Microelectronics International

Dorota Szwagierczak

2014 Microelectronics International

doi: 10.1108/MI-10-2013-0056

Purpose – This paper aims to present the comparative study on the composition, microstructure and dielectric behavior of a group of new nonferroelectric high‐permittivity A 2/3 CuTa 4 O 12 (A = Y, Nd, Sm, Gd, Dy or Bi) ceramics. Design/methodology/approach – The materials under investigation were synthesized by solid‐state reaction method and sintered at 1,120‐1,230°C. Dielectric properties were investigated in the temperature range from −55 to 740°C at frequencies 10 Hz to 2 MHz. Microstructure, elemental composition and phase composition of the ceramics were examined by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS) and X‐ray diffraction (XRD) methods. DC conductivity was studied in the temperature range 20‐740°C. Findings – XRD analysis revealed peaks corresponding to Cu 2 Ta 4 O 12 along with small amounts of secondary phases based on tantalum oxides. Impedance spectroscopic data and the results of SEM and EDS studies imply the spontaneous formation of internal barrier layer capacitors in the investigated materials. Two steps can be distinguished in the dielectric permittivity versus frequency plots. The low‐frequency step of 1,000‐100,000 is assigned to grain boundary barrier layer effect, while the high‐frequency one of 34‐46 is related to intrinsic properties of grains. Originality/value – Search for new high‐permittivity capacitor materials is important for the progress in miniaturization and integration scale of electronic passive components. The paper reports on processing, microstructure, microanalysis studies and dielectric properties of a group of novel nonferroelectric materials with the perovskite structure of CaCu 3 Ti 4 O 12 and the general formula A 2/3 CuTa 4 O 12 , being spontaneously formed internal barrier layer capacitors.

Thomas Maeder

2014 Microelectronics International

doi: 10.1108/MI-12-2013-0079

Purpose – The purpose of this paper is to study tuneable positive temperature coefficient (PTC) effect in polymer‐wax‐carbon composite resistors. The resistivity dependence on temperature of composite resistors made of carbon fillers dispersed in an organic matrix is known to be strongly affected by the matrix thermal expansion. High PTC effects, i.e. essentially switching from resistive to quasi‐insulating behaviour, can be caused by phase changes in the matrix and the assorted volume expansion, a behaviour that has been previously shown with both simple organic waxes and semi‐crystalline polymers. However, waxes become very liquid on melting, possibly resulting in carbon sedimentation, and tuneability of semi‐crystalline polymers is limited. Design/methodology/approach – The authors therefore study a ternary polymer‐wax‐conductor (ethylcellulose‐octadecanol‐graphite) composite resistor system, where polymer and wax fuse to a viscous liquid on heating, and re‐solidify and separate by crystallisation of the wax on cooling. Findings – It is shown that with appropriate formulation, the resulting resistors exhibit strong PTC effects, linked with the melting and crystallisation of the wax component. The behaviour somewhat depends on sample history, and notably cooling speed. Research limitations/implications – The phase equilibria and transformation kinetics of the polymer‐wax system (including possible wax polymorphism), as well as the exact mechanism of the conductivity transition, remain to be investigated. Originality/value – As many compatible polymer‐wax systems with different melting/solidification behaviours are available, ternary polymer‐wax‐conductor composite PTC resistors allow a high tuneability of properties. Moreover, the high viscosity in the liquid state should largely avoid the sedimentation issues present with binary wax‐conductor systems.

P. Kowalik

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0068

Purpose – This paper aims to select parameters such as temperature thermal stability and temperature coefficient of resistance (TCR) for Ni–P resistive alloys obtained by electroless metallization. Ni–P alloys are used in the manufacture of precision resistors characterized by TCR in the range of ± 10 ppm/K. The correlation of the technological parameters with the electrical properties of resistors enables the accurate prediction of the TCR resistors. Design/methodology/approach – The Ni–P layers were obtained by a continuous process at about 373 K in a solution with the acidity of pH = 2 and then dried for two hours at 393 K. Subsequently, the Ni–P layer was stabilized for two hours in the temperature range of 453‐533 K. Resistance was measured with an accuracy of 1 mΩ. TCR was determined with an accuracy of 1 ppm/K in the temperature range 298‐398 K. In the next stage of the investigation, the increase in TCR of the Ni–P alloy was correlated with the increase in stabilization temperature. Scanning electron microscope images of the alloy surface were studied to assess grain sizes and to relate the average grain size with TCR values of resistive alloys. The X‐ray diffraction analysis was performed to determine the crystallization temperature of Ni–P alloy. Findings – The conducted investigation showed that the TCR increase in alloy is a linear function of stabilization temperature in the temperature range in which transition from amorphous phase to crystalline phases did not occur. TCR increase in Ni–P alloy arises from the increase of average size of grains resulting in decrease of scattering of electrons on grain boundaries. The analysis of alloy composition in chosen fragments of surface shows inhomogeneity growing with decreasing analyzed surface dimensions which proves that, before the stabilization, the structural arrangement of alloy is inconsiderable. Originality/value – The obtained results are the first attempt to relate the morphology of surface with TCR of alloy and demonstration of linear dependence between an increase in TCR of amorphic Ni–P alloy and stabilization temperature of resistive layer. Such correlations are not described in available literature.

Katarina Cvejin

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0075

Purpose – This paper aims to investigate different properties of synthesized perovskite Sm 0.9 Sr 0.1 CoO 3‐δ and its potential for application in potentiometric oxygen sensors. Design/methodology/approach – The powder was obtained through solid‐state reaction method and characterized by thermogravimetric/differential thermal analyzer and X‐ray diffraction. It was used for both making a paste and pressing into rods for sintering. The prepared paste was deposited on alumina and yttria‐stabilized zirconia substrates, by screen printing. Thick film conductivity, bulk conductivity and Seebeck coefficient of sintered rods were measured as a function of temperature. An oxygen concentration cell was fabricated with the screen‐printed perovskite material as electrodes. Findings – Electrical conductivity of the bulk sample and thick film increases with the increase in temperature, showing semiconductor‐like behavior, which is also indicated by relatively high values of the measured Seebeck coefficient. Estimated values of the activation energy for conduction are found to be of the same magnitude as those reported in the literature for similar composition. An investigation of Nernstian behavior of the fabricated cell confirmed that Sm 0.9 Sr 0.1 CoO 3‐δ is a promising material for application in oxygen potentiometric sensors. Originality/value – Gas sensor research is focused on the development of new sensitive materials. Although there is scarce information on SmCoO 3‐δ in the literature, it is mostly investigated for fuel cell applications. Results of this study imply that Sr‐doped SmCoO 3‐δ is a good candidate material for oxygen potentiometric sensor.

Monika Zawadzka

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0076

Purpose – The purpose of this paper is to present fabrication process of volatile organic compounds (VOCs) sensors based on polypyrrole material deposited on different substrates and to show and compare the responses of the produced sensors to different VOCs. Design/methodology/approach – Polypyrrole sensing layers were prepared by in situ chemical polymerisation on two different substrates: alumina and poly(ethylene terephthalate) (PET). The time of the polymerisation was varied. After film deposition, an interdigitated electrode was screen‐printed on the material deposited on the substrate. Findings – It was demonstrated that both polymerisation time and substrate type provide means to vary the sensitivity of polypyrrole‐based sensors to VOCs. Practical implications – VOCs, which are released in manufacturing or use of various products and materials, pose a threat to the environment and human health. Therefore, measures must be taken to control their concentration both in indoor and outdoor air. Originality/value – Deposition of a conductive polymer film on the substrate via in situ chemical polymerisation followed by screen‐printing of an interdigitated electrode on the polymer surface offers a fast and an effective method of chemiresistor‐type sensor fabrication.

Jan Kulawik

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0059

Purpose – This paper aims to fabricate and characterize ZnO‐based multilayer varistors. Design/methodology/approach – Tape casting technique was utilized for preparation of multilayer varistors based on ZnO doped with Pr, Bi, Sb, Co, Cr, Mn and Si oxides. Scanning electron microscope (SEM), energy‐dispersive X‐ray spectroscopy (EDS) and X‐ray diffraction (XRD) methods were used to study the microstructure, elemental and phase compositions, respectively, of the varistors. Dielectric properties were investigated by impedance spectroscopy. Current–voltage (I–U) dependences were measured to characterize nonlinear behavior of the fabricated varistors. Findings – XRD, SEM and EDS studies revealed dense microstructure of ceramic layers with ZnO grains sized 1‐4 μm surrounded by nanometric Bi‐rich films, submicrometer Zn 7 Sb 2 O 12 spinel grains and needle‐shaped Pr 3 SbO 7 crystallites. Praseodymium oxide was found to be very effective as an additive restricting the ZnO grain growth. I–U characteristics of the fabricated multilayer varistors were nonlinear, with the nonlinearity coefficients of 23‐27 and 19‐51 for the lower and higher Pr 2 O 3 content, respectively. The breakdown voltages were 60‐150 V, decreasing with increasing sintering temperature. Originality/value – Low‐temperature cofired ceramics technology enables attaining a significant progress in miniaturization of electronic passive components. Literature concerning application of this technology for multilayer varistors fabrication is limited. In the present work, the results of XRD, SEM and EDS studies along with the I–U and complex impedance dependences are analyzed to elucidate the origin of the observed varistor effect. The influence of sintering temperature and Pr 2 O 3 ‐doping level was investigated.

Beata Barteczka

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0067

Purpose – The purpose of this paper was to investigate the influence of non‐uniform temperature distribution inside a box furnace during the firing process on electrical properties of the low‐temperature co‐fired ceramic (LTCC) materials used in radio frequency (RF)/microwave applications. Design/methodology/approach – The authors studied the change in dielectric constant of two popular LTCC materials (DP 951 and DP 9K7) depending on the position of their samples inside the box furnace. Before firing of the samples, temperature distribution inside the box furnace was determined. The dielectric constant was measured using the method of two microstrip lines. Findings – The findings showed that non‐uniform temperature distribution with spatial difference of 6°C can result in 3‐4 per cent change of the dielectric constant. It was also found that dielectric constant of the two tested materials shows disparate behavior under the same temperature distribution inside the box furnace. Practical implications – The dielectric constant of the substrate materials is crucial for RF/microwave applications. Therefore, it was shown that 3‐4 per cent deviation in dielectric constant can result in considerable detuning of microwave circuits and antennas. Originality/value – To the best of the authors’ knowledge, the quantitative description of the impact of temperature distribution inside a box furnace on electrical properties of the LTCC materials has never been published in the open literature. The findings should be helpful when optimizing production process for high yield of reliable LTCC components like filters, baluns and chip antennas.

Piotr Markowski

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0077

Purpose – The purpose of this work was fabrication of a small energy harvester. Design/methodology/approach – The multilayer thermoelectric power generator based on thick‐film and low temperature co‐fired ceramic (LTCC) technology was fabricated. Precise paths printing method was used to fabricate Ag/Ni and Ag/PdAg thermocouples on a number of unfired LTCC tapes. The tapes were put together to form a multilayer stack. The via holes were used to make the electrical connections between adjacent layers. Finally, the multilayer stack was fired in the appropriate thermal profile. Findings – It consists of 450 thermocouples and generates output voltage of about 0.45 V and output electrical power of about 0.13 mW when a temperature difference along the structure is 135°C. In the paper, individual stages of energy harvester fabrication process as well as its output parameters are presented. Originality/value – Miniaturized thermoelectric energy harvester based on thick‐film and LTCC technology was fabricated. As materials, metal‐based pastes were used. This is the first paper where multilayer thermoelectric harvester, fabricated with the aid of LTCC technology, was described.

Arkadiusz Dabrowski

2014 Microelectronics International

doi: 10.1108/MI-10-2013-0052

Purpose – The purpose of this paper is to develop the device made of low temperature co‐fired ceramics (LTCC) and lead zirconate titanate (PZT) by co‐firing both materials. In the paper, the technology and properties of a miniature uniaxial ceramic accelerometer are presented. Design/methodology/approach – Finite element method (FEM) is applied to predict properties of the sensor vs main dimensions of the sensor. The LTCC process is applied during manufacturing of the device. All the advantages of the technology are taken into account during designing three‐dimensional structure of the sensor. The sensitivity and resonant frequency of the accelerometer are measured. Real material parameters of PZT are estimated according to measurement results and FEM simulations. Findings – The ceramic sensor integrated with SMD package with outer dimensions of 5 × 5 × 5 mm 3 is manufactured. The accelerometer exhibits sensitivity of 0.75 pC/g measured at 100 Hz. The resonant frequency is equal to about 2 kHz. Useful frequency range is limited by 3 dB sensitivity change at about 1 kHz. Research limitations/implications – Sensitivity of the device is limited by interaction between LTCC and PZT materials during co‐firing process. The estimated d parameters are ten times worse comparing to bulk Pz27 material. Further research on materials compatibility should be carried out. Practical implications – The sensor can be easily integrated into various devices made of standard electronic printed circuit boards (PCBs). Applied method of direct integration of piezoelectric transducers with LTCC material enables manufacturing of complex ceramic systems with built‐in accelerometer in the substrate. Originality/value – The accelerometer is a sensor and a package simultaneously. The miniature ceramic device is compatible with surface mounting technology; hence, it can be used directly on PCBs for vibration monitoring inside electronic devices and systems.

Dominik Jurków

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0058

Purpose – The paper aims to present the influence of the co‐firing process conditions of low temperature co‐fired ceramics (LTCC) on the deformation of thin LTCC membranes. Design/methodology/approach – The statistical design of the experiment methodology was used in the frame of these investigations to reduce the time and costs of the experiments and to ensure easier interpretation of the obtained results. Moreover, this conception permits the rough estimation of the membrane deflection fired at optimal process conditions. Findings – The applied design of the experiment methodology allowed the researchers to find the optimal co‐firing process conditions and to estimate the membrane deflection at the optimal process conditions. The estimation fits well with the results of real measurement that was conducted to confirm the estimation precision. Research limitations/implications – The experiment was conducted for only one type of LTCC, DP951. The precision of the design of the experiment optimization and estimation of the response at optimal conditions depend on the described object. Therefore, the findings of this paper do not have to be generally true for other LTCC tapes, and if other LTCC tapes deformation should be investigated, then similar analysis shall be conducted for them. Practical implications – The deformation of LTCC membranes affects the sensitivity and repeatability of LTCC acceleration and pressure sensors. Hence, the decrease of membrane deflection increases the usability of LTCC in such applications. Originality/value – This paper presents simple optimization of co‐firing process conditions of LTCC devices using statistical design of the experiment.

Karol Malecha

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0072

Purpose – The purpose of this paper is to focus on development and electrical characterization of miniature ion‐selective electrode (ISE) for application in micro total analysis system or lab‐on‐chip devices. The presented ISE is made using low temperature co‐fired ceramics (LTCC). It shows possibility of integration chemically sensitive layers with structures fabricated using modern microelectronic technology. Design/methodology/approach – The presented ISEs were fabricated using LTCC microelectronic technology. The possibility of ISE fabrication on multilayer ceramic substrate made of two different LTCC material systems (CeramTec GC, Du Pont 951) with deposited thick‐film silver pad is studied. Different configurations of LTCC/silver pad (surface, embedded) are taken into account. Electrical performance of all LTCC‐based structures with integrated ISE was examined experimentally. Findings – The preliminary measurements made for ammonium ions have shown good repeatability and linear response with slope of about 30‐35 mV/dec. Moreover, no significant impact of the LTCC material system and silver pad configuration on fabricated ISEs’ electrical properties was noticed. Research limitations/implications – The presented research is a preliminary work. The authors focused on ISE fabrication on LTCC substrates without any microfluidic structures. Therefore, further research work will be needed to evolve ion‐selective membrane deposition inside microfluidic structures made in LTCC substrates. Practical implications – Development of the LTCC‐based ISE makes the fabrication of detection units for integrated microfluidic systems possible. These devices can find practical applications in analytical diagnosis and continuous monitoring of various biochemical parameters. Originality/value – This paper shows design, fabrication and performance of the novel ISE fabrication using LTCC technology.

Barbara Dziurdzia

2014 Microelectronics International

doi: 10.1108/MI-12-2013-0081

Purpose – The paper aims to present the innovative design of a planar multilayered high temperature solid oxide fuel cell (SOFC), which is easy to manufacture, and features high resistance to rapid temperature changes. Temperature resistance was accomplished thanks to easy to heat, thin flat ceramic structure of the cell and elimination of metallic interconnections. Design/methodology/approach – The ceramic fuel cell consists of the anode core made of six to eight layers of nickel/yttria‐stabilized zirconia tapes (Ni/YSZ) isostatically pressed into a laminate. Two networks of fuel distribution microchannels are engraved on both sides of the anode laminate. The microchannels are subsequently covered with a thin layer of the functional anode tape made of Ni/YSZ and a solid electrolyte tape made of YSZ. Findings – The single planar double‐sided ceramic SOFC of dimensions 19 × 60 × 1.2 mm 3 provides 3.2 Watts of electric power. The prototype of the battery which consists of four SOFCs provides an output power of > 12 W. Tests show that the stack is resistant to the rapid temperature change. If inserted into a chamber preheated to 800°C, the stack provides the full power within 5 minutes. Multiple cycling does not destroy the stack. Originality/value – This anode‐supported fuel cell structure is provided with thin anode functional layers suspended on a large number of fine beams. The whole anode structure is made with the same ceramic material, so the mechanical stress is minimized during the cell operation.

Aneta Araźna

2014 Microelectronics International

doi: 10.1108/MI-10-2013-0047

Purpose – The purpose of this paper was to determine the influence of thermal aging on the stability of organic light‐emitting diode (OLED) glass samples made in ambient condition. Design/methodology/approach – The samples with yellow emitting layer (named as ADS5) and poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer were examined. Some of the devices were ultraviolet‐curable epoxy encapsulation directly after performance. All samples were thermally annealed at 70°C for 1, 2, 3 and 4 hours. The characteristics current–voltage for fresh and aging samples in the range of voltage from 0‐15 V were made. The temperature of OLEDs samples in real‐time with a thermographic camera was measured too. Additionally, scanning electron microscope image of surface Al cathode immediately after OLED performance and after annealing tests was made. Findings – The authors stated, that irrespective of the type, the samples were undergoing the degradation. The decrease in value of the current density was registered. That were about 44 per cent and about 24 per cent after thermally annealing the samples with and without encapsulation, respectively (at tension 13 V). Additionally, there were observed massive delamination of the metal cathode. Originality/value – Influence of thermal annealing and encapsulation on the dynamic characteristics of the OLED devices fabricated in ambient condition was analyzed. There are not many papers in the literature describing examinations of OLED samples which were made in environmental conditions.

Krzysztof Górecki

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0069

Purpose – The purpose of this paper is to present a new method of measuring thermal resistance of power light‐emitting diodes (LEDs). Properties of power LEDs strongly depend on their internal temperature. The value of this temperature depends on the cooling conditions characterized by thermal resistance. Design/methodology/approach – The new method of measuring the value of this parameter belongs to the group of electric methods. In this method, the problem of estimating the value of electrical power converted into light is solved. By comparing the values of the case temperature obtained for the LED operating in the forward mode and the reverse‐breakdown mode, the thermal power is estimated. On the basis of the measured value of the thermally sensitive parameter (the LED forward voltage) and the estimated value of the thermal power, thermal resistance is calculated. Findings – The elaborated method was used to measure thermal resistance of the selected types of power LEDs operating at different cooling conditions. The correctness of the elaborated measurement method was proved by comparing the results of measurements obtained with the use of the new method and the infrared method. Research limitations/implications – On the basis of the obtained results of measurements and the catalog data of the tested diodes, the dependence of the measurement error of thermal resistance of the LED on its luminous efficiency is discussed. Originality/value – The new measurement method is easy to use and more accurate than the classical method of thermal resistance measurement of the diode.

Wojciech Grzesiak

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0071

Purpose – The purpose of this paper is to report the system solution expressed in the form of a block diagram. In this paper, a multi‐functional demonstrator of the interactive system designed to modelling, monitoring and validation of hybrid photovoltaic (PV) systems assisted by fuel cells and thermoelectric generators is presented. Technical parameters of demonstrator components such as: silicon PV modules, fuel cells, thermoelectric generators, gel batteries, control and monitoring systems are described. Design/methodology/approach – The design shows the implementation of PV system modelling by four universal PV module simulators supported by two 65 W fuel cell and 12 modules, 6 W thermoelectric generators battery. Findings – The paper provides practical proof that the combination of PV technology with both thermoelecric generators and fuel cells technologies shows promising results for the development of hybrid PV systems with increased effectiveness and efficiency. Research limitations/implications – The design idea can be developed for many applications gaining electricity from many distributed sources of wasted energy. Practical implications – In practice, hybrid systems can be used to support the operation of classic PV systems, for example, working in various climatic conditions. Originality/value – The proposed model demonstrates new technical solution leading to the enlargement of the PV systems application.

Ewa Klimiec

2014 Microelectronics International

doi: 10.1108/MI-11-2013-0074

Purpose – This paper aims to present a prototype of the diagnostic system for the examination of the distribution of the force applied by foot to substrate during usual human moving. Presented system is competitive to other currently available devices, thanks to sensors reliability, user‐friendly operation manner and design based on cheap parts. The results of examinations are transmitted by radiomodem. Its recording and visualization are possible on either personal or mobile computers. Design/methodology/approach – During selection of the sensors substrate, many polymeric electrets were examined. Polyvinylidene fluoride films were selected, because they have good charge uniformity across the surface, wide range of acceptable temperatures, linear relation between mechanical stress and output signal and high resistance for squeezing. The system measures the charge generated in film. Findings – The pressures are recorded in relation to maximum value; therefore, measuring system does not require calibration. The simultaneous recording of data from all eight sensors allows tracking the signal without distortion. Originality/value – An array of sensors is installed in the shoe insole. The measuring device is fixed to the outer surface of the shoe. Its weight is 75 g. The range of transmission is suitable for examination in the natural environment, outside traditional consulting room. Software is dedicated for analysis of the pressure distribution in every moment of the foot movement. The system is suitable for examination of flat feet, diabetic foot and recovery progress after injures.