• Journal of KIISE:Computer Systems and Theory
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• v.37 no.2
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• pp.90-102
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• 2010

Flash memory has been widely used as an important storage device for consumer electronics. For the flash memory-based storage systems, FTL (Flash Translation Layer) is used to handle the mapping between a logical page address and a physical page address. Especially, log buffer-based FTLs provide a good performance with small-sized mapping information. In designing the log buffer-based FTL, one important factor is to determine the mapping structure between data blocks and log blocks, called associativity. While previous works use static associativity fixed at the design time, we propose a new log block mapping scheme which adjusts associativity based on the run-time workload. Our proposed scheme improves the I/O performance about 5~16% compared to the static scheme by adjusting the associativity to provide the best performance.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.236.2-236.2
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• 2014

세계 반도체 시장은 컴퓨터 기능이 더해진 모바일 기기의 수요가 증가함에 따라 메모리반도체의 시장규모가 최근 빠른 속도로 증가했다. 특히 모바일 기기에서 저장장치 역할을 하는 비휘발성 반도체인 NAND Flash Memory는 스마트폰 및 태블릿PC 등 휴대용 기기의 수요 증가, SSD (Solid State Drive)를 탑재한 PC의 수요 확대, 서버용 SSD시장의 활성화 등으로 연평균 18.9%의 성장을 보이고 있다. 이러한 경제적인 배경 속에서 NAND Flash 미세공정 기술의 마지막 단계로 여겨지는 1Xnm 공정이 개발되었다. 그러나 1Xnm Flash Memory의 생산은 새로운 제조설비 구축과 차세대 공정 기술의 적용으로 제조비용이 상승하는 단점이 있다. 이에 따라 제조공정기술을 미세화하지 않고 기존의 수평적 셀구조에서 수직적 셀구조로 설계 구조를 다양화하는 기술이 대두되고 있는데 이 중 Flash Memory의 대용량화와 수명 향상을 동시에 추구할 수 있는 3D NAND 기술이 주목을 받게 되면서 공정기술의 변화도 함께 대두되고 있다. 3D NAND 기술은 기존라인에서 전환하는데 드는 비용이 크지 않으며, 노광장비의 중요도가 축소되는 반면, 증착(Chemical Vapor Deposition) 및 식각공정(Etching)의 기술적 난이도와 스텝수가 증가한다. 이 중 V-NAND 3D 기술에서 사용하는 박막증착 공정의 경우 산화막과 질화막을 번갈아 증착하여 30layer 이상을 하나의 챔버 내에서 연속으로 증착한다. 다층막 증착 공정이 비정상적으로 진행되었을 경우, V-NAND Flash Memory를 제조하기 위한 후속공정에 영향을 미쳐 웨이퍼를 폐기해야 하는 손실을 초래할 수 있다. 본 연구에서는 V-NAND 다층막 증착공정 중에 다층막의 두께를 가상 계측하는 알고리즘을 개발하고자 하였다. 증착공정이 진행될수록 박막의 두께는 증가하여 커패시터 관점에서 변화가 생겨 RF 신호의 진폭과 위상의 변화가 생긴다는 점을 착안하여 증착 공정 중 PECVD 장비 RF matcher와 heater에서 RF 신호의 진폭과 위상을 실시간으로 측정하여 데이터를 수집하고, 박막의 두께와의 상관성을 분석하였다. 이 연구 결과를 토대로 V-NAND Flash memory 제조 품질향상 및 웨이퍼 손실 최소화를 실현하여 제조 시스템을 효율적으로 운영할 수 있는 효과를 기대할 수 있다.

• Journal of the Korea Society of Computer and Information
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• v.14 no.6
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• pp.1-10
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• 2009

Flash memory has the advantages of nonvolatile, low power consumption, light weight, and high endurance. This enables the flash memory to be utilized as a storage of mobile computing device such as PMP(Portable Multimedia Player). Potable device with a mass flash memory can store various multimedia data such as video, audio, or image. Typical index systems for mobile computer are inefficient to search a form of text like lyric or title. In this paper, we propose a new text index system, named EMTEX(Embedded Text Index). EMTEX has the following salient features. First, it uses a compression algorithm for embedded system. Second, if a new insert or delete operation is executed on the base table. EMTEX updates the text index immediately. Third, EMTEX considers the characteristics of flash memory to design insert, delete, and rebuild operations on the text index. Finally, EMTEX is executed as an upper layer of DBMS. Therefore, it is independent of the underlying DBMS. We evaluate the performance of EMTEX. The Experiment results show that EMTEX can outperform th conventional index systems such as Oracle Text and FT3.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.32-43
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• 2023

Resistive Random Access Memory (RRAM), based on resistive switching characteristics, is emerging as a next-generation memory device capable of efficiently processing large amounts of data through its fast operation speed, simple device structure, and high-density implementation. Interface type resistive switching offer the advantage of low operation currents without the need for a forming process. Especially, for RRAM devices based on transition metal oxides, various studies are underway to enhance the memory characteristics, including precise material composition control and improving the reliability and stability of the device. In this paper, we introduce various methods, such as doping of heterogeneous elements, formation of multilayer films, chemical composition adjustment, and surface treatment to prevent degradation of interface type resistive switching properties and enhance the device characteristics. Through these approaches, we propose the feasibility of implementing high-efficient next-generation non-volatile memory devices based on improved resistive switching properties.

• Korean Journal of Poultry Science
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• v.50 no.3
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• pp.143-159
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• 2023

The study aimed to evaluate the antioxidative effects of rosemary (Rosmarinus officinalis L.) and clove (Syzgyium aromaticum L.) essential oils on fried Korean native thigh meat, including their impact on processed characteristics and flavor compounds. Clove essential oil showed higher DPPH scavenging activity, FRAP and total phenol content compared to rosemary essential oil (P<0.05). The treatments with the addition of 0.005% and 0.01% rosemary (0.005RB and 0.01RB) and clove (0.005CB and 0.01CB) essential oils to the batter weight compared to control that did not include essential oils in batter. The addition of rosemary and clove essential oils to fried Korean native chicken thigh meat did not significant affect proximate composition, pH, TBARS, sensory characteristics. Except for 0.005CB, treatments adding essential oils decreased cooking loss (P<0.05) and 0.005CB showed significantly higher pick-up value than control. Addition of clove essential oil in fried Korean native chicken thigh meat resulted in higher levels of arachidonic acid compared to control (P<0.05). Volatile organic compounds (VOCs) analysis showed that addition of rosemary essential oil might mask its own VOCs, while clove essential oil addition reduced some pyrazine compounds. Although addition of rosemary and clove essential oil did not have significant sensory characteristics on fried Korean native chicken thigh meat, instrumental analysis revealed changes in the compounds that influenced flavor. Further studies are required to evaluate the stability of flavor and sensory characteristics of fried Korean native chicken thigh meat with added essential oils during storage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.12
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• pp.4997-5006
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• 2010

A flash-memory-based SSDs(Solid State Disks) are one of the best media to support portable and desktop computers' storage devices. Their features include non-volatility, low power consumption, and fast access time for read operations, which are sufficient to present flash memories as major database storage components for desktop and server computers. However, we need to improve traditional storage management schemes based on HDD(Hard Disk Drive) and RAID(Redundant array of independent disks) due to the relatively slow or freezing characteristics of write operations of SSDs, as compared to fast read operations. In order to achieve this goal, we propose a new storage management scheme called Hetero-Mirroring based on traditional HDD mirroring scheme. Hetero-Mirroring-based scheme improves RAID-1 operation performance by balancing write-workloads and delaying write operations to avoid SSD freezing. Our test results show that our scheme significantly reduces the write operation overheads and freezing overheads, and improves the performance of traditional SSD-RAID-1 scheme by 18 percent, and the response time of the scheme by 38 percent.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.1
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• pp.166-174
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• 2010

SSDs are one of the best media to support portable and desktop computers' storage devices. Their features include non-volatility, low power consumption, and fast access time for read operations, which are sufficient to present flash memories as major database storage components for desktop and server computers. However, we need to improve traditional index management schemes based on B-Tree due to the relatively slow characteristics of flash memory operations, as compared to RAM memory. In order to achieve this goal, we propose a new index management scheme based on a compressed hot-cold clustering called CHC-Tree. CHC-Tree-based index management improves index operation performance by dividing index nodes into hot or cold segments and compressing pointers and keys in the index nodes and clustering the hot or cold segments. The offset compression techniques using unused free area in cold index node lead to reduce the number of slow erase operations in index node insert/delete processes. Simulation results show that our scheme significantly reduces the write and erase operation overheads, improving the index search performance of B-Tree by up to 26 percent, and the index update performance by up to 23 percent.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.159-160
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• 2012

지난 30년 동안 플래시 메모리의 주류 역할을 하였던 부유 게이트 플래시 메모리는 40 nm 기술 노드 이하에서 셀간 간섭, 터널 산화막의 누설전류 등에 의한 오동작으로 기술적 한계를 맞게 되었다. 또한 기존의 비휘발성 메모리는 동작 시 높은 전압을 요구하므로 전력소비 측면에서도 취약한 단점이 있다. 그러나 이러한 문제점들을 기존의 Si기반의 소자기술이 아닌 새로운 재료나 공정을 통해서 해결하려는 연구가 최근 활발하게 진행되고 있다. 특히, 플래시 메모리의 중요한 구성요소의 하나인 터널 산화막은 메모리 소자의 크기가 줄어듦에 따라서 SiO2단층 구조로서는 7 nm 이하에서 stress induced leakage current (SILC), 직접 터널링 전류의 증가와 같은 많은 문제점들이 발생한다. 한편, 기존의 부유 게이트 타입의 메모리를 대신할 것으로 기대되는 전하 포획형 메모리는 쓰기/지우기 속도를 향상시킬 수 있으며 소자의 축소화에도 셀간 간섭이 일어나지 않으므로 부유 게이트 플래시 메모리를 대체할 수 있는 기술로 주목받고 있다. 특히, TBM (tunnel barrier engineered memory) 소자는 유전율이 큰 절연막을 적층하여 전계에 대한 터널 산화막의 민감도를 증가시키고, 적층된 물리적 두께의 증가에 의해 메모리의 데이터 유지 특성을 크게 개선시킬 수 있는 기술로 관심이 증가하고 있다. 본 연구에서는 Si3N4/Ta2O5를 적층시킨 staggered구조의 tunnel barrier를 제안하였고, Si기판 위에 tunnel layer로 Si3N4를 Low Pressure Chemical Vapor Deposition (LPCVD) 방법과 Ta2O5를 RF Sputtering 방법으로 각각 3/3 nm 증착한 후 e-beam evaporation을 이용하여 게이트 전극으로 Al을 150 nm 증착하여 MIS- capacitor구조의 메모리 소자를 제작하여 동작 특성을 평가하였다. 또한, Si3N4/Ta2O5 staggered tunnel barrier 형성 후의 후속 열처리에 따른 전기적 특성의 개선효과를 확인하였다.

• Journal of the Korea Society of Computer and Information
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• v.15 no.8
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• pp.23-30
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• 2010

Flash memory is non-volatile and can retain data even after system is powered off. Besides, it has many other features such as fast access speed, low power consumption, attractive shock resistance, small size, and light-weight. As its price decreases and capacity increases, the flash memory is expected to be widely used in consumer electronics, embedded systems, and mobile devices. Flash storage systems generally adopt a software layer, called FTL. In this research, we proposed a new FTL mechanism for overcoming the major drawback of conventional block mapping algorithm. In addition to the block mapping table, a index block mapping table with a small size is used to indicate sector location. The proposed indexed block mapping algorithm by adding a small size. By the simulation result, the proposed FTL provides an enhanced speed than a conventional hybrid mapping algorithm by around 45% in average, and the requirement of mapping memory is also reduced by around 12%.

• The KIPS Transactions:PartD
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• v.14D no.7
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• pp.719-726
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• 2007

Recently, NAND flash memory has been used for a storage device in various mobile computing devices such as MP3 players, mobile phones and laptops because of its shock-resistant, low-power consumption, and none-volatile properties. However, due to the very distinct characteristics of flash memory, disk based systems and applications may result in severe performance degradation when directly adopting them on flash memory storage systems. Especially, when a B-tree is constructed, intensive overwrite operations may be caused by record inserting, deleting, and its reorganizing, This could result in severe performance degradation on NAND flash memory. In this paper, we propose an efficient buffer management scheme, called IBSF, which eliminates redundant index units in the index buffer and then delays the time that the index buffer is filled up. Consequently, IBSF significantly reduces the number of write operations to a flash memory when constructing a B-tree. We also show that IBSF yields a better performance on a flash memory by comparing it to the related technique called BFTL through various experiments.