• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.243-248
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• 1997

The effect of $O_2$ partial pressure on microstructure and soft magnetic properties of as-deposited Fe-Hf-O thin film alloys, which are produced by rf magnetron sputtering method in $Ar+O_2$ mixed gas atmosphere, are investigated. Saturation magnetization ($4{\pi}M_s$) of Fe-Hf-O film were decreased with increasing $O_2$ partial pressure, the best soft magnetic properties exhibit at $O_2$ partial pressure of 10%. With further increase of $O_2$ partial pressure, soft magnetic properties decreased continuously. The $Fe_{82}Hf_{3.4}O_{14.6}$ film with $P_{O2}=10%$ exhibits good soft magnetic properties with $4{\pi}M_s=17.7kG$, $H_c=0.7Oe$ and ${\mu}_ {eff}$ (1~100 MHz)=2,500, respectively. The addition of O is effective in grain refinement. In case of $P_{O2}=15%$, it is observed that $Fe_3O_4$ compound is formed and high frequency soft magnetic properties are decrease. The electrical resistvity($\rho$) of Fe-Hf-O film is increased with increasing $O_2$ partial pressure. Electrical resistivity of $Fe_{82}Hf_{3.4}O_{14.6}$ film was 5 times higher than that of the film without oxygen. Thus, it is considered that the good magnetic properties of $Fe_{82}Hf_{3.4}O_{14.6}$ film results from decreasing the $\alpha$-Fe grain size by precipitates (Hf and O), high electrical resistivity.

• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.237-242
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• 1997

The microstructure and soft magnetic properties of as-deposited Fe-Hf-O thin film alloys, which are produced at $P_{O2}=10%$ by rf magnetron sputtering method in $Ar+O_2$ mixed gas atmosphere, is investigated. Newly developed $Fe_{82}Hf_{3.4}O_{14.6}$ film exhibits good soft magnetic properties with $4{\pi}M_s=17.7$ kG, $H_c=0.7$ Oe and ${\mu}_{eff}$(0.5~100MHz)=2,500, respectively. The Fe-Hf-O films are composed of $\alpha$-Fe nanograins and amorphous phase with larger amounts of Hf and O elements which chemically combine each other. With increasing Hf area fraction, Hf and O contents increased proportionally. It was considered that O content in films was determined by Hf contents, because O was chemically combined with Hf. It results from decreasing the $\alpha$-Fe grain size by precipitates (Hf and O), high electrical resistivity. The $Fe_{82}Hf_{3.4}O_{14.6}$ film exhibits the quality factor (Q=$\mu$'/$\mu$") of 25 at 20 MHz. These good frequency characteristics are considered to be superior to other films already reported.o other films already reported.

• Journal of the Korean Magnetics Society
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• v.7 no.5
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• pp.250-257
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• 1997

The microstructure and magnetic properties of Fe-Nb-B-N thin film alloys, which produced by rf magnetron sputtering method in $Ar+N_2$ mixed gas atmosphere, were investigated. The $Fe_{70}Nb_{14}B_{11}N_5$ films, annealed at 59$0^{\circ}C$, exhibit soft magnetic properties: $4{\pi}M_s=16.5kG$ , $H_c=0.13Oe$ and ${\mu}_{eff}$ (1~10 MHz)=5, 000. The frequency stability of the Fe-Nb-B-N films has also been found to be good up to 10 MHz. The Fe-Nb-B-N thin film alloys annealed at 59$0^{\circ}C$ consist of three phase; fine crystalline $\alpha$-Fe phase with grain size of about 5~10 nm, Nb-B rich amorphous phase and Nb-nitride precipitates with the size of less than 3 nm. Annealed Fe-Nb-B films have two phases; $\alpha$-Fe grains with the size of about 10 nm and Nb-B rich amorphous phase. The addition of N decreased $\alpha$-Fe grain size due to the precipitation of NbN. The good magnetic properties of the Fe-Nb-B-N film alloys are due to fine $\alpha$-Fe grains resulting from the precipitation of NbN.

• Journal of the Korean Magnetics Society
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• v.14 no.6
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• pp.236-239
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• 2004

We studied the specular spin valve (SSV) having the spin filter layer (SFL) in contact with the ultrathin free layer composed of Ta3/NiFe2/IrMn7/CoFel/(NOLl)/CoFe2/Cu1.8/CoFe( $t_{F}$)/Cu( $t_{SF}$ )/(NOL2)/Ta3.5 (in nm) by the magnetron sputtering system. For this antiferromagnetic I $r_{22}$M $n_{78}$-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness ( $t_{F}$) and the SFL thickness ( $t_{SF}$ ) were 1.5 nm, and the MR ratio higher than 11% was maintained even when the $t_{F}$ was reduced to 1.0 nm. It was due to increase of specular electron by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field ( $H_{int}$) between free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer ( $H_{cf}$ ) was significantly reduced as compared to the traditional spin valve (TSV), and was remained as low as 4 Oe when the $t_{F}$ varied from 1 nm to 4 urn. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer.

• Korean Journal of Materials Research
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• v.18 no.4
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• pp.169-174
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• 2008

The structural and electrical properties of amorphous $BaSm_2Ti_4O_{12}$ (BSmT) films on a $TiN/SiO_2/Si$ substrate deposited using a RF magnetron sputtering method were investigated. The deposition of BSmT films was carried out at $300^{\circ}C$ in a mixed oxygen and argon ($O_2$ : Ar = 1 : 4) atmosphere with a total pressure of 8.0 mTorr. In particular, a 45 nm-thick amorphous BSmT film exhibited a high capacitance density and low dissipation factor of $7.60\;fF/{\mu}m2$ and 1.3%, respectively, with a dielectric constant of 38 at 100 kHz. Its capacitance showed very little change, even in GHz ranges from 1.0 GHz to 6.0 GHz. The quality factor of the BSmT film was as high as 67 at 6 GHz. The leakage current density of the BSmT film was also very low, at approximately $5.11\;nA/cm^2$ at 2 V; its conduction mechanism was explained by the the Poole-Frenkel emission. The quadratic voltage coefficient of capacitance of the BSmT film was approximately $698\;ppm/V^2$, which is higher than the required value (<$100\;ppm/V^2$) for RF application. This could be reduced by improving the process condition. The temperature coefficient of capacitance of the film was low at nearly $296\;ppm/^{\circ}C$ at 100 kHz. Therefore, amorphous BSmT grown on a TiN substrate is a viable candidate material for a metal-insulator-metal capacitor.

• Korean Journal of Materials Research
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• v.18 no.4
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• pp.222-227
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• 2008

In this study, $BaTiO_3$ thin films were grown by RF-magnetron sputtering, and the effects of a post-annealing process on the structural characteristics of the $BaTiO_3$ thin films were investigated. For the crystallization of the grown thin films, post-annealing was carried out in air at an annealing temperature that varied from $500-1000^{\circ}C$. XRD results showed that the highest crystal quality was obtained from the samples annealed at $600-700^{\circ}C$. From the SEM analysis, no crystal grains were observed after annealing at temperatures ranging from 500 to $600^{\circ}C$; and 80 nm grains were obtained at $700^{\circ}C$. The surface roughness of the $BaTiO_3$ thin films from AFM measurements and the crystal quality from Raman analysis also showed that the optimum annealing temperature was $700^{\circ}C$. XPS results demonstrated that the binding energy of each element of the thin-film-type $BaTiO_3$ in this study shifted with the annealing temperature. Additionally, a Ti-rich phenomenon was observed for samples annealed at $1000^{\circ}C$. Depth-profiling analysis through a GDS (glow discharge spectrometer) showed that a stoichiometric composition could be obtained when the annealing temperature was in the range of 500 to $700^{\circ}C$. All of the results obtained in this study clearly demonstrate that an annealing temperature of $700^{\circ}C$ results in optimal structural properties of $BaTiO_3$ thin films in terms of their crystal quality, surface roughness, and composition.

• Korean Journal of Optics and Photonics
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• v.16 no.2
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• pp.168-173
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• 2005

Ag-doped $TiO_2$ thin films were prepared by RF magnetron co-sputtering method, and their physical and chemical properties were examined as a function of calcination temperature. XRD results showed that the crystallite size of Ag-doped films was smaller than that of the $TiO_2$ thin films. SEM results showed that the particle size of $Ag/TiO_2$ film was smaller and more uniform than pure $TiO_2$ film. The films had high transparency in the visible range. The films calcined at $600^{\circ}C$ were the anatase phase, and the films calcined at $900^{\circ}C$ were a mixture of anatase and rutile phases. The absorption edge of films calcined at $900^{\circ}C$ was red-shifted. This is due to the augmented absorption resulting from the phase transformation from anatase to rutile phase. And the transmittance of films decreased by the light scattering and absorption in the films. Photocatalytic activity of $Ag/TiO_2$ thin films was higher than that of the pure $TiO_2$ thin films.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.323-329
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• 2000

In this study we have calculated an ideal complex refractive index of a TiN trim used in a layer of anl1reilecnon (I\R) coatmg, [air$ISiO_2ITiNIglass$] in the visible. Also we simulated the rellectance of lwo-layer AR coating by varying the thicknesses of TiN and $SiO_2$ layers, respecl1vely. The simolation results show that we can controllhe lowest reflectance and AR band of tile AR coating. The TIN fihns were fabricated by a RF magnetron sputtering apparalus. The chemical, structural and electrical properties of TiN fih11S were inveshgated by the Rutherford backscattering spech'oscopy (RBS), atomic force microscope (AFM) and 4-point probe. The optical properlies were inve,tigated by the spectrophotometer and vanable angle spectroscopic ellipsometer (VASE). The smface roughness of TiN flhns \vas $9~10\AA$. TIle resistivity of TiN films was TEX>$360~730\mu$\Omega $ cm. The ,toichlOllletry of TiN film was 1'1: O:N = I: 0.65 :0.95 and ilic oxygen wa~ found on ilie smface. With these experimental and simu]al1on resulLs, we deposited duo: two-layer AR coating, [air$ISiO_2ITiNIglass$] and the refleClance was under 0.5% ill the regIOn of 440-650 run. 0 run.

• Journal of the Korean Magnetics Society
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• v.9 no.2
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• pp.111-120
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• 1999

The effects of annealing in rotating magnetic field after deposition on electromagnetic properties of $Co_{82}Zr_6Mo_{12}$ thin (200~1200 $\AA$) films prepared by RF-magnetron sputtering were investigated in terms of microstructure and surface morphology. The coercivity decreases, but $4{\pi}M_5$ does not change with increasing the film thickness. The coercivity of the films was decreased below 300 $^{\circ}C$ due to stress relief and decreasing the surface roughness, while increased at 400 $^{\circ}C$ due to partial grain growth. And then, $4{\rho}M_5$ was almost independent of annealing temperatures below 200 $^{\circ}C$, but increased from 7.4 kG to 8.0 kG at 300 $^{\circ}C$ and at 400 $^{\circ}C$, which was caused by precipitation and growth of fine Co particles in the films. The electrical resistivity of films was decreased with increasing annealing temperatures and the magnetoresistance was a negative value of nearly 0 $\mu$$\Omega$cm. After annealing at 300 $^{\circ}C$, maximum effective permeability was 1200 to the hard axis of the thin films according to high frequency change. Considering the practical application of biasing layers of the films for magnetoresistive heads, optimal annealing conditions was obtained after one hour annealing at 300 $^{\circ}C$ in 400 Oe rotating magnetic field.

• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.159-163
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• 2000

MR characteristics in magnetic tunnel junction using CoO as the oxide barrier were investigated. Spin-dependent tunnel junctions were fabricated on 4$\^$o/ tilt-cut (111)Si substrates in 3-gun magnetron sputtering system. The top and bottom ferromagnetic electrodes were Ni$\_$80/Fe$\_$20/(300 $\AA$) and Co(300 $\AA$), respectively. The oxide barriers (CoO) were formed by the thermal oxidation at room temperature in an O$_2$ atmosphere and the plasma oxidation. The increase of coercive field due to antiferromagnetic-ferromagnetic coupling has been observed in O$_2$plasma-oxidized CoO based junctions at room temperature. At a sensing current of 1 mA, MR ratios of O$_2$plasma-oxidized CoO based junction and thermal-oxidized CoO based junction at room temperature were 1% and 5%, respectively. Larger MR ratios are observed in magnetic tunnel juctions with thermal oxidized CoO when sensing current more than applied 1.5 mA. At a sensing current of 1.5 mA, we have observed MR value of 28 % and specific resistance (RA=R$\times$A) value of 10.9 ㏀$\times$㎛$^2$. When specific resistance values reached 2.28 ㏀$\times$㎛$^2$, we have observed that MR ratios become as high as 120%.