臺灣博碩士論文加值系統

隨著科技的進步，造成大數據的產生，為了分析大數據的資訊並且進行儲存，便需要有新的運算架構，為了解決傳統運算架構所帶來的問題，便有了類神經計算的架構提出，而此架構便是受到生物大腦的啟發，生物大腦可以以較低的能耗，便可以進行運算以及記憶的存儲。而在眾多非揮發記憶體中，氧化物電阻式記憶體有著低能耗、低操作電壓、快速的操作速度、相容於互補式金屬氧化物半導體製程中，使得其在模擬類神經運算上能成為熱門的候選者。
本文將探討基於氧化鉭的透明突觸氧化物電阻式記憶體的電阻轉換特性和電導的線性度，並加以優化其特性。我們先探討了加入氧化鈦對氧化鉭電阻式記憶體的電阻轉換特性以及其耐久性，之後藉由調整氧化鉭和氧化鈦的厚度來得到最佳的電阻轉換特性以及耐久性。接著我們運用400oC氮環境退火氧化鉭和氧化鈦層，來改善其穩定性，便將其作為最終元件進行後續的突觸特性的量測，我們可以得到良好的線性度和多態轉換特性。在實驗中所量測的突觸性可以得到非線性度各為1.8和1.45的增強以及抑制的特性，並且元件可以多達1000次增強和抑制的循環操作，總共有468800個脈衝。另外，也可以實現神經可塑性中的脈衝時序依賴可塑性。並且我們也運用了藍光進行光特性上的量測，並且實現了運用光電流來模擬突觸的性質。最後，我們運用電流傳導機制和量測材料的性質，來分析電阻轉換的機制以及導電絲的模型。因此，我們認為經過退火的ITO/TiOx (5 nm)/TaOx (10 nm)/ITO元件可以展現良好的電特性，在類神經特性上也有著良好的表現，因此適合作為類神經運算的元件。

With the advancement of technology, the generation of big data requires new computing architectures for information analysis and storage. To address the problems of traditional computing architectures, the neural computing architecture was proposed, inspired by the biological brain's ability to perform computation and memory storage with low energy consumption. Among various non-volatile memories, OxRAM is a popular candidate for simulating neural computing due to its low energy consumption, low operating voltage, fast operating speed, and compatibility with complementary metal-oxide-semiconductor processes.
In this thesis, we explored the resistance switching characteristics and linearity of the conductivity of transparent tantalum oxide-based OxRAM synaptic device and optimizes their properties. We first investigated the effect of adding titanium oxide on the resistive switching characteristics and durability of tantalum oxide-based resistive memories, and then adjust the thicknesses of tantalum oxide and titanium oxide to obtain optimal resistance switching characteristics and durability. Then, we use 400°C nitrogen ambient to anneal the tantalum oxide and titanium oxide layers to further improve their stability and use the resulting devices as final components for subsequent synaptic property measurements. We obtain good linearity and resistive switching characteristics. In the experiments, the measured synaptic properties exhibit potentiation and depression characteristics with the nonlinearity of 1.8 and 1.45, respectively, and the devices can perform up to 1000 cycles of potentiation and depression operations with a total of 468800 pulses. Additionally, we can achieve synaptic plasticity of pulse-timing-dependent plasticity. We also use blue light to measure the optical properties and simulate synaptic properties using photocurrent. Finally, we analyze the resistive switching mechanism and the model of conductive filaments by using the current conduction mechanism and material property measurement. Therefore, we believe that annealed ITO/TiOx (5 nm)/TaOx (10 nm)/ITO devices exhibit good electrical properties and perform well in synaptic characteristics, making them suitable as components for neural computing.

摘要 i
Abstract iii
Acknowledgement v
Contents vi
Table captions ix
Figure captions x
Chapter 1 Introduction 1
1.1 The Evolution of Computing System 1
1.2 Neuromorphic System 1
1.3 Biologically Inspired Synaptic Device 2
1.3.1 Conductive Bridge Access Memory 2
1.3.2 Oxide Random Access Memory 3
1.4 Transparent RRAM 3
1.5 Motivation 3
Chapter 2 Overview of Synaptic OxRAM 10
2.1 Electrical Operation in OxRAM 10
2.1.1 Forming Process 10
2.1.2 Set Process and Reset Process 10
2.2 Conduction Mechanism 11
2.2.1 Schottky Emission 11
2.2.2 Fowler-Nordheim Tunneling & Direct Tunneling 12
2.2.3 Poole-Frenkel Emission 13
2.2.4 Hopping Emission 13
2.2.5 Ohmic Conduction 14
2.3 Electrical Characteristic in Synaptic RRAM 14
2.3.1 Operation of Potentiation and Depression 14
2.3.2 Multilevel State 15
2.3.3 Spike-Timing-Dependent Plasticity (STDP) 16
2.3.4 Paired-Pulse Facilitation (PPF) 16
Chapter 3 Experimental Details 25
3.1 Experimental Process 25
3.2 Sample Fabrication 25
3.2.1 Substrate Cleaning 25
3.2.2 Fabrication of ITO/TiOx/TaOx/ITO Device 25
3.2.3 Fabrication of ITO/TiOx/TaOx/ITO Device with Annealing 26
3.3 Electrical Measurement 26
3.3.1 DC Current-Voltage Measurement 27
3.3.2 Endurance Test Measurement 27
3.3.3 Retention Time Measurement 27
3.3.4 AC Electrical-Induced Resistance Switching Measurement 28
3.3.4.1 Linear Conductance Change 28
3.3.4.2 Spike-Timing-Dependent Plasticity Test 29
3.4 Optical Measurement 29
Chapter 4 Results and Discussion 33
4.1 Electrical Properties of ITO/TiOx/TaOx/ITO with Different Thickness of TiOx Layer 33
4.2 Electrical Properties of ITO/TiOx/TaOx/ITO with Different Thickness of TaOx Layer 34
4.3 Effect of ITO/TiOx/TaOx/ITO with Annealing 35
4.3.1 DC I-V Property and Endurance Characteristic for the Device with Annealing 35
4.3.2 Electrical Analysis 35
4.3.3 Comparison of the ITO/TiOx/TaOx/ITO Device with and without Annealing in Hopfield Simulation 38
4.3.4 Analysis of Conduction Mechanism 38
4.3.5 Multilevel Characteristic 40
4.3.6 Retention 40
4.3.7 STDP Performance 40
4.3.8 Current Change for the device Illuminated by Laser Light 41
4.3.8.1 The Mechanism for Optical Measurement 42
4.3.9 Material Analysis 43
4.3.9.1 TEM & EDS Mapping Results 43
4.3.9.2 XPS Analysis 43
4.3.9.3 Resistive Switching Model for Electrical Measurement 44
4.3.9.4 XRD Analysis 45
4.3.9.5 AFM Analysis 45
4.3.9.6 Optical Property of the ITO/TiOx/TaOx/ITO with Annealing 45
4.3.9.7 The Analysis for the Dielectric Layer with the Absorbance Results 46
Chapter 5 Conclusions 72
Chapter 6 Future Work 73
References 74

[1] Philip Chen, C. L.; Zhang, C.-Y., Data-intensive applications, challenges, techniques and technologies: A survey on Big Data. Information Sciences 2014, 275, 314-347.
[2] Indiveri, G.; Liu, S. C., Memory and Information Processing in Neuromorphic Systems. Proceedings of the IEEE 2015, 103 (8), 1379-1397.
[3] Hong, X.; Loy, D. J.; Dananjaya, P. A.; Tan, F.; Ng, C.; Lew, W., Oxide-based RRAM materials for neuromorphic computing. Journal of Materials Science 2018, 53 (12), 8720-8746.
[4] Kuzum, D.; Yu, S.; Philip Wong, H. S., Synaptic electronics: materials, devices and applications. Nanotechnology 2013, 24 (38), 382001.
[5] Ohno, T.; Hasegawa, T.; Tsuruoka, T.; Terabe, K.; Gimzewski, J. K.; Aono, M., Short-term plasticity and long-term potentiation mimicked in single inorganic synapses. Nat Mater 2011, 10 (8), 591-5
[6] Bousoulas, P.; Kitsios, S.; Chatzinikolaou, T. P.; Fyrigos, I.-A.; Ntinas, V.; Tsompanas, M.-A.; Sirakoulis, G. C.; Tsoukalas, D., Material design strategies for emulating neuromorphic functionalities with resistive switching memories. Japanese Journal of Applied Physics 2022, 61 (SM), SM0806.
[7] Chang, T.-C.; Chang, K.-C.; Tsai, T.-M.; Chu, T.-J.; Sze, S. M., Resistance random access memory. Materials Today 2016, 19 (5), 254-264
[8] Garbin, D. In A variability study of PCM and OxRAM technologies for use as synapses in neuromorphic systems, 2015
[9] Russo, U.; Ielmini, D.; Cagli, C.; Lacaita, A. L., Filament Conduction and Reset Mechanism in NiO-Based Resistive-Switching Memory (RRAM) Devices. Ieee Transactions on Electron Devices 2009, 56 (2), 186-192.
[10] Chen, X.; Feng, J.; Ma, H. In The resistive switching characteristics in tantalum oxide-based RRAM device via combining high-temperature sputtering with plasma oxidation, 2015 15th Non-Volatile Memory Technology Symposium (NVMTS), 12-14 Oct. 2015; 2015; pp 1-5.
[11] Swathi, S. P.; Angappane, S., Low power multilevel resistive switching in titanium oxide-based RRAM devices by interface engineering. Journal of Science: Advanced Materials and Devices 2021, 6 (4), 601-610.
[12] Predanocy, M.; Hotový, I.; Čaplovičová, M., Structural, optical and electrical properties of sputtered NiO thin films for gas detection. Applied Surface Science 2017, 395, 208-213.
[13] Hitosugi, T.; Yamada, N.; Nakao, S.; Hirose, Y.; Hasegawa, T., Properties of TiO2-based transparent conducting oxides. Physica Status Solidi a-Applications and Materials Science 2010, 207 (7), 1529-1537.
[14] Braune, B.; Muller, P.; Schmidt, H. In Tantalum oxide nanomers for optical applications, Conference on Organic-Inorganic Hybrid Materials for Photonics, San Diego, Ca, Jul 19-20; San Diego, Ca, 1998; pp 124-132
[15] Seo, J. W.; Park, J. W.; Lim, K. S.; Yang, J. H.; Kang, S. J., Transparent resistive random access memory and its characteristics for nonvolatile resistive switching. Applied Physics Letters 2008, 93 (22)
[16] Grabowska, E.; Marchelek, M.; Paszkiewicz-Gawron, M.; Zaleska-Medynska, A., 3 - Metal oxide photocatalysts. In Metal Oxide-Based Photocatalysis, Zaleska-Medynska, A., Ed. Elsevier: 2018; pp 51-209
[17] Robertson, J., High dielectric constant oxides. Eur. Phys. J. Appl. Phys. 2004, 28 (3), 265-291.
[18] Birks N, Meier GH, Pettit FS. Introduction to the high-temperature oxidation of metals. Cambridge: Cambridge University Press; 2006.
[19] Suri, M., Applications of Emerging Memory Technology. Springer: 2020.
[20] Chen, A., A review of emerging non-volatile memory (NVM) technologies and applications. Solid-State Electronics 2016, 125, 25-38.
[21] Abbas, Y.; Sokolov, A. S.; Jeon, Y.-R.; Kim, S.; Ku, B.; Choi, C., Structural engineering of tantalum oxide based memristor and its electrical switching responses using rapid thermal annealing. Journal of Alloys and Compounds 2018, 759, 44-51.
[22] Wu, L.; Wang, Z.; Fang, Y.; Yu, Z.; Kang, J.; Chen, Q.; Yang, Y.; Ji, Z.; Cai, Y.; Huang, R. In Study on High-Resistance State Instability of TaOx-Based RRAM, 2018 14th IEEE International Conference on Solid-State and Integrated Circuit Technology (ICSICT), IEEE: 2018; pp 1-3.
[23] Zhu, Y.; Zheng, K.; Wu, X.; Ang, L., Enhanced stability of filament-type resistive switching by interface engineering. Scientific Reports 2017, 7 (1), 1-7.
[24] Jeon, H.; Park, J.; Jang, W.; Kim, H.; Kang, C.; Song, H.; Kim, H.; Seo, H.; Jeon, H., Stabilized resistive switching behaviors of a Pt/TaOx/TiN RRAM under different oxygen contents. physica status solidi (a) 2014, 211 (9), 2189-2194.
[25] Li, C.; Wang, F.; Zhang, J.; She, Y.; Zhang, Z.; Liu, L.; Liu, Q.; Hao, Y.; Zhang, K., Improved Uniformity of TaOx-Based Resistive Random Access Memory with Ultralow Operating Voltage by Electrodes Engineering. ECS Journal of Solid State Science and Technology 2020, 9 (4), 041005.
[26] Qin, Y.; Wang, Z.; Ling, Y.; Cai, Y.; Huang, R., A TaOx-based RRAM with improved uniformity and excellent analog characteristics by local dopant engineering. Electronics 2021, 10 (20), 2451.
[27] Kim, D.; Kim, J.; Kim, S., Enhancement of Resistive and Synaptic Characteristics in Tantalum Oxide-Based RRAM by Nitrogen Doping. Nanomaterials 2022, 12 (19), 3334.
[28] She, Y.; Pan, H.; Wang, F.; Li, C.; Zhang, Z.; Han, Y.; Zhang, K. In Improvement on Electronic Characteristics of TAOX/TIOX Dual-Layer Structure Resiative Memory, 2020 China Semiconductor Technology International Conference (CSTIC), IEEE: 2020; pp 1-3.
[29] Wu, J.; Cao, J.; Han, W.-Q.; Janotti, A.; Kim, H.-C., Functional metal oxide nanostructures. Springer Science & Business Media: 2011; Vol. 149.
[30] Chiu, F.-C., A review on conduction mechanisms in dielectric films. Advances in Materials Science and Engineering 2014, 2014.
[31] Lim, E. W.; Ismail, R., Conduction mechanism of valence change resistive switching memory: a survey. Electronics 2015, 4 (3), 586-613.
[32] Kumar, A.; Das, M.; Mukherjee, S., Oxide based memristors: fabrication, mechanism, and application. 2018.
[33] Zahoor, F.; Azni Zulkifli, T. Z.; Khanday, F. A., Resistive random access memory (RRAM): an overview of materials, switching mechanism, performance, multilevel cell (MLC) storage, modeling, and applications. Nanoscale Res Lett 2020, 15 (1), 1-26.
[34] Li, Y.; Zhong, Y.; Zhang, J.; Xu, L.; Wang, Q.; Sun, H.; Tong, H.; Cheng, X.; Miao, X., Activity-dependent synaptic plasticity of a chalcogenide electronic synapse for neuromorphic systems. Scientific reports 2014, 4 (1), 4906.
[35] Sagar, S.; Udaya Mohanan, K.; Cho, S.; Majewski, L. A.; Das, B. C., Emulation of synaptic functions with low voltage organic memtransistor for hardware oriented neuromorphic computing. Scientific reports 2022, 12 (1), 3808.
[36] Prakash, A.; Hwang, H., Multilevel cell storage and resistance variability in resistive random access memory. Physical Sciences Reviews 2016, 1 (6).
[37] Chen, P.-Y.; Lin, B.; Wang, I.-T.; Hou, T.-H.; Ye, J.; Vrudhula, S.; Seo, J.-s.; Cao, Y.; Yu, S. In Mitigating effects of non-ideal synaptic device characteristics for on-chip learning, 2015 IEEE/ACM International Conference on Computer-Aided Design (ICCAD), IEEE: 2015; pp 194-199.
[38] Chen, P.-A.; Hsu, W.-C.; Chiang, M.-H., Bilayer Modulation With Dual Vacancy Filaments by Intentionally Oxidized Titanium Oxide for Multilayer-hBN RRAM. IEEE Transactions on Nanotechnology 2021, 20, 687-694.
[39] Yao, C.; Ismail, M.; Hao, A.; Thatikonda, S. K.; Huang, W.; Qin, N.; Bao, D., Annealing atmosphere effect on the resistive switching and magnetic properties of spinel Co 3 O 4 thin films prepared by a sol–gel technique. RSC advances 2019, 9 (22), 12615-12625.
[40] Rittich, J.; Jung, S.; Siekmann, J.; Wuttig, M., Indium‐Tin‐Oxide (ITO) Work Function Tailoring by Covalently Bound Carboxylic Acid Self‐Assembled Monolayers. physica status solidi (b) 2018, 255 (8), 1800075.
[41] Liu, Z.; Liu, Y.; Wang, X.; Li, W.; Zhi, Y.; Wang, X.; Li, P.; Tang, W., Energy-band alignments at ZnO/Ga2O3 and Ta2O5/Ga2O3 heterointerfaces by X-ray photoelectron spectroscopy and electron affinity rule. Journal of Applied Physics 2019, 126 (4), 045707.
[42] Chen, J.-Z.; Chen, T.-H.; Lai, L.-W.; Li, P.-Y.; Liu, H.-W.; Hong, Y.-Y.; Liu, D.-S., Preparation and characterization of surface photocatalytic activity with NiO/TiO2 nanocomposite structure. Materials 2015, 8 (7), 4273-4286.
[43] Birks, N.; Meier, G. H.; Pettit, F. S., Introduction to the high temperature oxidation of metals. Cambridge university press: 2006.
[44] Prakash, A.; Jana, D.; Maikap, S., TaO x-based resistive switching memories: prospective and challenges. Nanoscale Res Lett 2013, 8 (1), 1-17.