• Korean Journal of Materials Research
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• v.5 no.6
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• pp.754-762
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• 1995

Strontium titanate(SrTiO$_3$) thin film was prepared on Si substrates by RF magnetron sputtering for a high capacitance density required for the next generation of LSTs. The optimum deposition conditions for SrTiO$_3$thin film were investigated by controlling the deposition parameters. The crystallinity of films and the interface reactions between SrTO$_3$film and Si substrate were characterized by XRD and AES respectively. High quality films were obtained by using the mixed gas of Ar and $O_2$for sputtering. The films were deposited at various bias voltages to obtain the optimum conditions for a high quality file. The best crystallinity was obtained at film thickness of 300nm with the sputtering gas of Ar+20% $O_2$and the bias voltage of 100V. The barrier layer of Pt(100nm)/Ti(50nm) was very effective in avoiding the formation of SiO$_2$layer at the interface between SrTiO$_3$film and Si substrate. The capacitor with Au/SrTiO$_3$/Pt/Ti/SiO$_2$/Si structure was prepared to measure the electric and the dielectric properties. The highest capacitance and the lowest leakage current density were obtained by annealing at $600^{\circ}C$ for 2hrs. The typical specific capacitance was 6.4fF/$\textrm{cm}^2$, the relative dielectric constant was 217, and the leakage current density was about 2.0$\times$10$^{-8}$ A/$\textrm{cm}^2$ at the SrTiO$_3$film with the thickness of 300nm.

• Composites Research
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• v.24 no.4
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• pp.23-28
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• 2011

Recently CFRP laminate joints process by bolts and nets are developed rapidly in aircraft industries. However, there are serious drawback during jointing process. Many hole processes are needed for the manufacturing and structural applications using composite materials. Generally, very durable polycrystalline crystalline diamond (PCD) drill has been used for the CFRP hole process. However, due to the expensive price and slow process speed, chemical vapor deposition (CVD) diamond drill has been used increasingly which are relatively-low durability but easily-adjustable process speed via drill shape change and price is much lower. In this study, the comparison of hole process between PCD and CVD diamond coated drills was done. First of all, CFRP hole processbility was evaluated using the equations of hole processing conditions (feed amount per blade, feed speed). The comparison on thermal damage occurring from the CFRP specimen was also studied during drilling process. Empirical equation was made from the temperature photo profile being taken during hole process by infrared thermal camera. In addition, hole processability was compared by checking hole inside condition upon chip exhausting state for two drills. Generally, although the PCD can exhibit better hole processability, hole processing speed of CVD diamond drill exhibited faster than PCD case.

• Journal of the Korean Magnetics Society
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• v.13 no.3
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• pp.97-102
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• 2003

Synthetic ferrimagnetic layer (SyFL) with structure NiFe/Ru/NiFe which can be applied high density TMR device in free layer were prepared by an inductively coupled plasma (ICP) helicon-sputter. We proposed a model of predicting coercivity (H$\_$c/), spin-flopping field (H$\_$sf/), and saturation field (H$\_$s/) as a function of Ru thicknesses, from the equilibrium state of energies of Zeeman, exchange, and uniaxial anisotropy. We fabricated the samples of Ta(50 ${\AA}$)/NiFe(50${\AA}$)nu(4∼20${\AA}$)NiFe(30 ${\AA}$)/Ta(50${\AA}$), and measured the M-H loops with a superconduction quantum interference device (SQUID) applying the external field up to ${\pm}$ 15 kOe. The result was well agreed with the proposed model, and reveal K$\_$u = 1000 erg/㎤, J$\_$ex/ =0.7 erg/$\textrm{cm}^2$. We report that H$\_$c/ below 10 Oe is available, and R$\_$u/ thickness range should be in 4-10 ${\AA}$ for MRAM application. Our result implies that permalloy layers may lead to considerable magnetostriction effect in SyFL and intermixing in NiFe/Ru interfaces.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.2
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• pp.193-197
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• 2013

In this study, ultrasonic nonlinear characteristics in the heat-treated aluminum alloy have been evaluated. The nonlinearity of ultrasonic wave has been measured as the acoustic nonlinear parameter ${\beta}$, depending upon the amplitude ratio of the second-order harmonic and the fundamental frequency component of ultrasonic wave propagating through the materials. The parameter ${\beta}$ measurement has been carried out with the reflected signals from the back-wall of specimens at the same plane using the contact-type transducers. The heat-treatment, aging, has been achieved at $300^{\circ}C$ for various durations in the range of 1 to 50 hours. The tensile strength and elongation are obtained by the tensile test and then compared with the parameter ${\beta}$. There is a peak of the acoustic nonlinear parameter ${\beta}$ on 5 hours aging and the ${\beta}$ decreases thereafter, exhibiting closed relations with tensile strength and elongation. Also, the heat-treatment time showing peak in the parameter ${\beta}$ was identical to that showing severe change in the ${\sigma}-{\varepsilon}$ curve. These results suggest that the acoustic nonlinear parameter ${\beta}$ can be used for monitoring the strength variations with aging of aluminum alloys.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.2
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• pp.189-195
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• 2003

The objective of this study is to improve the optical sensitivity of laser fluorescence for detection of incipient enamel caries. An incipient carious lesion was formed in various stages by placing an enamel specimen of a bovine tooth in STPP demineralization solution. After measuring the optical density of the lesion surface by laser fluorescence induced by argon laser and various alter of yellow(500-520nm), amber(520-540nm), orange(540-560nm), and red(560-580nm), the specimen was cut vertically to measure the depth of the lesion using a polarizing microscope. SAS statistical program was used to analyze the relationship between the optical density of the lesion suface and the depth of the lesion. The results were as follows: 1. The optical density of early carious lesion, measured by laser fluorescence with amber and orange filter, and lesion depth observed by polarizing microscope, were increased as demineralization time increased. 2. The correlation coefficient between optical density of the lesion surface and the histological depth of the lesion was the highest in orange filter(r=0.49), followed by amber(r=0.32), yellow(r=0.13) and red(0.01). 3. Regression analysis showed that the most linear relationship between the optical density and the lesion depth was existed in orange filter group. In regard above results, laser fluorescence could be considered to be reliable for optical diagnosis of dental caries.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.28-33
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• 2008

Lanthanum modified lead zirconate titanate ($Pb_{1.1}La_{0.08}Zr_{0.65}Ti_{0.35}O_3$) thin films were fabricated on indium doped tin oxide (ITO)-coated glass substrate by R.F magnetron sputtering method. The thin films were deposited at $500^{\circ}C$ and post-annealed with various temperature ($550-750^{\circ}C$) by rapid thermal annealing technique. The structure and morphology of the films were characterized with X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. The hysteresis loops and fatigue properties of thin films were measured by precision material analyzer. As the annealing temperature was increased, the remnant polarization value was increased from $10.6{\mu}C/cm^2$ to $31.4{\mu}C/cm^2$, and coercive field was reduced from 79.9 kV/cm to 60.9 kV/cm. As a result of polarization endurance analysis, the remnant polarization of PLZT thin films annealed at $700^{\circ}C$ was decreased 15% after $10^9$ switching cycles using 1MHz square wave form at ${\pm}5V$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.389.1-389.1
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• 2014

최근의 환경 및 에너지에 대한 관심으로 수요가 증가하고 있는 하이브리드 및 전기 자동차나 태양광발전, 풍력발전용의 인버터기기에는 고에너지밀도 커패시터가 필수적이 되었다. 높은 에너지 밀도를 요구하는 전력전자, 펄스파워 등의 응용분야에 사용되는 고에너지밀도 커패시터는 PET (Polyethylene terephtalate)와 PP (Polypropylene)와 같은 폴리머 유전체를 사용하는 범용 필름 커패시터가 사용되었으나 사용 요구 조건의 한계에 도달하여, 새로운 유전체를 적용하는 커패시터가 절실히 필요한 상황이다. PET와 PP와 같은 유전체는 유전상수가 2~3의 낮은 값을 가지고 있어 고에너지밀도를 구현하기가 어렵다. 본 연구에서는 새롭게 요구되고 있는 고에너지 밀도 커패시터의의 성능을 만족시키기 위하여 $20{\sim}50{\mu}m$ 두께의 PET 필름상에 세라믹 유전체인 $ZrO_2$ 박막을 스퍼터(Sputter) 증착법에 의해 코팅하여 종래의 필름 커패시터와 세라믹 커패시터의 장점을 갖는 커패시터를 제조하기 위한 박막 유전재료의 개발을 목표로 하였다. 수백 nm~수 ${\mu}m$ 두께의 $ZrO_2$ 박막을 스퍼터링 공정조건에 따라 증착한 후 박막의 결정성, 기판과의 부착성, 증착속도, 유전상수, 절연파괴강도, 온도안정성 등을 XRD, SEM, AFM, EDS, XPS, Impedance analyzer 등에 의해 평가하였다. $ZrO_2$ 유전체막은 상온에서 증착하였음에도 정방정(tetragonal)구조의 결정질로 성장하였고 증착압력이 증가함에 따라 주피크의 세기가 감소하였다. 증착 중 산소가스를 주입하였을 경우에도 결정질막으로 성장하였다. 증착막들은 산소가스의 양이 증가함에 따라 짙은 흰색으로 변하였으며 PET 기판과의 접착력도 약해졌다. 또한 거칠기는 Ar가스만으로 증착한 경우보다 증가하였으며 24~66 nm의 평균 거칠기값을 보였다. PET위에 Ar가스만으로 증착한 $ZrO_2$의 비유전율은 1kHz에서 116~87의 비유전율을 보여 PET에 비해 매우 우수한 특성을 보였다. $ZrO_2$ 막들은 300kV/cm의 전계에서 대략 10-8A 이하의 누설전류를 보였다. 증착가스비를 달리하여 제조된 시편에서도 유사한 누설전류값을 나타내었다. 300 kV/cm 전후의 전계까지 측정한 $ZrO_2$ 막의 P-E (polarization-electric field) 특성을 확인하였는데, 5 mTorr의 압력에서 증착한 막은 253 kV/cm에서 $5.5{\mu}C/cm^2$의 분극값을 보였다. P-E커브의 기울기와 분극량에 따라 에너지밀도가 달라지므로 공정조건에 따라 에너지밀도가 변화됨을 예측할 수 있었다. PET위에 스퍼터 증착한 $ZrO_2$ 유전체막은 5mTorr의 Ar가스분위기에서 제조할 때 가장 안정적인 구조를 보였으며, 고에너지밀도 커패시터에의 적용가능성을 보였다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.110-110
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• 2016

금속재료 중 철강은 기계적 성질이 우수하고 대량생산에 의한 뛰어난 경제성을 가지기 때문에 다양한 산업 분야에서 널리 사용되고 있다. 그러나 스테인리스강 등과 같은 일부 특수한 용도의 강을 제외하고는 부식 환경에 취약하기 때문에 그 용도에 따라 표면처리를 함으로서 내식특성을 부여하고 있다. 일반적으로 이러한 철강재료에 대한 부식문제를 해결하기 위한 방법으로는 습식프로세스 중 아연(Zn)도금이 사용되는데, 아연은 그 자체가 보유하고 있는 차폐(barrier)효과는 물론 상대적으로 이온화 경향이 크기 때문에 철에 대하여 전자를 공급하는 희생양극적(Sacrificial anode)역할을 하여 철을 방식하는 원리를 가지고 있다. 하지만 최근에 이르러 기존의 도금 프로세스 처리된 제품의 사용 및 적용분야가 확대되고 가혹해 짐에 따라서 내식성 향상을 위한 새로운 재료 및 신기술 개발이 요구되고 있는 실정이다. 본 연구에서는 친환경 프로세스 방법인 PVD법 중 하나인 스퍼터링(Sputtering)을 이용하여 0.8mm 두께의 냉연강판 (cold rolled steel) 상에 Al에 대한 Mg 함량을 10~30wt.%로 하여 약 $5{\mu}m$ 두께의 막을 제작하였다. 이때 20wt.% 막의 경우 공정압력조건을 증가시켜 증착 막의 결정배향성을 변화시켰다. 뿐만 아니라 제작된 막들에 대해서 $400^{\circ}C$온도에서 10분간 열처리함으로서 코팅막의 성분변화에 따른 영향을 살펴보기 위해 시편을 추가 제작하였다. 이와 같이 제작된 막들에 대한 형성메커니즘과 내식성의 상관관계 해명을 위해 막의 조성분포, 표면 및 단면의 모폴로지 관찰 및 결정구조 등 재료특성분석과 더불어 염수분무(Salt spray test), 침지시험 그리고 양극분극 시험 등을 통해 내식성 평가를 진행하였다. 이상의 종합적인 결과를 살펴보면 제작된 Al-Mg 막은 마그네슘 함량비 및 열처리 조건에 따라 조성분포와 막의 모폴로지 및 결정배향성이 변화한다는 것을 알 수 있었는데, 마그네슘 함량이 증가하고 열처리한 막의 내식성이 가장 양호한 것으로 나타났다. 이것은 Al-Mg 성분이 표면을 중심으로 균일 분산-분포하며, Al에 대한 Mg의 고용으로 인해 안정적으로 형성된 부식생성물과 금속화합물의 단계적 반응 효과에 의해 차폐효과와 희생양극적 특성이 동시에 향상되었기 때문으로 생각된다. 한편 공정 압력을 증가시켜 형성한 막은 결정학적 구조에서 보다 높은 표면 에너지와 증가한 격자 정수에 의해 Mg이 부식환경에서 빠르게 반응하여 안정적 피막을 형성하기 때문에 내식성이 향상된 것으로 보여 진다. 이상의 연구를 통해서 고내식성을 Al-Mg막의 유효성 확인하였으며, 설계에 대한 기초적인 응용지침을 제시할 수 있을 것으로 사료된다.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.2 s.35
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• pp.105-109
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• 2005

A compact antenna switch module for GSM/DCS dual band applications based on multilayer low temperature co-fired ceramic (LTCC) substrate is presented. Its size is $4.5{\times}3.2{\times}0.8 mm^3$ and insertion loss is lower than 1.0 dB at Rx mode and 1.2 dB at Tx mode. To verify the stability of the developed module to the process window, each block that is diplexer, LPF's and bias circuit is measured by probing method in the variation with the thickness of ceramic layer and the correlation between each block is quantified by calculating the VSWR In the mean while, two types of bias circuits -lumped and distributed - are compared. The measurement of each block and the calculation of VSWR give good information on the behavior of full module. The reaction of diplexer to the thickness is similar to those of LPF's and bias circuit, which means good relative matching and low value of VSWR, so total insertion loss is maintained in quite wide range of the thickness of ceramic layer at both band. And lumped type bias circuit has smaller insertion itself and better correspondence with other circuit than distributed stripline structure. Evaluated ceramic module adopting lumped type bias circuit has low insertion loss and wider stability region of thickness over than 6um and this can be suitable for the mass production. Stability characterization by probing method can be applied widely to the development of ceramic modules with embedded passives in them.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.333-340
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• 2010

This paper presents the distributions of the tensile and fracture properties of an alloy 82/182 dissimilar weld joint between an SA508 Gr.3 nozzle and F316L SS safe-end at ambient temperature. Tensile and J-R tests were conducted using specimens extracted from base metals, heat-affected zones (HAZs), buttering regions, and various regions of the weld metal. The results show that the root region of the weld has higher strength than the upper region. The yield and tensile strengths vary considerably within the root region of the weld. The buttering region had the lowest strengths. The strengths gradually increased as the F316L stainless steel weld boundary was approached. The variation of the strengths within the upper region of the weld is insignificant. The fracture toughness of the alloy 82/182 weld metal is less than those of both the base metals and both HAZs. Within the alloy 82/182 weld, the center of weld has a slightly lower fracture toughness than the weld boundary and buttering region, and the root region has greater toughness than the upper region of the weld.