• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.24-24
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• 2003

Metallic magnetoelectronic devices have studied intensively and extensively for last decade because of the scientific interest as well as great technological importance. Recently, the scientific activity in spintronics field is extending to the hybrid devices using ferromagnetic/semiconductor heterostructures and to new ferromagnetic semiconductor materials for future devices. In case of the hybrid device, conductivity mismatch problem for metal/semiconductor interface will be able to circumvent when the device operates in ballistic regime. In this respect, spin-valve transistor, first reported by Monsma, is based on spin dependent transport of hot electrons rather than electron near the Fermi energy. Although the spin-valve transistor showed large magnetocurrent ratio more than 300%, but low transfer ratio of the order of 10$\^$-5/ prevents the potential applications. In order to enhance the collector current, we have prepared magnetic tunneling transistor (MTT) with single ferromagnetic base on Si(100) collector by magnetron sputtering process. We have changed the resistance of tunneling emitter and the thickness of baser layer in the MTT structure to increase collector current. The high transfer ratio of 10$\^$-4/ range at bias voltage of more than 1.8 V, collector current of near l ${\mu}$A, and magnetocurrent ratio or 55% in Si-based MTT are obtained at 77K. These results suggest a promising candidate for future spintronic applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.160-160
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• 2015

InGaZnO (IGZO) thin-film transistors (TFTs) are very promising due to their potential use in high performance display backplane [1]. However, the stability of IGZO TFTs under the various stresses has been issued for the practical IGZO applications [2]. Up to now, many researchers have studied to understand the sub-gap density of states (DOS) as the root cause of instability [3]. Nomura et al. reported that these deep defects are located in the surface layer of the IGZO channel [4]. Also, Kim et al. reported that the interfacial traps can be affected by different RF-power during RF magnetron sputtering process [5]. It is well known that these trap states can influence on the performances and stabilities of IGZO TFTs. Nevertheless, it has not been reported how these defect states are created during conventional RF magnetron sputtering. In general, during conventional RF magnetron sputtering process, negative oxygen ions (NOI) can be generated by electron attachment in oxygen atom near target surface and accelerated up to few hundreds eV by self-bias of RF magnetron sputter; the high energy bombardment of NOIs generates bulk defects in oxide thin films [6-10] and can change the defect states of IGZO thin film. In this study, we have confirmed that the NOIs accelerated by the self-bias were one of the dominant causes of instability in IGZO TFTs when the channel layer was deposited by conventional RF magnetron sputtering system. Finally, we will introduce our novel technology named as Magnetic Field Shielded Sputtering (MFSS) process [9-10] to eliminate the NOI bombardment effects and present how much to be improved the instability of IGZO TFTs by this new deposition method.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.16-17
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• 2010

Molecular spintronics has attracted attentions, which combines molecular electronics with the spin degree of freedom in electron transport. Among various molecules as candidates of the molecular spintronics, single molecule magnet (SMM) is one of the most promising material. SMM molecules show a ferromagnetic behavior even as a single molecule and hold the spin information even after the magnetic field is turned off. Here in this report, we show the spin behavior of SMM molecules adsorbed on the Au surface by combining the observation of Kondo peak in the STS and ESR-STM measurement. Kondo resonance state is formed near the Fermi level when degenerated spin state interacts with conduction electrons. ESR-STM detects the Larmor frequency of the spin in the presence of a magnet field. The sample include $MPc_2$ and $M_2Pc_3$ molecules ($M\;=\;Tb^{3+}$, $Dy^{3+}$, and $Y^{3+}$ Pc=phthalocyanine) whose critical temperature as a ferromagnet reaches 40 K. A clear Kondo peak was observed which is originated from an unpaired electron in the ligand of the molecule, which is the first demonstration of the Kondo peak originated from electron observed in the STS measurement. We also observed corresponding peaks in ESR-STM spectra. [1] In addition we found that the Kondo peak intensity shows a clear variation with the conformational change of the molecule; namely the azimuthal rotational angle of the Pc planes. This indicates that the Kondo resonance is correlated with the molecule electronic state. We examined this phenomena by using STM manipulation technique, where pulse bias application can rotate the relative azimuthal angle of the Pc planes. The result indicates that an application of ~1V pulse to the bias voltage can rotate the Pc plane and the Kondo peaks shows a clear variation in intensity by the molecule's conformational change.

• 한국자기학회지
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• 제14권5호
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• pp.192-195
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• 2004

본 연구는 [Pd(0.8 nm)/Co(0.8 nm)]$_{5}$FeMn(15 nm)구조의 다층박막을 dc마그네트론 스퍼터링 시스템을 이용하여 교환결합된 수직자기이방성에 대한 자기적 특성을 조사하였다. [Pd/Co]다층막과 FeMn 층 사이에 Pd층을 얇게 삽입함으로서 교환바이어스 세기(exchange biasing field : H$_{ex}$)가 127 Oe에서 145 Oe로 개선된 길과를 얻었다. 하지만 열적안정성 실험 결과 삽입층이 삽입 된 경우 삽입되지 않은 경우 보다 약 5$0^{\circ}C$낮은 20$0^{\circ}C$ 에서부터 감소하는 결과를 얻었다. 바닥층 물질에 따른 H$_{ex}$와 보자력 (coercivity : H$_{c}$)의 변화를 조사한 결과, H$_{ex}$는 바닥층이 Ta그리고 Pd인 경우, 각각 최대 127Oe, 169Oe를 얻었다. 반면, H$_{c}$는 바닥층이 Ta그리고 Pd층인 경우, 각각 최대 203 Oe, 453 Oe를 얻었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.408-408
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• 2012

It is well known that magnetic random access memory (MRAM) is nonvolatile memory devices using ferromagnetic materials. MRAM has the merits such as fast access time, unlimited read/write endurance and nonvolatility. Although DRAM has many advantages containing high storage density, fast access time and low power consumption, it becomes volatile when the power is turned off. Owing to the attractive advantages of MRAM, MRAM is being spotlighted as an alternative device in the future. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal- oxide semiconductor (CMOS). MTJ stacks are composed of various magnetic materials. FePt thin films are used as a pinned layer of MTJ stack. Up to date, an inductively coupled plasma reactive ion etching (ICPRIE) method of MTJ stacks showed better results in terms of etch rate and etch profile than any other methods such as ion milling, chemical assisted ion etching (CAIE), reactive ion etching (RIE). In order to improve etch profiles without redepositon, a better etching process of MTJ stack needs to be developed by using different etch gases and etch parameters. In this research, influences of $O_2$ gas on the etching characteristics of FePt thin films were investigated. FePt thin films were etched using ICPRIE in $CH_4/O_2/Ar$ gas mix. The etch rate and the etch selectivity were investigated in various $O_2$ concentrations. The etch profiles were studied in varying etch parameters such as coil rf power, dc-bias voltage, and gas pressure. TiN was employed as a hard mask. For observation etch profiles, field emission scanning electron microscopy (FESEM) was used.

• 한국자기학회지
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• 제16권3호
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• pp.186-191
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• 2006

자기터널접합 기반의 MRAM(magnetic random access memory)은 자기저항효과를 응용하는 메모리소자로서 비휘발성과 고속 정보처리가 가능할 뿐만 아니라 고집적화 할 수 있는 차세대 통합형 비휘발성 메모리이다. 그러나 기존의 메모리 소자들에 비해 스위칭 산포가 크고, 기록마진(writing margin)이 확보되지 않아 아직까지는 고집적화가 어려운 실정이다. 최근 포화자화가 낮은 NiFeSiB 및 CoFeSiB과 같은 비정질 강자성체를 자기터널접합의 자유층 재료로 사용하여 스위칭 자기장의 거대화를 크게 감소시켜 MRAM의 기록마진을 높이는 연구결과에 관해 정리하여 보았다. 그리고 이러한 물질을 이용하여 자기터널접합의 재생마진(reading margin)과 관련된 터널자기저항비의 인가전압의존성을 저감시킬 수 있었다. 본고에서는 나노자기소자 기술의 중요한 분야인 MRAM의 기술발전 방향과 연구사례를 소개하고자 한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.683-687
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• 1997

The purpose of this work is to develop a highly reliable solar cell based on the diamond-like carbon(DLC)/silicon heterojunction. Thin films of DLC have been deposited by employing both filtered cathodic vacuum arc(FCVA) and magnetron plasma-enhanced chemical vapor deposition(m-PECVD) systems. Structural, electrical, and optical properties of DLC films deposited are systematically analyzed as a function of deposition conditions, such as magnetic field, substrate bias voltage, gas pressure, and nitrogen content. The I-V measurement has been used to elucidate the mechanism responsible for the conduction process in the DLC/Si junction. Photoresponse characteristics of the junction are measured and its reliability against temperature and light stresses is also analyzed.

• 한국소음진동공학회논문집
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• 제21권10호
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• pp.924-933
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• 2011

The possibility of noncontact excitation of vibrations in a shaft was investigated in order to enable online structural health monitoring of a shaft during its rotating condition without stop operation. The proposed noncontact exciter was devised to exclusively generate one of two shaft vibration modes, so called longitudinal and flexural. Using the prototypes and a lot of experiments on them, it was proven that bias magnetic field, exciting voltage, center frequency, and geometry of yokes have crucial impacts on its output characteristics.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2002년도 동계연구발표회 논문개요집
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• pp.174-175
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• 2002

A ramp-type tunneling magnetoresistance (TMR) junction having structure NiO(60 nm)/pinned Co(10 nm)MiO(60 nm)/barrier SrTiO$_3$(2-10 nm)/free NiFe(10 nm) with the 15 degree slope was investigated. We obtained nonlinear I(V) characteristics for ramp-type tunneling junctions that have distinctive difference with and without applied magnetic field. In the barrier SrTiO$_3$ thickness of 4 nm, the TMR was about 52% at a bias voltage of 50 mV. (omitted)

• 한국전기전자재료학회논문지
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• 제11권4호
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• pp.261-266
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• 1998

In developing the high density memory device, the etching of fine pattern is becoming increasingly important. Therefore, definition of ultra fine line and space pattern and minimization of damage and contamination are essential process. Also, the high density plasma in low operating pressure is necessary. The candidates of high density plasma sources are electron cyclotron resonance plasma, helicon wave plasma, helical resonator, and inductively coupled plasma. In this study, planar type magnetized inductively coupled plasma etcher has been built. The density and temperature of Ar plasma are measured as a function of rf power, flow rate, external magnetic field, and pressure. The oxide etch rate and selectivity to polysilicon are measured as the above mentioned conditions and self-bias voltage.