• Title/Summary/Keyword: Ferroelectric thin films

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SUPPRESSION OF THE TETRAGONAL DISTORTION IN THIN Pb(Zr, Ti)$O_3$/MgO(100)

  • Kang, H.C.;Noh, D.Y.;Je, J.H.
    • Journal of the Korean Vacuum Society
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    • v.6 no.S1
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    • pp.141-153
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    • 1997
  • The paraelectric cubic-to-ferroelectric tetragonal phase transition of the thin Pb(Zr, Ti)$O_3$ (PZT) films grown on MgO(001) substrate was investigated in a series of synchrotron x-ray scattering experiments. As the thickness of the film decreases the transition temperature and the amount of the tetragonal distortion were decreased continuously Different from only the c-domains were existent in the thinnest 25nm thick film. Based on this we propose a model for the domain structure of the tetragonal PZT/MgO(100) film that is very different from the ones suggested in literature. We attribute the suppression of the transition to the substrate field that prefers the c-type domains near the interface and suppresses the tetragonal distortion to minimize the film-substrate lattice mismatch.

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Characterization of Pt thin Fiims for Bottom Electrode of Ferroelectric Thin Films Using Metal-organic Chemical Vapor Deposition (강 유전체 박막을 위한 하부전극 MOCVD-pt 박막의 특성)

  • Gwon, Ju-Hong;Yun, Sun-Gil
    • Korean Journal of Materials Research
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    • v.6 no.12
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    • pp.1263-1269
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    • 1996
  • 반도체 메모리 소자에 이용되는 하부전극의 Pt 박막을 MOCVD 증착방법을 이용하여 SiO2(100nm)/Si 기판위에 증착하였다. 반응개스로 O2개스를 사용하였을 경우에 순수한 Pt 박막을 얻었으며 증착층은(11)우선방향을 가지고 성장하였다. 증착온도가 45$0^{\circ}C$에서는 결정립 경계에 많은 hole이 형성되어 박막의 비저항을 증가시켰다. MOCVD에 의해 얻어진 Pt 박막은 전 증착온도범위에서 인장응력을 가지고 있었으며 40$0^{\circ}C$이상의 온도에서 hole이 형성되면서 응력은 감소하였다. MOCVD-Pt 위에 PEMOCVD로 증착한 강 유전체 SrBi2Ta2O9박막은 균일하고 치밀한 미세구조를 보였다.

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In-situ structural analysis during heating of an epitaxial $BaTiO_3$ thin film (에피탁시 $BaTiO_3$박막의 승온중 in-situ 구조분석)

  • 김상섭;제정호
    • Journal of the Korean Vacuum Society
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    • v.8 no.2
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    • pp.111-115
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    • 1999
  • The structural characteristics of an epitaxial $BaTiO_3$ film on MgO(001) grown by sputtering were studied as a function of temperature using in-situ, real time synchrotron x-ray scattering experiments. We found that the as-grown film was single c-domain but strained at room temperature and tetragonally distorted with the c-axis normal to the film surface. Interestingly, its lattice parameters were found to be expanded in both the in-plane and the out-of -plane directions, i.e. biaxially, comparing with those of a bulk $BaTiO_3$ . More importantly, as it was heated up to $600^{\circ}C$, the tetragonal structure was kept up through without and any phase transition, which is usually observed in other epitaxial ferroelectric thin films.

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Ferroelectric and Leakage current Properteis of SBT Capacitor with post-annealing Temperature (후속 열처리에 따른 SBT 캐패시터의 강유전 특성과 누설전류 특성)

  • 오용철;조춘남;김진사;신철기;박건호;최운식;김충혁;이준웅
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.07a
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    • pp.668-671
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    • 2001
  • The Sr$\_$0.8/Si$\_$2.4/Ta$_2$O$\_$9/(SBT) thin films are deposited on Pt-coated electrode(Pt/TiO$_2$/SiO$_2$/Si) using RF magnetron sputtering method. With increasing post-annealing temperature from 600[$^{\circ}C$] to 850[$^{\circ}C$], Bi-layered perovskite phase was crystallized above 650[$^{\circ}C$]. The maximum remanent polarization and the coercive electric field is 11.60[${\mu}$C/$\textrm{cm}^2$], 48[kV/cm] respectively. The leakage current density of SBT capacitor at post-annealing temperature of 750[$^{\circ}C$] is 1.01${\times}$10$\^$-8/ A/$\textrm{cm}^2$ at 100[kV/cm]. The fatigue characteristics of SBT thin films did not change up to 10$\^$10/ switching cycles.

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Structural and Electrical Properties of RaRuO$_3$ Thin Film for Electrode of Ferroelectric Capacitors (강유전체 캐패시터 전극으로의 BaRuO$_3$박막의 구조적 및 전기적 특성)

  • 박봉태;구상모;문병무
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.12 no.1
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    • pp.56-61
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    • 1999
  • Highly conductive oxide films of BaRuO$_3$ have been grown heteroepitaxially on (100) LaAlO$_3$ single crystalline substrates by using pulsed laser deposition. The films are c-axis oriented with an in-plane epitaxial relationship of <010><100>BaRuO$_3$ // <110>LaAlO$_3$. Atomic force microscopy (AFM) observation shows that they consist of a fine-arranged network of grains and have a mosaic microstructure. Generally temperature-dependent resistivity shows the transition from metallic curve to semiconductor-metallic twofold curve by the deposition conditions for Ru oxide based materials like SrRuO$_3$, CaRuO$_3$, BaRuO$_3$, etc.. This twofold curve comes from the structural similarity of Ru oxide based materials including BaRuO$_3$. We find that the distance of Ru-Ru bonding in the unit cell of BaRuO$_3$ as well as the grain boundary scattering could be the two important causes of these interesting conductive properties.

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Etching Characteristics of YMnO3 Thin Films in Cl Based Inductively Coupled Plasma

  • Kim, Dong-Pyo;Kim, Chang-Il
    • Transactions on Electrical and Electronic Materials
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    • v.4 no.2
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    • pp.29-34
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    • 2003
  • Ferroelectric YMnO$_3$ thin films were etched with Ar/C1$_2$ and CF$_4$/C1$_2$ Plasma. The maximum etch rate of YMnO$_3$ thin film was 300 $\AA$/min at a Cl$_2$/Ar gas mixing ratio of 8/2, an RF power of 800 W, a do bias of-200 V, a chamber pressure of 15 mTorr, and a substrate temperature of 3$0^{\circ}C$. From the X-ray photoelectron spectroscopy (XPS) analysis, yttrium was not only etched by chemical reactions with Cl atoms, but also assisted by Ar ion bombardments in Ar/C1$_2$ plasma. In CF$_4$/C1$_2$ plasma, yttrium formed nonvolatile YF$_{x}$ compounds and remained on and the etched surface of YMnO$_3$. Manganese etched effectively by forming volatile MnCl$_{x}$ and MnF$_{y}$. From the X-ray diffraction (XRD) analysis, the (0004) diffraction peak intensity of the YMnO$_3$ thin film etched in Ar/Cl$_2$ plasma shows lower than that in CF$_4$/Cl$_2$ plasma. It indicates that the crystallinty of the YMnO$_3$ thin film is more easily damaged by the Af ion bombardment than the changes of stoichiometry due to nonvolatile etch by-products.cts.s.

The Effects of Deposition Temperature of Pt Top Electrodes on the Electrical Properties of PZT Thin Films (Pt 상부 전극 증착온도가 PZR 박막의 전지적 특성에 미치는 영향)

  • Lee, Kang-Woon;Lee, Won-Jong
    • Korean Journal of Materials Research
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    • v.8 no.11
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    • pp.1048-1054
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    • 1998
  • The effects of deposition temperature of Pt top electrodes on the electrical properties of Pb(Zr,Ti))$O_3$, (PZT) thin film were investigated. When the Pt top electrodes were deposited at substrate temperatures of $200^{\circ}C$ or above,the ferroelectric properties of the PZT thin film under the Pt electrode were severely degraded. Whereas those of the PZT film where the Pt electrodes were not deposited were not degraded. Water vapors which remained in the vacuum chamber were dissociated into hydrogen atoms by the catalysis of Pt top electrode, and those hydrogen atoms diffused into the PZT film and produced oxygen vacancies at high substrate temperature, resulting in the degradation of the ferroelectric properties of the PZT film located under the Pt electrode. Since the water vapors could not be dissociated into hydrogen atoms without the catalysis of Pt. the degradation of the PZT film did not take place where the Pt electrode were not deposited. The degraded feroelectric properties could be recovered by rapid thermal annealing (RTA) treatment. On the other hand. leakage current characteristics were improved with increasing the deposition temperature of Pt top electrodes.

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Studies on the Deformation in the Hysteresis Loop of $Pb(Zr,Ti)O_3$ Ferroelectric Thin Films ($Pb(Zr,Ti)O_3$ 강유전체 박막 이력곡선의 변형에 관한 연구)

  • Lee, Eun-Gu;Lee, Jong-Guk;Lee, Jae-Gap;Kim, Seon-Jae
    • Korean Journal of Materials Research
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    • v.10 no.5
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    • pp.360-363
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    • 2000
  • Deformation in the hysteresis loop of $Pb(Zr,Ti)O_3$ (PZT) thin films with various Zr/Ti ratios has been studied by varying the top electrode preparation method and the annealing temperature. Pt/PZT/Pt capacitors was found to be positively poled due to dc plasma potential generated during reactive ion etch (RIE) of Rt. Internal field is formed by space charges trapped at domain boundaries. Aging phenomenon such as constriction in the middle of the hysteresis loop was observed in the PZT film with top electrode deposited by sputtering. Top electrode annealing restores the hysteresis loop by removing the space charges. As Zr/Ti ratio decrease, voltage shift increases and an-nealing temperature at which internal field disappears also increases.

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Phase Evolution Behavior of (Bi,Nd)(Fe,Ti)$O_3$ Ceramics and Thin Films

  • Kim, Kyung-Man;Byun, Seung-Hyun;Yang, Pan;Lee, Yoon-Ho;Lee, Jai-Yeoul;Lee, Hee-Young
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2008.06a
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    • pp.331-332
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    • 2008
  • Couplings between electric, magnetic, and structural order parameters result in the so-called multiferroic phenomena with two or more ferroic phenomena such as ferroelectricity, ferromagnetism, or ferroelasticity. The simultaneous ferroelectricity and ferromagnetism (magnetoelectricity) permits potential applications in information storage, spintronics, and magnetic or electric field sensors. The perovskite BiFeO3(BFO) is known to be antiferromagnetic below the Neel temperature of 647K and ferroelectric with a high Curie temperature of 1043K. It exhibits weak magnetism at room temperature due to the residual moment from a canted spin structure. It is likely that non-stoichiometry and second-phase formation are the factors responsible for leakage current in BFO. It has been suggested that oxygen non-stoichiometry leads to valence fluctuations of Fe ions in BFO, resulting in high conductivity. To reduce the large leakage current of BFO, one attempt is to make donor-doped BFO compounds and thin films. In this study, (Bi1-x,Ndx)(Fe1-y,Tiy)O3 thin films have been deposited on Pt(111)/TiO2/SiO2/Si substrates by pulsed laser deposition. The effect of dopants on the phase evolution and surface morphology are analyzed. Furthermore, electrical and magnetic properties are measured and their coupling characteristics are discussed.

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Formation and stability of a ruthenium-oxide thin film made of the $O_2$/Ar gas-mixture sputtering

  • Moonsup Han;Jung, Min-Cherl;Kim, H.-D.;William Jo
    • Journal of Korean Vacuum Science & Technology
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    • v.5 no.2
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    • pp.47-51
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    • 2001
  • To obtain high remnant polarization and good crystalinity of ferroelectric thin films in non-volatile memory devices, the high temperature treatment in oxygen ambient is inevitable. Severe problems that occur in this process are oxygen diffusion into substrate, oxidation of electrode and buffer layer, degradation of microstructure and so on. We made ruthenium dioxide thin film by reactive sputtering with oxygen and argon mixture atmosphere. Comparing quantitatively the core-level spectra of Ru and RuO$_2$ obtained by x-ray photoelectron spectroscopy(XPS), we found that chemical state of RuO$_2$ is very stable and of good resistance to oxygen diffusion and oxidation of adjacent layers. It opens the use of RuO$_2$ thin film as a multifunctional layer of good conducting electrode and resistive barrier for the diffusion and the oxidation. We also suggest a correct understanding of Ru 3d core-level spectrum for RuO$_2$ based on the scheme of final state screening and charge transfer satellites.

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