• 한국전기전자재료학회논문지
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• 제30권10호
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• pp.646-650
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• 2017

We have evaluated the ferroelectric and electrical properties of pure $BiFeO_3$ (BFO) and $Bi_{0.9}A_{0.1}Fe_{0.975}V_{0.025}O_{3+{\alpha}}$ (A=Nd, Tb) thin films on $Pt(111)/Ti/SiO_2/Si(100)$ substrates by using a chemical solution deposition method. The remnant polarization ($2P_r$) of the $Bi_{0.9}Tb_{0.1}Fe_{0.975}V_{0.025}O_{3+{\alpha}}$ (BTFVO) thin film was approximately $65{\mu}C/cm^2$, with a maximum applied electric field of 950 kV/cm and a frequency of 10 kHz, where as that of the $Bi_{0.9}Nd_{0.1}Fe_{0.975}V_{0.025}O_{3+{\alpha}}$ (BNFVO) thin film was approximately $37{\mu}C/cm^2$ with a maximum applied electric field of 910 kV/cm. The leakage current density of the co-doped BNFVO thin film was four orders of magnitude lower than that of the pure BFO thin film, at $2.75{\times}10^{-7}A/cm^2$ with an applied electric field of 100 kV/cm. The grain size and uniformity of the co-doped BNFVO and BTFVO thin films were improved, in comparison to the pure BFO thin film, through structural modificationsdue to the co-doping with Nd and Tb.

• 한국결정학회:학술대회논문집
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• 한국결정학회 2002년도 정기총회 및 추계학술연구발표회
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• pp.19-19
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• 2002

Perovskite-type titanate dielectrics have attracted much attention in memory devices such as DRAMs or FeRAMs due to their high dielectric constants. However, low volatility of the Ba, Sr, Pb or Zr precursors with only thd ligands has limitations in obtaining high quality thin films by liquid source metal organic chemical vapor deposition (LS-MOCVD) processes. To improve the volatility of these precursors, many attempts have been made such as adding polyether ligands to satisfy the coordinative saturation. We report the synthesis of new precursors Ba(thd)₂(tmeea) and Sr(thd)₂(tmeea), where tmeea = tris[2-(2-methoxyethoxy)ethyl]amino, and LS-MOCVD of barium strontium titanate (BSTO) thin films using these precursors. Due to increased basicity of amines compared with ethers, it is expected that the nitrogen-donor ligand will make a strong bond to a metal than an analogous oxygen-donor ligand, consequently improving the volatility and thermal behavior of these precursors. Thin films of BSTO were grown on Pt(111)/SiO₂/Si(100) substrates by LS-MOCVD using a cocktail source consisting of the conventional Ti precursor Ti(thd)₂(O/sup i/Pr), and these new Ba and Sr precursors. As-grown films were characterized by XPS, SEM, XRD, XRF, and C-V and I-V measurements. BSTO films grown at 420℃ were stoichiometric barium strontium titanate with very smooth surface morphology and their dielectric constants were found to be as targe as 450. Dependence of the composition, microstructure and the electrical properties of the BSTO films on the growth temperature, annealing temperature, working pressure, and the composition of the cocktail source will be discussed.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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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.

• 한국전기전자재료학회논문지
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• 제16권3호
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• pp.186-189
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• 2003

The role of excess Pb about the crystallization behavior and electrical properties in b(Zr$\sub$0.52/Ti$\sub$0.48/)O3(PZT) thin films has not been precisely defined. In this work, the effect of excess Pb content on the ferroelectric properties of these films was investigated. To analyze the effect, PZT films containing various amounts of excess Pb were Prepared. PZT thin films were deposited on the Pt/Ti bottom electrode by rf magnetron sputtering method and then they were crystallized by rapid thermal annealing (RTA). The experiment showed that all PZT films indicated perovskite polycrystalline structure with preferred orientation (111) and no pyrochlore phase was observed. As higher excess Pb was included, the films showed that value of leakage current shift from 2.03${\times}$10$\^$-6/ to 6.63 ${\times}$ 10$\^$-8/A/cm$^2$ at 100kV/cm, and value of remanent polarization shift from 8.587 ${\mu}$C /cm$^2$ to 4.256 ${\mu}$C/ cm$^2$. Electrical properties of PZT thin film affected by Pb excess content of target were explained to be caused of defect among space charges and defect grain boundaries.

• 한국세라믹학회지
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• 제35권10호
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• pp.1107-1112
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• 1998

We could obtan c-axis oriented $SrBi_2$$Ta_2$$O_9$ thin films on usual Pt(111)/Ti/$SiO_2$/Si(100) substrate using a r. f. magnetron sputtering technique. According to the increase of sputtering pressure from 250 to 300 mTorr the Bi content and degree of the c-a xis preferred orientation of $SrBi_2$$Ta_2$$O_9$ thin films were increased. By controlling Bi(or $Bi_2O_3$) loss from $SrBi_2$$Ta_2$$O_9$ thin films during post annealing and by inserting $Bi_2O_3$ layer in $SrBi_2$$Ta_2$$O_9$ thin films the effect of Bi content on the c-axis oriented growth of $SrBi_2$$Ta_2$$O_9$ thin films could be investigated without the effect of sputtering pressure. The degree of the c-axis preferred orientation of $SrBi_2$$Ta_2$$O_9$ thin films was increased with increasing with increasing Bi content by control of Bi(or $Bi_2O_3$) loss of $SrBi_2$$Ta_2$$O_9$ thin films. But the c-axis oriented growth of $SrBi_2$$Ta_2$$O_9$ thin films disappeared by the inserting of $Bi_2O_3$ lay-er in $SrBi_2$$Ta_2$$O_9$ thin films.

• 한국세라믹학회지
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• 제43권11호
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• pp.688-692
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• 2006

Ferroelectric lanthanides-substituted $Bi_4Ti_3O_{12}$ $(Bi_{4-x}Ln_xTi_3O_{12}, BLnT)$ thin films approximately 200 nm in thickness were deposited by metal organic chemical vapor deposition onto Pt(111)/Ti/SiO$_2$/Si(100) substrates. Many researchers reported that the lanthanides substitution for Bi in the pseudo-perovskite layer caused the distortion of TiO$_6$ octahedron in the a-b plane accompanied with a shift of the octahedron along the a-axis. In this study, the effect of lanthanides (Ln=Pr, Eu, Gd, Dy)-substitution and crystallization temperature on their ferroelectric properties of bismuth titanate $(Bi_4Ti_3O_{12}, BIT)$ thin films were investigated. As BLnT thin films were substituted to lanthanide elements (Pr, Eu, Gd, Dy) with a smaller ionic radius, the remnant polarization (2P$_r$) values had a tendency to increase and made an exception of the Eu-substituted case because $Bi_{4-x}Eu_xTi_3O_{12}$ (BET) thin films had the smaller grain sizes than the others. In this study, we confirmed that better ferroelectric properties can be expected for films composed of larger grains in bismuth layered peroskite materials. The crystallinity of the thin films was improved and the average grain size increased as the crystallization temperature,increased from 600 to 720$^{\circ}C$. Moreover, the BLnT thin film capacitor is characterized by well-saturated polarization-electric field (P-E) curves with an increase in annealing temperature. The BLnT thin films exhibited no significant degradation of switching charge for at least up to $1.0\times10^{11}$ switching cycles at a frequency of 1 MHz. From these results, we can suggest that the BLnT thin films are the suitable dielectric materials for ferroelectric random access memory applications.

• 한국전기전자재료학회논문지
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• 제31권4호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.851-856
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• 2003

We have investigated the material and electrical properties of $Bi_{4-x}La_xTi_3O_{12}$ (BLT) ferroelectric thin film for ferroelectric nonvolatile memory applications of capacitor type and single transistor type. The 120nm thick BLT films were deposited on $Pt/Ti/SiO_2/Si$ and $SiO_2/Nitride/SiO_2$ (ONO) substrates by the sol-gel spin coating method and were annealed at $700^{\circ}C$. It was observed that the crystallographic orientation of BLT thin films were strongly affected by the excess Bi content and the intermediate rapid thermal annealing (RTA) treatment conditions regardeless of two type substrates. However, the surface microstructure and roughness of BLT films showed dependence of two different type substrates with orientation of (111) plane and amorphous phase. As increase excess Bi content, the crystallographic orientation of the BLT films varied drastically in BLT films and exhibited well-crystallized phase. Also, the conversion of crystallographic orientation at intermediate RTA temperature of above $450^{\circ}C$ started to be observed in BLT thin films with above excess 6.5% Bi content and the rms roughness of films is decreased. We found that the electrical properties of BLT films such as the P-V hysteresis loop and leakage current were effectively modulated by the crystallographic orientations change of thin films.

• 센서학회지
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• 제12권3호
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• pp.103-111
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• 2003

$Si_3N_4/SiO_2/Si_3N_4$ 열차단막을 이용한 크로멜-알루멜(chromel-alumel) 열전(thermoelectric) 유량센서를 제작하였다. 백금 박막 히터의 저항온도계수는 약 $0.00397/^{\circ}C$이었고, 크로멜-알루멜 열전쌍(thermocouple)의 Seebeck 계수는 약 $36\;{\mu}V/K$이었다. 기체의 열전도도가 증가할수록 유량센서가 나타내는 열기전력은 감소하였으며, 히터의 온도가 증가하거나 히터와 열전쌍 사이의 간격이 감소할수록 유량센서의 $N_2$ 유량에 대한 감도는 증가하였다. 히터 전압을 약 2.5 V로 하였을 때 유량센서의 $N_2$ 유량에 대한 감도는 약 $1.5\;mV/sccm^{1/2}$이었고, 열 응답시간은 약 0.18초이었다. 크로멜-알루멜 열전 유량센서의 유량감도에 있어서 선형 범위가 Bi-Sb 유랑센서의 것보다 더 넓게 나타났다.

• 농촌의학ㆍ지역보건
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• 제31권1호
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• pp.35-46
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• 2006

명동의, 실습기록에 관한 취급과 지도실태를 파악, 검토하여 앞으로 환자실습 시에 도움이 되는 자료를 얻고자 한국과 일본의 전국간호교육기관의 성인간호학, 아동간호학 및 정신간호학을 담당하는 교수를 대상으로 우편조사를 실시한 결과, 30.9%(한국), 45.2%(일본)의 응답율을 보였다. 조사내용은 일반적 특성 4문항, 학생실습에 관한 환자 설명동의 내용으로 구성된 29문항, 교수의 실습기록에 대한 지도와 관리에 관한 15문항 및 병동의 간호기록에 대한 학생의 기록에 대한 3문항으로 총 54문항으로 구성하였다. 분석방법으로 일반적 실태는 백분율을 보았으며, 영역별로는 ${\chi}^2-test$ 및 프리드만 검정을 하였으며, 개방식질문(자유기술)에 대해서는 응답자의 내용을 카드화하고 KJ법에 기초하여 관심내용을 추출하였다. 조사결과는 다음과 같다. 간호대학생의 임상실습 시에 "환자를 정해서 실습한다"고 응답한 비율은 50.0%(한국), 99.0%(일본)였으며, 주로 "수간호사"가 환자에게 설명하였는데, 분야별로는 성인, 아동, 정신간호학의 순으로 통계적으로도 유의한 차이를 보였다. 환자의 승인을 얻는 방법으로는 "구두승인"이 대부분이었으며, 실제로 동의서를 받는 경우는 두나라 모두 없는 것으로 조사되었다. 환자배정 시 설명에서는 한국과 일본 모두 "학생이 실습으로 맡게 된다" 49.0%, 100.0%로 가장 높았고, 반대로 가장 낮은 비율은 "실습기록을 보이면서 설명한다" 7.8%(한국), "환자는 실습기록을 볼 수 있다" 0.7%(일본)로 거의 비슷한 상황이었다. 환자실습 시 설명동의에 관한 교수의견에서 일본은 "환자에 대한 설명방법의 현상", "설명동의에 관한 사고와 설명동의의 바람직한 모습", "설명동의서를 받는 것과 관련된 불안과 딜렘마", "설명동의의 도입과 교육적 기대", "설명동의에 필요한 환경", 및 "과제"의 6개로 분류되었다. 한국에서는 "환자에 대한 설명방법의 현상", "설명동의서를 받는 것과 관련된 어려움" 및 "과제"의 3개로 분류되었다. 간호대학생이 실습 시 간호기록지에 기록은 "기재한다"가 한국이 46.1%로 일본의 17.7%보다 2.6배 높게 나타났다. 환자 개인정보가 기재되고 있는 학생의 실습기록의 취급에 관한 것으로 병원 밖으로 "가지고 나간다"가 한 일 각각 50.0%, 89.7%로 유의한 차이가 있었다. 실습기록의 지도에서는 두 나라 모두 "비밀을 지킬 것을 지도하고 있다"는 것이 가장 높아 한국과 일본이 각각 92.2%, 98.3%이었으며, 가장 낮은 항목은 한국이 "실습기록에 워드프로세스를 사용하지 않도록 지도한다" 17.6% 인 반면 일본은 "실습기록에 워드프로세스를 허용하는 경우, 규칙을 정하고 있다" 6.3%로 나타났다. 학생이 병동의 간호기록지에 기재하는 것에 대한 교수의 의견을 개방식으로 질문한 결과를 범주화하여 분류한 결과, "학생이 간호기록에 기재하지 않는 것이 좋다", "과제이다", "기재하고 있다. 기재할 수 있다", "기재하는 것은 의미가 있다", "상황에 따라 판단한다", "현재는 판단하기 어렵다"의 6개 범주로 구분할 수 있었다. 결론적으로 간호대학생의 임상실습 시 환자의 설명동의는 절대적으로 필요하며 실습기록의 관리지도도 교육과 학습의 목적뿐만 아니라 환자의 개인정보의 보호라는 맥락에서 고려되어야 할 것이다. 임상현장에서는 교육적 관점에서만 해결할 수 없는 문제도 있으므로 실습기관과의 대화를 통한 실습기록과 교육의 개선을 시도할 필요가 있음을 제언한다.