臺灣博碩士論文加值系統

類神經網路運算有望在不久的將來來模擬大腦功能。目前已有相變化記憶體、金屬導電橋記憶體、電阻式記憶體等多種非揮發性記憶體被提出作突觸記憶裝置。綜上所述，電阻式記憶體被視為最有潛力的，因為其具備各項優點，低功耗、結構簡單、高操作速度……等優點。但是突觸元件的理想特性不同於傳統的電阻式記憶體。它需要類比電阻切換和多層次的電導態，這有利於深度學習的準確性。
在本文中，使用氧化鈦基電阻式記憶體來探討電阻轉換特性和突觸可塑性。實驗探討分成三個部分，第一部分，利用在TiN/Ti/TiOx/TiN結構中沉積了不同厚度的氧化鈦膜來探討厚度和電性之間的關係，氧化鈦的厚度決定了元件的操作電流，越厚的氧化鈦元件可以操作在比較低的限電流，而且所形成的導電絲較小。此外，研究不同脈衝振幅對突觸元件可塑性的影響，振幅越小元件電導變化越緩和、線性度越好但同時dynamic range 變小、noise增加。第二部分是沉積不同厚度的鈦在氧化鈦基電阻式記憶體上來比較電性特性和突觸可塑性。加了一層鈦在元件上，可以使元件從數位電阻切換變成類比電阻切換，而不同厚度的鈦會產生不同厚度的介面層在氧化鈦基電阻式記憶體上，導致元件形成和破壞導電絲的能力不同，所以呈現不同電性和電導變化。最後一部分是比較突觸元件上有無氧化鋯熱增強層的差異。突觸元件上加上一層氧化鋯熱增強層，類比電阻切換可以更穩定，且增強和抑制的非線性度可被改善到2.08和1.84。此外，它具有良好的資料保存性，在室溫環境下阻態可以維持104秒不變化。它表現出良好的性能，不僅適用於數據儲存應用，還適用於模擬生物突觸。

Neuromorphic computing is expected to emulate brain functions in the near future. There are several nonvolatile memory such as PCRAM, CBRAM, RRAM have been proposed as synaptic memory device. All of above, RRAM is the most promising candidate, due to its several advantages, low power consumption, simple structure, excellent endurance, high operation speed. However, the desirable characteristic of synaptic device is different from traditional RRAM. It requires analog switching behavior and multi-level conductance states, which are beneficial to learning accuracy.
In this thesis, the bipolar resistive switching behavior and synaptic characteristics are investigated in TiOx-based synaptic memory device. There are three parts in this thesis. First, different thickness TiOx film are deposited in TiN/Ti/TiOx/TiN structure. The relationship between thickness and electrical characteristics is discussed. The thickness of the TiOx switching layer determine the working operation current of the devices. The thicker layer device can work at lower compliance current and make smaller conductive filament. In addition, the influence of different pulse amplitudes applied on potentiation and depression is investigated. When lower pulse amplitude was applied on the device, conductance can gradually change and the nonlinearity is better. However, dynamic range become small and noise increase. The second part is that different Ti thickness effect on TiOx-based synaptic device. We compare their electrical characteristics and synaptic characteristics. We observed that the analog behavior can be improved after inserting a thin Ti layer. Different thickness of Ti layer make different thickness of interfacial layer, which leads the TiOx- based memory device has different capability to form and rupture the filament. As a result, they perform different electrical characteristics and weight update behavior. The other part is that comparing ZrOx/TiOx synaptic device and TiOx synaptic device. The ZrOx/TiOx synaptic device shows more stable analog switching and the nonlinearity of potentiation and depression can be improved to 2.08 and 1.84. Furthermore, it exhibits good endurance and data retention properties.It demonstrates good performance not only for data storage application but also for mimicking biological synapse.

Abstract iii
Acknowledgement v
目錄 vi
Figure captions ix
Table caption xiii
Chapter 1 Introduction 1
1.1 Introduction of Random Access Memory 1
1.2 Volatile memory 1
1.2.1 DRAM 1
1.2.2 SRAM 2
1.3 Nonvolatile Memory 2
1.3.1 Flash memory 3
1.3.2 FeRAM 4
1.3.3 PCRAM 4
1.3.4 MRAM 5
1.3.5 RRAM 5
1.4 Neuromorphic systems and Memristor synapses 6
1.4.1 Neuromorphic systems 6
1.4.2 Memristor synapses 6
Chapter 2 Resistive Random Access Memory and Analog Memristive Synapse 14
2.1 Electric Characteristics in RRAM 14
2.2 Resistive Switching Mechanism 15
2.3 Characteristic of synaptic device 17
2.3.1 Nonlinearity in weight update 17
2.3.2 Multilevel states 17
2.3.3 Dynamic range 18
2.3.4 Device variation 18
Chapter 3 Experimental Details 23
3.1 Experiment process flow 23
3.2 Substrate Preparation 23
3.3 Sample fabrication 23
3.3.1 Fabrication of different TiOx thickness in TiN/Ti/TiOx/TiN synaptic device 24
3.3.2 Fabrication of different Ti thickness in TiN/Ti/TiOx/TiN synaptic device 24
3.3.3 Fabrication of TiN/Ti/ZrOx/TiOx/TiN synaptic device 25
3.4 Electrical analysis 25
3.5 Analyze synaptic device characteristic 26
Chapter 4 Bipolar switching behavior in TiOx-based synaptic memory device 31
4.1 Motivation 31
4.2 TiOx thickness effect on TiN/Ti/TiOx/TiN synaptic device 31
4.2.1 Electrical characteristic in synaptic device 32
4.2.2 Synaptic device characteristic analysis 33
4.3 Ti thickness effect on TiN/Ti/TiOx/TiN synaptic device 35
4.3.1 Electrical characteristic in synaptic device 35
4.3.2 Synaptic device characteristic analysis 37
4.4 ZrOx effect on TiN/Ti/ZrOx/TiOx/TiN synaptic device 38
4.4.1 Electrical characteristic in synaptic device 39
4.4.2 Synaptic device characteristic analysis 39
4.4.3 Discussion 40
4.4.4 TiN/Ti/ZrOx/TiOx/TiN synaptic device 40
4.5 Supplementary data 41
Chapter 5 Conclusion 52
References 54

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