• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.19-20
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• 2007

At first the $Ba_{0.5}Sr_{0.5}TiO_3$-MgO powder with $B_2O_3-Li_2CO_3$ were made by the Sol-Gel method. The thick films of BST-MgO with $B_2O_3-Li_2CO_3$ were fabricated on the $Al_2O_3$ substrates coated with Pt by the screen printing method. The structural and dielectric properties of the BST-MgO thick film with $B_2O_3-Li_2CO_3$, addition were investigated. The structure of the BST-MgO with $B_2O_3-Li_2CO_3$ thick films were dense and homogeneous with no pores. The dielectric constant was increased and dielectric loss was decreased with increasing the sintering temperature.

• Progress in Superconductivity
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• v.13 no.2
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• pp.122-126
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• 2011

Superconducting $MgB_2$ thin films were fabricated by using a novel aerosol deposition technique wherein the pre-reacted powder is directly transformed into respective thin film. The formed thin films were characterized by X-ray diffraction technique and FE-SEM to understand its structure and morphology and the superconducting behavior has been characterized with the four probe resistivity measurement. The as-deposited thin films were formed into the frustrated amorphous structure, which were relaxed on the further heat treatment at $900^{\circ}C$ for 3 hrs. The relaxed amorphous $MgB_2$ thin films showed a comparatively high superconducting onset at about 38 K.

• Progress in Superconductivity
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• v.4 no.2
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• pp.153-156
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• 2003

We have studied fabrication of $MgB_2$ thin film on $SrTiO_3$ (001) and r-cut $A1_2$$O_3$ substrates by rf magnetron sputtering method using and $ MgB_2$ single target and two targets of Mg and B, respectively. Based on P -T phase diagram of $MgB_2$ and vapor pressure curves of Mg and B, a three-step process was employed. B layer was deposited at the bottom to enhance the film adhesion to the substrate. Secondly, co-sputtering of Mg and B was done. Finally, Mg was sputtered on top to compensate fur the loss of Mg during annealing. Subsequently, $MgB_2$ films were in-situ annealed in various conditions. The sample fabricated using the three-step process showed $T_{c}$ of 24 K and formation of superconducting $MgB_2$ phase was confirmed by XRD spectra. In case of co-sputtering deposition, $T_{c}$ depended on annealing time and argon pressure. However, those made by single-target sputtering showed non-superconducting behavior or low transition temperature, at best.est.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1261-1262
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• 2007

At first the $Ba_{0.5}Sr_{0.5}TiO_{3}$-MgO powder with $B_{2}O_{3}-Li_{2}CO_{3}$ were made by the Sol-Gel method. And then the thick films of BST-MgO with $B_{2}O_{3}-Li_{2}CO_{3}$ were fabricated on the $Al_{2}O_{3}$ substrates coated with Pt by the screen printing method. The structural and dielectric properties of the BST-MgO thick film with $B_{2}O_{3}-Li_{2}CO_{3}$ addition were investigated. The structure of the BST-MgO with $B_{2}O_{3}-Li_{2}CO_{3}$ thick films were dense and homogeneous with no pores. The dielectric constant and dielectric loss were increased with decreasing the $B_{2}O_{3}-Li_{2}CO_{3}$ addition ratio.

• Progress in Superconductivity and Cryogenics
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• v.21 no.3
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• pp.13-17
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• 2019

We investigate the effect of thermal annealing on $MgB_2$ thin films with thicknesses of 400 and 800 nm, irradiated by 350 keV C-ions with a dose of $1{\times}10^{15}atoms/cm^2$. Irradiation by low-energy C-ions produces atomic lattice displacement in $MgB_2$ thin films, improving magnetic field performance of critical current density ($J_c$) while reducing the superconducting transition temperature ($T_c$). Interestingly, the lattice displacement and the $T_c$ are gradually restored to the original values with increasing thermal annealing temperature. In addition, the magnetic field dependence of $J_c$ also returns to that of the pristine state together with the restoration of $T_c$. Because $J_c$(H) is sensitive to the type and density of the disorder, i.e. vortex pinning, the recovery of $J_c$(H) in irradiated $MgB_2$ thin films by thermal annealing indicates that low-energy C-ion irradiation on $MgB_2$ thin films primarily causes lattice displacement. These results provide new insights into the application of low-energy irradiation in strategically engineering critical properties of superconductors.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.1-5
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• 2022

We investigate the effect of surface disorder on the lower critical field (H_c1) of MgB₂ thin films with a thickness of 850 nm, where the disorder on the surface region is produced by the irradiation of 140 keV Co ions with the dose of 1 × 10¹⁴ ions/cm². The thickness of the damaged region by the irradiation is around 143 nm, corresponding to ~17% of the whole thickness of the film, thereby forming the disordered MgB₂ overlayer on the pure MgB₂ layer. The magnetic field dependence of magnetization, M(H), for the pristine MgB₂ thin film and the film with overlayer is measured at various temperatures, and H_c1 is determined from the difference (△M) between the Meissner line and magnetization signal with the criterion of △M = 10^-3 emu. Intriguingly, the film with the disordered overlayer shows a remarkably large H_c1(0) = 108 Oe compared to the H_c1(0) = 84 Oe of pristine film, indicating that the disordered MgB₂ overlayer on the pure MgB₂ layer serves to prevent the penetration of vortices into the sample. These results provide new ideas for improving the superheating field to design high-performance superconducting radio-frequency cavities.

• Progress in Superconductivity
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• v.9 no.2
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• pp.177-182
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• 2008

[ $MgB_2$ ] thin films were fabricated using hybrid physical-chemical vapor deposition (HPCVD) method on silicon substrates with buffers of alumina grown by using atomic layer deposition method. The growth war in a range of temperatures $500\;{\sim}\;600^{\circ}C$ and under the reactor pressures of $25\;{\sim}\;50\;Torr$. There are some interfacial reactions in the as-grown films with impurities of mostly $Mg_2Si$, $MgAl_2O_4$, and other phases. The $T_c$'s of $MgB_2$ films were observed to be as high as 39 K, but the transition widths were increased with growth temperatures. The magnetization was measured as a function of temperature down to the temperature of 5 K, but the complete Meissner effect was not observed, which shows that the granular nature of weak links is prevailing. The formation of mostly $Mg_2Si$ impurity in HPCVD process is discussed, considering the diffusion and reaction of Mg vapor with silicon substrates.

• Progress in Superconductivity
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• v.10 no.2
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• pp.116-122
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• 2009

We introduce a measurement method that enables to measure the penetration depth($\lambda$) of superconductor films by using a short-ended parallel plate sapphire resonator. Variations in the $\lambda$ of $MgB_2$ films could be measured down to the lowest temperature using a sapphire resonator with a $YBa_2Cu_3O_{7-x}$ film at the bottom. A model equation of $\lambda=\lambda_0[1-(T/T_c)^{\tau}]^{-1/2}$ for $MgB_2$ films appeared to describe the observed variations of the resonant frequency of the sapphire resonator with temperature, with $\lambda_0,\;\tau$, and $T_C$ used as the fitting parameters.

• 한국초전도학회:학술대회논문집
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• 2008.08a
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• pp.39-39
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• 2008

• 한국초전도학회:학술대회논문집
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• v.13
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• pp.39-39
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• 2003