Inductors For High-frequency Applications Research Articles

Densification of Core-Less Power Inductor for High Frequency Applications

Densification of Core-Less Power Inductor for High Frequency Applications

Co2Y-NiCuZn Ferrite Composites for High Frequency Applications

It is very important and urgent to develop a magnetic material that has a higher initial permeability and quality factor above 200-300 MHz for use in making high frequency inductors. This study produced a Co2Y-NiCuZn ferrite composite with high permeability by coating NiCuZn ferrites onto the surface of Co2Y ferrites using a heterogeneous nucleation process. The NiCuZn ferrites addition effects on the densification behavior, micro-structure and magnetic property of Co2Y-NiCuZn ferrite composites were investigated. A NiCuZn ferrites coating onto the surface of Co2Y ferrites can effectively enhance the densification and improve the magnetic property of Co2Y ferrites. Co2Y-NiCuZn ferrite composites sintered at 1200° show a sintered density of 5.34g/cm3, high initial permeability of 4 and quality factor above 30 in the 300-600 MHz frequency, which can be used in inductors for high frequency applications.

Zn- and Cu-substituted Co2Y hexagonal ferrites: Sintering behavior and permeability

Y-type polycrystalline hexagonal ferrites Ba2Co2−x−yZnxCuyFe12O22 with 0≤x≤2 and 0≤y≤0.8 were prepared by the mixed-oxide route. Single phase Y-type ferrite powders were obtained after calcinations at 1000°C. Samples sintered at 1200°C show a permeability that increases with the substitution of Zn for Co and display maximum permeability of μ′=35 at 1MHz for x=1.6 and y=0.4. A resonance frequency fr=500MHz is observed for Zn-rich ferrites with y=0 and 0.4. The saturation magnetization increases with substitution of Zn for Co. Addition of Bi2O3 shifts the temperature of maximum shrinkage down to T≤950°C. Moreover, an increase of the Cu-concentration further lowers the sintering temperature to T≤900°C, enabling co-firing of the ferrites with Ag metallization for multilayer technologies. However, low-temperature firing reduces the permeability to μ′=10 and the resonance frequency is shifted to 1GHz. Thus substituted hexagonal Y-type ferrites can be used as soft magnetic materials for multilayer inductors for high frequency applications.

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.

Synthesis, sintering behavior and magnetic properties of Cu-substituted Co2Z hexagonal ferrites

Cu-substituted Z-type Ba3Co2−x Cu x Fe24O41 hexagonal ferrites (0 ≤ x ≤ 1) were prepared by the standard oxide route. Almost single phase Z-type ferrite powders were observed after calcination at 1,260 °C. The permeability of samples sintered at 1,260 °C varies with the Cu content; a maximum permeability at 10 MHz of μ′ = 17 was found for x = 0.6. It is shown that the permeability behavior is determined by the concentration of Z-type ferrite in the sample and the microstructure. Addition of 3 wt% Bi2O3 leads to almost complete densification of Co2Z samples under low temperature ceramic cofiring (LTCC) conditions at 900 °C. However, the permeability of samples sintered at 900 °C is reduced to μ′ = 5 with resonance frequency at 2 GHz. It is shown that Cu-substituted Co2Z ferrites are not stable at T < 1,260 °C. Partial decomposition into other hexagonal ferrites causes a reduction of the permeability. In spite of this severe drawback, Co2Z hexagonal ferrites with Cu modifications are suitable materials for multilayer inductors for high frequency applications.

Design of high-Q 3-D integrated inductors for high frequency applications

Design of 3-Dimensional micromachined inductors on high-(10 K ·cm) and low-resistivity(10 ·cm) Si substrate fabricated using stress metal technology we have developed [1, 2] is presented. Using hig...

Surface micromachined solenoid inductors for high frequency applications

As operation frequencies and performance requirements of wireless devices increase, the resultant demands on the performance of passive components also increase. Miniaturization of inductive components for high frequency has been a key research area to address this issue; however, in general, miniaturized integrated inductors can suffer from low Q factors and/or self-resonant frequencies when compared to their discrete counterparts. In this research, a modified geometry of a solenoid type inductor using a surface micromachining technique is proposed. This inductor has an air core and an electroplated copper coil to reduce the series resistance, and its low temperature process is suitable for various packaging applications. An important feature of the proposed inductor geometry is the introduction of an air gap between the substrate and the conductor coil in order to reduce the effects of the substrate dielectric constant. This air gap can be realized using a polyimide sacrificial layer and a surface micromachining technique. Therefore, the resulting inductor can have less substrate-dependent magnetic properties, less stray capacitance, and higher Q-factor. The measurement result shows that this inductor has high Q-factor and stable inductance over a wide range of operating frequency. Also, various effects of geometrical factors have been investigated. Various inductors with the inductance varying from 1 to 20 nH and maximum Q-factor from 7 to 60 have been fabricated and measured.