• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.226-230
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• 2018

Pure $BiFeO_3$ (BFO) and codoped $Bi_{0.9}A_{0.1}Fe_{0.975}Zn_{0.025}O_{3-{\delta}}$ (A=Eu, Dy) thin films were prepared on Pt(111)/Ti/$SiO_2$/Si(100) substrates by chemical solution deposition. The remnant polarizations (2Pr) of the $Bi_{0.9}Eu_{0.1}Fe_{0.975}Zn_{0.025}O_{3-{\delta}}$ (BEFZO) and $Bi_{0.9}Dy_{0.1}Fe_{0.975}Zn_{0.025}O_{3-{\delta}}$ (BDFZO) thin films were about 36 and $26{\mu}C/cm^2$ at the maximum electric fields of 900 and 917 kV/cm, respectively, at 1 kHz. The codoped BEFZO and BDFZO thin films showed improved electrical properties, and leakage current densities of 3.68 and $1.21{\times}10^{-6}A/cm^2$, respectively, which were three orders of magnitude lower than that of the pure BFO film, at 100 kV/cm.

• Journal of the Korean Magnetics Society
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• v.11 no.5
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• pp.222-225
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• 2001

The planar type inductors have a good potential for the application of miniaturized low power DC-DC converters. For those high quality application, the reduction of coil loss and also magnetic films which have good high frequency properties are required. Fabricated inductor was consisted of FeTaN/Ti magnetic film and electroplated Cu coil thickness of 100$\mu\textrm{m}$ and $SiO_2$ as a insulating layer. The inductor was designed double rectangular spiral shape for magnetic field highly confining within the device. The measured value of inductance and resistance were 980 nH and 1.7 $\Omega$ at 1 MHz as operating frequency of device. The Q factor is 3.55 at 1 MHz.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.2
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• pp.178-183
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• 2004

PBT thin film was known to be a representative for the FeRAM devices because of its good ferroelectric proporties and the ease in fabricating the thin film. However, there have been several problems such as polarization fatigue and leakage current in memory devices with a PZT thin film. In this study, Sm-dolled PZT thin films were fabricated by the so1-gel method, and their ferroelectric and dielectric proportrics were compared as a function of Sm content. We investigated the effect of the Sm dopant on structural and electrical properties of PZT film. Sm-doped PZT thin films on the Pt/Ti/SiO$_2$/Si substrates have been prepared by a sol-gel method. The remanent polarization and coercive field decreased with increasing the concentration of Sm. The dielectric constant and dielectric loss decreased with Increasing Sm content. Sm-doped PZT thin films showed improved fatigue characteristics compared to the undoped PZT thin film.

• Progress in Superconductivity
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• v.9 no.1
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• pp.85-90
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• 2007

Lanthanum aluminate($LaAlO_3$) film has been prepared on single crystal and metal substrates by dip coating method. Lanthanum acetate and aluminum were prepared via ligand exchange starting from lanthanum nitrate hexahydrate and aluminum nitrate hexahydrate in acetate glacial acetic acid solution after being refluxed. Coating solution was obtained by diluting the gel with methanol and 2-methoxyethanol to adjust the total cation concentration to 0.67 M. Precursor coated film was prepared by dip-coating with a speed of 25 mm/min on various substrates such as $LaAlO_3$ (001), MgO(001), $SrTiO_3$(001) single crystal, LMO/MgO/Ni-alloy. Thin films have been obtained by heat treating the precursor film at various temperatures from $600^{\circ}C{\sim}900^{\circ}C$ and various heating rate from $0.83^{\circ}C/min{\sim}1.25^{\circ}C/min$ under $Ar/O_2$ mixture containing 1000ppm oxygen. The films have been characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). XRD analysis for the prepared film showed that $LaAlO_3$ thin films with a preferred orientation of (100) plane parallel to substrate surface were obtained at $800^{\circ}C(1.11\;^{\circ}C/min)$ on LMO/MgO/Ni-alloy substrate, but the intensity decreased with the increase of heat treatment temperature.

• Korean Journal of Materials Research
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• v.12 no.6
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• pp.464-469
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• 2002

$SrBi_2Nb_2O_9(SBN)$ thin films were grown on Pt/Ti/Si and p-type Si(100) substrates by rf-magnetron co-sputtering method using two ceramic targets, $SrNb_2O_6\; and \;Bi_2O_3$. The structural and electrical characteristics have been investigated to confirm the possibility of the SBN thin films for the applications to destructive and nondestructive read out ferroelectric random access memory(FRAM). For the optimum growth condition X-ray diffraction patterns showed that SBN films had well crystallized Bi-layered perovskite structure after $700^{\circ}C$ heat-treatment in furnace. From this specimen we got remnant polarization $(2P_r)$ of about 6 uC/$\textrm{cm}^2$ and coercive voltage $(V_c)$ of about 1.5 V at an applied voltage of 5 V. The leakage current density was $7.6{\times}10^{-7}$/A/$\textrm{cm}^2$ at an applied voltage of 5V. And for the NDRO-FRAM application, properties of SBN films on Si substrate has been investigated. From transmission electron microscopy (TEM) analysis, we found the furnace treated sample had a native oxide about 2 times thicker than the RTA treated sample and this thick native oxide layer had a bad effect on C-V characteristics of SBN/Si thin film. After $650^{\circ}C$ RTA process, we got the improved memory window of 1.3 V at an applied voltage of 5 V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.5
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• pp.427-431
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• 2020

In this research, we evaluated the electrical properties of polycrystalline-gallium-oxIde (Ga₂O₃) thin films grown by mist-CVD. A 500~800 nm-thick Ga₂O₃ film was used as a channel in a fabricated bottom-gate MOSFET device. The phase stability of the β-phase Ga₂O₃ layer was enhanced by an annealing treatment. A Ti/Al metal stack served as source and drain electrodes. Maximum drain current (I_D) exceeded 1 mA at a drain voltage (V_D) of 20 V. Electron mobility of the β-Ga₂O₃ channel was determined from maximum transconductance (g_m), as approximately, 1.39 ㎠/Vs. Reasonable device characteristics were demonstrated, from measurement of drain current-gate voltage, for mist-CVD-grown Ga₂O₃ thin films.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2119_2120
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• 2009

전압을 인가하였을 때 전계방향에 의해 가역적으로 색이 변화하는 현상을 전기변색(electrochromism)이라고 한다. 이러한 전기채색현상을 보이는 물질을 전기채색물질(electrochromism materials)이라고 하며, 전기채색 물질에 의한 소자를 전기채색소자(electrochromism device : ECD)라고 한다. 전기채색현상은 투과율(transmittance), 반사율(reflectance)의 가역적이며 가시적인 변화이고, 전기화학적인 산화환원 반응과 관련이 있다. 따라서 본 연구에서는 Titanate nanotube(TNT)를 제조하고 전기변색소자(ECD)에 응용하였다. SEM, XRD, UV-Vis등을 이용하여 재료학적 분석을 시행하였으며, 전기화학적 테스트로 cyclic voltammetry를 측정 하였다. 그 결과 TNT 분말은 직경 약 20~30 nm, 길이 약 500~600 nm 의 입자형상을 나타내었으며, X-선 회절시험결과 $H_2Ti_2O_5{\cdot}H_2O$의 층상구조를 나타내었다. 제조된 막은 FTO glass 위에 PEI/(TNT/TBAOH)$_{n-1}$/PDDA의 순으로 코팅되었다. 전기화학적 테스트를 위하여 2전극 시스템을 제작하였으며, 여러 종류의 액체 전해질을 제작하여 cycle voltammetry를 시행하였다. 그 결과, 각각의 전해질에서 "-"영역의 산화환원전위 피크가 뚜렷하게 나타났으며, 짙은 갈색으로의 채색현상을 나타냈다. 본 연구의 결과로서 TNT 박막을 이용한 ECD은 광조절 유리로서 뿐만 아니라, 여러 전기채색 디바이스에 응용될 것으로 사료된다.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.4
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• pp.538-540
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• 2009

The SBN thin films were deposited at substrate temperature of 300[$^{\circ}C$] on Pt-coated electrode (Pt/Ti/$SiO_2$/Si(100)) using RF sputtering method. The grain and crystallinity of SBN thin films were increased with the increase of annealing temperature. The dielectric constant(150) of SBN thin film was obtained by annealing temperature above 750[$^{\circ}C$]. The voltage dependence of dielectric loss showed a value within 0.01 in voltage ranges of -5~+5[V]. The capacitance characteristics showed a stable value of about 0.7[${\mu}F/cm^2$].