Earticle

LMO(LaMnO3) buffer layer of superconducting coated conductor was deposited on IBAD-MgO template in the plasma atmosphere at 650 oC which is relatively low compared with conventional deposition temperature of more than 800 oC. Deposition method of LMO was DC sputtering, and target and deposition chamber were connected to the cathode and anode respectively. When DC voltage was applied between target and chamber, plasma was formed on the surface of target. The tape substrate was located with the distance of 10 cm between target and tape substrate . When anode bias was connected to the tape substrate, electrons were attracted from plasma in target surface to the tape substrate, and only tape substrate was heated by electron bombardment without heating any other zone. The effect of electron bombardment on the surface of substrate was investigated by increasing bias voltage to the substrate. We found out that the sample of electron bombardment had the effect of surface heating and had good texturing at low controlling temperature.

The BaHfO3 (BHO) buffer layer on the IBAD MgO template was turned to be effective for a successful fabrication of GdBa2Cu3O7-δ (GdBCO) films with high critical current density (Jc). Both the BHO buffer layers and GdBCO films were prepared by pulsed laser deposition (PLD). The effects of the PLD conditions, including substrate temperature (Ts), oxygen partial pressure (PO2), and deposition time on the in-plane texture, surface roughness, and microstructures of the BHO buffer layers on the IBAD MgO template were systematically studied for processing optimization. The c-axis oriented growth of BHO layers was insensitive to the deposition temperature and the film thickness, while the in-plane texture and surface roughness of those were improved with increasing Ts from 700 to 800°C. On the optimally processed BHO buffer layer, the highest Jc value (77 K, self-field) of 3.68 MA/cm2 could be obtained from GdBCO film deposited at 780°C, representing that BHO is a strong candidate for the buffer layer on the IBAD MgO template.

We investigated the structural suitability of GdFeO3 (GdFO) as a buffer layer for the GdBa2Cu3O7-x (GdBCO) superconducting films. GdFO films with different thicknesses and GdBCO thin films were all prepared by using a pulsed laser deposition technique. The analyses of X-ray diffraction and EXAFS data indicates that the c-axis parameter increases and the Fe-O bond length decreases with the GdFO thickness due to the compressive stain induced by the lattice mismatch between GdFO and STO substrate and as a result, the Debye-Waller factor, an index of disorder in the local structure near the Fe-O bond, increases with the GdFO thickness. However, for the GdBCO/GdFO bilayer structure, the Debye-Waller factor decreases as the GdFO thickness increases indicating a diminished disorder by the structural coupling between GdFO and GdBCO. These results indicate that an appropriate thickness of GdFO is required to be utilized as a magnetic buffer layer for the GdBCO superconducting films.

We have grown MgB2 on SiC buffer layer by using metallic Hastelloy tape as the substrate. Hastelloy tape was chosen for its potential practical applications, mainly in the power cable industry. SiC buffer layers were deposited on Hastelloy tapes at 400, 500, and 600 oC by using a pulsed laser deposition method, and then by using a hybrid physical-chemical vapor deposition technique, MgB2 films were grown on the three different SiC buffer layers. An enhancement of critical current density values were noticed in the MgB2 films on SiC/Hastelloy deposited at 500 and 600 oC. From the surface analysis, smaller and denser grains of MgB2 tapes are likely to cause this enhancement. This result infers that the addition of SiC buffer layers may contribute to the improvement of superconducting properties of MgB2 tapes.

CeO2 has been widely used for single buffer layer of coated conductor because of superior chemical and structural compatibility with ReBa2Cu3O7-δ(Re=Y, Nd, Sm, Gd, Dy, Ho, etc.). But, the surface of CeO2 layer showed cracks because of the large difference in thermal expansion coefficient between metal substrate and deposited CeO2 layer, when thickness of CeO2 layer exceeds 100 nm on the biaxially textured Ni-3%W substrate. The deposition rate has been limited to be less than 6 Å/sec in order to get a good epitaxy. In this research, we deposited CeO2 single buffer layers on biaxially textured Ni-3%W substrate with 2-step process such as thin nucleation layer(>10 nm) with low deposition rate(3 Å/sec) and thick homo epitaxial layer(>240 nm) with high deposition rate(30 Å/sec). Effect of deposition temperature on degree of texture development was tested. Thick homo epitaxial CeO2 layer with good texture without crack was obtained at 600 oC, which has Δφ value of 6.2 o, Δω value of 4.3 o and average surface roughness(Ra) of 7.2 nm within 10 ㎛ × 10 ㎛ area. This result shows the possibility of preparing advanced Ni substrate with simplified architecture of single CeO2 layer for low cost coated conductor.

This paper describes direct $\mu$C-Si/CaF$_2$/glass thin film growth by RPCVD system in a low temperature for thin film transistor (TFT), photovoltaic devices. and sensor applications. Experimental factors in a low temperature direct $\mu$ c-Si film growth are presented in terms of deposition parameters: SiH$_4$/H$_2$ ratio, chamber total pressure, substrate temperature, rf power, and CaF$_2$ buffer layer. The structural and electrical properties of the deposited films were studied by means of Raman spectroscopy, I-V, L-I-V, X-ray diffraction analysis and SEM. we obtain a crystalline volume fraction of 61%, preferential growth of (111) and (220) direction, and photosensitivity of 124. We achieved the improvement of crystallinity and electrical property by using the buffer layers of CaF$_2$ film.

MFIS(Metal-ferroelectric-insulator- semiconductor) structures using silicon oxynitride(SiON) buffer layers were fabricatied and demonstrated nonvolatile memory operations. Oxynitride(SiON) films have been formed on p-Si(100) by RTP(rapid thermal process) in O$_2$+N$_2$ ambient at 1100$^{\circ}C$. The gate leakage current density of Al/SiON/Si(100) capacitor was about the order of 10$\^$-8/ A/cm$^2$ at the range of ${\pm}$ 2.5 MV/cm. The C-V characteristics of Al/LiNbO$_3$/SiON/Si(100) capacitor showed a hysteresis loop due to the ferroelectric nature of the LiNbO$_3$ thin films. Typical dielectric constant value of LiNbO$_3$ film of MFIS device was about 24. The memory window width was about 1.2V at the electric field of ${\pm}$300 kV/cm ranges.

NdFeB 박막자석은 Sputtering, MBE, Laser ablation법에 의해 제조되고 있으며[1-3] milli-size motor[4], magnetic recording media[5], micro-patterning[3]등에 응용될 수 있다. 최근에는 MEMS(Micro-electro mechanical system)분야에서도 잠재적 응용가능성을 지니고 있는 것으로 알려져 있다. 최근에는 NdFeB 박막 제조 시 자성층의 산화방지 및 자기 특성을 향상을 위하여 buffer layer를 이용한 많은 연구가 이루어지고 있다.[6] (중략)