS analyses. However, the increase in the resistivity was linked to an increase of the beta factors. Therefore, the results show that the evaluated NTC thermistors on LTCC substrates can be used for temperature sensors in MCM-Cs as well as in MEMS LTCC structures. When the thermistors were buried in the LTCC substrates, the LTCC structures delaminated during firing, leading to high sheet resistivities and high noise indices. This delamination is attributed to the different sintering rates of the NTC and LTCC materials.

All-ceramic lead-free percolative composite, comprising RuO 2 with high electrical conductivity denoted as the conductive phase and ferroelectric (K, Na)NbO 3 ceramics, was developed. Structural analysis revealed a uniform distribution of conductive ceramic grains within the ceramic matrix. Consequently, the dielectric response in the (K, Na)NbO 3 –RuO 2 composite follows the predictions of the percolation theory. Thus, close to the percolation point exceptionally high values of the dielectric constant were obtained—values as high as 20,000 were detected at room temperature at 1 kHz. Fit of the data, obtained for samples of different compositions, revealed critical exponent and percolation point, which reasonably agree with the theoretically predicted values.

In this paper we present a novel approach to preparing large-displacement 65Pb(Mg1/3Nb2/3)O3–35PbTiO3/Pt (65/35 PMN–PT/Pt) bimorph actuators. These “substrate-free”, bending-type actuators were prepared by screen-printing the 65/35 PMN–PT and Pt thick-film pastes as the electrodes on alumina substrates. After this screen printing and the subsequent firing the 65/35 PMN–PT/Pt composites were peeled off from the substrates. Displacements of nearly 100 μm at 18 V were achieved for actuators with dimensions of 1.8 cm × 2.5 mm × 50 μm for the 65/35 PMN–PT layer. The normalized displacement (the displacement per unit length) was 40 μm/cm at 18 V. The experimental results together with a computation procedure were used to obtain the material parameters for a finite-element analysis of the 65/35 PMN–PT/Pt bimorph actuators.

The sequence of reactions during the synthesis of sodium niobate, potassium niobate, and sodium potassium niobate from alkaline carbonates and niobium oxide has been studied by diffusion couples in the temperature range between 500° and 700°C for up to 48 h. The reactions proceed by coupled diffusion of alkaline and oxygen ions into niobium oxide. The first phase to form at the interface Na 2 CO 3 /Nb 2 O 5 is Na 2 Nb 4 O 11 at 500°C. The perovskite phase forms only after heating at 700°C at the boundary between Na 2 Nb 4 O 11 and Na 2 CO 3 . In the K 2 CO 3 /Nb 2 O 5 diffusion couple, the sequence of phases after heating at 600°C is Nb 2 O 5 /K 6 ,Nb 10.88 O 30 /K 4 Nb 6 O 17 /KNb03/ K 2 CO 3 . In the (K 2 CO 3 +Na 2 CO 3 )/Nb 2 O 5 diffusion couple the (K,Na)NbO 3 solid solution forms via the intermediate phase (K,Na) 2 Nb 4 O 11 at 600°C. The order of magnitude of the parabolic reaction rate constant for the diffusion-controlled reaction at 600°C is about 10 -15 m 2 /s for the (K 2 CO 3 +Na 2 CO 3 )/ Nb 2 O 5 and the K 2 CO 3 /Nb 2 O 5 systems, which is about one order of magnitude less than that for Na 2 CO 3 /Nb 2 O 5 (10 -14 m 2 /s). The reaction rate in the ternary system is determined by the diffusion of the slower species, i.e., the potassium ions.

Lead zirconate titanate (PZT) is a piezoelectric material that can sense or respond to mechanical deformations and can be used in ceramic micro-electro-mechanical systems (C-MEMS). A thick-film paste was prepared from a pre-reacted PZT powder (PbZr0.53Ti0.47O3) and thick-film technology (screen-printing and firing) was used to deposit the PZT layers on LTCC tapes and on alumina substrates. The microstructural, electrical and piezoelectric characteristics of the thick PZT films on relatively inert alumina substrates and on LTCC tapes were studied. Preliminary experiments indicated that due to the interaction between the printed PZT layers and the LTCC substrates during firing the electrical characteristics deteriorate significantly. To minimise the influence of substrate-film interactions different electrode materials and the use of additional intermediate layers as a barrier were evaluated. The dielectric permittivities, dielectric losses, and piezoelectric coefficients (d 33) were measured. The dielectric permittivities of the thick films fired on LTCC substrates were lower (210 with gold electrodes and 430 with silver electrodes) than those measured on alumina substrates (500). The piezoelectric coefficients d33 were measured with a Berlincourt piezometer. The d 33 values measured on the LTCC substrates were relatively low (60–80 pC/N) compared with the values obtained for the alumina substrates (around 140 pC/N). The lower dielectric constants and piezoelectric coefficients d 33 of the films on LTCC substrates are attributed to the formation of phases with a lower permittivity. This was a result of the diffusion of SiO2 from the LTCC into the active PZT layer. The diffusion of silica was confirmed by the SEM and EDS analyses.

Subsolidus equilibria in the RuO2–Bi2O3–SiO2 diagram were studied with the aim of investigating possible interactions between the bismuth-ruthenate- based conductive phase and the silica-rich glasses in thick-film resistors. The tie lines are between Bi2Ru2O7 and Bi12SiO20 (gamma phase), between Bi2Ru2O7 and Bi4Si3O12, and between RuO2 and Bi4Si3O12. This indicates that the bismuth ruthenate is not stable in the presence of the silica-rich glass phase.

Piezoelectric thick films based on Pb(Zr,Ti)O 3 (PZT) were prepared on two types of LTCC tapes (Du Pont 951 and Electro Science Labs. 41020) and on relatively inert alumina substrates. The results obtained with the alumina were used as a reference. The microstructures of the cross-sections of the resistors were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis. The dielectric permittivities, dielectric losses, remanent polarisation, coercive field and piezoelectric constant d 33 were measured. The dielectric and piezoelectric characteristics of the PZT fired on the LTCC substrates deteriorated in comparison to the samples on alumina, due to interactions between the LTCC substrate and the PZT layer. Lower dielectric constants, remanent polarisations and piezoelectric constants indicate the formation of phases with a low permittivity. This was attributed to the diffusion of SiO 2 from the LTCC into the active PZT layer and to the diffusion of PbO from the PZT layer into the LTCC substrate. The diffusion was confirmed by the SEM and EDS analysis.

The piezoelectric, microstructural and electrical characteristics of thick PZT films on relatively inert alumina substrates and on two LTCC tapes, i.e., Du Pont 951 and Electro Science Labs 41020 were studied. A thick-film paste was prepared from the pre-reacted PZT powder (PbZr0.53Ti0.47O3) and printed and fired on LTCC tapes and on alumina substrates, respectively. Dielectric permittivities, dielectric losses, remnant polarizations and coercive fields were measured. The dielectric constants (100–150) of thick films fired on LTCC substrates are low. The piezoelectric coefficients d 33 were measured by different methods, i.e. Berlincourt piezometer, interferometry and piezoresponse force microscope (PFM). The d 33 values on LTCC substrates are low (30–70 pm/V) as compared with values obtained on alumina substrates (around 120 pm/V). Lower dielectric constants and piezoelectric coefficients d 33 of films on LTCC substrates are attributed to the formation of phases with a low permittivity due to the diffusion of silica from LTCC substrates into PZT films. The d 33 constants of samples with different thicknesses of PZT layers (from 20 to 160 μm) at first increase with the increasing thickness of PZT layers and then decrease for thicker films. As the cracks in the structure were not observed the reason for the decreasing d 33 values for thicker films is still unclear.

The results of the influence of lead-free solder paste, design and process parameters on the attachment reliability of chip surface-mounted components (SMCs) on thick-film conductor pads are presented. The purpose of the investigation was to compare the quality of the soldered joints made with new solder pastes that do not contain lead with joints soldered with standard SnPb solders. The miniature zero-ohm chip resistors were soldered with selected lead-free solder pastes. The visual appearance of the solder joint according to the standards of lead-free soldered components was compared with components soldered with SnPb solders. On the test sample with soldered chip resistors connected in series, the solder-joint resistance was measured before and after temperature cycling. On the same test sample the solder-joint resistance changes were measured with impedance spectroscopy. After temperature cycling the damaged samples were analysed with SEM and EDS. The reliability test results after temperature cycling indicate two lead-free solder pastes that are the most convenient for chip-component soldering on thick-film conductor pads with the reliability of the joints being equal or better than solder joints with Pb-containing solder paste.

Laminated 3D structures made using low-temperature co-fired ceramic (LTCC) technology are practical for ceramic micro-electro-mechanical systems (C-MEMS). The sensors for mechanical quantities, and/or actuators, are fundamental parts of MEMS. Thick-film resistors can be used to sense the mechanical deformations, and thick-film piezoelectric materials can be used as electro-mechanical transducers in a C-MEMS structure. The integration of these thick-film materials on LTCC substrates is in some cases difficult to realise due to interactions with the rather glassy LTCC substrates. The subject of our work is an investigation of thick-film materials for electro-mechanical transducers (sensors and actuators) and their compatibility with LTCC substrates. Resistors made with commercial thick-film resistor materials for use as sensors on LTCC substrates have been investigated and evaluated. Ferroelectric ceramic materials based on solid solutions of lead zirconate titanate (PZT) with low firing temperatures around 850°C were developed for thick-film technology and evaluated on LTCC substrates.

Four ternary compositions in the Ce2O3 rich part of the Ce2O3-SiO2-ZrO2 System were investigated. The corresponding mixtures of CeO2, SiO2 and ZrO2 were fired at 1400 degrees C in an Ar + 7% H-2 atmosphere until the phase equilibria were attained. The samples were characterized by XRD, SEM and EDS analysis. The thermal effects and the mass changes of the fired compositions were monitored by DTA/TG analyses. The oxyapatite phase, Ce-4.67(SiO4)(3)O, and the fee phases identified as the solid solutions (CeZr)O2-y, (CezZr1-z)O2-x, and Ce2Zr2O7+2 delta were observed in this part of the Ce2O3-SiO2-ZrO2 system. The DTA/TGA analyses indicated the presence of the Ce+4 ions in the fired compositions, while the lowest melting temperature was noticed at 1627 degrees C. (c) 2006 Elsevier Ltd. All rights reserved. 9th Conference and Exhibition of the European-Ceramic-Society, Jun 19-23, 2005, Portoroz, Slovenia

If the material is being sintered, grain size of its particles will depend on the sintering temperature, time of the sintering and the pressure applied on the material while sintering. It is well known that on the lower sintering temperatures grain size of the nano material is relatively small and thus the active area is large. Due to the low sintering temperature, high material porosity is expected as well. With a decrease of grain size, gas sensitive materials have larger selectivity, higher sensitivity, sensor response increases steeply and they are more immune to poisoning. The core of the investigation is to observe the influence of sintering temperature on grain size of the TiO 2 nano-paste and to determine its reflection on the material porosity. For the realization of gas sensors using Low Temperature Co-Fired Ceramic (LTCC) or High Temperature Co-Fired Ceramic (HTCC) technology, specimens have to be sintered at relatively high temperatures. For the first interaction, custom-designed TiO 2 nano-paste has been deposited on a sintered alumina (Al 2 O 3 ) substrates using screen printing. Specimens have been sintered at peak temperatures in a range of 800 °C – 1500 °C for 30 minutes and afterwards they have been characterized with Scanning Electron Microscopy (SEM) and energy dispersive x-ray spectroscopy EDS.

Subsolidus equilibria in the PbO-poor part of the TiO2–PbO–SiO2 diagram were studied with the aim of investigating possible applications for low-temperature thick-film dielectrics. The tie lines are between PbTiO2 and PbSiO3, and between PbTiO3 and SiO2. The results show that the TiO2, when added to low-temperature softening point glasses, reacts with the PbO from the glass, so forming PbTiO3. These results were applied to a low-temperature firing dielectric, consisting of a lead-rich PbO–SiO2–B2O3 glass filled with a TiO2 powder. The conversion of TiO2 to the PbTiO3 crystalline phase was observed above firing temperatures of approximately 600 °C. The kinetics of the reaction depend on the particle size of the TiO2.

Lead zirconate titanate (PZT) is a piezoelectric material that can sense or respond to mechanical deformations and can be used in ceramic electro-mechanical systems (C-MEMS). The microstructural, electrical, and piezoelectric characteristics of thick PZT films on low-temperature cofired ceramics (LTCC) and alumina substrates were studied. The PZT composition was prepared with low-melting-point additives in order to decrease the sintering temperature and to be compatible with thick-film technology. The integration of the PZT thick-film materials on ceramic substrates could lead to degradation of the PZT's characteristics due to the interactions between an active PZT layer and a substrate, particularly with glassy LTCC material. To minimize the interactions with LTCC substrates, an intermediate PZT barrier layer was integrated. The value of the piezoelectric coefficient d33 was found to be up to 120 pC/N on an alumina substrate and approximately 50 on an LTCC substrate. Based on these results, a cantilever-type actuator was designed and fabricated on alumina substrates. Under an applied voltage of 200 V, the maximum tip deflection was about 5 μm.

PurposeAims to evaluate different thick‐film materials for use in strain sensors and temperature sensors on low‐temperature co‐fired ceramic (LTCC) substrates.Design/methodology/approachLTCC materials are sintered at the low temperatures typically used for thick‐film processing, i.e. around 850°C, The thick‐film resistor materials for use as strain and temperature sensors on LTCC tapes are studied. Thick‐film piezo‐resistors in the form of strain‐gauges are realised with 10 kΩ/sq. 2041 (Du Pont)and 3414‐B (ESL), resistor materials; thick‐film temperature‐dependent resistors were made from PTC 5093 (Du Pont), and NTC‐4993 (EMCA Remex) resistor materials.FindingsThe X‐ray spectra of the 2041 and 3414‐Bb low TCR resistors after drying at 150°C and after firing display more or less the same peaks. The electrical characteristics of 2041 resistors fired on alumina and LTCC substrates are similar indicating that the resistors are compatible with the LTCC material. After firing on LTCC substrates the sheet resistivities and TCRs of the 3414‐B resistors increased. Also, there is a significant increase in the GFs from 13 to over 25.Originality/valueInvestigates the compatibility of thick‐film materials and the characteristics of the force and temperature sensors.

PZT thick films (PbZr 0.53 Ti 0.47 O 3 with the addition of 6% PbO and 2% Pb 5 Ge 3 O 11 ) with a low sintering temperature were printed and fired on LTCC substrates (951, Du Pont), covered with an alumina barrier layer. The electrical characteristics (remanent polarisation, coercive field, dielectric constant and dielectric loss) of these PZT thick films, together with sets prepared on “unprotected” LTCC substrates and on alumina substrates were compared. Whereas the electrical characteristics of the films on LTCC substrates deteriorated significantly due to interactions between the LTCC substrates and the PZT layers the values obtained for the LTCC/alumina barrier structures were comparable with those on ceramic alumina substrates.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive temperature coefficients of resistivity, i.e. PTC 5093 (Du Pont) fired either on “green” LTCC (low temperature cofired ceramics) substrates or buried within LTCC structures, were evaluated. The active phase (ruthenium oxide) in the PTC thermistors is not present in the dried films but is formed during firing due to the decomposition of the ruthenate phase. Because of interactions between a glassy LTCC material and thermistors electrical characteristic, i.e. sheet resistivities and noise indices of thermistors fired on the surface LTCC substrates, changed from values obtained on alumina substrates. The differences in the measured electrical parameters were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and Al 2 O 3 , was confirmed by microanalysis. In the case of buried thermistors, presumably due to the incompatibility of both materials, the structure de-laminated during firing. Cracks between the buried PTC films and the LTCC substrates as well as cracks in PTC films resulted in high sheet resistivities and high noise indices.

The electrical and microstructural characteristics of 1 kΩ/sq. thick-film thermistors with high positive or negative temperature coefficients of resistivity, i.e., PTC 5093 (Du Pont) and NTC 4993 (EMCA Remex), fired on alumina or co-fired on “green” low-temperature co-fired ceramic (LTCC) substrates, are compared. The active phase in both materials (the ruthenium oxide and the semiconducting spinel in the PTC and NTC thermistors, respectively) is not present in the dried films but is formed during firing. The differences in the measured electrical parameters (sheet resistivities, temperature dependence of resistivities and noise) of the thermistors, fired on alumina or on LTCC were attributed to the interactions between the thermistor layers and the glassy LTCC substrates. The inter-diffusion of oxides, mainly PbO and SiO 2 , was confirmed by microanalysis.

PurposeTo find properties of screen printed PZT (PbZr0.53Ti0.47O3 with 6 per cent of PbO and 2 per cent of Pb5Ge3O11) thick films layers on LTCC substrate.Design/methodology/approachThe influence of PZT firing time and electrode materials on electrical characteristics and microstructure were examined. A scanning electron microscope (SEM) equipped with an energy‐dispersive X‐ray (EDS) analyser was used for the microstructural and compositional analysis.FindingsMicrostructural and compositional analyses have shown the diffusion of SiO2 from LTCC into PZT layers and the diffusion of PbO in the opposite direction. SiO2 presumably forms low permitivity lead based silicates in PZT layer. The new phase deteriorates the piezoelectric properties. The amount of diffused materials was dependent upon the electrode material and increased with increasing firing time. Better properties, i.e. higher remanent polarisation and dielectric constant were achieved for samples with PdAg electrodes and shorter firing time.Originality/valueNew information on electrical and microstructural properties of thick film PZT made on LTCC substrate.

The stability of the La 3.5 Ru 4 O 13 and La 2 RuO 5 compounds in the La–Ru–O system in various atmospheres and various temperature ranges was investigated by thermal analysis, X-ray diffraction analysis and electron microscopy. The La 3.5 Ru 4 O 13 compound is stable in oxidizing and neutral atmospheres (N 2 with 10 ppm O 2 ), while La 2 RuO 5 is partially reduced in a neutral atmosphere to form La 2 RuO 4.6 . In a reducing atmosphere both compounds decompose into metallic Ru and La 2 O 3 . The thermal expansion coefficients of La 2 RuO 5 and La 3.5 Ru 4 O 13 at 800 °C are 11.2 × 10 −6 K −1 and 9.3 × 10 −6 K −1 , respectively. The specific electrical resistivity for La 3.5 Ru 4 O 13 is relatively independent of temperature and is 2 × 10 −2 Ω cm at 800 °C, while for La 2 RuO 5 it decreases with increasing temperature and is 1 Ω cm at 800 °C.

Thick-film PTC resistors (5093, Du Pont, 1 kΩ/sq.) with a high, linear and positive TCR were fired at temperatures between 750 and 950 °C. The development of the resistors’ conductive phase and microstructure was investigated by X-ray powder-diffraction analysis and by scanning electron microscopy, respectively. Temperature coefficients of resistivity, sheet resistivities and noise indices were measured as a function of firing temperature. The 5093 resistor material is based on ruthenate, which decomposes during firing at temperatures over 800 °C into RuO 2 . As the needle-like RuO 2 crystals form, the sheet resistivities decrease from very high values to a nominal resistivity of around 1 kΩ/sq. At firing temperatures higher than 850 °C the volume of the single-crystal RuO 2 grains increases and therefore their number in a given volume of thick-film PTC layer decreases. The network of “needles ” starts to break, leading to increased sheet resistivities and increased noise indices.

The subsolidus phase equilibria in air for the Al2O3–CeO2–PbO and Al2O3–CeO2–RuO2 systems were studied with the aim of obtaining information on possible interactions between a CeO2-based solid electrolyte in solid-oxide fuel cells (SOFCs) and other oxides. No ternary compound was found in either of the systems. The tie line in the Al2O3–PbO–CeO2 system is between Al2Pb2O5 and the CeO2.

New lead-free relaxors have been produced from the K0.5Na0.5NbO3–SrTiO3 (KNN-STO) system. The solid solubility within the studied range of compositions (1 - x) K0.5Na0.5NbO3–xSrTiO3 was observed for x up to 0.33. A pseudo-cubic perovskite structure was determined for x = 0.15 to 0.25. The high density and the uniform distribution of fine grains and pores were confirmed by the translucency of these ceramics. The 0.85KNN-0.15STO composition reaches the dielectric permittivity of above 3000 at room temperature. Dielectric spectroscopy measurements revealed that, as with lead-based complex perovskites, the cationic distribution disorder is reflected in relaxorlike properties, thus suggesting possible applications based on this environmentally friendly lead-free ceramic system.

Photoinduced IR absorption was measured in undoped (LaMn) 1-δ O 3 and (NdMn) 1-δ O 3 . We observe broadening and a ∼44% increase of the midinfrared anti-Jahn-Teller polaron peak energy when La 3+ is replaced with smaller Nd 3+ . The absence of any concurent large frequency shifts of the observed PI phonon bleaching peaks and the Brillouin-zone-center internal perovskite phonon modes measured by Raman and infrared spectroscopy indicate that the polaron peak energy shift is mainly a consequence of an increase of the electron phonon coupling constant with decreasing ionic radius on the perovskite A site. This indicates that the dynamical lattice effects strongly contribute to the electronic band narrowing with decreasing in doped giant magnetoresistance manganites.

The characteristics of 10 kohm/sq. thick-film resistors (2041, Du Pont and 2341-B, ESL) fired on tetragonal ZrO 2, low-temperature cofired ceramic (LTCC) and dielectric-on-steel substrates were investigated with the aim of determining the compatibility of these resistor materials, which were developed for firing on Al 2O3, with other substrates. Possible interactions between the thick-film resistors and the substrates were investigated. Sheet resistivities, temperature coefficients of resistivity, noise indices and gauge factors (GFs) were measured. The results indicate that the 2041 and 3414-B thick-film resistors could be used on the evaluated substrates if an allowance is made for the increased temperature coefficient of resistivities (TCRs) of both resistor materials on the zirconia substrates and for the increased sheet resistivities and TCRs of the 3414-B resistors on the LTCC substrates. © 2003 Elsevier B.V. All rights reserved.

Subsolidus equilibria in air in the NiO–PbO–TiO 2 system were studied with the aim of obtaining information about possible interactions between oxidised metallic nickel substrates and PZT thick films. No ternary compound was found in the system. The tie lines were between PbTiO 3 and NiTiO 3 and between PbTiO 3 and NiO.

Thick-film resistors that were developed for firing on alumina substrates have been evaluated in terms of their compatibility with ZrO 2 . The characteristics of a number of 10 kohm/sq. resistors that were fired on 96% alumina and on tetragonal zirconia substrates were investigated. Possible interactions between the resistor material and the zirconia were studied with X-ray powder-diffraction analysis, with scanning electron microscopy and with energy-dispersive X-ray analysis. Sheet resistivities, temperature coefficients of resistivity, current noise and gauge factors were measured. The results indicate that the evaluated thick-film resistors are compatible with zirconia ceramics.

Strain gauges can be realised by printing and firing thick‐film resistors on ceramic substrates that are usually based on alumina. However, sensing elements made on some other substrates – tetragonal zirconia or stainless steel – would exhibit some improved characteristics, either due to a lower modulus of elasticity or a higher mechanical strength. As thick‐film resistors are developed for firing on alumina substrates their compatibility and possible interactions with other kinds of substrates have to be evaluated. The sheet resistivities and noise indices of the resistors were comparable, whereas the gauge factors were lower for the dielectric‐on‐steel substrates. The temperature coefficients of resistivity (TCR) of the resistors on the ZrO2 and dielectric‐on‐steel substrates were higher than the TCRs on the alumina substrates, which was attributed to the higher thermal expansion coefficient of the tetragonal zirconia and the stainless steel.

Subsolidus equilibria in air in the RuO2–Bi2O3–CeO2 systems were studied with the aim of obtaining information on possible interactions between a Bi2Ru2O7-based cathode and a CeO2-based solid electrolyte in solid-oxide fuel cells. Bi2O3 is soluble in CeO2, and forms a cubic fluorite solid solution Bi1-xCexO2-x/2 up to Bi1/3Ce2/3O1.83, while no solid solubility of the CeO2 in Bi2O3 was detected. No ternary compound was found in the system. The tie line is between Bi2Ru2O7 and the CeO2 solid solution.

Some commercial 10 kΩ/sq. thick-film resistors based on RuO 2 , ruthenates or a mixture of RuO 2 and ruthenates, were evaluated. The resistors were fired at different temperatures to determine the influence of firing temperature on the electrical and microstructural characteristics. The conductive phase in the resistors (RuO 2 , ruthenate, and a mixture of RuO 2 and ruthenate) was determined with X-ray powder-diffraction analysis. The microstructures of the thick-film resistors were analysed with scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The temperature coefficients of resistivity, noise indices and gauge factors were measured as a function of firing temperature. After long-term high temperature firing (6 h at 950 °C) ruthenate transforms into RuO 2 coinciding with a significant increase of the temperature coefficients of resistivity.

The diffusion of cations and the formation of compounds at the interface of diffusion couples of BaTiO3 and LaNi0.6Co0.4O3 have been investigated by scanning electron microscopy and energy dispersive X-ray spectroscopy. The firing conditions have been varied with respect to firing temperature, firing time and heating rate. At the interface between BaTiO3 and LaNi0.6Co0.4O3 a layer of a perovskite type compound with varying composition is formed. Ti and La ions diffuse preferentially towards the reaction layer from the BaTiO3 and the LaNi0.6Co0.4O3, respectively. A consequence of the preferred diffusion of Ti towards the reaction layer is a depletion of Ti and the enrichment of Ba within the BaTiO3 adjacent to the interface causing the formation of overstoichiometric BaTiO3 (with respect to Ba), which is known to exhibit pronounced grain growth inhibition. The zone of reduced grain size is found to reach approximately 200 μm into the BaTiO3 bulk.

The characteristics of Pb(Zr,Ti)O3(PZT) thick films that were printed and fired on Ni substrates were studied. The dielectric characteristics of samples sintered at 850°C on Ni substrates could not be measured due to the formation of a NiO layer at the Ni/PZT interface. The scanning electron microscope and energy dispersive X-ray analysis of cross-sections of the PZT thick films on Ni substrates, and of a mixture of PZT and NiO powders, fired at 850°C, did not indicate the formation of secondary phases. However, the transmission electron microscopy showed around 8% solid solubility of NiO in the PZT. A new structure with a prefired, Au thick-film layer was designed in order to prevent the diffusion of the NiO to the PZT layer during sintering. The dielectric properties of the PZT layers printed and fired on the Ni substrates with the prefired Au electrode were significantly better than those of the layers on the uncoated substrate, the dielectric losses decreased from 0.23 to 0.05.