Masaaki Yagi

B-concentration dependence on anisotropy field of CoFeB thin film for gigahertz frequency use

B was added to the high moment CoFe thin films (Co/sub 35/Fe/sub 65/, Co/sub 25/Fe/sub 75/, and Co/sub 15/Fe/sub 85/) using synchronous triple-RF magnetron sputtering to obtain the films with large anisotropy fields greater than 500 Oe. These films required inductor core materials operating at the frequencies of several gigahertz. Magnetic properties and the crystalline structure of the CoFeB films were investigated. It was found that the B addition increased the anisotropy field to 400-700 Oe and that the increase in anisotropy field was associated with changes in the crystalline structure, crystallite sizes, and crystallite orientation. The results indicated that CoFeB films have potential for use in magnetic cores and inductors operating at gigahertz frequencies.

Soft magnetic properties of ultrathin Co-based amorphous alloy ribbons with thickness of 3-10 /spl mu/m

Ultrathin zero-magnetostrictive amorphous ((Fe/sub 0.05/Co/sub 0.95/)/sub 0.95/ Cr/sub 0.05/)/sub 75/(Si/sub 0.5/B/sub 0.5/)/sub 25/ ribbons with thickness of 3-10 mu m were fabricated by a single roller quenching method in vacuum. The ribbons obtained had a good smooth surface and dimensional uniformity. The core loss of toroidal samples 10 mm in diameter was measured after annealing and found to decrease with decreasing ribbon thickness. For 5.5- mu m-thick ribbons, the losses at 1 MHz and 10 MHz were 1.0 J/m/sup 3/ (=1.0 W/cm/sup 3/) and 8.8 J/m/sup 3/ (=88 W/cm/sup 3/) for B/sub m/=0.1 T, respectively. The former value was 2/5 that of Mn-Zn high-frequency ferrites and 1/3 that of 5- mu m Supermalloy tape wound cores. Furthermore, extremely low losses were obtained for 3.8- mu m-thick ribbon at 2-10 MHz. In addition, remarkably high initial permeability beyond 100 kHz was also attained. The values of 5.5- mu m-thick ribbons measured at 1 and 10 MHz were about 10000 and 1200 for H/sub m/=2 mOe, respectively. >

Very low loss ultrathin Co-based amorphous ribbon cores

Ultrathin Co‐based amorphous ribbons with a thickness of 6–10 μm were fabricated by a single roller quenching method in vacuum. The compositions of the alloys were zero magnetostrictive: Fe4.7Co70.3Si15B10 and (Fe0.05Co0.95)71(Si0.5B0.5)29. The ribbons obtained had good smoothness and dimensional uniformity. The core loss of toroidal samples 15 mm in diameter was measured after annealing. The loss decreased with decreasing ribbon thickness. In the case of 6.4‐μm‐thick (Fe,Co)71(Si,B)29 amorphous ribbon, the values at 100 kHz and 1 MHz were 40 mW/cm3 and 1.8 W/cm3 for Bm=0.1 T, respectively. The former was 1/4 that of Mn‐Zn ferrites or 1/2 that of 5‐μm‐thick Supermalloy tape wound core loss. The latter was (2)/(3) that of 5‐μm Supermalloy tape wound core loss. In addition, the initial permeability beyond 100 kHz was also markedly improved by thickness reduction. The values of 6.4‐μm‐thick (Fe,Co)71(Si,B)29 ribbon measured at 1 and 10 MHz were about 7000 and 1000 for Hm=2 mOe, respectively.

Magnetic Properties of Fe-Based Amorphous Powders With High-Saturation Induction Produced by Spinning Water Atomization Process (SWAP)

Fe-based amorphous powders with high magnetic flux density were fabricated in an extremely high cooling rate of over 10 ⁶ K/s by spinning water atomization process (SWAP). The composition of the alloys studied were Fe ₇₉(Si _0.5B _0.5) ₁₉C ₂ and Fe _x(Si _0.3B _0.7) _98-xC ₂ (x = 79,80,81,83,84). The saturation flux density Bs increased with increasing iron content. For Fe ₈₃(Si _0.3B _0.7) ₁₅C ₂, the Bs value was 1.64 T, which is 31% higher than that of our previously developed (Fe _0.97Cr _0.03) ₇₆(Si _0.5B _0.5) ₂₂C ₂ alloy. Furthermore, consolidated cores of amorphous powders were also fabricated by compact-pressing techniques.

High-resistive (CoFeB)-(SiO/sub 2/) soft magnetic amorphous film for micro-cores in a few MHz range

Highly resistive (CoFeB)-(SiO/sub 2/) amorphous films were deposited on glass substrates and polyimide sheets by synchronous dual-rf magnetron sputtering. SiO/sub 2/ volume fraction dependence of magnetic properties and resistivity was investigated. The as-deposited films for SiO/sub 2/ volume fraction /spl upsi/=20 vol.% had low coercivities of H/sub c/=0.2-0.3 Oe, together with high resistivities of 1500-2200 /spl mu/ /spl Omega/ cm. The film exhibited an anisotropy field 40 Oe, a relative permeability of 200 and a saturation magnetization of 7.3 kG. The core loss of the films was 1-1.5 J/m/sup 3/ at 1 MHz for maximum flux density B/sub m/=0.1 T. The loss was found to be as low as those of Co-based ultra-thin ribbons. The films are useful as thin film cores in the micromagnetic elements which work in the MHz range.

Magnetic Properties of Fe-Based Amorphous Powder Cores With High Magnetic Flux Density

Fe₈₁(Si_0.3B_0.7)₁₇C₂ amorphous powder cores with glass binder were fabricated by compact-pressing techniques, and the relation between magnetic properties and powder particle sizes was evaluated. The Fe₈₁ (Si_0.3B_0.7)₁₇C₂ powder core exhibited superior magnetic properties compared with our previously developed (Fe_0.97Cr_0.03)₇₆ (Si_0.5 B_0.5 )₂₂C₂ powder core. The magnetic flux density Bm of the core made of Fe₈₁ system powders at 20 000 A/m was about 29% higher than that of Fe₇₆ system core. The core loss decreased with decreasing particle sizes. For the core made of powders with mean particle size of 22 mum below 45 mum in diameter, the loss at 100 kHz for Bm = 0.1 T was 520 kW/m³. This value was comparable to that of Fe₇₆ system powder core with a lower flux density. In addition, fairly superior characteristics of permeability under dc bias field were also attained. The values of Fe₈₁ system core was about 10% higher than that of Fe ₇₆ system almost over the entire range measured.

Magnetic properties of compressed amorphous powder cores and their application to a fly-back converter

Fe-based amorphous powder cores with glass binder were fabricated by hot-pressing techniques. The cores exhibited low core losses, relatively low effective permeability and high flux density, which are superior magnetic properties when applied to choking coil or fly-back transformers operating in the high frequency range. The core obtained was applied to a fly-back converter working at 100 kHz. The conversion efficiency examined at output power up to 300 W was higher than that of converters using a typical commercial Sendust core and a single gap ferrite core.

Switching characteristics and domain structures in amorphous toroidal cores

The switching characteristics of amorphous toroidal cores were investigated in the range of flux reversal time 10-1∼ 10-6sec and related to the observed behavior of magnetic domains. Samples used were amorphous-ribbon toroidal cores with multi-layer of Fe 40 Ni 40 P 14 B 6 (METGLAS 2826), Fe 78 Si 10 B 12 , Co 74 Si 10 B 16 , Fe 5 CO 70 Si 15 B 10 and Fe 80 P 13 C 7 . The switching time Ts for the flux reversal by constant-current pulse fields was measured for these cores as a function of effective applied field He (=applied field H - coercive force Hc). Domain patterns were observed for single-layer toroidal cores of Fe 40 Ni 40 P 14 B 6 (METGLAS 2826) by the Kerr effect. Both the number of domain walls and the average wall velocity were estimated from observed patterns. The non-linear dependences of Ts on He were explained in terms of the number of domain walls and the average wall velocity based on the observed domain behaviors.

Magnetic domains and magnetization process of amorphous granular (CoFeB)–SiO2 thin films

The domain structure and magnetization process of a granular film were explored using a Kerr microscope. Narrow line-shaped reversal domains were observed in a granular (Co25Fe66B9)75–(SiO2)25 film, and no increase in the width of the domains was observed during the magnetization reversal process by applying a dc field along the easy axis. In addition, no wall displacement was observed in an ac field along the hard axis because only magnetization rotation occurs due to wall pinning. It was found that wall motion that causes excess eddy current losses at high frequencies is hard to occur by the granular structure.

Directional coupler composed of CoFeB metallic magnetic film/polyimide dielectric film hybrid transmission line

This paper describes a novel thin film type directional coupler using magnetic/dielectric hybrid transmission line device. The hybrid transmission line with a dielectric/magnetic/dielectric sandwich structure has a large effect of wavelength shortening. As a result of signal characteristics evaluation, the directivity of the signal in the device was higher than 18 dB, and insertion loss was less than 0.6 dB at the operating frequency of 0.8/spl sim/2 GHz of the cellular phones.