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研究生: 蔡瑋慈
Tsai, Wei-Tzu
論文名稱: 利用TCAD及Pytorch實現應用於非監督式學習的鐵電材料脈衝式神經元之模型建構及模擬
Modeling and Simulation of Ferroelectric Spiking Neuron for Unsupervised Clustering via TCAD and PyTorch
指導教授: 盧達生
Darsen Lu
學位類別: 碩士
Master
系所名稱: 電機資訊學院 - 微電子工程研究所
Institute of Microelectronics
論文出版年: 2022
畢業學年度: 110
語文別: 英文
論文頁數: 62
中文關鍵詞: 第三代神經網路脈衝式神經網路鐵電電晶體LIF模型記憶體內運算
外文關鍵詞: Third-generation neural networks, spiking neural networks, ferroelectric transistors, LIF models, in-memory computing
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  • 近年來類神經網路的快速發展為人類帶來十分便利的生活,第一代及第二代神經網路在各種不同的領域都大放異彩,例如影像辨識、語音辨識等等。其中第二代神經網路:卷積神經網路(CNN)更是在影像辨識方面取得非常好的成績,但其代價是大量的能量消耗及冗長的運算時間,對於運算核心的要求也相當高,相較於這種高成本的運算方式,第三代神經網路(SNN)因為其更加仿生的特性,能夠以相當低的功耗及運算成本達成訓練神經網路的效果。而傳統的馮紐曼結構式運算將記憶體和運算單元分開,無法應付在訓練神經網路時所需要的大量資料傳輸,作為馮紐曼結構的改進方法,記憶體內運算被提出,他將記憶體和運算單元結合在同一個結構當中,大幅度地改進了運算所需的時間及功耗,很適合運用在類神經網路上。
    在人腦當中,訊息的傳遞是透過神經元(neurons)及連結神經元的突觸(synapses)所達成,在研究仿生之神經網路時,許多不同的神經元模型被提出,其中最為仿生的是Hodgkin-Huxley模型,但因其複雜度及運算成本太高而不常被使用,另一種模型也是 最為廣泛使用的是Leaky Integrate-and-Fire (LIF)模型,相較於Hodgkin-Huxley模型它的複雜度不高且也可以有效達到仿生的效果。
    運用不同的新型元件,例如鐵電材料電晶體、磁阻式記憶體等等,可以模擬LIF的特性並建構出神經元模型,其中鐵電電晶體作為新型材料的電晶體,具有磁滯特性且基於氧化鉿的鐵電電晶體具有很好的微縮性和CMOS兼容性,因此本篇論文是以運用在第三代神經網路的鐵電電晶體神經元模型之建構及模擬為主題,並用TCAD和PyTorch做為模擬工具呈現最後的模擬和訓練結果。

    In recent years, the rapid development of neural networks has brought a convenience life to human beings. The second generation of neural network, convolutional neural networks (CNN), has achieved great results in image recognition but at the cost of large energy consumption and long computation time. Also, the requirements for the computational core to process the CNN are very high. Comparing to the second generation of neural networks, the third generation of neural networks (SNN) is more bionic in nature and can achieve similar effects of training neural networks with lower power and computational cost.
    The traditional Von Neumann architecture, which seperates memory units and computational units, can not cope with the large amount of data transmitting required for training neural networks. As an improvement of the Von Neumann architecture, in-memory computing was proposed, which combines memory and computational units in the same structure, dramatically improves the time and power consumption required for computing and training a neural network. 
    In the human brain, the transmission of information is accomplished through neurons and synapses that connect neurons. In the studies of bionic neural networks, ,any different neuron models have been proposed, among which the most bionic one is the Hodgkin-Huxley model, but it is not often used because of its high complexity and computational cost. Another model and also the most widely used model is the LIF neuron model, which is less complex than Hodgkin-Huxley model and can effectively achieve the bionic effect.
    Using different novel devices, such as ferroelectric transistors, magnetic random access memory, etc., we can simulate the characteristics of LIF and build a model of it. Among the emerging devices, ferroelectric transistors with hysteresis properties and are based on hafnium oxide have good microscopicity and CMOS compatibility. Therefore, this thesis focuses on the construction and simulation of FeFET neuron models for third generation of neural networks, and uses TCAD and Pytorch as simulation tools to present the final simulation and training results.

    摘要 I Abstract II Acknowledgement IV Content V List of Figure VII 1 Chapter 1 Introduction 1 1.1 Research Background 1 1.1.1 In-Memory Computing 1 1.1.2 Third Generation of Neural Networks 2 1.1.3 Emerging NVMs 2 1.2 Research Motivation and Objectives 3 1.2.1 Motivation 3 1.2.2 Research Objective 4 2 Chapter 2 Literature Review 5 2.1 Neural Networks 5 2.1.1 Multi-Layer Perceptron 7 2.1.2 Convolutional Neural Networks 8 2.1.3 Spiking Neural Networks 10 2.2 Spiking Neuron Devices 12 2.2.1 Phase Change Neuron 12 2.2.2 MTJ Neuron 14 2.2.3 SOI-MOSFET Neuron 16 2.2.4 FeFET Neuron 18 2.3 Hardware Synapses for SNN 20 2.3.1 Resistive Random Access Memory 20 2.3.2 Magnetic Random Access Memory 21 2.3.3 Phase Change Memory 22 3 Chapter 3 Methodology 23 3.1 SNN Network Architecture 23 3.1.1 Network Connection and Classification 24 3.1.2 Input Encoding Scheme 25 3.1.3 Leaky Integrate-and-Fire Neuron Model 27 3.1.4 STDP Learning Rule 28 3.2 TCAD Simulation of a FeFET Neuron 30 3.2.1 TCAD Environment Setting 30 3.2.2 FeFET LIF Model 31 3.2.3 Load-line Analysis 37 3.2.4 Operating Principles 38 4 Chapter 4 Results and Discussion 42 4.1 Output Waveforms 42 4.2 SNN Implementation 44 4.2.1 Neuron Parameters 44 4.2.2 Energy Consumption 46 4.2.3 Performance for Rate Coding 47 4.2.4 Performance for Temporal Coding (Rank-order Coding) 49 5 Chapter 5 Conclusions and Future Works 51 5.1 Conclusions 51 5.2 Future Works 52 6 Answer to Thesis Defense Questions 53 7 Reference 58 8 Appendix 62

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