머신 러닝 기반의 낸드 플래시 칩 eFuse 구성 생성 자동화 방법론

학위논문(석사)--서울대학교 대학원 :공과대학 컴퓨터공학부,2019. 8. 유승주.Post fabrication process is becoming more and more important as memory technology becomes complex, in the bid to satisfy target performance and yield across diverse business domains, such as servers, PCs, automotive, mobiles, and embedded devices, etc. Electronic fuse adjustment (eFuse optimization and trimming) is a traditional method used in the post fabrication processing of memory chips. Engineers adjust eFuse to compensate for wafer inter-chip variations or guarantee the operating characteristics, such as reliability, latency, power consumption, and I/O bandwidth. These require highly skilled expert engineers and yet take significant time. This paper proposes a novel machine learning-based method of automatic eFuse configuration to meet the target NAND flash operating characteristics. The proposed techniques can maximally reduce the expert engineers workload. The techniques consist of two steps: initial eFuse generation and eFuse optimization. In the first step, we apply the variational autoencoder (VAE) method to generate an initial eFuse configuration that will probably satisfy the target characteristics. In the second step, we apply the genetic algorithm (GA), which attempts to improve the initial eFuse configuration and finally achieve the target operating characteristics. We evaluate the proposed techniques with Samsung 64-Stacked vertical NAND (VNAND) in mass production. The automatic eFuse configuration takes only two days to complete the implementation.메모리 공정 기술이 발전하고 비즈니스 시장이 다양해 짐에 따라 웨이퍼 수율을 높이고 비즈니스 특성 목표를 만족하기 위한 후 공정 과정이 매우 중요해 지고 있다. 전기적 퓨즈 조절 방식(이-퓨즈 최적화 및 트림)은 메모리 칩 후 공정 과정에서 사용되는 전통적인 방식이다. 엔지니어는 이-퓨즈 조절을 통해 웨이퍼 상의 칩들 간의 초기 특성의 변화를 보상하거나, 신뢰성, 레이턴시, 파워 소모, 그리고 I/O 대역폭 등의 칩 목표 특성을 보장한다. 이-퓨즈 조절 업무는 다수의 숙련된 엔지니어가 필요하고 또한 상당히 많은 시간을 소모한다. 본 논문에서는 낸드 플래시 칩의 동작 특성 목표를 얻기 위한 기계 학습 기반의 이-퓨즈 자동 생성 기술을 제안하고, 해당 기술은 엔지니어의 작업시간을 획기적으로 단축시킬 수 있다. 논문의 기술은 두 단계로 구성 된다. 첫 번째 단계에서는 variational autoencoder (VAE) 기술을 적용하여 목표하는 동작 특성을 만족시키는 초기 이-퓨즈 구성을 생성한다. 두 번째 단계에서는 유전 알고리즘을 적용하여 초기 생성된 이-퓨즈 구성에 대하여 목표하는 성능 특성과의 정합성을 추가로 개선하여 최종적으로 목표하는 성능 특성을 얻는다. 논문의 평가는 실제 양산중인 삼성 64단 브이낸드 제품을 이용하여 진행하였다. 논문의 이-퓨즈 자동화 생성 기술은 2일 이내의 구현 시간만이 소요된다.Contents I. Introduction..........................................................................1 II. Background..........................................................................4 2.1. NAND Flash Block Architecture..................................................4 2.2. NAND Cell Vth Distribution........................................................5 2.3. eFuse Operation of NAND Flash Chip.......................................6 III. Basic Idea and Background...............................................7 3.1. Basic Idea.......................................................................................7 3.2. Background: Variational Autoencoder........................................10 IV. Initial eFuse Generation: VAE-Based Dual Network....14 V. eFuse Optimization: Genetic Algorithm..........................17 VI. Experimental Results.........................................................21 6.1. Experimental Setup......................................................................21 6.2. Initial eFuse Generation Results................................................23 6.3. eFuse Optimization Results........................................................26 6.4. Discussion.....................................................................................29 VII. Related Work..................................................................31 VIII. Conclusion.......................................................................33Maste

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Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a 'snapshot' introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation

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