Search

For transducer design, it is essential to know the acoustic properties of the materials in their operating conditions. At frequencies over 15 MHz, standard methods are not well adapted because layers are very thin and backings have very high attenuation. In this article, we report on an original method for measuring the acoustic properties in the 15–25 MHz frequency range, corresponding to typical skin-imaging applications, using a backing/piezoelectric multilayer structure. Onto a porous Pb(Zr0.53Ti0.47O3 (PZT) substrate, a piezoelectric PZT-based layer with a thickness of $\sim 20~\mu \text{m}$ was deposited and directly used to excite an acoustic signal into water. Herein, the measured signal corresponds to the wave that is first reflected on a target in water, then propagates back to the multilayer structure, and is transmitted through the thick film and further to the rear face of the porous backing, where it is again reflected and returns to the piezoelectric thick film, thus avoiding overlap with the electrical excitation signal. Two types of PZT backings with similar porosity of ~20% and spherical pores with size of 1.5 and 10 $\mu \text{m}$ were processed. The ultrasound group velocities were measured at ~3500 m/s for both samples. The acoustic attenuation of the backings with pore size of 1.5 and 10 $\mu \text{m}$ were 12 and 33 dB/mm, respectively, measured at 19 MHz. This advanced measuring technique demonstrated potential for the simple measurements of acoustic properties of backing at high frequencies in operating conditions. Importantly, this method also enables rapid determination of the minimum required thickness of the backing to act as a semi-infinite medium, for high-frequency transducer applications.

A systematic investigation of the seeding effects on the mechanochemical synthesis of lead magnesium niobate – lead titanate 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN–10PT), one of the most studied relaxor-ferroelectric material for electrocaloric applications, is reported. The perovskite crystallisation process was followed by X-ray diffraction using the Rietveld refinement method and transmission electron microscopy. Compared to the mixed-oxides case which requires 143 h of high-energy milling, the milling time needed to obtain a phase-pure PMN–10PT perovskite using PT seeds is reduced almost twice. The presence of PT seeds leads to faster transitions from the amorphous to pyrochlore and to perovskite phases compared to the mixed-oxides case. A sintering study demonstrates, for the first time, that a second, metastable, pyrochlore phase is taking part in the processes of perovskite formation. The PMN–10PT ceramic prepared from the PT-seeded powder exhibits electrocaloric properties comparable to reported values for PMN–10 PT prepared from oxides.

This work reports the growth of 170 nm to 400 nm thick tetragonal {001}-textured Nb-doped Pb(Zr,Ti)O 3 (PNZT) thin films on AISI 304 stainless steel substrates by pulsed laser deposition. Al 2 O 3 and LaNiO 3 buffer layers prevent substrate oxidation and act as growth template to promote the PNZT thin film texture. The thin films have a dielectric constant of 390 at 1 kHz, with dielectric losses below 0.05. After P-E loop measurements, permittivity increases up to 430 with a remanent polarization of 31.3E-6 C/cm2 and a coercive field of 164 kV/cm1. As compared to previously reported PZT thin films on stainless steel substrates, the improved ferroelectric properties of these PNZT thin films make them promising candidates for future piezoelectric MEMS applications requiring non-brittle substrates, especially for sensing purposes.

The electrocaloric effect (ECE), i.e., the conversion of the electric into the thermal energy has recently become of great importance for development of a new generation of cooling technologies. Here, we explore utilization of [Pb(Mg1∕3Nb2∕3)O3]0.9[PbTiO3]0.1 (PMN-10PT) relaxor ceramics as active elements of the heat regenerator in an ECE cooling device. We show that the PMN-10PT relaxor ceramic exhibits a relatively large electrocaloric change of temperature ΔTEC > 1 K at room temperature. The experimental testing of the cooling device demonstrates the efficient regeneration and establishment of the temperature span between the hot and the cold sides of the regenerator, exceeding several times the ΔTEC within a single PMN-10PT ceramic plate.

We have investigated the processing of lead-zirconate-titanate-based thick films by inkjet printing Pb(Zr0.53Ti0.47)0.98Nb0.02O3 with a 6 mol% excess of PbO nanosized powder dispersed in water. Different waveforms were employed to determine the optimum size and shape of the drops. A uniform, defect-free pattern with dimensions of 4 mm × 4 mm can be printed using 20 V and a drop spacing of 20 μm. The inkjet-printed films were heated to 400 °C to remove the organics and subsequently sintered at 750 and 850 °C. The correlations between the density, grain size and electromechanical properties of the thick films and bulk ceramics are qualitatively discussed. A thickness coupling factor of 46% was obtained for a 15-μm-thick film sintered at low temperature of 850 °C, which is comparable to the value of the bulk ceramic with an identical nominal chemical composition. Our results are important for the economic and environmental-benign printing of piezoelectric materials applicable in variety of electronic devices, such as sensors, actuators, transformers, piezoelectric energy harvesters and transducers.

Lead-free piezoelectric 0.95(Na0.49K0.49Li0.02)(Nb0.8Ta0.2)O3&ndash, 0.05CaZrO3 with 2 wt % MnO2 addition was prepared using mechanochemically-assisted solid-state synthesis. Upon mechanochemical activation of the mixture of reagents partial amorphization occurs which contributes to a significantly lower temperature of completion of the solid-state reaction, ~600 &deg, C as opposed to ~700 &deg, C for the conventional solid-state synthesis as determined by thermal analysis. The ceramic specimens prepared by the mechanochemically-assisted route exhibit improved compositional homogeneity and slightly enhanced piezoelectric properties, achieved in a considerably shorter processing time compared to the conventional solid-state synthesis route, which was studied as a reference.

Electrocaloric (EC) cooling elements in the form of multilayers (MLs) were prepared. The elements consist of five layers of the relaxor-ferroelectric 0.9Pb(Mg 1/3 Nb 2/3 )O 3 –0.1PbTiO 3 , about 60 μm thick, with internal platinum electrodes and exhibiting a dense, uniform microstructure with a grain size of 1.7 μm. The largest temperature change Δ T EC of 2.26 K was achieved at an electric field ( E ) of 100 kV cm −1 and at 105 °C, measured by a high-resolution calorimeter. These results agree well with the indirect measurements. The EC coefficient, Δ T EC /Δ E, obtained for the MLs, is similar to the value obtained for bulk ceramics of the same composition. The Δ T EC values above 2 K over a broad temperature range from 75 to 105 °C make the ML elements suitable candidates for EC cooling devices at significantly lower voltages than bulk ceramic plates with comparable dimensions and mass.

We have investigated the electrocaloric (EC) properties of the ceramic 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3. A variety of samples with different median grain sizes, i.e., 1.0, 2.2 and 4.0 μm, and relative densities of about 96% were prepared using atmospheric sintering at 1200oC for 2, 8 and 16 h. The ceramic material with a median grain size of 2.2 μm exhibited the highest value for the EC temperature change, i.e., 1.27 K at 60 kV cm−1, measured with a high-resolution calorimeter. This value is 25 and 19% higher than the value for the ceramics with the finer and the coarser grains, respectively.

It is shown that a substantial enhancement of the electrocaloric (EC) effect can be achieved with a properly engineered, ceramic microstructure. In particular, a significant impact of the grain size on the EC effect in 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 ceramics is demonstrated. The single-phase perovskite ceramics with grain sizes ranging from 2.8 to 9.4 mm were prepared. The largest EC coefficient ΔTEC/ΔE is obtained for the ceramic with 5.8-μm grains, as a consequence of its larger saturation polarization. The EC response is limited by the breakdown strength of the material, which is higher than 160 kV cm−1 for the fine-grained ceramics. For the material with a ∼98% relative density and 3.6-μm grains, the large EC temperature change (ΔTEC) of 3.45 °C is achieved. This value is the highest reported so far for Pb-based perovskites and is comparable to best results obtained by multi-critical-point enhancement.

PbZr0.38Ti0.62O3 and PbZr0.36Ti0.64O3 thick films deposited by screen printing on (0 0 0 1) single crystal sapphire substrates and prepared at two different sintering temperatures, were studied by Fourier-transform infrared reflectivity, time-domain THz transmission spectroscopy and micro-Raman spectroscopy. The dielectric response is discussed using the Lichtenecker model to account for the porosity of the films and to obtain the dense bulk dielectric functions. Results are compared with bulk tetragonal PZT 42/58 ceramics. The dynamic response in the films is dominated by an overdamped lead-based vibration in the THz range, as known in PZT, but its evaluated dielectric contribution is affected by the porosity and roughness of the surface.

In the contribution the design and the fabrication of two different types of ceramic packaging for PiezoMEMS devices is presented. The first ceramic packaging is designed for housing the piezoelectric energy harvester. This packaging is made using LTCC technology and in the final application will integrate piezoelectric device, electronic circuit, storage capacitor and other components into the complex microsystem. The second packaging is developed for piezoelectric vibrating device as a part of water-purification system. In this case, the thick-film technology is used for electrical interconnection of piezoelectric actuators and for the hermetic watertight insulation of the system.

Dielectric properties of (PSN) ceramic system, prepared from mechanochemically activated powder, were studied in a broad temperature range of 150–750 K. Various distinctive contributions were recognized in the detected reponse. A typical relaxor dispersive maximum, accompanied by a sharp dielectric anomaly showing a hysteretic behavior, reveals that developed disordered PSN ceramics undergoes a spontaneous relaxor-to-ferroelectric phase transition, even in zero electric field. At high temperatures, a strong dielectric dispersion due to the Maxwell–Wagner-type contributions of interface layers between the sample and contacts governs the detected response above 500 K. The intrinsic high-temperature dielectric response follows, however, the universal scaling rather than the classical mean-field behavior. The latter can be rejected on the confidence level better than 99% according to the F-test and, furthermore, the analysis revealed a critical exponent that indicates a critical behavior associated with universality classes typically found in spin glasses. Finally, nearly perfect agreement between the fitting parameter of K (obtained by analysis in the interval of 600–775 K) and the experimentally detected value of this relaxor-to-ferroelectric phase transition temperature manifests that the low-temperature fingerprint behavior can be observed at much higher temperatures, well above the dispersive relaxor dielectric maximum.

The delafossite CuAlO2 powder was prepared from the nano-boehmite AlOOH·xH2O and Cu2O by the solid state synthesis at 1100 °C in argon. The inherently slow solid state reaction was accelerated by introducing rod-like boehmite nano-particles which fully covered the 1 μm sized Cu2O particles in the reactant mixture, and decomposition of the nano-boehmite upon calcination. In contrast, the reaction between the Cu2O and Al2O3, introduced as a reference, resulted in mixed phases under the same experimental conditions. Sintering of the nano-boehmite derived CuAlO2 powder compact at 1100 °C for 2 h in air resulted in the delafossite ceramic with 86% of theoretical density, without any impurities detectable by X-ray diffraction analysis. The analysis of the microstructure by scanning electron microscopy confirmed that the bulk of the sintered sample was delafossite phase with uniformly distributed porosity, with only traces of Cu-rich impurities at the surface.

In this work the screen-printed piezoelectric 0.65Pb(Mg 1/3 Nb 2/3 )O 3 -0.35PbTiO 3 thick films were prepared on metalized low-temperature co-fired ceramic substrates. Such substrates are interesting for micro-electro mechanical systems, for example for piezoelectric sensors and actuators. The prepared thick films exhibit the piezoelectric coefficient d 33 equal to 120 pC/N.

The existence and feasibility of the multicaloric, polycrystalline material 0.8Pb(Fe1/2Nb1/2)O3-0.2Pb(Mg1/2W1/2)O3, exhibiting magnetocaloric and electrocaloric properties, are demonstrated. Both the electrocaloric and magnetocaloric effects are observed over a broad temperature range below room temperature. The maximum magnetocaloric temperature change of ~0.26 K is obtained with a magnetic-field amplitude of 70 kOe at a temperature of 5 K, while the maximum electrocaloric temperature change of ~0.25 K is obtained with an electric-field amplitude of 60 kV/cm at a temperature of 180 K. The material allows a multicaloric cooling mode or a separate caloric-modes operation depending on the origin of the external field and the temperature at which the field is applied.

Oxygen octahedra tilting is a common structural phenomenon in perovskites and has been subject of intensive studies, particularly in rhombohedral Pb(Zr,Ti)O3 (PZT). Early reports suggest that the tilted octahedra may strongly affect the domain switching behavior as well as the dielectric and piezoelectric properties of PZT ceramics. In a way similar to that proposed for tilts, however, charged defects, associated with oxygen vacancies, may also inhibit the motion of the domain walls, resulting macroscopically in pinched hysteresis loops and reduced piezoelectric response. Here, we revisit the early studies on rhombohedral PZT ceramics with tilted octahedra by considering a possible role of both tilts and charged defects on domain-wall motion. We show that the observed pinched hysteresis loops are likely associated with the presence of defect complexes containing charged oxygen vacancies, and not tilts, as suggested in some cases. Regardless of the presence or absence of long-range ordered tilts in rhombohedral PZT, the effect of charged defects is also prominent in weak-field permittivity and piezoelectric properties, particularly at sub-Hertz driving conditions where the conductivity, related to the motion of oxygen vacancies, gives rise to strong frequency dispersion.

In this work, the effect of introducing tetragonal yttria-stabilized zirconia (TZ) particles in soft [Pb0.98Ba0.01][(Zr0.53Ti0.47)(0.98)Nb-0.02]O-3 (PZT) was investigated. Both microstructure and electrical properties of the PZT-xTZ (x = 0, 2, 5, 10, 20 vol%) composites were studied and correlated. The addition of zirconia hinders the matrix grain growth, resulting in smaller grains. According to X-ray diffraction analysis, zirconia containing composites have a higher rhombohedral-to-tetragonal phase ratio, in addition to lower dielectric and piezoelectric properties, in comparison to pure PZT. Electrical properties, in terms of strain- and polarization-electric field hysteresis curves, are presented and correlated with the observed phase compositions and microstructures. The extrinsic contribution to the piezoelectric properties in PZT and PZT-xTZ was studied by measuring the frequency and the stress field amplitude dependences of the piezoelectric d(33) coefficient.

We report detailed dielectric investigations of Pr 1− x Ca x MnO 3 (PCMO, x =0.5) ceramics, a member of the perovskite manganite family that exhibits a colossal magnetoresistance. Analysis of the electrical conductivity and dielectric constant data revealed that in the low temperature phase, below 42 K, small polarons are responsible for the charge transport in the system. This provides a new understanding of the phase diagrams in PCMO systems

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.

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.

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 phase composition, microstructure and electrical properties of thick-film structures based on 0.65Pb(Mg 1/3 Nb 2/3 )O 3 –0.35PbTiO 3 (PMN–PT) were studied. PMN–PT powder with 2 mol% of excess PbO was prepared by high-energy milling from the constituent oxides. A high yield of perovskite PMN–PT with nano-sized particles was obtained after the synthesis. A paste was prepared from the obtained powder, screen printed on platinised alumina substrates and sintered at 850, 900 and 950 °C. Single-phase PMN–PT thick-film structures without any pyrochlore phase were obtained after the sintering. The dense PMN–PT layers had good dielectric, piezoelectric and ferroelectric properties. The relative dielectric permittivity of 4100 and the peak value of 41,000 for the film sintered at 950 °C compare well with bulk ceramics sintered at much higher temperatures. The d 33 value of the film was 170 pC/N. The obtained values for the dielectric properties demonstrate the good chemical homogeneity of material synthesized by high-energy milling.

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.

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.

Thick film varistors based on the system ZnO–Bi 2 O 3 –Sb 2 O 3 have been prepared by screen printing technology on dense alumina substrates. Different processing strategies have been designed in order to control the excessive volatilization of Bi 2 O 3 in varistor films during the sintering, due to the high area–volume ratio, and as a means to improving their electrical response. Starting powders were selected and pre-treated in different ways to obtain different phases and control the Bi-rich liquid phase formation. Significant differences have been observed in the electrical properties which are related to the selection of the starting powders.

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.

0.5Pb(Zr0.575Ti0.425)O3–0.5Pb(Fe2/3W1/3)O3 (0.5PZT–0.5PFW) belongs to the solid solutions which exhibits some bi-relaxor properties, with both ferroelectric and magnetic relaxor properties. Recently it was reported that the thin film of 0.8Pb(Zr0.53Ti0.47)O3–0.2Pb(Fe2/3W1/3)O3 (0.8PZT–0.2PFW) has a new and very large magnetoelectric effect—switching from Pr to zero with applied magnetic field of less than a Tesla. We report dielectric and ac electric conductivity investigations of the 0.5PZT–0.5PFW bulk ceramics. A detailed analysis of the temperature dependence of the universal dielectric response parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 450 K this mechanism governs the charge transport in the system. This provides a new understanding of the magnetoelectric effect in 0.5PZT–0.5PFW.

Ferroelectric ceramic materials based on solid solutions of Pb(Zr,Ti)O3 (PZT) are used in the electronics industry for sensors and actuators and for electromechanical transducers, to name just a few examples. Thick-film technology, i.e., the deposition of thick-film pastes by screen printing, primarily on alumina substrates, is a relatively simple and convenient method to produce layers with a thickness up to 100 μm. The characteristics of thick-film ferroelectrics are similar to those of bulk materials [1–4]. Low-temperature co-fired ceramics (LTCC) materials, which are sintered at the low temperatures typically used for thick-film processing, i.e., around 850 ◦C, are based either on crystallizable glass [5, 6] or a mixture of glass and ceramics, for example, alumina, silica or cordierite (Mg2Al4Si5O18) [7, 8]. Jones et al. have presented a comparison of the mechanical and chemical characteristics of both green and fired LTCC tapes from different suppliers in [9]. Ceramic multi-chip modules (MCM-C) are multilayer substrates with buried conductor lines. An additional contribution to the smaller size and the higher density of MCM-C is the ability to integrate screenprinted resistors, or sometimes capacitors and inductors. These screen-printed components can be placed either beneath the discrete components on the surface of the multilayer dielectric or buried within the multilayer structure. For an overview of passive integrated components in MCM see, for example [10]. For some applications, for example integrated sensors or micro-actuators, PZT thick-films on LTCC that are sintered at relatively low temperatures (around 850 ◦C) comparable with LTCC’s firing temperatures, would be of interest [11, 12]. The aim of this work was to study the compatibility between LTCC and screenprinted PZT as well as the electrical characteristics of the PZT layer. PZT 53/47 powder (PbZr0.53Ti0.47O3) with an excess 6 mol% of PbO was prepared by mixed-oxide synthesis at 900 ◦C for 1 h from high-purity PbO (litharge) 99.9% (Fluka), ZrO2 99% (Tosoh), and TiO2 99% (Fluka). To this was added 2 wt% of lead germanate, with the composition Pb5Ge3O11 (melting point 738 ◦C) as a sintering aid. Lead germanate (PGO) was also prepared by mixed-oxide synthesis from PbO and GeO2 99% (Ventron) at 700 ◦C. After synthesis, both compositions were ball milled in acetone for 1 h and dried. A thick-film paste was prepared from the PZT (2% PGO) and an organic vehicle (ethyl cellulose, alpha-terpineol and butil carbitol acetate) by mixing on a three roll mill. The green LTCC 951 tape (Du Pont) and alumina ceramics were used for substrates. The thick-film structure was prepared by first printing gold film (Remex 3243) and then the PZT film. The PZT film was printed 6 times with intermediate drying. The gold and PZT layers were cofired at 850 ◦C for 8 h in a closed alumina crucible. The thickness of the PZT films after the thermal treatment was around 50 μm. The green and fired Du Pont LTCC 951 tapes were analyzed by X-ray diffraction (XRD) analysis with a Philips PW 1710 X-ray diffractometer using Cu Kα radiation. X-ray spectra were measured from 2 = 20 ◦ to 2 = 70 ◦ in steps of 0.04 ◦. X-ray spectra are shown in Fig. 1. The unfired material is a mixture of alumina and glass. After firing at 850 ◦C peaks of anorthite ((Na,Ca)(Al,Si)4O8) phase appear. The peaks of alumina and anorthite are denoted by “A” and asterisk, respectively. For the electrical measurements gold electrodes were sputtered onto the PZT films. The values of the remanent polarization and the coercive field were determined from ferroelectric hysteresis curves measured with an Aixact TF Analyzer 2000 at 50 Hz. The real and imaginary parts of the complex dielectric constant were measured with an HP 4284 A Precision LCR Meter at 1 kHz. In Table I the electrical parameters, i.e., remanent polarization Pr, coercive field Ec, dielectric constant e′ and dielectric loss tan δ, of the co-fired LTCC/Au/PZT structure are presented. The electrical characteristics of this structure are compared to the characteristics of a similar structure printed on alumina substrates [13]. Hysteresis loops of the PZT films on the alumina and LTCC substrates are shown in Fig. 2.

In this investigation we show that the dielectric, ferroelectric and piezoelectric properties of stoichiometric 0.57Pb(Sc 1/2 Nb 1/2 )O 3 –0.43PbTiO 3 (0.57PSN–0.43PT) ceramics prepared by mechanochemical synthesis are comparable or even better than the properties of 0.57PSN–0.43PT ceramics with Nb doping, which was proposed to enhance the electrical properties. Here, the stoichiometric ceramic was sintered to 97% of theoretical density at a temperature of 1000 °C, which is 200–300 °C lower than previously reported. The dielectric constant ɛ , remnant polarization P r , piezoelectric coefficient d 33 , coupling coefficients k p and k t and mechanical quality factor Q m of the ceramics prepared by mechanochemical synthesis were 2200, 43 μC/cm 2 , 570 pC/N, 0.71, 0.56 and 38, respectively. The effects of the poling field on the structural and electrical properties of the 0.57PSN–0.43PT ceramics were investigated. The results show that the ratio of the monoclinic to the tetragonal phases is influenced by the application of the poling electric field. The non-poled ceramics contain 71% of the monoclinic phase and 29% of the tetragonal phase. The highest d 33 , k p and k t were measured for ceramics poled at an electric field of 3 kV/mm. For these poled ceramics a phase determination of 86% monoclinic phase and 14% tetragonal phase was obtained from Rietveld refinements.

International audience; Thick films with the nominal composition 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) (0.65PMN-0.35PT) were produced by screen-printing and firing paste prepared from an organic vehicle and pre-reacted powder. The films were fired for 2 h at 950 degrees C on alumina (Al2O3), platinum (Pt), aluminium nitride (AlN) and 0.65PMN-0.35PT substrates. The films were then characterized using scanning electron microscopy, X-ray diffraction and dielectric constant measurements. The X-ray analysis did not detect the presence of any undesirable pyrochlore phase, and the differences in the phase compositions were determined with a Rietveld refinement. The variations of the cell parameters vs. the temperature for the monoclinic and tetragonal phases were calculated. It was demonstrated that under similar processing conditions the microstructures, phase compositions and dielectric properties strongly depended on the stress in the thick films due to the different temperature expansion coefficients of the thick films and the substrates. The 0.65PMN-0.35PT thick films under compressive stresses (for the case of the Al2O3 and Pt substrates) exhibited a tetragonal phase in addition to the monoclinic one. The films were sintered to a high density and with a coarse microstructure. These microstructures favour a high dielectric constant. In contrast, for the films under a tensile stress, like the films on AlN substrates, the films were sintered to a lower density and the microstructure consisted of smaller grains. The X-ray analysis showed mainly a monoclinic phase, while the tetragonal phase was not detected. These results indicate the importance of the stresses in 0.65PMN-0.35PT thick films and their influence on the structural and electrical characteristics of the films.

Piezoelectric thick films based on Pb(Zr, Ti)O 3 (PZT) were prepared on LTCC substrates 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 PZT layers were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis. The dielectric permittivities, dielectric losses, remanent polarisations, coercitive fields and piezoelectric constants d 33 were measured. The dielectric and piezo electric characteristics of the PZT fired on the LTCC substrate deteriorated, as compared with samples on alumina, due to interactions between the LTCC substratse and the PZT layers. This was attributed to the diffusion of the glassy phasee from the LTCC into the active PZT layer and to the diffusion of the PbO from PZT layer into the LTCC substrates.

Modern advanced 3D microelectronic packages are in many cases made as multilayer ceramic modules with integrated electronic components and sub-circuits. The Low Temperature Co-Fired Ceramics (LTCC) technology is considered as one of more advanced technologies for fabrication of these structures. The increasing versatility of LTCC technology applications is a consequence of such attractive features of this technology as possibility of creation of three-dimensional structures as many of applications demand possibility of structuring of channels, cavities and reaction chambers, membranes and free-standing beams within LTCC ceramics. To obtain these buried structures without delamination and/or sagging during lamination processes (compressing of green LTCC foils at around 70°C) so called sacrificial layers are often used. During lamination sacrificial layers (screen printed thick film pastes or tapes) support buried cavities. During firing layers must burn out before LTCC tapes are densely sintered to enable the diffusion of air into structures. Six different carbon based materials (four pastes and two tapes) were evaluated. The thermo gravimetrical analysis (TGA) was used to determine the optimised burn-out temperatures and times. LTCC test structures were designed to evaluate the “quality” of buried cavities with different sacrificial materials and with different processing parameters.

${\text{Pr}}_{1\ensuremath{-}x}{\text{Ca}}_{x}{\text{MnO}}_{3}$ (PCMO, $x=0.3$) ceramic is a member of the manganite family that exhibits a colossal magnetoresistance. We report a comprehensive study of perovskite manganite PCMO $(x=0.3)$ ceramic with EPR, dielectric spectroscopy, and ac electrical conductivity. Activated-type temperature dependence of EPR linewidth is a strong signature for a hopping of Jahn-Teller polarons above $\ensuremath{\approx}150\text{ }\text{K}$. Analysis of the electrical conductivity and dielectric constant data suggests the ordering of polarons in the charge-disordered state of PCMO $(x=0.3)$ below 60 K. This provides a new understanding of the phase diagrams in PCMO systems.

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.

PZT (PbZr/sub 0.53/Ti/sub 0.47/O/sub 3/ with 6% of PbO and 2% of Pb/sub 5/Ge/sub 3/O/sub 11/) thick films with a low sintering temperature were printed and fired on either pre-fired or green LTCC foils (LTCC 951, Du Pont). The electrical characteristics of these PZT thick films, together with a set prepared on alumina substrates, were compared. The electrical characteristics of the samples fired at 800/spl deg/C deteriorated significantly due to interactions between the LTCC substrate and the PZT layer. It is presumed that the SiO/sub 2/ that diffused from the LTCC into the PZT layers formed low-permitivity lead-based silicates, which are detrimental to the dielectric properties of the PZT.

The effects of the poling field on the structural and electrical properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 (0.65PMN–0.35PT) ceramics were investigated. The highest piezoelectric coefficient d 33, coupling coefficients k p, k t, and mechanical quality factor Q m were achieved for ceramics poled at electric fields between 2 and 3.5 kV/mm, whereas the d 33, k p, k t, and Q m of ceramics poled at higher electric fields, i.e., 4 and 4.5 kV/mm, were lower. The non-poled ceramics contained 86% of the monoclinic phase with the space group P m and 14% of the tetragonal phase with the space group P4m m. However, the ceramics poled at 2.5 kV/mm contained 99% of the monoclinic phase and the rest is the tetragonal phase. The results show that the ratio of the monoclinic to the tetragonal phases can be changed by the application of a poling electric field and that the extent of this change is dependent on the field strength.