Juha Hagberg

Electrocaloric characteristics in reactive sintered 0.87Pb(Mg1∕3Nb2∕3)O3–0.13PbTiO3

Only little data have been published on direct electrocaloric measurement of Pb(Mg1∕3Nb2∕3)O3–PbTiO3 (PMN-PT) ceramics. In this paper, the electrocaloric characteristics of 0.87PMN-0.13PT ceramic were determined by direct measurements. A strong transition in the electrocaloric effect was found at about 18°C, which is the same as the depolarization temperature Td. The maximum electrocaloric temperature rise was ΔT=0.558°C at TECm=70°C and E=2400kV∕m, well above the transition at Td=18°C. The existence of two maximums could be an indication of several mechanisms being responsible for the electrocaloric effect.

Gravure offset printing development for fine line thick film circuits

The resolution of conventional graphical gravures is limited to about 50 to 100 microns depending on the technology used. For these gravures the depths are dependent on the widths of the grooves. For electrical circuitry, the target is to achieve 25 microns line and space widths in the near future. To obtain a reasonably high sheet resistance, the printed ink height must be reasonably high. The stated requirements require further development of the whole printing process together with the associated inks. The first step was to evaluate the gravure manufacturing method, which is capable of producing gravures of sufficient accuracy and uniform depth. In this paper a new gravure printing plate manufacturing method with high accuracy is presented. Printing results made with the manufactured gravure and tailored inks are reported.

Preparation of Bi-Pb-Sr-Ca-Cu-O high Tc superconducting material via oxalate route at various pH values

Abstract A method for coprecipitation of Bi-Pb-Sr-Ca-Cu-O superconducting material via the oxalate route is presented. Bismuth, lead, strontium, calcium and copper nitrates and oxalic acid are used as starting materials. The precipitation of precursor from these materials is studied at different pH values The compositions of the coprecipitated powders are determined by direct current plasma atomic emission spectrometry. Two useful pH regions for precipitation are found. The first is a low pH region between 2 to 4 and the second is a high pH region of over 10. The precursors and sintered bulk samples are investigated by TEM, SEM/EDS and XRD. Resistivity measurements are carried out. The composition of the decomposed precursor is found to be homogeneous. The decomposed precursor has a particle size of around 300 nm. The sintered material consists of approximately 50% of the high T c phase and shows zero resistance at 104 K.

Direct gravure printing (DGP) method for printing fine-line electrical circuits on ceramics

The tendency toward higher packing densities and higher frequencies for telecommunication devices based on ceramic technology requires smaller dimensions for electrical wiring. Electrical thick-film circuits for ceramic and LTCC-substrates have, up to now, been printed with screen printing, where the printing lines width limit is about 125 /spl mu/m in mass production. A silicone polymer direct gravure printing (Si-DGP) process has been developed to perform smaller dimensions, down to 20 /spl mu/m lines width, for electrical circuitry. In the DGP process, the conductor paste is doctored to the grooves of the gravure and then it is pressed against the substrate. The paste is, thus, printed directly onto the substrate from the patterned gravure. The results showed that, using the DGP process, it was possible to print conductor lines down to 20 /spl mu/m in width. It was also noted that a 100% transfer of paste from the grooves of the gravure could be obtained with commercial pastes using the silicone polymer gravure. A dried thickness of up to 28 /spl mu/m was measured for the narrowest lines. Also conductor lines printed by the Si-DGP method were embedded inside LTCC-module.

Temperature characteristics and development of field-induced phase transition in relaxor ferroelectric Pb(Mg1/3Nb2/3)0.87Ti0.13O3 ceramics

Ferroelectric phase inducing threshold electric field Eth and its temperature dependence were determined in relaxor ferroelectric 0.87Pb(Mg1/3Nb2/3)O3−0.13PbTiO3 (PMN–13PT) ceramics by measuring dielectric response on a dc field pulse. Evolution of the induced ferroelectricity was observed by means of polarization measurements. An inducing threshold field was found to have a minimum of Eth,min=1.55 kV/cm at T=−5 °C. In contrast to pure PMN, which shows a minimum threshold field near the depolarization temperature, the temperature of the minimum threshold field differs by an amount of ΔT=23 °C from the depolarization temperature Tdp=18 °C in PMN-13PT.

Roller-type gravure offset printing of conductive inks for high-resolution printing on ceramic substrates

The use of gravure offset printing methods at an industrial level requires a wide and deep knowledge of the printing properties of the inks. Novel hydrocarbon inks were developed with superior printing properties compared to alternative ethyl cellulose-based inks. There are principal behaviour properties of these inks that can be generally described. In particular, the resistance dependence of printed mass for single and multiprints and on the other hand, the effect of multiprinting on printed area smoothness and line height. This article summarizes the results obtained and describes printing properties and defects: line widening, hair formation, ink flow from the gravure grooves, pinholes, image distortions, ribbing, scooping, streaking and gravure groove blocking. Three different printed samples were demonstrated, which are best suited for this manufacturing method: interdigital capacitor, inductor coil and laser soldering substrates.

Application of Wide-Band Material Characterization Methods to Printable Electronics

In this paper, characterization methods are presented with results from test structures printed with varying printing parameters and materials. It is shown that different process parameters affect both physical and electrical material properties and hence high-frequency material characterization is a vital part of the process providing important information for design purposes. The conductivities and loss information of nanoparticle inks and properties of dielectric material are achieved in addition to structural properties. In particular, dc measurement results from 1.1e7 S/m to 3.7e7 S/m and high-frequency attenuation values from 0.5 dB/cm to 2.8 dB/cm (at 10 GHz) are achieved for printed conductors.

Method for manufacturing high-quality gravure plates for printing fine-line electrical circuits

Electrical thick film circuits have, up to now, been printed with screen printing. This technology and PCB-processing technology are well known and widely used in commercial production. In conventional screen printing and PCB- technology, the accuracy limit is at about 150 microns. The tendency towards higher packing densities requires smaller dimensions to be printed. THerefore, a gravure offset printing process for electronic circuitry is under development. One important task in printing process development is the requirement for high quality and accurate gravure plates. In conventional pad printing, etching, laser engraving and photopolymer methods are the processes mainly used for gravure plate making. For the production of high quality and accurate gravure plates, a new process has been developed. A grooved gravure plate is electrodoped on a substrate upon which a photoresist pattern has been formed. After electrodeposition, the plate is peeled from the substrate. There are several advantages over the existing process. The surfaces of the grooves so formed are smooth. The depth of the grooves can be accurately controlled because it is the same as the thickness of the applied resist layer. Grooves deep enough to transfer sufficient ink needed for the electrical circuit patterns may be realized.

Application of wide-band material parameter extraction techniques to printable electronics characterization

Material characterization is an important part of printable electronics design, since material properties depend strongly on the manufacturing process. This paper reviews application of wide-band extraction techniques to printable electronics characterization. The extraction methods are validated using full-wave simulation data with exactly known reference for material parameters. Suitable test structures are evaluated and applied to printable electronics characterization.

Field-induced thermal response and irreversible phase transition enthalpy change in Pb(Mg1/3Nb2/3)O3–PbTiO3

In order to determine the enthalpy change in an irreversible field-induced phase transition, the thermal response to an electric field in 0.87Pb(Mg1/3Nb2/3)O3−0.13PbTiO3 was measured and dismantled into characteristic dielectric hysteresis, reversible electrocaloric, and irreversible phase transition responses. Below the depolarization temperature Tdp=18 °C, the phase transition enthalpy change increases rapidly to a maximum value of |ΔH|=77 J/kg. Above Tdp, the field-induced thermal response shows a reversible nature with an increased electrocaloric effect. In addition to earlier enthalpy data presented for temperature-induced transitions, this letter provides information on the enthalpy change in a field-induced phase transition of relaxor ferroelectrics.