• KEPCO Journal on Electric Power and Energy
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• 제8권2호
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• pp.93-96
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• 2022

The boiler tubes of thermal power plants are exposed to harsh environment of high temperature and high pressure, and the deterioration state of materials rapidly increases. In particular, parent material and welds of the materials used are subjected to a temperature change and various constraints, resulting in deformation and its growth, resulting in frequent leakage accidents caused by tube failure. The power plant checks the integrity of boiler tubes through non-destructive testing as it may act as huge costs loss and limitation of power supply during power station shutdown period due to boiler tube leakage. However, the current non-destructive testing is extremely limited in the field to detect micro cracks. In this study, the ability of metal magnetic memory technique to detect flaws of size that are difficult to inspect by the visual or general non-destructive methods was verified in the early stage of their occurrence.

• Steel and Composite Structures
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• 제19권3호
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• pp.601-614
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• 2015

The Metal Magnetic Memory (MMM) method is a non-destructive testing method based on an analysis of the self-magnetic leakage field distribution on the surface of a component. It is used for determining the stress concentration zones or any irregularities on the surface or inside the components fabricated from ferrous-based materials. Thus, this paper presents the MMM signal behaviour due to the application of fatigue loading. A series of MMM data measurements were performed to obtain the magnetic leakage signal characteristics at the elastic, pre-crack and crack propagation regions that might be caused by residual stresses when cyclic loadings were applied onto the A283 Grade C steel specimens. It was found that the MMM method was able to detect the defects that occurred in the specimens. In addition, a justification of the Self Magnetic Flux Leakage patterns is discussed for demonstrating the effectiveness of this method in assessing the A283 Grade C steel under cyclic loadings.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 추계학술대회 논문집 Vol.18
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• pp.348-349
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• 2005

An electromagnetic memory effect observed in superconducting YBCO system was studied. From the measurement of differential conductance, it was cleared that the mechanism of electromagnetic memory can not be explained by using conventional flux flow model. By changing the density of external magnetic flux, changes in inductance of a coil in which a superconducting bar is inserted were also measured. It was concluded that the electromagnetic memory effect aries from the interaction between the trapped magnetic flux and the weak link of the filament formed in the superconducting bar.

• 대한전자공학회논문지SD
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• 제45권8호
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• pp.1-10
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• 2008

본 논문에서는 새로운 스위칭 방식인 LFS (Local Field Switching)을 이용하여 설계한 128비트 MRAM (Magnetoresistive Random Access Memo교)에 대해 기술하였다. LFS 방식은 MTJ (Magnetic Tunnel Junction)를 직접 통과해 흐르는 전류에 의해 형성되는 국소 자기장을 이용하여 MTJ의 극성을 변환시킨다. 이 방식은 MTJ와 전류의 거리가 가깝기 때문에 작은 전류로도 충분히 큰 자기장을 형성하므로 writing current가 적어도 된다. 또한 Digit Line이 없어도 되므로 half select disturbance가 발생하지 않아 기존 MTJ를 이용한 방식에 비해 셀 선택도가 우수하다. 설계한 MRAM은 IT(트랜지스터)-1MTJ의 메모리 셀 구조를 가지며 양방향 write driver와 mid-point reference cell block, current mode sense amplifier를 사용한다. 그리고 MTJ 공정 없이 회로 동작을 확인하기 위해 LFS-MTJ cell을 CMOS emulation cell로 대체하였다. 설계한 회로를 6 metal을 사용하는 $0.18{\mu}m$ CMOS 공정으로 구현하였고 제작된 chip을 custom board 상에서 테스트하여 동작을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2002년도 제22회 학술발표회 초록집
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• pp.135-135
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• 2002

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.387-387
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• 2013

Currently, the flash memory and the dynamic random access memory (DRAM) have been used in a variety of applications. However, the downsizing of devices and the increasing density of recording medias are now in progress. So there are many demands for development of new semiconductor memory for next generation. Magnetic random access memory (MRAM) is one of the prospective semiconductor memories with excellent features including non-volatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM is composed of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack consists of various magnetic materials, metals, and a tunneling barrier layer. Recently, MgO thin films have attracted a great attention as the prominent candidates for a tunneling barrier layer in the MTJ stack instead of the conventional Al2O3 films, because it has low Gibbs energy, low dielectric constant and high tunneling magnetoresistance value. For the successful etching of high density MRAM, the etching characteristics of MgO thin films as a tunneling barrier layer should be developed. In this study, the etch characteristics of MgO thin films have been investigated in various gas mixes using an inductively coupled plasma reactive ion etching (ICPRIE). The Cl2/Ar, CH3OH/Ar, and CH4/Ar gas mix were employed to find an optimized etching gas for MgO thin film etching. TiN thin films were employed as a hard mask to increase the etch selectivity. The etch rates were obtained using surface profilometer and etch profiles were observed by using the field emission scanning electron microscopy (FESEM).

• Journal of Magnetics
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• 제9권2호
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• pp.37-39
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• 2004

Polycrystalline Ni-Mn-Ga films have been deposited onto mica substrates held at 720 K by flash-evaporation method. At room temperature the films have a tetragonal structure with a = b = 0.598 and c = 0.576 nm typical for bulk $Ni_2MnGa$ below a martensitic transformation. Temperature measurements of ferromagnetic resonance reveal a martensitic phase transformation at 310 K. The transformation brings about a substantial decrease in the effective magnetization and a drastic increase in the ferromagnetic resonance linewidth due to a strong increase in the magnetic anisotropy in the martensitic phase.

• 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.

• 한국통신학회논문지
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• 제19권10호
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• pp.1849-1860
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• 1994

본 논문은 비정질 회토류 천이 급속 박막내에서의 자벽 역학(Magnetic domain wall dynamics)을 란다우 리프쉬츠 길버트 (Landau Lifshitz Gilbert) 방정식을 이용한 수치적 해석을 수행하여 연구하였다. 박막을 이차원 정방형 격자($30\times30$)로 나누고, 각 격자 셀(Cell)에 쌍극자간 존재한다고 상정하여, 이들 쌍극자간의 상호 교환 작용과 자기 이방성, 외부 인가 자계, 그리고 감자계의 영향이 고려되었다. 단축 자기 이방성이 존재하고 역방향의 자화가 존재한다고 가정된 상태에서 자벽이 형성되는 시간과 자벽의 두께를 알아보았다. 또한 외부 자계의 인가에 따른 자벽 이동을 연구하였다. 시뮬레이션 결과, 감자계를 고려했을 때 자벽 형성 시간이 상당히 빨라졌고, 평균 자벽의 이동도(Mobility)는 약간 증가되었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.167-167
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• 2011

Magnetic random access memory (MRAM) is one of the prospective semiconductor memories for next generation. It has the excellent features including nonvolatility, fast access time, unlimited read/write endurance, low operating voltage, and high storage density. MRAM consists of magnetic tunnel junction (MTJ) stack and complementary metal-oxide semiconductor (CMOS). The MTJ stack is composed of various magnetic materials, metals, and a tunneling barrier layer. For the successful realization of high density MRAM, the etching process of magnetic materials should be developed. Among various magnetic materials, FePt has been used for pinned layer of MTJ stack. The previous etch study of FePt magnetic thin films was carried out using $CH_4/O_2/NH_3$. It reported only the etch characteristics with respect to the variation of RF bias powers. In this study, the etch characteristics of FePt thin films have been investigated using an inductively coupled plasma reactive ion etcher in various etch chemistries containing $CH_4$/Ar and $CH_4/O_2/Ar$ gas mixes. TiN thin film was employed as a hard mask. FePt thin films are etched by varying the gas concentration. The etch characteristics have been investigated in terms of etch rate, etch selectivity and etch profile. Furthermore, x-ray photoelectron spectroscopy is applied to elucidate the etch mechanism of FePt thin films in $CH_4$/Ar and $CH_4/O_2/Ar$ chemistries.