Ferrite Devices Research Articles

Millimeter wave complementary metal–oxide–semiconductor on-chip hexagonal nano-ferrite circulator

Hexagonal ferrites such as M-type BaFe12O19 and SrFe12O19 have strong uniaxial anisotropic magnetic field and remanent magnetism. The nano-sized ferrite powder exhibits high compatibility and processability in composite material. New magnetic devices using the M-type ferrite materials can work in the tens of GHz frequency range from microwave to millimeter wave without the application of strong external magnetic field. The micro- and nano-sized hexagonal ferrite can be conveniently utilized to fabricate magnetic components integrated in CMOS integrated circuits as thin as several micrometers. The micro-fabrication method of such nano ferrite device is presented in this paper. A circulator working at 60 GHz is designed and integrated into the commercial CMOS process. The circulator exhibits distinct circulation properties in the frequency range from 56 GHz to 58 GHz.

Regulation of the forming process and the set voltage distribution of unipolar resistance switching in spin-coated CoFe2O4 thin films.

We report the preparation of (111) preferentially oriented CoFe2O4 thin films on Pt(111)/TiO2/SiO2/Si substrates using a spin-coating process. The post-annealing conditions and film thickness were varied for cobalt ferrite (CFO) thin films, and Pt/CFO/Pt structures were prepared to investigate the resistance switching behaviors. Our results showed that resistance switching without a forming process is preferred to obtain less fluctuation in the set voltage, which can be regulated directly from the preparation conditions of the CFO thin films. Therefore, instead of thicker film, CFO thin films deposited by two times spin-coating with a thickness about 100 nm gave stable resistance switching with the most stable set voltage. Since the forming process and the large variation in set voltage have been considered as serious obstacles for the practical application of resistance switching for non-volatile memory devices, our results could provide meaningful insights in improving the performance of ferrite material-based resistance switching memory devices.

Influence of DC Bias on the Electrical Characteristics of SMD Inductors

As the dc bias flows through a ferrite chip surface mount device (SMD) inductor, it tends to premagnetize the core and reduce its inductance and impedance. It is observed that this drop is especially emphasized when the dc current exceeds the safety limit given by the manufacturer. Therefore, it is necessary to investigate and predict the degree of electrical characteristics degradation as well as the dependence of the core losses on core temperature. In this paper, a measurement technique for the investigation of the influence of dc bias on the electrical characteristics of SMD inductors (i.e., inductance, resistance, Q factor, and real and imaginary part of impedance) for printed circuit board applications is presented. Analysis is based on the model of the SMD inductor, which can be presented as a two-port equivalent circuit with intrinsic and extrinsic parameters. For calculation of the parameters of the SMD inductor, extracted from measured S-parameters using vector network analyzer, the in-house software tool IndCalc was used.

Multiferroic oxide composites: synthesis, characterisation and applications

The nature of mechanical strain mediated electromagnetic coupling in multiferroic composites has been studied extensively in recent years. This review is on composites with ferromagnetic or ferrimagnetic oxides and ferroelectrics. Systems studied so far include samples with spinel ferrites, hexagonal ferrites or lanthanum manganites for the ferromagnetic phase and barium titanate, lead zirconate titanate (PZT), lead magnesium niobate–lead titanate (PMN-PT) or lead zinc niobate–lead titanate (PZN-PT) for the ferroelectric phase. Bilayer and multilayer heterostructures, bulk composites, core shell nanoparticles and core shell nanotubes and nanowires were investigated for their response to magnetic fields, termed direct magnetoelectric effect (DME). Several systems show a giant low frequency DME and resonance enhancement at bending and electromechanical resonance. The response of the composites to an electric field, called converse ME effect, is found to be strong in several ferrite–ferroelectric composites. The potential for use of the composites for pico-Tesla magnetic sensors and high frequency electric field tunable ferrite signal processing devices are also addressed in this review.

Mitigate the Interference: Nonlinear Frequency Selective Ferrite Devices

The linear small-signal properties of ferrites gave rise to several well-known microwave devices [1], [2], such as circulators, isolators, phase shifters, tunable oscillators, and tunable filters, that have had a significant impact on microwave systems following their first synthesis by Snoek [3], [4] in 1945. However, ferrites also show useful nonlinear large-signal properties that have been applied in power-limiter and power-enhancer devices. While these devices have not seen widespread application, their unique frequency-selective signal attenuation properties offer potential solutions to current and anticipated radiofrequency (RF) interference problems resulting from ever-increasing signal density and demands on scarce RF bandwidth.

Epitaxial growth of 100-μm thick M-type hexaferrite crystals on wide bandgap semiconductor GaN/Al2O3 substrates

Thick barium hexaferrite BaFe12O19 (BaM) films having thicknesses of ∼100 μm were epitaxially grown on GaN/Al2O3 substrates from a molten-salt solution by vaporizing the solvent. X-ray diffraction measurement verified the growth of BaM (001) textured growth of thick films. Saturation magnetization, 4πMs, was measured for as-grown films to be 4.6 ± 0.2 kG and ferromagnetic resonance measurements revealed a microwave linewidth of ∼100 Oe at X-band. Scanning electron microscopy indicated clear hexagonal crystals distributed on the semiconductor substrate. These results demonstrate feasibility of growing M-type hexaferrite crystal films on wide bandgap semiconductor substrates by using a simple powder melting method. It also presents a potential pathway for the integration of ferrite microwave passive devices with active semiconductor circuit elements creating system-on-a-wafer architectures.

Ferrite-Piezoelectric Heterostructures for Microwave and Millimeter Devices: Recent Advances and Future Possibilities

There have been considerable interests in recent years in ferrite-ferroelectric composites for dual magneticand electric field tunable microwave and mm-wave devices such as resonators, filters, and phase shifters. Low-loss spinel and hexagonal ferrites are used in high frequency devices and the tuning in general is with a magnetic field H. When the ferrite is replaced by a ferrite-ferroelectric composite, however, the piezoelectric strain due to an electric field E applied to the ferroelectric will manifest as an induced anisotropy in the ferrite and facilitate E-tuning of the device. This review focuses on recent efforts on voltage tunable ferrite filters. A related phenomenon of importance is the nature of magneto-dielectric resonance in ferrites and its potential for low-loss H-tunable dielectric resonators, filters, isolators, and phase shifters for the frequency range 18-110 GHz. Potential avenues for enhancing the E-tuning of ferrite devices are also addressed.

Finite Element Simulation of Electromagnetic Properties of Ferrite Material

As the inductance of magnetic cores is the most important parameter for their service performance. Four coupling models of EE-type ferrite cores are established to analyze the relationship between surface quality and the inductance of ferrite cores. Besides, 3D FEM simulation of different models is made by ANSOFT MAXWELL software. The results show that the surface quality has a direct influence on the service performance of ferrite devices.

Measurement and Evaluation of Ferrite Materials Surface Quality

A measurement on the topography and 3D roughness parameters of the ferrite surface has been taken by using a 3D optical profiler. Based on the analysis of the experimental data and the contradistinction between the ferrite devices with different quality and service performance, one preliminary conclusion has been obtained that the surface quality of ferrite materials can be evaluated by using the 3D roughness parameters, and this method is applicable and stable. With qualitative and quantitative analysis, it could be predicted that the surface quality has a direct influence on the service performance of ferrite devices.

Temperature stabilization of spin-wave ferrite devices

A method for the self-compensation of the temperature drift of frequency in spin-wave ferrite devices using reversible thermal demagnetization of permanent magnets is proposed. The efficiency of the method is demonstrated for the normal magnetization of the yttrium-iron garnet (YIG) film. A configuration of the magnetic system with the built-in system for the thermal stabilization and electric frequency tuning is presented. The advantages of the system are demonstrated for the frequency stabilization of a YIG film cavity.

Ferrite film growth on semiconductor substrates towards microwave and millimeter wave integrated circuits

It is widely recognized that as electronic systems’ operating frequency shifts to microwave and millimeter wave bands, the integration of ferrite passive devices with semiconductor solid state active devices holds significant advantages in improved miniaturization, bandwidth, speed, power and production costs, among others. Traditionally, ferrites have been employed in discrete bulk form, despite attempts to integrate ferrite as films within microwave integrated circuits. Technical barriers remain centric to the incompatibility between ferrite and semiconductor materials and their processing protocols. In this review, we present past and present efforts at ferrite integration with semiconductor platforms with the aim to identify the most promising paths to realizing the complete integration of on-chip ferrite and semiconductor devices, assemblies and systems.

ChemInform Abstract: Consequences of Magnetic Anisotropy in Realizing Practical Microwave Hexaferrite Devices

AbstractReview: 26 refs.

Characterization and modelling of miniature ferrite transformer for high frequency applications

PurposeSignificant achievements in ferrite material processing enable developments of many ferrite devices with a wide range of power levels and working frequencies, which make demands for new characterization and modelling methods for ferrite materials and components. The purpose of this paper is to introduce a modelling and measurement procedure, which can be used for the characterization of two‐port ferrite components in high frequency range.Design/methodology/approachThis paper presents a commercially available ferrite component (transformer) modelling and determination of its electrical parameters using in‐house developed software. The components are measured and characterized using a vector network analyzer E5071B and adaptation test fixture on PCB board. The parameters of electrical equivalent circuit of the ferrite transformer parameters are compared with values extracted out of measured scattering parameters.FindingsA good agreement between modelled and extracted electrical parameters of the ferrite transformer is found. The modelled inductance curves have the same dependence versus frequency as extracted ones. That confirms the model validity in the wide frequency range.Originality/valueIn‐house developed software based on proposed model provides inclusion of the ferrite material dispersive characteristics, which dominantly determines high‐frequency behaviour of two‐port ferrite components. Developed software enables fast and accurate calculation of the ferrite transformer electrical parameters and its redesign in order to achieve the best performance for required application.

Consequences of magnetic anisotropy in realizing practical microwave hexaferrite devices

With the rapidly growing demand for bandwidth in wireless communication systems and increasing frequencies of operation of electronic devices, in recent years resurgence in scientific interest in highly anisotropic hexagonal ferrites has been noted. This interest stems in part from a number of emerging applications that pose significant materials challenges that cannot be addressed using traditional rf and microwave ferrite materials. In this manuscript, several specific applications that could benefit from the unique properties of hexagonal ferrites are discussed. Fundamental principles of operation, materials requirements, as well as unique device design and modeling challenges are reviewed. Applications of textured magnetically uniaxial hexagonal ferrite composites in microwave and mm-wave non-reciprocal ferrite control devices are discussed. Applications of textured magnetically planar hexagonal ferrite composites as antenna and electronic bandgap metamaterial substrates, rf inductors and transformers, and electromagnetic interference suppression devices are reviewed. Suggestions on directions for future research and development are provided.

Magnetostriction measured by holographic interferometry with the simple and inexpensive arrowhead setup

Double-exposure holographic interferometry is applied to measure the linear or longitudinal magnetostriction constant of a soft-ferrite rod. This high-accuracy measurement is done indirectly, by measuring the small rotations of a lever in contact with the rod using double-exposure holographic interferometry implemented with a robust arrowhead-shaped holographic setup. Ferrite devices are used in a large number of well-known technologies and hold a promise for more advanced applications, so the study of ferrites properties is therefore very important. The experiments and methods described here and the magnetic phenomena studied are suitable for an undergraduate project or an open-ended experiment.

Simultaneous observation of magnetostatic backward volume waves and surface waves in single crystal barium ferrite platelets with in-plane easy axis

Resonances corresponding to backward volume magnetostatic waves as well as magnetostatic surface waves have been observed in single crystal barium hexaferrite rectangular platelets with in-plane easy axis. Samples placed directly on waveguide wall or on a quartz substrate show a surface mode. A series of backward volume wave modes in the U-band are observed, with the sample placed on quartz showing a relatively few modes. Data on H-dependence of the mode frequency have been obtained for both kinds of magnetostatic waves and theoretical estimates of the mode frequencies are in reasonable agreement with the data. Quality-factor for the modes is in the range 400-750. The results are of interest for non-reciprocal ferrite devices in the U-band.

Z-, Y- and M-type Hexagonal Ferrites for High-Frequency Inductive Multilayer Devices

Hexagonal ferrites can be used as soft magnetic materials for multilayer inductors for high frequency applications up to 3 GHz. We report on the preparation, thermal stability and magnetic properties of Z-, Y- and M-type hexagonal ferrites. Co2Z-type ferrite Ba3Co2Fe24O41 and iron excess Ba3Co2−yFe24+yO41 (0 ≤ y ≤ 0.8) were prepared by the mixed oxide route. Single phase Z-type ferrites were obtained after sintering at 1300°C. The permeability of a sample with y = 0.6 sintered at 1300°C is μ = 30 with a resonance frequency of 1 GHz. The addition of Bi2O3 as sintering aid shifts the maximum shrinkage down to 950°C and dense samples were sintered at 950°C; however, their permeability is only μ = 3…5. It is shown that Co2Z ferrites are not stable under LTCC conditions. Cu-substituted Z-type ferrites Ba3Co2-xCuxFe24O41 exhibit enhanced sintering ability, but sintering at 950°C also results in low permeability. Y-type hexagonal ferrites Ba2Co2−x−yZnxCuyFe12O22 were prepared at 1100°C and a permeability of μ = 20 was found for x = 1.2 and y = 0.8. Samples with Bi2O3 addition were sintered at 950 and 900°C exhibiting a permeability of μ = 10. Similar values were measured for M-type ferrites BaFe12-2yCoyTiyO19 with y = 1.2 which were sintered at 900°C using additives. Co/Ti co-substitution is an essential prerequisite for tailoring the magneto-crystalline anisotropy. Co/Ti- substituted M-type materials are stable under LTCC conditions. Ferrite multilayer devices were fabricated by screen printing coils onto ferrite tapes, stacking and lamination. Firing was performed between 1300°C and 900°C, i.e. at HTCC and LTCC conditions, respectively. The inductance behavior of the devices was evaluated and modeled. It is shown that hexagonal ferrites are suitable materials for the high-frequency multilayer inductors; however, Y- and M-type ferrites are preferred for LTCC-type inductors cofired at 900°C with Ag metallization.

Efficient characterization of multilayered microwave wireless circuits on gyrotropic dielectric media including magnetized ferrites

The ever-growing use of anisotropic ferrite devices in modern wireless communication systems highlighted the need for robust design tools to reliably characterize the dispersion behavior of such devices in radio frequency (RF)/microwave bands, especially for multilayered configurations. Indeed, as ferrites present a biaxial anisotropy, spectral analysis of multilayered configurations with such substrates is not generalized, however, restricted to some particular cases of tensors. Therefore, this article deals with the characterization of anisotropy effects on the dispersion parameters of multilayered wireless circuits with ferrite substrates, particular case of gyrotropic medias. In the proposed approach, a rigorous analysis was carried out by taking into account, for the first time, the electrical aspect of anisotropy. The computed results are in good agreement with those available in the literature. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:978–982, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25951

Structure, magnetic, and microwave properties of thick Ba-hexaferrite films epitaxially grown on GaN/Al2O3 substrates

Thick barium hexaferrite [BaO⋅(Fe2O3)6] films, having the magnetoplumbite structure (i.e., Ba M), were epitaxially grown on c-axis oriented GaN/Al2O3 substrates by pulsed laser deposition followed by liquid phase epitaxy. X-ray diffraction showed (0,0,2n) crystallographic alignment with pole figure analyses confirming epitaxial growth. High resolution transmission electron microscopy images revealed magnetoplumbite unit cells stacked with limited interfacial mixing. Saturation magnetization, 4πMs, was measured for as-grown films to be 4.1±0.3 kG with a perpendicular magnetic anisotropy field of 16±0.3 kOe. Ferromagnetic resonance linewidth, the peak-to-peak power absorption derivative at 53 GHz, was 86 Oe. These properties will prove enabling for the integration of low loss Ba M ferrite microwave passive devices with active semiconductor circuit elements in systems-on-a-wafer architecture.

Helical Ferrite Devices for Non-Reciprocal Applications

This paper introduces the use of Viscous Plastic Processing (VPP) for the production of microwave ferrite materials and components. Conventional ceramic processing methods produce bulk ferrite materials restricted to relatively simple shapes and that can possess significant micro-structural defects resulting in poor mechanical properties. Using VPP the microstructures and physical strength of ferrite materials can be substantially enhanced and entirely new and unique device geometries produced, such as those based on ferrite helices. Ferrite Materials produced by VPP, such as lithium based ferrites, will be compared to those produced by standard methods of production such as powder pressing.