Multilayer Chip Inductors Research Articles

Effect of BaCu(B2O5) additions on the sintering behaviors and dielectric-magnetic properties of Co2Z hexaferrite

Abstract

Effect of Synthesis methods on the Properties of Magnetic Material

Ba1-xPbxFe12O19 composition (x=0.0 to 1.0) synthesized by Co-precipitation and Sol-Gel methods. In Co-precipitation method BaCO3, PbO and Fe (NO3)3 .9H2O were used as basic ingredients. Acids and Di-H2O were used as solvents. Molar ratio of cations was 12.  pH of solution kept constant at 13. All samples sintered at 965±5oC for three hours. Lead own properties, synthesis at room temperature and substitution in R-block of structure were the reasons for decrease of phase purity from “x” =0.0 to 70% for “x”=1.0. Decrease in phase purity  and heterogeneity of material caused the properties to decrease. In Sol gel method, Nitrates (salts) and Ethylene glycol (liquid) were the basic material used. The mixed solutions dried out on a hot plate whose temperature was maintained constant at 200±2oC. Pellets formed by applying suitable hydraulic pressure and then sintered at same temperature written above i.e. 965±5oC for three hours. 100% phase purity achieved. All properties modified. Temperature and frequency dependent electrical properties investigated and reported here. DC and AC obtained properties were useful for different electronics and computer devices like capacitors, smart storage devices and multilayer chip inductors. Overall, both these properties improved through sol-gel method as compared to co-precipitation method. It was because of improvement in phase purity and change in morphology of synthesized material.Â

Microwave Processing of Multilayer Chip Inductors Using MgCuZn Ferrites

MgCuZn ferrites are synthesized by the microwave-hydrothermal method and are processed with varying concentrations of PbO. The nanocrystalline ferrites are sintered using microwaves at a temperature of 900 °C for 30 min. SEM pictures reveal that the grains are uniformly distributed and the addition of PbO causes a small amount of grain growth. The radio frequency behaviors (μ* and a*) of the ferrite samples are tested in the frequency range of 1 MHz to 1.8 GHz. The well-densified MgCuZn ferrite with good electromagnetic properties at high frequency is prepared by incorporation of 0.6 wt% PbO. Using this ferrite powder, the multilayer chip inductors (MLCIs) are prepared by the screen printing method. The inductors of 0.56, 0.88, and 1.44 μH that exhibit self-resonant frequency of 260-600 MHz are made. The size of these inductors is 2 mm × 1.2 mm × 0.8 mm. The inductance and resonant frequency of MLCIs can be adjusted by changing the number of ferrite layers.

Investigation of the magnetic properties of nanometric SrSmCoNi ferrite/PST matrix

Y-type hexa-ferrite Sr1.8Sm0.2Co2Ni1.50Fe10.50O22 was synthesized via micro-emulsion route. Ferrite/PST composites were obtained by mixing the different ferrite ratio in the pure PST matrix. The microstructure was examined by scanning electron microscopy (SEM) and exhibited heterogonous distribution of grains. A keen observation of these SEM images revealed that the grain morphology changes noticeably with increasing ferrite filler contents. The electrical modulus, Cole–Cole plots and quality factor of ferrite polymer composites have been investigated in the frequency range (1MHz to 3GHz). The field dependent magnetic properties of the prepared samples were investigated at room temperature by using vibrating sample magnetometer (VSM). The shape of hysteresis loops and linearity of Ms, Mr, Hc values vs. ferrite contents unfold that the ferrite nanoparticles are evenly dispersed within the composite. The occurrence of resonance at high frequency suggests that the present investigated composite samples are best candidate for multilayer chip inductors.

Study of electrical and dielectric behavior of Tb+3 substituted Y-type hexagonal ferrite

A series of Y-type hexa-ferrites with composition, Ba2Zn2TbxFe12−xO22 (0⩽x⩽0.1), were synthesized by the sol–gel auto-combustion technique. The X-ray powder diffraction technique was employed to confirm the formation of Y-type phase. The dispersion in dielectric constant, dielectric loss, and σac with frequency shows that the dispersion at low frequencies is due to Maxwell–Wagner type of interfacial polarization in general and the hopping of charge carrier between Fe2+ and Fe3+ ions. The substitution of Tb+3 inhibit the valence exchange of Fe+2 and Fe3+ and therefore the dielectric permittivity decreased. The DC resistivity increased from 7.29×107 to 4.73×108Ωcm with increasing Tb-contents due to the unavailability of Fe3+ ions at octahedral sites. The enhanced resistivity of Y-type hexa ferrites makes them suitable candidates for multi-layer chip inductor applications.

Structural, morphological, dielectric and magnetic characterizations of Ni0.6Cu0.2Zn0.2Fe2O4 (NCZF/MWCNTs/PVDF) nanocomposites for multilayer chip inductor (MLCI) applications

Nanocomposites of Ni0.6Cu0.2Zn0.2Fe2O4 (NCZF/PVDF) with and without Multiwalled Carbon Nanotubes (MWCNTs)were prepared via sol–gel auto combustion method. Structural, morphological, dielectric and magnetic properties of nanocrystalline NCZF/PVDF/MWCNTs composites have been studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and impedance analyzer. The average particle size was found to increase by increasing sintering temperature from 550°C to 750°C. FESEM and TEM images showed homogenous and well distributed crystallized grains of MWCNTs. The real and imaginary part of the dielectric constant and dielectric loss tangent have been illustrated according to the polarization phenomenon in ferrites based on Koop׳s theory and Maxwell–Wagner model. The high initial permeability and dielectric constant were found in Ni0.6Cu0.2Zn0.2Fe2O4/PVDF/MWCNTs sintered at 750°C; whereas very low electric and magnetic loss factors were investigated. This was attributed to the densification and grain growth of NCZF ferrites combined with remarkable properties of MWCNTs. The optimized dielectric and magnetic properties of NCZF nanocomposites with MWCNTs indicated that these types of nanoferrites can be used for the device fabrication such as multilayer chip inductors (MLCI׳s) and for high frequency applications.

Effect of BiVO4 doping on the magnetic properties and microstructure of NiCuZn ferrites

Effects of BiVO4 addition on the microstructural development and magnetic properties of a NiCuZn ferrite were investigated by conventional solid state reaction method. For the low temperature sintering (<961 °C), 0–2 wt% of BiVO4 was added to the ferrites. The grain size and bulk density gradually increased with the increase in the BiVO4 content and more uniform and compact structure at 1.0 wt% BiVO4 were obtained. The permeability decreases gradually with increase in BiVO4 content BiVO4 doped in NiCuZn ferrites improved magnetic properties and reduced the magnetic loss tangent. The samples may be excellent candidates to fabricate multilayer chip inductors and LTCC passive devices.

Nanosized Ce–Zn substituted microwave absorber material for X-band applications

The sol–gel autocombustion method has been used to synthesize the Ce–Zn substituted with composition Sr2−xCexNi2Fe28−yZnyO46 (x=0.02, 0.04, 0.06, 0.08, 0.010 and y=0.1, 0.2, 0.3, 0.4, 0.5) X-type hexagonal ferrites. The XRD analysis confirms the single phase of the material. The variation in lattice parameters can be observed with addition of Ce–Zn dopant. The ferrites substituted with Ce–Zn contents have low value of grain size than the unsubstituted ferrites. The crystallite size measured from TEM and HRTEM analysis was found in the range of 40–45nm which is in good agreement with the theoretically measured by Scherer formula. The room temperature electrical resistivity lies in the range of ~109Ω-cm, so the investigated sample can be considered good material for reducing the eddy current losses. The enhancement in magnetic properties (saturation magnetization, retentivity and coercivity) has been observed with the substitution of Ce–Zn contents in pure ferrites. The increment in resistivity and magnetic properties with the substitution of Ce–Zn dopant makes it important candidate to be used in the formation of multilayer chip inductors (MLCIs). The maximum reflection loss of −23.4dB at 12.858GHz is obtained by Ce–Zn doped ferrites and attenuation constant agrees well with the reflection loss. The microwave absorption properties of this substituted material reflect its applications in super high frequency (SHF) devices.

Role of grain boundaries in the conduction of Eu–Ni substituted Y-type hexaferrites

Single phase nanostructured (Eu–Ni) substituted Y-type hexaferrites with nominal composition of Sr2Co2−xNixEuyFe12−yO22 (x=0.0–1, y=0.0–0.1) were synthesized by the microemulsion method. Temperature dependent DC electrical conductivity and drift mobility were found in good agreement with each other, reflecting semiconducting behavior. The presence of Debye peaks in imaginary electric modulus curves confirmed the existence of relaxation phenomena in given frequency range. The AC conductivity follows power law, with exponent (n) value, ranges from 0.81–0.97, indicating that the mechanism is due to polaron hopping. In the present ferrite system, Cole–Cole plots were used to separate the grain and grain boundary effects. Eu–Ni substitution leads to a remarkable rise of grain boundary resistance as compared to the grain resistance. As both AC conductivity and Cole–Cole plots are the functions of concentration, they reveal the dominant contribution of grain boundaries in the conduction mechanism. It was also observed that the AC activation energy is lower than the DC activation energy. Appreciable improved values of quality factor suggested the possible use of these synthesized materials for power applications and high frequency multilayer chip inductors.

Bi2O3 liquid phase assisted and Mn substituted permeability and magnetic properties of Ni-Cu-Zn ferrite for multilayer chip inductor application

In the present work, low-temperature fired MnxNi0.5−xCu0.25Zn0.25Fe2O4 + Bi2O3 (x = 0.0 to 0.45) was synthesized by the sol-gel auto combustion technique at a temperature of 1073 K. Bi2O3 (with 2 wt. %) was used as a sintering aid for improving the density, microstructure and lowering the sintering temperature of Mn-Ni-Cu-Zn ferrites. Synthesized samples were investigated for their structural, magnetic, and electrical properties such as density, porosity, saturation magnetization, and permeability as a function of Mn2+ substitution. Permeability and saturation magnetization were found to increase with the replacement of Ni2+ with Mn2+. Bulk density of 4.5 g/cm3 was observed for Mn-Ni-Cu-Zn ferrite with Bi2O3 additives which is greater than that of pure Mn-Ni-Cu-Zn ferrite (4.1 g/cm3). Saturation magnetization of NiCuZn ferrite increased from 37 to 63 emu/g with increase in Mn2+ substitution. Mn substituted NiCuZn ferrite shows higher complex permeability (μ′ = 672) than that of the pure NiCuZn ferrite (μ′ = 433). Curie temperature determined from temperature dependent permeability data shows that Tc attains maximum value of 707 K.

Studies on Structural and Electrical Properties of Ball-Milled NiCuZn-MgCuZn Nanocomposites Ferrites

Multilayer chip inductors (MLCIs) have been rapidly developed for electromagnetic applications. NiCuZn ferrites are the most preferred ferrite materials to produce MLCIs, and MgCuZn ferrites have similar electromagnetic properties to those of NiCuZn ferrites. In view of this, ferrite composites with ferromagnetic phase (X) Ni0.35Cu0.05 Zn0.6Fe2O4 + (1 – X) Mg0.25Cu0.25Zn0.5Fe2O4, in which X varies from 0.0 to 1.0, were prepared by the conventional ceramic double-sintering process. The sintered ferrite was characterized for direct current (DC) and alternating current (AC) electrical conductivities, and thermoelectric effect studies. The X-ray diffraction pattern confirms the formation of single-phase spinel structure; the grain size was estimated using an scanning electron micrograph (SEM). The electrical properties were studied as a function of temperature and composition. The temperature variations of these samples were carried out from 303 K to 523 K (30 °C to 250 °C) within the frequency range 100 Hz to 1 MHz. The sintered NiCuZn-MgCuZn ferrites prepared possess good electromagnetic properties and good structure, thus making them suitable materials for MLCIs due to its high resistivity.

Microstructure and Electromagnetic Properties of Microwave Sintered CoCuZn Ferrites

Co-Cu-Zn ferrite material has been extensively used in multilayer chip inductors because of their good electromagnetic properties at higher frequencies and low sintering temperatures. In this research work, a comparative study on Co-Cu-Zn ferrite prepared from two different routes is reported. The two different routes are conventional ceramic sintering method (CS) and is microwave sintered (MS) method. The former route is most commonly used while the latter one is now gaining popularity in sintering processes. The work highlights that the sintering temperature and time were significantly reduced from 4 h and 1250 °C for the CS process to 20 min and 900 °C for MS process. Moreover, microwave sintering also improves the physical and electromagnetic properties of ferrite.

Microstructure and Electromagnetic Properties of Microwave Sintered CoCuZn Ferrites

Co-Cu-Zn ferrite material has been extensively used in multilayer chip inductors because of their good electromagnetic properties at higher frequencies and low sintering temperatures. In this research work, a comparative study on Co-Cu-Zn ferrite prepared from two different routes is reported. The two different routes are conventional ceramic sintering method (CS) and is microwave sintered (MS) method. The former route is most commonly used while the latter one is now gaining popularity in sintering processes. The work highlights that the sintering temperature and time were significantly reduced from 4 h and 1250 °C for the CS process to 20 min and 900 °C for MS process. Moreover, microwave sintering also improves the physical and electromagnetic properties of ferrite.

Characterization of Low Temperature Sintered Ferrite Laminates for High Frequency Point-of-Load Converters

The high power density Point-of-Load (POL) converter with high operating frequency has gained increasing interest in the growing market for portable communications and handheld electronics. Low profile magnetic components and associated integration techniques are desired for design and fabrication of highly integrated POL converters. Low fired ferrite tapes for multilayer chip inductors and high frequency applications have been developed and used in hybrid integration of power modules. The inductor made of multilayer ferrites can be fabricated as the magnetic substrate in an integrated POL converter with active components on top. The developed 3-D integration approach is applied to reduce footprint and increase power density for the high frequency POL converter. The current work reports the characterization of magnetic properties, microstructures, and chemical compositions of commercially available low-fire Ni-Cu-Zn ferrite materials (ESL 40010, 40011, and 40012) and their mixed laminates. Permeability and core loss density are measured on toroidal shaped samples sintered at 885 °C for 3.5 hrs. Because high DC current is always applied to bias the core for the inductors used in high frequency POL converters, the influence of superimposed DC bias on the magnetic properties of ferrite laminates has also been evaluated. The microstructures and chemical compositions of low temperature sintered ferrite laminates are observed and analyzed in order to explain the difference of magnetic properties among samples. The mixed laminate with alternating layers of ESL 40010 and ESL 40012 in 1:1 ratio presents the highest permeability and the lowest core loss density among all examined samples when DC bias is above 1000 A/m. Finally, a 12 V to 1.2 V, 15 A, high frequency (1.5–5 MHz) integrated POL converter with laminated ferrite inductor has been fabricated and demonstrated working at high efficiency with power density as high as 1000 W/in3.

Investigation of Co-Substituted Nanosized Mn2Y-Hexaferrites Synthesized by Sol-Gel Autocombustion Method

The structural and electrical properties of Co-substituted and nano-sized Y-type hexagonal ferrites have been investigated in the present work. The samples with chemical composition Ba2Co x Mn2−x Fe12O22 (x = 0.0, 0.5, 1.0, 1.5, 2.0) were prepared by sol-gel autocombustion method. The powdered samples and pellets were sintered simultaneously at 1000 °C for 5 h and characterized by means of DTA/TGA, FTIR spectroscopy, x-ray diffraction (XRD), field emission gun scanning electron microscopy, and energy dispersive x-ray spectroscopy. The XRD analysis confirms that the investigated ferrites have single phased Y-type hexagonal structure without showing any impurity phase. Lattice constants (a and c), cell volume (V), crystallite size (D), and x-ray density (ρ x ) have also been calculated from the XRD data. DC electrical resistivity is measured within the temperature range of 30-100 °C for each sample and is observed to increase with increasing Co-substitution. The dielectric constant (∈) has also been measured which is observed to decrease with Co-substitution. Thus, high electrical resistivity and low dielectric constant make these materials suitable for multi-layer chip inductors and also for RF components and circuits.

Effect of Tb–Mn substitution on DC and AC conductivity of Y-type hexagonal ferrite

Abstract Single phase nanostructured Tb–Mn substituted Y-type hexaferrites with nominal composition Sr2Co2−xMnx TbyFe12−yO22 (x = 0.0–1, Y = 0.0–0.1) were synthesized by the normal microemulsion method. The values of activation energy calculated from DC electrical conductivity increases with the substitution of Tb–Mn suggests that the conduction mechanism in the present ferrite system is polaron hopping. The appearance of broad Debye peaks in imaginary electric modulus plots (m″) show the existence of relaxation process in all these samples. The complex impedance plane plots show a single semicircle, which indicates the capacitive and resistive properties of the materials are due to contribution of grains and grain boundaries in ferrites. It is observed that Tb–Mn Substitution makes comparatively small difference on the grain resistance, but leads to a remarkable rise of grain boundary resistance. High values of quality factor are obtained required for power applications and high frequency multilayer chip inductors.

A Study of Reducing the Residual Stresses for Multilayer Chip Inductors

The residual stress built up by sintering causes not only the destruction of the structure of magnetic components but also a reduction in their permeability. In this paper, the relationship between residual stress and permeability is examined, and two possible methods for improving this situation are presented. Because one of the causes of increased residual stress is competition between the shrinking behaviors from the silver and ceramic layers inside the components during sintering, the first method is changing the particle size of the silver paste to alter its shrinking behavior. The results show that choosing a finer silver particle paste as the inner electrode material can reduce the onset temperature of shrinkage of the silver layer and then separate the silver layer from the ceramic layer to shrink the layers individually, reducing the residual stress. The second method is based on the phenomenon of separate shrinking seen in the first method, and we used carbon paste as the isolation layer for the silver and ceramic layers to achieve this. The results show that this method can reduce the residual stress more than the first one, although it can cause a high direct current resistance (DCR) and a low bending strength, and other conditions should be considered in order to avoid these weaknesses.

Transport properties of microwave sintered pure and glass added MgCuZn ferrites

Abstract A series of pure stoichiometric and 1 wt% lead borosilicate (PBS) glass added MgCuZn ferrite with the general formula Mg 0.5 Cu x Zn 0.5− x Fe 2 O 4 with x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 were synthesized by microwave sintering technique. Single phase spinel structure is exhibited by the XRD patterns of these ferrites. DC and AC conductivity were investigated as a function of composition, temperature and frequency. DC conductivities were also estimated using the impedance spectroscopy analysis of Cole–Cole plots. The DC conductivities thus obtained are in good agreement with the experimental results. All the investigated samples exhibited two regions of conductivity one in the low temperature and the second in the high temperature region. It is observed that PBS glass added samples have lower conductivities than pure samples. Due to their lower conductivities and sintering temperatures the 1 wt% PBS glass added samples are suitable for multilayer chip inductor (MLCI) and high definition TV deflection yoke material application.

Effect of Mg substitution on electromagnetic properties of NiCuZn ferrite

Mg substituted NiCuZn ferrites were prepared through sol–gel method using polyvinyl alcohol (PVA) as a chelating agent. The samples after annealing at 500°C to remove PVA were sintered at 950°C for 1h. The structural and electromagnetic properties of the samples were investigated. All the samples showed single phase spinel structure with increased lattice constant as a function of Mg concentration. The morphology reveals polyhedral shaped grains with increased grain size as a function of Mg composition. Dielectric parameters showed low values at higher frequencies. The initial permeability increased with Mg substitution in place of Ni in accordance with the microstructure. The samples sintered at low temperature having low dielectric losses and improved permeability along with the high frequency stability of permeability find applications in multilayer chip inductors.

Complex permeability and optical studies of Cr+3 doped nano-structured γ-Fe2O3 synthesized by auto-combustion technique

We have successfully synthesized chromium doped gamma ferrite (γ-Fe2O3) nanopowders (16.9nm to 25.6nm) of the composition (Fe2−xCrxO3 for x=0.00, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10) by a slightly modified solution combustion method using citric acid as fuel at considerably low temperature. The so prepared powders were extensively studied for complex permeability and optical behaviour. It was found that Cr3+ doped γ-Fe2O3 has significant permeability values and it can therefore be used as a high permeability core material and in Multi-layer Chip Inductor (MLCI) applications in electronic products, such as cellular phones, computers and video cameras. The results obtained in terms of permeability spectra suggest that γ-Fe2O3 and its doped variants when made in nano-form behave as a high permeability material at ultra high frequencies (5–25MHz) with permeability showing unusual inverse dependence on the grain dimension. Optical studies of the material confirm the presence of two band gaps BGd1 and BGd2 falling within the solar energy spectrum, thereby making this material a promising candidate for single junction photovoltaics with enhanced power conversion efficiency. We have also shown that the nano-sized γ-Fe2O3 synthesized by cost effective and modified sol–gel auto-combustion technique can be a good alternative to highly mismatched alloys (HMAs).