Ki Hyeon Kim

A megahertz switching DC/DC converter using FeBN thin film inductor

A dual spiral sandwiched thin film inductor with a dimension of 5 mm /spl times/ 5 mm was fabricated by a LIGA-like micromachined process. FeBN magnetic films were used as a core material. The inductance and quality factor value of the inductor were measured approximately 1 /spl mu/H and 4 up to 5 MHz, respectively. Using the FeBN film inductor, a hybrid dc/dc converter (15 mm /spl times/ 12 mm /spl times/ 1.5 mm) was designed and fabricated. The circuit topology of the converter was a zero voltage switching clamp voltage (ZVS-CV) buck converter. An input of 3.6 V was bucked to 2.7 V at a switching frequency of 1.8 MHz. The maximum power was 1.5 W. The measured efficiency of the buck converter reached a maximum value of 80% and kept stable up to 300 mA of load currents at 1.8 MHz.

Effect of radio-frequency noise suppression on the coplanar transmission line using soft magnetic thin films

We demonstrated the radio-frequency (rf) noise suppressor using soft magnetic films on a coplanar transmission line from 0.1 to 20 GHz. The coplanar transmission line is composed of magnetic film/polyimide/Cu transmission line/seed layer (Cu/Ti)/glass substrate with the dimension of 50 μm width of the signal line and 3 μm thickness (characteristic impedance: 50 Ω). The magnetic films (CoPdAlO, CoZrO, and CoNbZr) as a noise suppressor are prepared by rf sputtering. The saturation magnetization of each magnetic film is about 10 kG. The magnetic anisotropy field and the ferromagnetic resonance frequency are 230, 89, and 6 Oe and 4.2, 2.5, and 0.7 GHz, respectively. The power loss of the coplanar line with magnetic films is significantly larger than without magnetic and nonmagnetic films due to ferromagnetic resonance losses.

Granular thin films with high RF permeability

In this article, we have studied high permeability films with the granular structure for use in the magnetic recording technologies. Also we discuss the advantages, drawbacks and some new development of the granular films.

RF integrated noise suppressor using soft magnetic films

RF integrated noise suppressors were fabricated by integration of soft magnetic films on coplanar transmission lines. The vertical structure of suppressor was composed of the magnetic film (2 mm/spl times/15 mm/spl times/1, 2 /spl mu/m)/2-/spl mu/m-thick polyimide/15.2-mm-long and 3-/spl mu/m-thick Cu transmission line/seed layer (Ti/Cu)/1 mm-thick glass substrate. The coplanar transmission lines were prepared by electroplated Cu with 50 /spl Omega/-characteristic impedance. The width of the signal line was 50 /spl mu/m. The magnetic films, e.g., CoPdAlO and CoNbZr films were deposited by rf magnetron sputtering. Compared with those of the nonintegrated noise suppressor, the magnitude of signal attenuation at resonance point of integrated noise suppressor greatly increased from - 4 to - 30 dB for the 1-/spl mu/m-thick CoNbZr film, and from -15 to - 57 dB for the 2-/spl mu/m-thick CoPdAlO film, respectively.

Development of FeCo-based thin films for gigahertz applications

For improving high-frequency characteristics and soft magnetic properties of (Fe/sub 7/Co/sub 3/)B-based thin films, the effects of Ni addition and an oblique deposition method on the microstructures have been examined. The Ni addition to (Fe/sub 7/Co/sub 3/)B films was found to enhance B segregation on grain boundaries, which resulted in the formation of a well-defined columnar structure and the increase of film resistivity. Utilizing the columnar structure, large in-plane anisotropy was induced by an oblique deposition method which enabled the control of the inclination angle of the columns. As a result, the ferromagnetic resonance of (Fe/sub 7/Co/sub 3/)/sub 71/Ni/sub 7/B/sub 22/ thin films reached 6.2GHz.

Effects of boron contents on magnetic properties of Fe-Co-B thin films

Effects of B on the magnetic properties and high frequency characteristics of the Fe/sub 7/Co/sub 3/ based thin films were investigated through the microstructural analysis. It was found that B addition was very effective in increasing anisotropy field and resistivity and in decreasing coercivity without much loss of saturation magnetization. These enhancements were shown to be strongly related to grain size, grain morphology and preferred orientations. As a result, a Fe/sub 55/Co/sub 28/B/sub 17/ film with small dispersion angle of /spl sim/0.5/spl deg/ showed the ferromagnetic resonance frequency of 3.3 GHz and a linear effective permeability of /spl sim/350 up to 2 GHz.

Modeling for RF noise suppressor using a magnetic film on coplanar transmission line

A finite-element method is applied to analyze the electromagnetic field and loss generation of a soft magnetic thin film on a coplanar transmission line for which the dimension of the magnetic film is designed to control the center frequency and bandwidth of the radio-frequency (RF) electromagnetic noise attenuation in the gigahertz range without external applied magnetic fields. The coplanar transmission line with characteristic impedance of 50 /spl Omega/ has total width, width of signal line, and thickness of 400, 50, and 3 /spl mu/m, respectively. The change of the magnetic field distribution, the induced surface current density on the coplanar transmission line, and hence the RF noise suppression by soft magnetic films are significant as a function of the width (50-2000 /spl mu/m) and thickness (0.1, 0.3, 0.5, and 1 /spl mu/m) of the magnetic film.

Ferromagnetic RF integrated inductor with closed magnetic circuit structure

Closed magnetic circuit type ferromagnetic RF integrated inductors have been fabricated based on MEMS-like micro fabrication techniques. The taper etching process greatly helped to endure sufficient magnetic flux flow at the edge of the top and bottom magnetic layers. Air cores and three different sandwich type ferromagnetic inductos are also microfabricated. Measured results exhibited the quality factor Q=12, being highest among the published data of ferromagnetic RF integrated inductor at 1 GHz. Index Terms — integrated inductor, magnetic film, electromagnetic field simulation, quality factor.

Magnetic and Microwave Properties of NiFe Nanowires Embedded in Anodized Aluminum Oxide (AAO) Templates

Ferromagnetic NiFe nanowire arrays were fabricated on porous alumina templates by an electrochemical method. The nanowires were controlled to have different diameter (100, 200 nm) and length (10, 20, 30 ¿m) in order to understand the magnetostatic interactions between nanowires. Through the control of geometry of the arrays, the magnetization direction was shown to change from parallel to perpendicular to wire direction. The anisotropy field of these arrays was measured much higher than 1 kOe, which resulted in excellent microwave properties, particularly for noise suppression properties over 10 GHz.

Broadband RF Noise Suppression by Magnetic Nanowire-Filled Composite Films

The characteristics of the electromagnetic noise suppression have evaluated using magnetic nanowire-filled composite film on a microstrip line in the broadband radio-frequency range from 0.5 to 20 GHz. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by Kittels and Landau-Lifshitz-Gilbert equations. The FMR frequency is gradually increased with the increment of aspect ratio (up to 50) of magnetic nanowire. When the magnetic nanowires were mixed with various aspect ratio in composite, the FMR frequency exhibited the broadband frequency regions with 10-28 GHz, 5-14 GHz, 2.5-7 GHz, and 1-2.7 GHz for the change of magnetizations (4piMs: 20, 10, 5, and 2 kG), respectively. Using the calculated FMR frequency profile, the power losses were obtained in broadband frequency region. The transmission power absorption of the composite film on microstrip line was simulated using a 3-D FEM HFSS simulation program. The microstrip line model was composed of Cu conductor line and grounded dielectric substrates, which was designed by IEC standard (IEC 62333-2). The conduction electromagnetic noise was suppressed by the various aspect ratios of the magnetic nanowire-filled composite films in broadband frequency region.