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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.

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.

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.

This paper presents manufacturing process of laser-shaped thick-film resistors as well as their chosen electrical, geometrical, microstructural and stability properties. Test structures were based on commercially available conductive and resistive pastes deposited on Al 2 O 3 substrates. Resistors made in standard screen printing process after firing were patterned using laser beam in order to minimize their planar dimensions to tenths of millimeter and below. Prepared samples were subjected to number of electrical tests and some characteristic parameters like temperature coefficient of resistance (TCR) were calculated based on these measurements. Test samples were also exposed to long-term thermal ageing. Moreover the laser profilometer was used for three-dimensional characterization of components. Scanning electron microscope (SEM) was used for the microstructural analysis and the EDS (Energy Dispersive X-ray Spectroscopy) of samples is given.

For temperature sensors in MEMS (the ceramic micro electro-mechanical systems) thick-film temperature-dependent resistors PTC-5093 (Du Pont) and NTC-4993 (Ferro) resistor materials were evaluated. Thick-film piezo-resistors for strain-gauges were realised with Du Pont 2041 (low noise and very stable resistors) and ESL 341-B (high gauge factor) 10 kohm/sq. resistor materials. The PZT paste was prepared from a pre-reacted PZT powder with the composition near the morphotropic phase boundary (Zr/Ti 53/47). Thick-film PTC and NTC thermistors, ldquonormalrdquo low TCR resistors and PTZ piezoelectric pastes were printed and fired on Heraeus HL-2000 LTCC zero shrink substrates. Results obtained on relatively inert alumina substrates were used for the comparison. In most cases the required characteristics of thick film materials on LTCC substrates were inferior to those obtained on relatively inert alumina substrates. This is attributed to the inter-diffusion of oxides, mainly SiO2, from the rather glassy LTCC substrates into active layers and presumably also to the diffusion of some from oxides from thick fil layers into LTCC substrates.

The electrical and microstructural characteristics of thick-film resistors fired at different temperatures and ldquoover-firedrdquo to reach an equilibrium between the glass and the conductive phases was presented. Two cases are described: resistors with a conductive phase included in the resistor paste (the majority of thick-film resistors) and resistors where the required characteristics depend on a conductive phase that forms during firing.

The electrical and microstructural characteristics of NTC thick-film resistors, fired either on alumina or cofired on "green" LTCC substrates are compared. The NTC resistors, fired on LTCC (as compared to resistors on alumina substrates), have higher sheet resistivities, higher beta factors, and also significantly higher noise indices. SEM and EDX analysis indicated the interaction between NTC and LTCC materials, mainly the diffusion of the glass phase from the LTCC substrate into the NTC resistor.

The development of the conductive phase in some thick-film resistors with both low and with high temperature coefficients of resistivity was studied using X-ray diffraction analysis and electron microscopy. After long-term high-temperature firing the conductive phase in thick-film resistors based on RuO2 remains unchanged, while the ruthenates decompose. This is presumably due to interactions of the ruthenate with the silica-rich glass phase in the resistors. The reaction kinetics is faster for higher concentrations of SiO2

Stoichiometric K0.5Na0.5NbO3 solid solution(KNN) was prepared by solid-state synthesis from alkaline carbonates and niobium oxide. Thermal decomposition of the powder mixture occurs upon heating to 700 °C followed by crystallization of the perovskite phase. After sintering at 1100 °C, 2h the stoichiometric KNN reaches 94 % of theoretical density. Dielectric constant of stoichiometric KNN is 620, and the losses 0.03.

International audience; Piezoelectric nanogenerators are attracting substantial attention due to the environmental constraints and ecological considerations of energy harvesting. However, the Achilles' heel of the majority of these nanogenerators is the presence of toxic compounds or the requirement of a poling process to promote higher piezoelectric effect. Here, a self-poled and bio-flexible piezoelectric nanogenerator (BF-PNG) is designed, based on lead-free biocompatible Ba0.85Ca0.15Zr0.10Ti0.90O3 nanoparticles that are functionalized with polydopamine and embedded in the polylactic acid biodegradable polymer. The BF-PNG can generate open-circuit voltage and short-circuit current of 14.4 V and 0.55 µA, respectively, under gentle finger tapping. Furthermore, it demonstrates an outstanding high mechanical robustness, stable and durable output even after one year. It achieves a maximum power density of about 7.54 mW/cm3 at a low resistive load of 3.5 MΩ. The feasibility of the BF-PNG by trigging commercial electronics such as charging capacitors and lighting a LED is verified, and the BF-PNG can drive a 1 µF capacitor to store the energy of 3.92 µJ within 115 s under gentle finger tapping. This research demonstrates that a lead-free piezoceramic in combination with a biodegradable piezopolymer can lead to a design of bio-flexible piezoelectric nanogenerators with outstanding performances and in particular useful in self-powered medical devices.