Bi(Fe_{0.9}Mn_{0.1})O_{3} 박막의 강유전 및 자기 특성

도달현 한국물리학회 2014 새물리 Vol.64 No.6

Bi(Fe_{0.9}Mn_{0.1})O_{3} (BFMO) thin films were prepared on Pt(111)/Ti/SiO_{2}/Si substrates by using a pulsed laser deposition method. The crystal structure, the oxidation states of the Mn and the Fe ions, and the ferroelectric and the magnetic properties were investigated. There was no changes in the crystal structure of the BFMO thin films compared to the BiFeO_{3} (BFO) thin films. According to the X-ray photoelectron spectroscopy results, Mn²+, Mn³+, Mn⁴+ ions coexisted in the BFMO thin films. Also, the reduced volume fraction of Fe²+ ions, compared to that in BFO thin films, was confirmed. Although ferroelectric hysteresis loops were not observed in the BFMO thin films at low frequencies hysteresis loops were observed at high frequencies. The remnant polarization (2P_{r}) of the BFMO thin film was 156 μC/cm² measured under a 10 kHz voltage pulse. The saturation magnetization (M_{s}) of the BFMO thin film was 4.7 emu/cm³. The magnetic hysteresis loops of the BFMO thin films were similar to these of the BFO thin films. 펄스 레이저 증착법을 이용하여 Pt(111)/Ti/SiO_{2}/Si 기판 위에 Bi(Fe_{0.9}Mn_{0.1})O_{3} (BFMO) 박막을 제작하여 Mn 치환에 따른 결정구조, Mn 및 Fe의 산화수, 강유전 및 자기 특성을 연구하였다. X-선 회절 측정 결과에 의하면, BiFeO_{3} (BFO) 박막과 비교해서, Mn의 치환으로 인한 결정구조에서의 큰 변화는 확인할 수 없었다. BFMO 박막에는 Mn²+, Mn³+, Mn⁴+가 동시에 존재하는 것을 확인하였으며, 순수한 BFO 박막과 비교해서 Fe²+의 양이 줄어들었음을 확인하였다. 순수한 BFO 박막과 비교해서, BFMO 박막의 강유전 특성은 낮은 주파수 영역에서는 도체의 특성을 보인 반면, 높은 주파수 영역에서는 BFO 박막과 유사한 강유전 이력곡선을 얻을 수 있었다. 10 kHz에서 측정된 BFMO 박막의 잔류분극(P_{r})은 2P_{r} = 156 μC/cm² 이었다. 포화 자화값(M_{s})은 4.7 emu/cm³로 Mn의 치환에 따른 자기 특성에서의 변화는 관찰할 수 없었으며, BFO 박막에서 관찰되는 자기 이력곡선과 유사한 특성을 보였다.

Fabrication of c-axis-oriented K_(0.5)Bi_(4.5)Ti_4O_(15) Ferroelectric Thin Films by Using Chemical Solution Deposition

도달현,김상수,김진원,송태권,최병춘 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31

The effects of crystal structure on the ferroelectric properties of K_(0.5)Bi_(4.5)Ti_4O_(15) (KBTi) thin films were investigated. Randomly-oriented and c-axis-oriented KBTi thin films were prepared by using a chemical solution deposition method. Both thin films were annealed at 750 ℃ under an oxygen atmosphere. The randomly-oriented thin film showed better ferroelectric properties than the c-axis-oriented film. The remnant polarization (2P_r) of the randomly-oriented thin film was 13.5 μC/cm_2 at an applied electric field of 233 kV/cm, which is larger than that of the c-axis-oriented thin film, 4.8 μC/cm^2. This indicates that the polarization vector is not along the c-axis. The randomly-oriented thin film also showed a lower leakage current density than the c-axis-oriented thin film, as well as good fatigue endurance.

La-doping Effects on the Properties of Bi5Ti3FeO15 Thin Films

도달현,김상수,송태권,최병춘 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2

0.5BiFeO3-0.5Bi4Ti3O12 (Bi5Ti3FeO15) and 0.5BiFeO3-0.5Bi3.25La0.75Ti3O12 (La-doped Bi5Ti3FeO15) thin films have been prepared on Pt(111)/Ti/SiO2/Si substrates by using a chemical solution deposition method. The thin films were crystallized at 650C under an oxygen atmosphere. X-ray diffraction revealed that both thin films showed a polycrystalline Bi5Ti3FeO15 phase. However, different microstructures were observed in the two thin films. The remnant polarization (2Pr) and the coercive electric field (2Ec) of the La-doped Bi5Ti3FeO15 thin film were 24 μC/cm2 and 129 kV/cm at an applied electric field of 200 kV/cm, respectively. The 2Pr is larger than that of the Bi5Ti3FeO15 thin film, 17 μC/cm2 at 219 kV/cm. A lower leakage current density was obtained in the La-doped Bi5Ti3FeO15 thin film. The La-doped Bi5Ti3FeO15 thin film showed good fatigue endurance compared to the Bi5Ti3FeO15 thin film. Also, weak ferromagnetism was observed in both thin films.

xBiFeO₃-(1-x)Na0.5Bi4.5Ti₄O15(x=0.5)박막의 제조 및 강유전 특성

도달현,김진원,김상수,송태권,최병춘 한국물리학회 2010 New Physics: Sae Mulli Vol.60 No.5

We prepared a 300 nm-thick xBiFeO₃-(1-x)Na0.5Bi4.5Ti₄O15(x=0.5) film on a Pt(111)/Ti/SiO₂/Si(100) substrate by using a chemical solution deposition method. The thin film was annealed at 650℃ for 3 min by using a rapid thermal annealing process under an oxygen atmosphere. The crystal structure and the surface microstructure of the thin film were investigated by using X-ray diffraction and scanning electron microscopy, respectively. The remnant polarization (2Pr) and the coercive field (2Ec) of the BFO-NaBTi55 thin film were 76㎛/㎠ and kV/㎝ at an applied electric field of 667 kV/㎝, respectively. The dielectric constant and the dielectric loss were 756 and 0.03 at 1 kHz, respectively, the leakage current density of the thin film was 5.1×10−6/㎠ at 100 kV/㎝. The switchable polarization of the thin film was decreased by 15% after 1.44×1010 switching cycles. The good ferroelectric properties observed in the BFO-NaBTi55 thin film may be related to reductions in the number of bismuth vacancies and oxygen vacancies. 화학 용액 증착법을 이용하여 Pt(111)/Ti/SiO₂/Si(100) 기판 위에 300 nm 두께의 xBiFeO₃-(1-x)Na0.5Bi4.5Ti₄O15(x=0.5 BFO-NaBTi55) 박막을 성장시켜 박막의 미세구조와 강유전 특성을 측정, 비교 분석하였다. 성장된 박막은 650℃의 산소 분위기에서 급속 열처리 법으로 열처리하였으며 박막의 결정화 상태와 미세구조는 x-선 회절장치, 주사 전자 현미경 측정 결과로부터 알아 보았다. 이 박막의 강유전 특성에서 외부 전기장 667 kV/㎝일 때 BFO-NaBTi55 박막의 잔류 분극 (2Pr)과 항전기장 (2Ec) 값은 각각 76㎛/㎠, 403 kV/㎝이었으며 1 kHz에서 유전율과 유전손실은 각각 756, 0.03이었다. 또 외부 전기장 100 kV/㎝일 때 누설전류 밀도는 5.1×10−6A/㎠이었으며 1.44×1010까지 15% 이하의 피로 현상을 보였다. BFO-NaBTi55 박막이 좋은 전기적 특성을 보이는 것은 비스무스 휘발에 의한 비스무스 빈자리나 산소 빈자리의 감소 때문이라고 보여진다.

Effects of Bi Content on the Ferroelectric Properties of BiFeO3 Thin Films

도달현,김원정,Myang Hwan Lee,송태권,김진원,김상수 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61

Two polycrystalline BiFeO3 thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using pulsed laser deposition from nominal composition Bi1.0FeO3 and Bi1.1FeO3 targets. X-ray diffraction results confirmed that different impurity phases were formed in the Bi1.0FeO3 and the Bi1.1FeO3 thin films. The preferred orientation of the Bi1.0FeO3 thin films is the <110> direction while that of the Bi1.1FeO3thin films is the <100> direction. The values of the remnant polarization (2Pr)of the Bi1.0FeO3 and the Bi1.0FeO3 film capacitors were 49 µC/cm2at an applied electric field of 500 kV/cm and 40 µC/cm2 at 467 kV/cm. A similar leakage current property was observed in both films.

Multiferroic (Bi_(0.9)Dy_(0.1))(Fe_(0.9)Mn_(0.1))O_3 Thin Film

도달현,배유리,김진원,김은선,김가현,김상수 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31

(Bi_(0.9)Dy_(0.1))(Fe_(0.9)Mn_(0.1))O_3 (BDFM) and pure BiFeO_3 (BFO) thin films were prepared on Pt(111)/Ti/SiO_2/Si(100) substrates by using a chemical solution deposition method. The films were annealed at 550 ℃ using a conventional annealing process under a nitrogen atmosphere. Remnant polarization (2P_r) and coercive electric field (2E_c) of the BDFM thin film capacitor were 90 μ/cm_2 and 529 kV/cm at an applied electric field of 663 kV/cm, respectively. However, the BFO thin film capacitor showed a leaky hysteresis loop. The values of leakage current density of the BDFM and the BFO thin film capacitors were 4.55 × 10^(-5) and 5.44 × 10^(-3) A/cm^2 at 100 kV/cm, respectively. The reduced leakage current and the improved ferroelectric property were discussed based on the investigation of electronic structure and microstructure.

Reduced Leakage Current and Improved Ferroelectric Properties of Eu and Mn codoped BiFeO3 Thin Films

도달현,김진원,김상수,김원정,M. H. Lee,J. H. Cho,송태권,성연수,김명호 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.2

We prepared (Bi0.94Eu0.06)(Fe0.94Mn0.06)O3 (BEFM), (Bi0.94Eu0.06)FeO3 (BEFO), and BiFeO3(BFO) thin films on Pt(111)/Ti/SiO2/Si(100) substrates by using a pulsed laser deposition method. X-ray diffraction and Raman scattering results showed that the rhombohedral structure of the BFO film was not affected by the substitution of Eu and Mn ions. A much reduced leakage current was observed in the BEFM thin film capacitor compared to the BEFO and BFO thin film capacitors. Higher electrical breakdown field was observed in the BEFM and BEFO thin film capacitors than in the BFO thin film capacitor.

Effects of Zn2+ and Mn4+ Co-doping in BiFeO3 Thin Films

도달현 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.7

Bi(Fe0.99−xZn0.01Mnx)O3 (x = 0.01, 0.03, 0.05) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using a pulsed laser deposition method. The effects of Mn4+ contentin the BiFeO3 thin films on their leakage current and their ferroelectric properties were mainlyinvestigated. Bi(Fe0.96Zn0.01Mn0.03)O3 thin film exhibited the best ferroelectric properties amongthem. The leakage current density of the film capacitor was 2.0 × 10−5 A/cm2 at 200 kV/cm. The remnant polarization (2Pr) and the coercive electric field (2Ec) of the film capacitor were 83μC/cm2 and 577 kV/cm at an applied electric field of 695 kV/cm, respectively. This can be explainedbased on the Fe2+ concentration associated with oxygen vacancies and the grain size causedby doping of Zn2+ and Mn4+ in BiFeO3 thin films.

Electrical Properties in Lanthanides Substituted (Bi0.9A0.1)(Fe0.975Co0.025)O3−δ(A = La, Eu, Gd) Thin Films

도달현,김진원,김상수,송태권,김명호 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.61 No.9

Multiferroic BFO and (Bi<SUB>0.9</SUB><I>A</I><SUB>0.1</SUB>)(Fe<SUB>0.975</SUB>Co<SUB>0.025</SUB>)O<SUB>3-δ</SUB> (<I>A</I>=La, Eu, Gd) thin films were prepared on Pt(111)/Ti/SiO<SUB>2</SUB>/Si(100) substrates by using a chemical solution deposition method. The thin films were annealed at 550 ℃ for 30 min using a conventional annealing process under a nitrogen atmosphere. Reduced leakage current density and improved ferroelectric properties were observed in the co-doped thin films compared to the BFO thin film. The enhanced properties observed in the co-doped thin films could be considered as the suppression of oxygen vacancies and modified microstructure.

화학용액 증착법으로 제조한 바나듐이 첨가된 Na0.5Bi4.5Ti₄O15 박막의 전기적 성질

김진원,도달현,김상수 한국물리학회 2010 새물리 Vol.60 No.5

Ferroelectric thin films have been extensively investigated for integrated device applications, such as nonvolatile ferroelectric random access memories, microelectromechanical systems, tunable mi-crowave devices, integrated optical modulators, and infrared sensors. Bismuth-layer-structured fer-roelectrics belonging to the Aurivillus family, denoted by (Bi₂O₂)²+(Am−₁BmO3m+₁)²−, where m=1, 2, 3, 4, 5, etc., have been considered to be promising materials. The ferroelectric Na0.5Bi4.5Ti₄O15 (NaBTi) thin film, an Aurivillius family with m=4, is not fully understood yet. Especially, there are almost no reports regarding the properties of NaBTi thin films. Pure Na0.5Bi4.5Ti₄O15 (NaBTi) and V-doped Na0.5Bi4.5−x/3Ti4−xVxO15 (NaBTiV-x, x=0.01, 0.03 and 0.05) thin films were prepared by using a chemical solution deposition. For all samples, a layered perovskite structure with a single phase and with a good crystalline structure was observed in the X-ray diffraction (XRD) patterns, and the surface was composed of fine grains without cracks in the SEM results. The NaBTiV-0.01 thin film exhibited a better saturated hysteresis loop than the NaBTi thin film. For the NaBTiV-0.01 thin film, the remnant polarization (2Pr) was 61㎛/㎠ at room temperature, and the leakage current density measured at room temperature was 2.4×10−7 A/㎠ at an external electric field of 100 kV/㎝. There results show that V-doping is an effective method for improving the ferroelectric properties of the NaBTi thin film. 순수한 Na0.5Bi4.5Ti₄O15 (NaBTi) 박막과 바나듐이 첨가된 Na0.5Bi4.5−x/3Ti4−xVxO15 (NaBTiV-x, x=0.01, 0.03 그리고 0.05) 박막을 화학 용액 증착법으로 Pt(111)/Ti/SiO₂/Si(100) 기판 위에 성장시켜 바나듐 첨가량에 따른 박막의 미세구조와 전기적 특성을 측정, 비교 분석하였다. 성장된 NaBTi 및 NaBTiV-x 박막들은 결정화를 위해 750℃의 산소 분위기에서 RTA법으로 열처리하였으며 박막의 결정화 상태와 미세구조는 XRD, SEM 측정 결과로부터 알아 보았다. 바나듐이 첨가된 박막이 큰 잔류 분극과 작은 항전기장 및 누설 전류, 좋은 피로 특성을 보였는데 바나듐이 x=0.01 첨가된 NaBTiV-0.01 박막은 외부 전기장 648 kV/cm 일 때 잔류 분극(2Pr)과 항전기장(2Ec)은 각각 61㎛/㎠, 311 kV/㎝이었고 외부 전기장 100 kV/㎝일 때 누설전류 밀도는 2.4×10−7A/㎠이었으며 4.44×108까지 피로 현상을 보이지 않았다. 이러한 특성 향상은 바나듐울 첨가하였을 때 박막 내 산소 빈자리의 수가 감소하고 산소 빈자리의 이동도가 약화된 것에 기인한 것으로 판단된다.