유연 소자 적용을 위한 단극성 비휘발 메모리의 저항변화 스위칭 동작 연구

학위논문 (박사) -- 서울대학교 대학원 : 자연과학대학 물리학과, 2021. 2. 이탁희.오늘날 트랜지스터 및 메모리 소자와 같은 전자 소자를 유연, 또는 투명하거나 신축성이 있도록 제작하는 시도가 늘어나고 있다. 하지만, 전자 소자에 가장 많이 사용되는 기판인 실리콘은 이러한 특성이 거의 없다. 실리콘 기판의 한계를 극복하기 위해 휘어지는 기판과 휘어지는 반도체 물질을 탐색하는 연구가 진행되고 있다. 플라스틱 필름, 섬유 종이 또는 테이프와 같은 많은 종류의 기판이 휘어지는 전자 소자를 제작하기 위해 기판으로 사용되고 있다. 이 중 테이프는 유연성, 부착성 및 저렴한 가격 등 기판으로 활용되기에 좋은 특성을 가지고 있다. 한편, 유기물은 유연성이 우수하여 휘어지는 전자 소자의 활물질로 사용되고 있다. 유기 저항변화 메모리는 유기 재료의 다양성, 저렴한 소자 제조 비용, 인쇄 가능성 등과 같은 여러 장점을 갖는 유망한 데이터 저장 기술이다. 그러나 유기 저항변화 메모리 소자에서 저항 스위칭 현상의 메커니즘은 명확하게 이해되지 않았다는 문제점이 있다. 먼저, 휘어지는 메모리 소자를 만들기 위해 시판되는 테이프를 기판으로 사용하여 메모리를 제작하였다. 휘어지는 기판인 테이프 위에 8 X 8 어레이의 비휘발성 저항변화 메모리 소자를 제작했다. 메모리 소자 구조는 Au/AlOx/Au/AlOx/Al/tape 이다. 제조 공정은 저온, 건식 공정을 활용하여 테이프 기판의 손상 없이 메모리 소자를 제작할 수 있었다. 제작된 메모리 소자는 전형적인 단극성 비휘발 저항변화 메모리 특성을 나타냈다. 메모리 소자는 ~3.5 V에서 ON 상태로 바뀌고 5 V 후에 음의 기울기 영역을 나타내며, ~10 V에서 OFF 상태로 바뀌었다. 메모리 소자는 높은 ON/OFF 비율, 우수한 재현성, 우수한 안정성, 그리고 높은 수율을 나타냈다. 특히 ON/OFF 비율은 ~10^4으로 높았으며 장치는 200 번 이상의 읽기/쓰기 동작을 견뎌냈다. 소자의 데이터 유지 시간은 ~10^4 초 이상이었다. 수율은 ~68 %로 나타났으며, 이 메모리 소자는 극도로 휘어진 상태에서도 안정적인 전기적 특성을 보여주었다. 휘어지는 저항변화 메모리 소자를 제작하였으나, 뚜렷한 단극 저항변화 메모리의 작동원리는 밝혀지지 않은 상황이었다. 이에 단극 저항변화 메모리의 작동원리를 조사하기 위해 메커니즘 탐구에 적합한 새로운 단극 저항변화 메모리를 제작하였다. 메모리 소자에 일정한 전압 스트레스를 메모리 소자에 인가하였고, 시간에 따른 전류 동작을 조사하였다. 이 측정에서 가해진 스트레스 전압은 ON 상태로 만들기 위한 알려진 문턱 전압보다 낮음에도 불구하고 전류는 급격하게 증가하였고 결국 메모리 소자는 ON 상태에 도달했다. 낮은 전압 스트레스 하에서 ON 상태에 도달하는 데 필요한 시간의 분포는 Weibull 분포로 설명할 수 있었다. 켜지는 데 걸리는 시간에 대한 통계 분석을 통해 전류의 급격한 증가가 일정한 확률 법칙을 따르는 것을 발견하였다. 시간이 지남에 따라 전류가 증가할 확률은 동일한 전압 스트레스 하에서 OFF 상태와 모든 중간 저항 상태에서 일정하게 나타났다. 스트레스 전압이 증가함에 따라 전류가 증가할 확률은 기하 급수적으로 상승했다. 이러한 통계적 분석을 통해 메모리가 켜지는 과정은 활물질 내부에 전류가 잘 통하는 percolation network 통로가 확률적으로 형성되며 저항값이 낮아진다고 추정하였다. 박사학위 과정 동안의 연구에서 단극 저항변화 메모리를 활용하여 휘어지는 메모리 소자를 제작하였고, 단극 저항변화 메모리 소자의 작동원리에 대하여 탐구하였다. 본 연구를 통하여 단극 저항변화 메모리 소자의 작동원리의 많은 부분을 이해할 수 있었으며, 메모리 소자의 효율적으로 활용하기 위한 작동 방식을 제시하였다. 또한, 이 연구는 앞으로 더 향상된 단극 저항변화 메모리를 제작할 수 있도록 돕는 발판을 제공하였다.Nowadays, electronic devices such as transistors and memory devices have become flexible, transparent, or stretchable. Si which has been the most commonly used substrate for electronic devices barely has these properties. To overcome the limitation of Si for flexible electronic devices, researchers have been looking for flexible substrates and flexible active materials. Many kinds of substrates such as plastic films, fiber papers, or tapes have been used for flexible application. Among these, the scotch tape can be a good flexible substrate with good flexibility, attach-ability, and low price On the other hand, organic materials have also been used as active materials of flexible electronic devices because of their good flexibility. Organic resistive memory is one of the promising data storage technologies due to several advantages such as versatility of organic materials, low-cost device fabrication, and application on printable and flexible devices. However, the mechanism of the resistive switching phenomenon in organic resistive memory devices has not been clearly understood In this regard, first, I have fabricated 8 X 8 arrays of non-volatile resistive memory devices on a commercially available tape as the flexible substrate. The memory device structure was Au/AlOx/Au/AlOx/Al/tape. The fabrication process to make memory devices was dry and did not require a high-temperature process. Therefore, the tape substrate did not suffer from any damage during the fabrication. The fabricated memory devices showed typical unipolar non-volatile resistive memory property. The memory devices were turned to ON-state at ~3.5 V and turned to OFF state at ~10 V, showing a negative differential region after ~5 V. The memory devices exhibited a high ON/OFF ratio, good reproducibility, good stability, and high yield. Specifically, the ON/OFF ratio was high as ~10^4, and the devices endured over 200 cycles of reading/writing process. The retention time of the devices was longer than ~10^4 s. I observed that ~68 % of the total fabricated memory cells were well-operated. More importantly, the devices showed stable electrical properties under various bending conditions. Although flexible memory devices were fabricated, the operating mechanism of the unipolar resistive memory device was still not clear. I investigated the time-dependent current behavior of unipolar-type memory devices under constant voltage stress. In this measurement, the current abruptly increased several times and reached ON state even when the applied stress voltage was below the turn-on voltage which was obtained from voltage sweeping. The distribution of the time required to reach ON state (denoted as turn-on time) could be described with Weibull distribution which has often been used for time-dependent gate dielectric breakdown in semiconductor transistors. Through statistical analysis of the turn-on times, I found that the abrupt increase of current followed a specific probability law. The probability of current increase over time was found to be constant in the OFF state and in all intermediate resistance states under the same voltage stress. The probability exponentially increased as the stress voltage bias increased. Through the statistical analysis, I estimated that the process of turning on the memory is probabilistically forming a conducting percolation network through which the current passes through the active layer. During my thesis study, I fabricated flexible memory devices using unipolar resistive memory and investigated the switching mechanism of unipolar resistive memory devices. This research has led to understanding a large part of the switching mechanism of unipolar resistive memory devices and suggested operating methods for efficient use of the memory devices. Furthermore, this research may provide a foothold to manufacture more improved unipolar resistive memory devices in the future.Abstract i List of Contents iii List of Figures vi Chapter 1. Introduction 1 Chapter 2. Electrical Properties of MoS2 FETs Influenced by Environment 5 2.1. Introduction 5 2.2. Experiments 7 2.3. Results and discussions 10 2.4. Conclusion 19 References 21 Chapter 3. Investigation of Time-Dependent Resistive Switching Behaviors of Unipolar Non-Volatile Organic Memory Devices 23 3.1. Introduction 23 3.2. Results and discussions 25 3.3. Experiments 56 3.4. Conclusion 58 References 59 Chapter 4. Controllable deposition of organic metal halide perovskite films with wafer-scale uniformity by single source flash evaporation 62 4.1. Introduction 62 4.2. Results and discussions 65 4.3. Experiments 76 4.4. Conclusion 77 References 79 Chapter 5. Tailored Design-of-Experiments Approach for Optimization of Flash-Evaporated Organic Inorganic Halide Perovskite-based 83 5.1. Introduction 83 5.2. Results and discussions 86 5.3. Experiments 100 5.4. Conclusion 102 References 104 Chapter 6. Summary 108 국문초록(Abstract in Korean) 110Docto

Dynamic Data Encoding for Page-Oriented Memories

This dissertation presents a key portion of the system architecture for a high performance page-oriented memory. The focus of this research is the development of new dynamic encoding algorithms that provide high data reliability with code density that is higher than in the conventional static modulation schemes. It also presents an intelligent read/write head architecture capable of implementing the most promising of these algorithms in real-time.Data encoding techniques for page-oriented mass storage devices are typically conservative in order to overcome the destructive effects of inter-symbol interference and noise due to the physical characteristics of the media. Therefore significantly more bits are required in an encoded version of data than in the original information. This penalty in the code density, usually referred to as code rate, keeps the utilization of the media relatively low, often less than 50% of the capacity of a maximally dense code. This is partially because encoding techniques are static and assume the worst case for the information surrounding the data block being encoded. However, in the context of page-oriented data transfers it is possible to evaluate the surrounding information for each code block location, and, thus, to apply a custom code set for each code block. Since evaluating each possible code during runtime leads to very high time complexity for encoding and decoding algorithms, we also present alternative algorithms that successfully trade time complexity for code density and are a strong competition to the traditional static modulation schemes. In order to verify that the encoding algorithms are both efficient and applicable, they were analyzed using a two-photon optical memory model. The analysis focused on how well the algorithms performed as a trade off between complexity and code density. It resulted that a full enumeration of codes yielded code density as high as 83%, although the time complexity for the enumeration approach was exponential. In another study, a linear time algorithm was analyzed. The code density of this algorithm was just over 54% percent. Finally, a novel quasidynamic encoding algorithm was created, which yielded 76% code density and had constant time complexity

Roadmap on holography

From its inception holography has proven an extremely productive and attractive area of research. While specific technical applications give rise to 'hot topics', and three-dimensional (3D) visualisation comes in and out of fashion, the core principals involved continue to lead to exciting innovations in a wide range of areas. We humbly submit that it is impossible, in any journal document of this type, to fully reflect current and potential activity; however, our valiant contributors have produced a series of documents that go no small way to neatly capture progress across a wide range of core activities. As editors we have attempted to spread our net wide in order to illustrate the breadth of international activity. In relation to this we believe we have been at least partially successful.This work was supported by Ministerio de Economía, Industria y Competitividad (Spain) under projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and FIS2015-66570-P (MINECO/FEDER), and by Generalitat Valenciana (Spain) under project PROMETEO II/2015/015

Organická paměť v embryonálním vývoji

Předložená disertační práce se zabývá tématem organické paměti, její definicí a funkcí, a stejně tak i jejími pojetími z různých historických hledisek. Užívám pojem "organické paměti" ve vztahu k autorům, kteří se tímto tématem již dříve zabývali (Elsasser 1987, Otis 1994, Barbieri 2003) a dále i jako pojem, který představuje paměť jinou než neuronovou/mozkovou. Obecné metafory paměti (v tomto případě paměti neuronové) jsou zásadně spojeny s pojmy jako úložiště, matice či místo. Pro spíše materialisticky založená pojetí paměti je navíc příznačné, že různé stavy jako emoce či vlastnosti mysli mohou být konkrétně lokalizovány v mozku. Na druhou stranu někteří filosofové popisovali paměť jako primárně časovou entitu bez konkrétní závislosti na hmotě či místě. Otázka organické paměti byla živá již v biologii 19. století, spojena především s filosofií lamarkismu (Hering 1870, Haeckel 1876, Butler 1910). Představy o organické paměti se v té době pohybovaly mezi vitalistickými a spíše materialistickými koncepcemi: v těch prvních byly buňkám či částečkám paměti přisuzovány psychologické atributy; ty druhé byly založeny na fyzikální či karteziánské doktríně a popisovaly paměť jako lokalizovatelné úložiště stop či fyzikálních vln. Nejdeterminističtější koncepce paměti jsou zakořeněny v metafoře počítače, i...The submitted thesis deals with the topic of organic memory, its definition and function, as well as its conceptions from various historical points of view. I use the term "organic memory" in respect to some authors who have previously dealt with this subject (Elsasser 1987, Otis 1994, Barbieri 2003) and also as a term by which to represent a kind of memory distinct from neuronal/cerebral memory. The general memory metaphors (in the case of neuronal memory) are essentially connected with terms such as storage, matrix, or place. For rather materialistic conception of memory, it is also symptomatic that different states such as emotions or mental faculties can be concretely localized in the brain tissue. On the contrary, some philosophers described memory as a primarily temporal entity without connection to place or matter. The question of organic memory was already vivid in 19th century biology, linked to Lamarckian philosophy (Hering 1870, Haeckel 1876, Butler 1910). The organic memory ideas floundered between vitalistic and rather materialistic conceptions: the first attributed some psychological features to cells or memory particles; the second was based on physics or in Cartesian doctrine, and described memory as essentially localized as a kind of storage of traces or patterns of physical waves....Katedra filosofie a dějin přírodních vědDepartment of Philosophy and History of SciencePřírodovědecká fakultaFaculty of Scienc

Goddard Conference on Mass Storage Systems and Technologies, volume 2

Papers and viewgraphs from the conference are presented. Discussion topics include the IEEE Mass Storage System Reference Model, data archiving standards, high-performance storage devices, magnetic and magneto-optic storage systems, magnetic and optical recording technologies, high-performance helical scan recording systems, and low end helical scan tape drives. Additional discussion topics addressed the evolution of the identifiable unit for processing (file, granule, data set, or some similar object) as data ingestion rates increase dramatically, and the present state of the art in mass storage technology

REAL TIME MICROPROCESSOR TECHNIQUES FOR A DIGITAL MULTITRACK TAPE RECORDER

Transport properties of a standard compact - cassette tape system are measured and software techniques devised to configure a low - cost,direct digital recording system. Tape - velocity variation is typically ± 10% of standard speed over tape lengths of 5 µm.with occasional variations of ±40%. Static tape - skew can result due to axial movement of the tape reel when it spools.Dynamic tape skew occurs and is primarily caused by tape - edge curvature with a constant contribution due to the transport mechanism.Spectral skew components range from 0.32 Hz to 8 Hz with magnitude normally within one 10 kbit/ sec- bit cell.The pinch roller works against the friction of the tape guides to cause tape deformation.Average values of tape deformation are 0.67 µm,0.85 µm and 1.08 µm for C60,C90 and C120 tape respectively. Parallel,software encoding / decoding algorithms have been developed for several channel codes.Adaptive software methods permit track data rates up to 3.33 k bits/sec in a rnultitrack system using a simple microcomputer.For a 4 - track system,raw error rates vary from 10ˉ⁷ at 500 bits/sec/track to 10ˉ⁵ at 3.33 kbits/sec/track.Adaptive software reduces skew - induced errors by 50%.A skew - correction technique has been developed and implemented on an 8 - track system at a track data rate of 10 k bits/sec. Real - time error correction gives a theoretical corrected error rate of 10ˉ¹¹for a raw error rate of 10ˉ⁷. Multiple track errors can cause mis - correction and interleaving is advised. Software algorithms have been devised for Reed - Solomon code. With a more powerful microprocessor this code m ay be combined with the above techniques in a layered error-correction scheme. The software techniques developed may be applied to N tracks with an N - bit computer.Recording density may be increased by using thin - film,multitrack heads and a faster computer.British Broadcasting Corporatio

Towards Successful Application of Phase Change Memories: Addressing Challenges from Write Operations

The emerging Phase Change Memory (PCM) technology is drawing increasing attention due to its advantages in non-volatility, byte-addressability and scalability. It is regarded as a promising candidate for future main memory. However, PCM's write operation has some limitations that pose challenges to its application in memory. The disadvantages include long write latency, high write power and limited write endurance. In this thesis, I present my effort towards successful application of PCM memory. My research consists of several optimizing techniques at both the circuit and architecture level. First, at the circuit level, I propose Differential Write to remove unnecessary bit changes in PCM writes. This is not only beneficial to endurance but also to the energy and latency of writes. Second, I propose two memory scheduling enhancements (AWP and RAWP) for a non-blocking bank design. My memory scheduling enhancements can exploit intra-bank parallelism provided by non-blocking bank design, and achieve significant throughput improvement. Third, I propose Bit Level Power Budgeting (BPB), a fine-grained power budgeting technique that leverages the information from Differential Write to achieve even higher memory throughput under the same power budget. Fourth, I propose techniques to improve the QoS tuning ability of high-priority applications when running on PCM memory. In summary, the techniques I propose effectively address the challenges of PCM's write operations. In addition, I present the experimental infrastructure in this work and my visions of potential future research topics, which could be helpful to other researchers in the area