• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.719-722
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• 2003

Ferroelectric $Pb(Zr_{1-x}Ti_x)O_3$ (PZT) films were deposited on (001) MgO single crystals using sol-gel method. Structural properties and surface morphologies of PZT films were investigated using an X-ray diffractometer and a scanning electron microscopy, respectively. The dielectric properties of PZT films were investigated with the dc bias field using interdigitated capacitors (IDC) which were fabricated on PZT films using a thick metal layer by photolithography and dry etching process. The small signal dielectric properties of PZT films were calculated by a modified conformal mapping method with low and high frequency data, such as capacitance measured by an impedance gain/phase analyzer at 100 kHz and reflection coefficient (S-parameter) measured by a HP 8510C vector network analyzer at 1 -20 GHz. The IDC on PZT films exhibited about 67% of capacitance change with an electric field of 135 kV/cm at 10 GHz. These PZT thin films can be applied to tunable microwave devices such as phase shifters, tunable resonators and tunable filters.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.346-346
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• 2008

최근 디지털 컨버젼스에 의해서 정보 단말기 network가 디지털 기술을 기반으로 유기적으로 융 복합화 되고 있으며 BT, NT, ET, IT의 융합 기술의 필요성이 점차적으로 증대되고 있다. 이러한 환경 하에서 다양한 정보 및 서비스의 송신 및 수신이 가능한 휴대 단말기의 필요성에 부응하여 기존의 전화 기능, 카메라, DMB 이외에도 홈 네트워크, mobile internet 등 더욱 다양한 기능들이 요구되고 있다. 종래에는 수동 부품과 능동 부품의 실장을 별개로 추진했으나 최근에는 수동 및 능동 부품을 하나의 패키지 내에 실장 가능하도록 하는 3-D Integration을 추진하고 있다. 지금까지 여러 부품들을 실장 시키기 위한 공정들의 대부분은 높은 온도에서 공정이 이루어졌으나 여러 부품들을 손상 없이 집적화하고 실장하기 위해서는 저온화 공정이 필요하다. 최근 많은 저온 공정 중에서 Aerosol Deposition Method는 상온에서 세라믹 후막을 성막할 수 있어 가장 주목받고 있는 공정중의 하나이다. 본 연구에서는 3-D Integration을 실현하기 위해 이종 접합에 유리하고 상온에서 성막 공정이 이루어지는 Aerosol Deposition Method를 이용하여 금속 기판 위에 금속, 폴리머, 세라믹 후막을 성막시켰다. 기판 재료로는 Cu 기판을 사용하였으며 출발 파우더로는 Polyimide 파우더와 $Al_2O_3$ 파우더, Ag 파우더를 사용하였으며 이종 접합간의 메커니즘의 양상을 보기 위해 같은 조건에서 이종 접합간의 성막률을 비교하였으며 FE-SEM으로 미세 구조를 관찰하였다. 또한 기판의 표면 거칠기에 따른 메커니즘의 양상을 연구하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.90.2-90.2
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• 2013

Vertically-aligned silicon nanostructure arrays (SNAs) have been drawing much attention due to their useful electrical properties, large surface area, and quantum confinement effect. SNAs are typically fabricated by chemical vapor deposition, reactive ion etching, or wet chemical etching. Recently, metal-assisted chemical etching process, which is relatively simple and cost-effective, in combination with nanosphere lithography was recently demonstrated for vertical SNA fabrication with controlled SNA diameters, lengths, and densities. However, this method exhibits limitations in terms of large-area preparation of unperiodic nanostructures and SNA geometry tuning independent of inter-structure separation. In this work, we introduced the layerby- layer deposition of polyelectrolytes for holding uniformly dispersed polystyrene beads as mask and demonstrated the fabrication of well-dispersed vertical SNAs with controlled geometric parameters on large substrates. Additionally, we present a new means of building in vitro neuronal networks using vertical nanowire arrays. Primary culture of rat hippocampal neurons were deposited on the bare and conducting polymer-coated SNAs and maintained for several weeks while their viability remains for several weeks. Combined with the recently-developed transfection method via nanowire internalization, the patterned vertical nanostructures will contribute to understanding how synaptic connectivity and site-specific perturbation will affect global neuronal network function in an extant in vitro neuronal circuit.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.142.2-142.2
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• 2018

One-dimensional metal oxide nanostructures have attracted considerable research activities owing to their strong application potential as components for nanosize electronic or optoelectronic devices utilizing superior optical and electrical properties. In which, semiconducting $SnO_2$ material with wide-bandgap Eg = 3.6 eV at room temperature, is one of the attractive candidates for optoelectronic devices operating at room temperature [1, 2], gas sensor [3, 4], and transparent conducting electrodes [5]. The synthesis and gas sensing properties of semiconducting $SnO_2$ nanomaterials have become one of important research issues since the first synthesis of SnO2 nanowires. In this study, $SnO_2$ nanowire networks were synthesized on a basis of a two-step process. In step 1, Sn spheres (30-800 nm in diameter) embedded in $SiO_2$ on a Si substrate was synthesized by a chemical vapor deposition method at $700^{\circ}C$. In step 2, using the source of these Sn spheres, $SnO_2$ nanowire (20-40 nm in diameter; $1-10{\mu}m$ in length) networks on a spherical Sn surface were synthesized by a thermal oxidation method at $800^{\circ}C$. The Au layers were pre-deposited on the surface of Sn spherical and subsequently oxidized Sn surface of Sn spherical formed SnO2 nanowires networks. Field emission scanning electron microscopy and high-resolution transmission electron microscopy images indicated that $SnO_2$ nanowires are single crystalline. In addition, the $SnO_2$ nanowire is also a tetragonal rutile, with the preferred growth directions along [100] and a lattice spacing of 0.237 nm. Subsequently, the $NO_2$ sensing properties of the $SnO_2$ network nanowires sensor at an operating temperature of $50-250^{\circ}C$ were examined, and showed a reversible response to $NO_2$ at various $NO_2$ concentrations. Finally, details of the growth mechanism and formation of Sn spheres and $SnO_2$ nanowire networks are also discussed.

• 마이크로전자및패키징학회지
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• 제12권3호
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• pp.267-274
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• 2005

This paper presents the fabrication of surface acoustic wave (SAW)-based pressure sensor for long-term stable mechanical compression force measurement. SAW pressure sensor has many attractive features for practical pressure measurement: no battery requirement, wireless pressure detection especially at hazardous environments, and easy other functionality integrations such as temperature, humidity, and RFID. A $41^{\circ}$ YX $LiNbO_3$ piezoelectric substrate was used because of its high SAW propagation velocity and large values of electromechanical coupling factors $K^2$. A silicon substrate with $\~200{\mu}m$ deep cavity was bonded to the diaphragm with epoxy, in which gold was covered all over the inner cavity in order to confine electromagnetic energy inside the sensor, and provide good isolation of the device from its environment. The reflection coefficient $S_{11}$ was measured using network analyzer. High S/N ratio, sharp reflected peaks, and clear separation between the peaks were observed. As a mechanical compression force was applied to the diaphragm from top with extremely sharp object, the diaphragm was bended, resulting in the phase shifts of the reflected peaks. The phase shifts were modulated depending on the amount of applied mechanical compression force. The measured $S_{11}$ results showed a good agreement with simulated results obtained from equivalent admittance circuit modeling.

• 공업화학
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• 제28권4호
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• pp.375-382
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• 2017

전기화학 방법을 이용한 이산화티타늄 나노구조에 대한 기존 연구는 불소 이온을 함유한 전해질에서의 산화반응으로 형성된 나노튜브가 연구의 주를 이루고 있다. 최근, 불소 이온이 아닌 고온 인산염이 함유된 글리세롤계 전해질의 개발로 관련 연구가 활발히 진행되고 있다. 본 총설은 이러한 전해질을 활용하여 다양한 이산화티타늄 나노구조를 형성하는 연구 동향에 대해 다루고 있다. 새로운 양극산화법을 통해 형성된 이산화티타늄 나노구조는 기존의 나노튜브에 비하여 비표면적이 넓고 결정성과 접착력이 우수하여 여러 응용분야에 활용가치가 높다. 이에 본 총설에서는 새로운 양극산화법을 이용한 나노구조의 형성 원리, 특성에 대한 개괄적 접근 뿐만 아니라 실제 응용분야에서의 소재성능을 기존 나노튜브 구조와 비교한 결과 등을 망라하여 자세히 소개하고 있다.

• 한국생산제조학회지
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• 제25권1호
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• pp.30-35
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• 2016

Tandem arc welding is a guarantor for high efficiency and cost saving since the quantity of wire which is deposited in the welding is approximated 30% greater that in conventional welding. The welding process is now being successfully applied in many industries. However, in the case of tandem arc welding, good quality and high productivity should depend on the welding parameters. Therefore, an intelligent algorithms for the automatic tandem arc welding process has been necessarily required. In this study, a predictive model based on the neural network by using the data acquired during tandem gas metal arc (GMA) welding process has been developed. To verify the reliability of the developed predictive model, a mutual comparison with the surface of the top-bead width obtained from actual experiments has been analyzed.

• Nuclear Engineering and Technology
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• 제39권3호
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• pp.193-206
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• 2007

The Korea Atomic Energy Research Institute has developed an advanced fast reactor concept, KALIMER-600, which satisfies the Generation IV reactor design goals of sustainability, economics, safety, and proliferation resistance. The concept enables an efficient utilization of uranium resources and a reduction of the radioactive waste. The core design has been developed with a strong emphasis on proliferation resistance by adopting a single enrichment fuel without blanket assemblies. In addition, a passive residual heat removal system, shortened intermediate heat-transport system piping and seismic isolation have been realized in the reactor system design as enhancements to its safety and economics. The inherent safety characteristics of the KALIMER-600 design have been confirmed by a safety analysis of its bounding events. Research on important thermal-hydraulic phenomena and sensing technologies were performed to support the design study. The integrity of the reactor head against creep fatigue was confirmed using a CFD method, and a model for density-wave instability in a helical-coiled steam generator was developed. Gas entrainment on an agitating pool surface was investigated and an experimental correlation on a critical entrainment condition was obtained. An experimental study on sodium-water reactions was also performed to validate the developed SELPSTA code, which predicts the data accurately. An acoustic leak detection method utilizing a neural network and signal processing units were developed and applied successfully for the detection of a signal up to a noise level of -20 dB. Waveguide sensor visualization technology is being developed to inspect the reactor internals and fuel subassemblies. These research and developmental efforts contribute significantly to enhance the safety, economics, and efficiency of the KALIMER-600 design concept.

• 공학논문집
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• 제6권2호
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• pp.23-32
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• 2004

현재까지 사용되어가지고 있는 임플란트 재료 중 commercially pure titanium (순수티탄; Cp-Ti)과 Ti-alloy들은 생체재료로 폭넓게 사용되어지고 있는데, Ti 금속들은 경도가 강하고 점도가 높기 때문에, 치과나 정형외과 등의 하중에 잘 견디는 곳에 이용되어지고 있다고 한다. 이것들은 생체적합성과 부식에 대한 저항성도 좋은 것으로 알려져 있다. 일반적으로 Ti은 4종류의 Grade로 강도의 차이에 의하여 분류되고 Ti의 강도에 영향을 미치는 것으로는 산소, 철, 질소등이 있다. 따라서 본 연구에서는 O와 Fe의 함량을 달리한 Ti alloy시편을 사용하여 생체적합성 실험을 하였다. 먼저 실험은 시편을 micropolishing하고 5M NaOH에서 $60^{\circ}C$에서24시간 처리하여서 비표면적을 넓혔으며, 표면의 $TiO_2$을 만들어주기 위하여 $600^{\circ}C$에서 열처리하였다. 그런 시편을 $36.5^{\circ}C$의 SBF에 넣어 1~14일까지 침적한 후에 표면에 형성된 apatite를 SEM과 EDAX로 조사하였다. 조사 결과 모든 시편에서 apatite가 생성되었지만, 시편의 조성에 따라서 apatite의 형성양이 다름을 확인하였다.