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낸드 플래시 메모리 시스템의 Lifetime 증대를 위한 관리 방법 설계
박이현 ( Yi-hyun Park ),이재빈 ( Jae-bin Lee ),김건명 ( Geon-myung Kim ),임승호 ( Seung-ho Lim ) 한국정보처리학회 2019 한국정보처리학회 학술대회논문집 Vol.26 No.1
낸드 플래시 메모리(NAND Flash Memory)는 컴퓨터 시스템의 대용량 저장장치를 위한 소자로써, 대용량화의 주요 원인으로는 메모리 셀(Cell) 당 저장할 수 있는 비트 수를 증가시킴으로써 집적도를 증가시킨 것이다. 그러나, 이러한 집적도의 증가는 에러의 증가를 가져와서 저장장치에서 가장 중요한 신뢰성이 급격하게 저하하는 요인이며, 저장장치의 생명주기(Lifetime)을 감소시키게 된다. 기존에 낸드플래시 메모리 저장장치의 Lifetime을 증대시키기 위해서 P/E cycle을 고려하여 데이터 영역의 일부를 점점 더 ECC 영역으로 변경시키는 방식을 적용한 바가 있다. 이러한 방식은 데이터 영역의 감소로 인한 저장장치 내에서 관리되는 호스트-플래시 간 데이터 관리 크기의 미스매치로 인한 여러 가지 오버헤드를 생성한다. 본 연구에서는 P/E cycle에 따른 데이터 영역의 ECC 영역으로의 전환을 통한 Lifetime을 증가시키는 방식에 있어서, 오버헤드를 줄이기 위한 캐쉬 관리 구조 및 매핑 관리 구조에 대한 설계를 진행하였다. 이러한 설계를 낸드 플래시 메모리 기반 저장장치에 적용할 경우, LifeTime을 증대시키기 위해서 ECC를 데이터 영역으로 확장하는 방식을 사용할 때 저하될 수 있는 일반 읽기 및 쓰기의 성능 저하를 어느 정도 감소시켜줄 수 있을 것으로 기대한다.
LPS-SiC 세라믹스 제조특성에 미치는 소결온도의 영향
박이현(Yi-Hyun Park),정헌채(Hun-Chae Jung),김동현(Dong-Hyun Kim),윤한기(Han-Ki Yoon),A. Kohyama 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, SiC<SUB>f</SUB>/SiC composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiC<SUB>f</SUB>/SiC composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760 ℃, 1780 ℃, 1800 ℃ and 1820 ℃ under 20 MPa using Al₂O₃ - Y₂O₃ system as sintering additives in order to low sintering temperature. The starting powder was high purity β-SiC nano-powder with an average particle size of 30 ㎚. Monolithic LPS-SiC was evaluated in terms of sintering density, micro-structure, flexural strength, elastic modulus and so on. Sintered density, flexural strength and elastic modulus of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintered body was grown from 30 ㎚ to 200 ㎚.
리튬용액 침투방법에 의한 Li<sub>2</sub>TiO<sub>3</sub> 페블 제조
유민우,박이현,이상진,Yu, Min-Woo,Park, Yi-Hyun,Lee, Sang-Jin 한국세라믹학회 2013 한국세라믹학회지 Vol.50 No.5
To fabricate spherical lithium titanate ($Li_2TiO_3$) pebbles which are used for a breeder material in fusion reactor, titanium oxide ($TiO_2$) granules were used as a starting material. The granules were pre-sintered, and then aqueous lithium nitrate solution infiltrated into the granules at vacuum condition. The granules were crystallized to $Li_2TiO_3$ after sintering under the control of process parameters. In this study, the concentration of lithium in the solution, as well as the number of penetration times and sintering temperature affected the final crystallite phase and the microstructure of the pebbles. In particular, the sphericity and size of the pebbles were effectively controlled by a technical rolling process. The useful spherical $Li_2TiO_3$ pebbles which have 10~20% porosity and 60~120 N compressive strength were obtained through the sintering at $1000{\sim}1100^{\circ}C$ in the multi-times infiltration process with 50 wt% solution. The physical properties of pebbles such as density, porosity and strength, can be controlled by a selection of $TiO_2$ powders and control of processing parameters. It can be thought that the lithium penetration method is a useful method for the fabrication of mass product of spherical $Li_2TiO_3$ pebbles.
이진경(Jin-Kyung Lee),박영철(Young-Chul Park),이상필(Sang-Pill Lee),박이현(Yi-Hyun Park) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
A hot press method was used to create the optimal fabrication condition for a Shape Memory Alloy(SMA)<br/> composite. The bonding strength between the matrix and the reinforcement within the SMA composite by the<br/> hot press method was more increased by cold rolling. In this study, the objective was to develop an on-line<br/> monitoring system in order to prevent the crack initiation and propagation by shape memory effect in SMA<br/> composite. Shape memory effect was used to prevent the SMA composite from crack propagation. For this<br/> system an optimal AE parameter should be determined according to the degree of damage and crack initiation.<br/> When the SMA composite was heated by the plate heater attached at the composite, the propagating cracks<br/> could be controlled by the compressive force of SMA.
고온용 SiC<SUB>f</SUB>/SiC 복합재료개발 기술과 활용방향
윤한기(Han Ki Yoon),이영주(Young Ju Lee),박이현(Yi Hyun Park) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.11
The development of the first wall whose major function is to withstand high neutron and heat fluxes is a critical path to fusion power. The materials database and the fabrication technology are being developed for design, construction and safety operation of the fusion reactor. The first wall was designed to consist of the plasma facing armor, the heat sink layer and the supporting plates. and Porous materials are of significant interest due to their wide applications in catalysis, separation, lightweight structural materials. In this study, the characteristics of the sintering process of SiC ceramic, SiCf/SiC composite and porous Cf/SiC composite have been introduced order to study of the fusion blanket materials and heat-exchange pannel.
이영주(Young-Ju Lee),윤한기(Han-ki Yoon),박이현(Yi-Hyun Park),박준수(Jun-Soo Park),A. Kohyama 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Nano Infiltration Transient Eutectic Phase - Silicon Carbide (NITE-SiC) have been fabricatied by a Hot Pressing (HP) process, using SiC powder with an average size of about 30㎚. Alumina (Al₂O₃) and Yttria (Y₂O₃) were used for additives meterials. These mixed powders were sintered at the temperature a of 1300℃, 1650℃, 1800℃ and 1900℃ under an applied pressure of 20㎫. Densification of microstructure gives an effect to density and strength. Specially, Densification Mechanism basically is important from the sintering which use the HP. In this study, nano size particle was used to HP and the densification of NITE-SiC mechanism by a press displacement appers investigated. The slope changes places by a press displacement shared a at three steps. The mechanism on the densification of each sintering temperature was investigated. The each step is shows a with each other different mechanism quality.
IF법을 이용한 LPS-SiC 세라믹스의 파괴인성 특성
김도형(Do-Hyoung Kim),윤한기(Han-Ki Yoon),박이현(Yi-Hyun Park) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
SiC materials have been extensively studied for high temperature components in advanced energy system and advanced gas turbine. However, the brittle characteristics of SiC such as low fracture toughness and low strain-to fracture still impose a severe limitation on practical applications of SiC materials. For these reasons, SiCf/SiC composites can be considered as a promising for various structural materials, because of their good fracture toughness compared with monolithic SiC ceramics. But, high temperature and pressure lead to the degradation of the reinforcing fiber during the hot pressing. Therefore, reduction of sintering temperature and pressure is key requirements for the fabrication of SiCf/SiC composites by hot pressing method. In the present work, Monolithic LPS-SiC was fabricated by hot pressing method in Ar atmosphere at 1760℃, 1780℃, 1800℃ and 1820℃ under 20 MPa using Al₂O₃ - Y₂O₃ system as sintering additives in other to low sintering temperature. The starting power was high purity β-SiC nano-powder with an average particle size of 30 ㎚. Monolithic LPS-SiC was evaluated in terms of sintering density, hardness and fracture toughness through indentation fracture method by the Vickers hardness tester. Sintered density, hardness and fracture toughness of fabricated LPS-SiC increased with increasing the sintering temperature. In the micro-structure of this specimen, it was found that grain of sintering body was grown from 30 ㎚ to 200 ㎚.