• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.28-31
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• 2005

The numerical simulation is conducted for analysis flame structure of superdetonative ram accelerator experiment by ISL(French-German Research Institute in Saint Louis). Fully coupled chemically non-equilibrium Navier-Stokes equation is used. Shockwave structure of superdetonative ram accelerator and behavior of detonation wave is studied. Maintaining of detonation wave is very important to accelerate projectile, Because detonation wave make high pressure gases and this high pressure accelerate projectile.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.1133-1134
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• 2008

There are several international standards, established by IEC, for RAMS management of railway system. Those int'l standards are described only total RAMS management, but RAM and safety activities have dissimilar characteristics. In this paper, we suggest the separated RAMS architecture with RAM and safety activity for railway signaling system.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.255-261
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• 2007

In this paper we introduce the method, procedure and result of RAM prediction for interlocking system which is applied for AREX signaling system. For RAM prediction, we breakdown the interlocking system to the LRU level and select the LRUs of which failure can cause the service delay. The prediction of reliability is based on the Reliability Block Diagram which is the functional diagram composed of selected LRUs and finally, the availability of interlocking system is estimated from the combination of reliability and maintainability.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.368.1-368.1
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• 2014

We proposed amorphous GeSe-based ReRAM device of metal-insulator-metal (M-I-M) structure. The operation characteristics of memory device occured unipolar switching characteristics. By introducing the concepts of valance-alternation-pairs (VAPs) and chalcogen vacancies, the unipolar resistive switching operation had been explained. In addition, the current transport behavior were analyzed with space charge effect of VAPs, Schottky emission in metal/GeSe interface and P-F emission by GeSe bulk trap in mind. The GeSe ReRAM device of M-I-M structure indicated the stable memory switching characteristics. Furthermore, excellent stability, endurance and retention characteristics were also verified.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.343-344
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• 2012

It has been known since the mid 1960s that Ag can be photodissolved in chalcogenide glasses to form materials with interesting technological properties. In the 40 years since, this effect has been used in diverse applications such as the fabrication of relief images in optical elements, micro photolithographic schemes, and for direct imaging by photoinduced Ag surface deposition. ReRAM, also known as conductive bridging RAM (CBRAM), is a resistive switching memory based on non-volatile formation and dissolution of a conductive filament in a solid electrolyte. Especially, Ag-doped chalcogenide glasses and thin films have become attractive materials for fundamental research of their structure, properties, and preparation. Ag-doped chalcogenide glasses have been used in the formation of solid electrolyte which is the active medium in ReRAM devices. In this paper, we investigated the nature of thin films formed by the photo-dissolution of Ag into Ge-Se glasses for use in ReRAM devices. These devices rely on ion transport in the film so produced to create electrically programmable resistance states. [1-3] We have demonstrated functionalities of Ag doped chalcogenide glasses based on their capabilities as solid electrolytes. Formation of such amorphous systems by the introduction of Ag+ ions photo-induced diffusion in thin chalcogenide films is considered. The influence of Ag+ ions is regarded in terms of diffusion kinetics and Ag saturation is related to the composition of the hosting material. Saturated Ag+ ions have been used in the formation of conductive filaments at the solid electrolyte which is the active medium in ReRAM devices. Following fabrication, the cell displays a metal-insulator-metal structure. We measured the I-V characteristics of a cell, similar results were obtained with different via sizes, due to the filamentary nature of resistance switching in ReRAM cell. As the voltage is swept from 0 V to a positive top electrode voltage, the device switches from a high resistive to a low resistive, or set. The low conducting, or reset, state can be restored by means of a negative voltage sweep where the switch-off of the device usually occurs.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.181.1-181.1
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• 2015

용액 공정을 이용한 Resistive random access memory (ReRAM)은 간단한 공정 과정, 대면적화, 저렴한 가격 등의 장점으로 인해 큰 관심을 받고 있으며, HfOx, TiOx, AlOx 등의 산화물이 ReRAM 절연 막으로 주로 연구되고 있다. 더 나아가 최근에는 organic 물질을 메모리 소자로 사용한 연구가 보고되고 있다. 이는 경제적이며, wearable 또는 flexible system에 적용이 용이하다. 그럼에도 불구하고, organic 물질을 갖는 메모리 소자는 기존의 산화물 소자에 비해 열에 취약하며 전기적인 특성과 신뢰성이 우수하지 못하다는 단점을 가지고 있다. 이를 위한 방안으로 본 연구에서는 AlOx - polymethylmethacrylate (PMMA) blended thin film ReRAM을 제안하였다. 이는 organic물질의 전기적 특성을 개선시킬 뿐 아니라, inorganic 물질을 wearable 소자에 적용했을 때 발생하는 crack과 같은 기계적 물리적 결함을 해결할 수 있는 새로운 방법이다. 먼저, P-type Si 위에 습식산화를 통하여 SiO2 300 nm 성장시킨 기판을 사용하여 electron beam evaporation으로 10 nm의 Ti, 100 nm의 Pt 층을 차례로 증착하였다. 그리고 PMMA 용액과 AlOx 용액을 초음파를 이용하여 혼합한 뒤, 이 용액을 Pt 하부 전극 상에서 spin coating방법으로 1000 rpm 10초, 5000 rpm 30초의 조건으로 증착하였다. Solvent 및 불순물 제거를 위하여 150, 180, $210^{\circ}C$의 온도로 30 분 동안 열처리를 진행하였고, shadow mask를 이용하여 상부 전극인 Ti를 sputtering 방식으로 100 nm 증착하였다. 150, 180, $210^{\circ}C$로 각각 열처리한 AlOx - PMMA blended ReRAM의 전기적 특성은 HP 4156B semiconductor parameter analyzer를 이용하여 측정하였다. 측정 결과 제작된 소자 전부에서 2 V이하의 낮은 동작전압, 안정된 DC endurance (>150cycles), 102 이상의 높은 on/off ratio를 확인하였고, 그 중 $180^{\circ}C$에서 열처리한 ReRAM은 더 높은 on/off ratio를 갖는 것을 확인하였다. 결론적으로 baking 온도를 최적화하였으며 AlOx - PMMA blended film ReRAM의 우수한 메모리 특성을 확인하였다. AlOx-PMMA blended film ReRAM은 organic과 inorganic의 장점을 갖는 wearable 및 system용 비휘발성 메모리소자에 적용이 가능한 경제적인 기술로 판단된다.

• Journal of the Korea Convergence Society
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• v.11 no.10
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• pp.1-7
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• 2020

The manufacturing process of the resistive variable memory device, which is the based of neuromorphic device, maintained the continuity of vacuum process and applied plasma module suitable for the production of the ReRAM(resistive random access memory) and process technology for the neuromorphic computing, which ensures high integrated and high reliability. The ReRAM device of the oxide thin-film applied to the plasma module was fabricated, and research to improve the properties of the device was conducted through various experiments through changes in materials and process methods. ReRAM device based on TiO₂/TiOx of oxide thin-film using plasma module was completed. Crystallinity measured by XRD rutile, HRS:LRS current value is 2.99 × 10³ ratio or higher, driving voltage was measured using a semiconductor parameter, and it was confirmed that it can be driven at low voltage of 0.3 V or less. It was possible to fabricate a neuromorphic ReRAM device using oxygen gas in a previously developed plasma module, and TiOx thin-films were deposited to confirm performance.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.12
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• pp.1-7
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• 2010

In this paper, we suggested a sensing method of PoRAM with the multilevel cell When a specific voltage is applied between top and bottom electrodes of PoRAM unit cell, we can distinguish cell states by changing resistance values of the cell. Especially, we can use the PoRAM as the multilevel cell due to have four stable resistance values per cell. Therefore, we proposed an address decoding method, sense amplifier and control signal for sensing of a multilevel cell. The sense amplifier is designed based on a current comparator that compared a cell current the cell with a reference current, and have a low input impedance for a amplification of the current. The proposed circuit was designed in a $0.13{\mu}m$ CMOS technology, we verified to sense each data "00", "01", "10", "10" by four states of a cell current.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.306.2-306.2
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• 2014

전자기기의 휴대성과 이동성이 강조되고 있는 현대사회에서 비휘발성 메모리는 메모리 산업에 있어 매우 매력적인 동시에 커다란 잠재성을 지닌다. 이미 공정의 한계에 부딪힌 Flash 메모리를 대신하여 10nm 이하의 공정이 가능한 상변화 메모리(Phase-Change Memory, PRAM), 스핀 주입 자화 반전 메모리(Spin Transfer Torque-Magnetic RAM, STT-MRAM), 저항 변화 메모리(Resistive Random Access Memory, ReRAM)가 차세대 비휘발성 메모리 후보로서 거론되고 있으며, 그 중에서도 ReRAM은 빠른 속도와 낮은 소비 전력, CMOS 공정 호환성, 그리고 비교적 단순한 3차원 적층 구조의 특성으로 인해 활발히 연구되고 있다. 특히 최근에는 질화물 또는 질소를 도핑한 산화물을 저항변화 물질로 사용하는 ReRAM이 보고되고 있는데, 이들은 동작전압이 낮을 뿐만 아니라 저항 변화(Resistive Switching, RS) 과정에서 일어나는 계면 산화를 방지할 수 있으므로 ReRAM의 저항 변화 재료로서 각광받고 있다. 그러나 Cell 단위의 ReRAM 소자를 Crossbar Array 구조에 적용시켰을 때 주변 Cell과의 저항 상태 차이로 인해 전류가 낮은 저항 상태(LRS)의 Cell로 흘러 의도치 않은 동작을 야기한다. 이와 같이 누설 전류(Leakage Current)로 인한 상호간의 간섭이 일어나는 Cross-talk 현상이 존재하며, 공정의 간소화와 집적도를 유지하면서 이 문제를 해결하는 것은 실용화하기에 앞서 매우 중요한 문제이다. 따라서, 본 논문에서는 Read 동작 시 발생하는 Cell과 Cell 사이의 Cross-talk 문제를 해결하기 위해 자가 정류 특성(Self-Rectifying)을 가지는 실리콘 질화물/알루미늄 질화물 이중층(Si3N4/AlN Bi-layer)으로 구성된 ReRAM 소자 구조를 제안하였으며, Sputtering 방법을 이용하여 제안된 소자를 제작하였다. 전압-전류 특성 실험결과, 제안된 구조에 대한 에너지 밴드 다이어그램 시뮬레이션 결과와 동일하게 Positive Bias 영역에서 자가 정류 특성을 획득하였고, 결과적으로 Read 동작 시 발생하는 Cross-talk 현상을 차단할 수 있는 결과를 확보하였다.

• Archives of Reconstructive Microsurgery
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• v.24 no.1
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• pp.7-12
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• 2015

Purpose: The rectus abdominis musculocutaneous (RAM) flap has contributed to the efficient reconstruction of soft tissue defects. The flap has the advantage of easy dissection, minimal donor site morbidity, and the constant vascular anatomy with long pedicle. Authors used the free RAM flap to reconstruct multi-located soft tissue defects while still considering functionality and aesthetics. We present the long-term outcomes and versatility of free RAM flaps. Materials and Methods: From 1994 to 2004, all patients who underwent soft tissue reconstruction with free RAM flap were reviewed retrospectively. The site of the reconstruction, vessels of anastomosis, type of RAM flap, and outcomes, including flap success rate, hospital stay after flap transfer, conduction of secondary procedure, flap complications, and donor-site complications were analyzed. Results: Twenty-one patients underwent 24 free RAM flaps in site of breast, face, upper extremity and lower extremity. Mean follow-up period was 36.1 months (range, 3~156 months). The overall success rate was 92% with only a loss of 2 flaps. Minor complications related to transferred flaps were necrosis of 2 partial flaps, hematoma formation in 3 cases, and a wound infection in 1 case. Donor site morbidity was not observed. Debulking surgery was performed in 4 patients, and scar revision was performed in 3 patients. Conclusion: Free RAM flap is a workhorse flap for general soft-tissue reconstruction with minimal donor site morbidity with aesthetically good results. Thus, the free RAM flaps are versatile, and sturdy for any sites of soft-tissue where reconstruction could be performed.