臺灣博碩士論文加值系統

近年來，隨著半導體技術不斷的演進與發展，透明非晶態金屬氧化物這種材料開始廣泛的被研究，因為其具有高的載子遷移率、高透明度、比較低的製程溫度還有相容於現有的顯示器製程等優秀的特性。而在眾多金屬氧化物半導體材料中，以擁有優異的元件電流驅動能力、均勻性以及薄膜穩定性等特性的非晶態銦鎵鋅氧化物(Amorphous InGaZnO: a-IGZO)最被眾人看好，被認為是下個世代最有潛力的薄膜電晶體材料。然而，在未來的市場中，薄膜電晶體將會應用在大尺寸高解析度的顯示面板(4K、8K)、有機發光元件與可撓性電子裝置如軟性電子元件或者是穿戴式的電子裝置，在元件特性的方面上會需要能夠承載更大的驅動電流與施加偏壓後操作穩定性，這些使得銦鎵鋅氧化物半導體材料會因為鎵元素的摻雜使其載子遷移率難以提升，這項缺點已不符合未來市場上的趨勢，勢必要尋找新的金屬氧化物材料來使用。另外大尺寸高解析度顯示器也面臨到嚴重的RC延遲問題，所以近年來將傳統的鋁(Al)和鉬(Mo)電極取代為銅(Cu)電極來降低電阻，並藉此方式去降低RC延遲的問題。
本論文注重於開發已非晶態氧化銦鎢鋅作為阻值切換層的銅電橋式記憶體(CBRAM)。透過在氧化銦中摻雜鎢元素，利用其與氧原子間的高鍵解離能(bond-dissociation energy)降低薄膜中氧空缺的數量達到提升元件的穩定性。藉由光罩的設計及後處理方法去整合異質元件，達到整合多功能於晶片上(System On Chip,SOC)或整合多功能於面板上(System On Panel,SOP)。此新穎的銅導電橋式記憶體之優勢為(1)非揮發性記憶體，透過電阻阻值的變化來開關元件，對於元件的微縮性有更好的發展，並且是非破壞性的讀取，比起快閃記憶體還有動態記憶體來較低的位元錯誤率;(2)金屬/絕緣體/金屬(metal-insulator-metal;MIM)的架構，這種結構相較於目前主流的快閃記憶體來說製程簡單，並且具有高密度堆疊的優勢;(3)優秀的元件操作速度、耐久度、低功耗以及多級的儲存資料能力等優點，被視為下個世代中最具潛力技術的非揮發性記憶體元件。
本論文提出以「銅上電極/鎢鈦合金/氧化銦鎢鋅/鉑底電極」作為銅導電橋式記憶體之結構，在較低氧通量下濺鍍出來的阻態切換層，直流操作下是無法正常操作的，但隨著調控到適當的製程氧通量，直流的操作可達到接近1×10^4，另外隨著氧通的增加，在一開始的時候會讓元件電特性有優化的作用，但是一直增加到氧分壓為26 %的時候，元件的耐久性(endurance)開始下降，所以為了進一步證明氧空缺對於我們元件的影響，我們有將元件進行XPS的分析，透過XPS分析，能夠證明氧空缺對於元件電特性的影響，隨後我們也有做不同厚度的測試，發現隨著厚度適當的增加，操作電壓雖然也要跟著往上提升，但是對於元件的耐久性(endurance)還有高低阻態分布的情況是有所改善的，另外有將在20 %氧分壓下製作不同厚度的IWZO CBRAM元件去進行阻態轉換時間的測試，也就是所謂的switch time的測試，從結果上表明了，隨著厚度的增加會讓阻態轉換的時間變長，還有隨著改變限制電流(compliance current)，也會使得切換的時間有所改變，而上面所述之元件資料保存時間在高溫85℃下皆能超過10000秒。
最後將最好氧通量及厚度的元件去進行AC的量測，從結果可以得知IWZO CBRAM是能夠在AC量測下進行10000次的操作的。

In recent years, with the continuous evolution and development of semiconductor technology, transparent amorphous oxide semiconductors (TAOSs) have been widely studied because of their high carrier mobility, high transparency, relatively low process temperature, and that it can be integrated with existing display processes. Among TAOSs, amorphous indium-gallium zinc oxide (a-IGZO), which has excellent characteristics such as current drive capability of device, uniformity, and film stability, is most interested by everyone. It is considered to be the most promising thin film transistor (TFT) material of the next generation. However, in the future market, TFT will be used in large-sized high-resolution display panels (4K, 8K), organic light-emitting elements and flexible electronic devices such as flexible electronic components or wearable electronic devices. In terms of device characteristics, it is required to be able to endure a larger driving current and the stability of operation after applying a bias. But, the indium gallium zinc oxide semiconductor material will be difficult to increase the carrier mobility due to the doping of gallium. So, it is necessary to find new metal oxide materials for instead. In addition, large-size high-resolution displays are also facing serious RC delay problems, so in recent years, conventional aluminum (Al) and molybdenum (Mo) electrodes have been replaced by copper (Cu) electrodes to reduce electrical resistance, and in this way, the issue of RC delay is reduced.
In this thesis, we focus on the development of copper bridge memory (CBRAM) with amorphous indium-tungsten-zinc-oxide as the resistance switching layer. By doping the indium oxide with tungsten, the bond-dissociation energy between it and the oxygen atom reduces the number of oxygen vacancies in the film to improve the stability of the element. Integrating heterogeneous device by mask design and post-processing methods to achieve integrated system on chip (SOC) or integrated system on panel (SOP). There are some advantages of CBRAM such as excellent device operating speed, great endurance characteristic, low power consumption, multi-level storage data capabilities and metal/insulator-metal (MIM) structure, which is simple to fabricate and has the advantage of high-density stacking. The CBRAM is considered the most potential technology of Non-volatile memory in the next generation.
In this thesis, the structure of IWZO CBRAM was Cu/TiW/IWZO/Pt. When the switching layer is sputtered at a lower oxygen flux. It will cause the IWZO CBRAM cannot operating. But with the regulation of the appropriate process oxygen flux, the IWZO CBRAM can operate close to 10000 times in the DC operation. In addition, the electrical characteristic of the device is optimized when the oxygen flux increases in the beginning. But the endurance of the IWZO CBRAM begins to decrease when the oxygen partial pressure is increased to 26%. Therefore, we have made an analysis on the device by XPS, in order to further prove the effect of oxygen vacancies on our device. Through XPS analysis, it is possible to prove the effect of oxygen vacancies on the electrical characteristics of the device. Then we also tested different thicknesses and found that the operating voltage is also increased upwards, but the endurance characteristic of device and the HRS and LRS distribution are improved when the thickness is appropriately increased. In addition, the operation speed of IWZO CBRAM is also tested. When the thick of IWZO is increase, the time of the resistance state switch becomes longer and change the compliance current. The switching time is also changed. As mentioned above, all the device can reach 10000 s of the retention test at a high temperature of 85 °C.
Finally, the best oxygen flux and thickness device were measured for AC measurement. From the results, IWZO CBRAM was able to demonstrate 10,000 operations under AC measurement.

Table of contents
摘 要 I
Abstract IV
Acknowledgement (誌謝) VII
Table of contents VIII
Figure captions XI
Table captions XVI
Chapter 1 Introduction 1
1.1 Introduction 1
1.1.1 Background 1
1.1.2 Emerging non-volatile memory (NVM) 2
1.1.3 Resistive random-access memory(ReRAM) 4
1.1.4 ReRAM operation mechanisms 5
1.1.5 Material classification 7
1.1.6 Introduction to CBRAM 8
1.1.7 Motivation 9
1.1.8 Organization of thesis 10
Chapter 2 Electrical performance of CBRAM 25
2.1 Electrical characteristics of CBRAM 25
2.1.1 Compliance current 25
2.1.2 Forming/set/reset process 25
2.1.3 Determination of LRS and HRS 26
2.1.4 Operation mode 26
2.1.5 Memory window 26
2.1.6 Endurance 27
2.1.7 Retention 28
2.1.8 Operation speed 28
Chapter 3 Experimental Procedures 30
3.1 Preparation of Si substrates 30
3.2 Fabrication of a-IWZO CBRAM 30
3.3 Electrical measurements 31
3.3.1 DC sweep measurement 31
3.3.2 Electric-pulse-induced resistance (EPIR) switching 32
3.3.3 Endurance test 32
3.3.4 Retention test 33
3.3.5 Temperature-dependent LRS test 33
3.4 Material analysis 34
3.4.1 Atomic force microscope(AFM) 34
3.4.2 Transmission electron microscopy (TEM) 34
3.4.3 X-ray photoelectron spectroscopy (XPS) 35
Chapter 4 Physical and electrical characteristics of IWZO CBRAM 41
4.1 The basic characteristics of CBRAM fabricated on silicon substrate 41
4.1.1 The resistive switching mode of IWZO CBRAM 41
4.2 Electrical properties with different oxygen flow rate 44
4.2.1 Structure and morphology 44
4.2.2 DC electrical characteristic 44
4.2.3 XPS analysis 45
4.3 The thickness effect for IWZO CBRAM 47
4.3.1 DC electrical characteristic 47
4.3.2 Switching time 48
4.3.3 Retention for IWZO CBRAM 49
4.4 AC endurance test for IWZO CBRAM 49
Chapter 5 Conclusions and future work 75
5.1 Conclusions 75
5.2 Future work 76
References 77
Vita 87

Figure captions
Chapter 1
Fig. 1- 1 Floating gate flash memory [1]. 13
Fig. 1- 2 Floating gate I-V curves of flash memory when there is no electron stored in the FG (curve 1) and when electron is stored in the FG (curve 0) [3] . 13
Fig. 1- 3 Polarization hysteresis curve of the FeRAM [5]. 14
Fig. 1- 4 The schematic diagram of ABO3 crystal structure [4]. 14
Fig. 1- 5 The diagram of MTJ device with series transistor [9]. 15
Fig. 1- 6 The basic operation theory of MRAM [8]. 15
Fig. 1- 7 The schematic structure of PCM device [10]. 16
Fig. 1- 8 The different crystallizing phase caused different resistance [12]. 16
Fig. 1- 9 The schematic structure of a ReRAM cell [17]. 17
Fig. 1- 10 (On the right) cross-sectional TEM image and (on the left) diagram with 0.18-μm CMOS technology [58]. 17
Fig. 1-11 (a) Unipolar switching mode. (b) Bipolar switching mode [17]. 18
Fig. 1. 12 Bipolar operation schematic is on the top and unipolar operation schematic is on the bottom [21]. 18
Fig. 1. 13 Three types formation filament mechanism of ReRAM. The I-V properties are demonstrated [23]. 19
Fig. 1-14 Typical current-voltage characteristic of a Ag/Ag-Ge-Se/Pt ECM cell. The insets A to D show the different stages of the switching procedure [24]. 19
Fig. 1-15 Z-contrast image and EDX analysis in STEM mode for bridge-like region in ON-state device. The results show that the protrusions composed of Ag have connected the electrode pair completely [26]. 20
Fig. 1-16 Schematic views of the unified physical model for the switching process between LRS and HRS [27]. 20
Fig. 1-17 (a) Initial state of the device. (b) After a forming process operate, a conductive filament (CF) is formed. (c)The reset operation locally disconnects the CF, leading to a high-reset state [28]. 21
Fig. 1-18 The materials, which are considered as electrode or switching layer [19]. 21
Fig. 1-19 The IGZO ternary system [40]. 22
Fig. 1-20 The silver dendrite bridge between the gap [41]. 22
Fig. 1-21 Filament growth from cathode to anode [42]. 22
Fig. 1-22 (a) Simulated quasi-static I–V characteristics using a sweep rate of 0.1 V μs−1 and a current compliance of ICC = 100 nA. (b) Snapshots of filament evolution in different stages (A)–(F) of the I–V characteristics shown in (a) [43]. 23
Fig. 1-23 Switching phenomenology depending on the operation range [46]. 23
Fig. 1-24 Influence of different x in CuxTe1-x electrode on CBRAM devices [47]. 24
Chapter 2
Fig. 2- 1 The typical I-V characteristics of CBRAM. 29
Chapter 3
Fig. 3-1 RCA clean flow. 37
Fig.3-2 (a) The top view of IWZO device. (b) Cross the section of the Cu/TiW/IWZO/Pt structure. 37
Fig. 3-3 The procedure of fabricating IWZO CBRAM flow. 38
Fig.3-4 The progress flow of experiment. 39
Fig. 3-5 DC sweep measurement system schematic diagram 39
Fig. 3-6 The fundamental DC sweeping I – V curve of IWZO CBRAM. 40
Fig. 3-7 AC pulse measurement system schematic diagram 40
Chapter 4
Fig. 4- 1 The reset process of Cu/TiW/ZrO2/Pt with 0 nm, 25 nm, 50 nm, 100nm thick [66]. 53
Fig. 4-2 Typical I-V transient drop property during operation at 10 nm thick IWZO with 20% oxygen partial. 53
Fig. 4-3 The forming process curve of Cu/TiW/ZrO2/Pt with 0 nm, 25 nm, 50nm and 100nm thick [66]. 54
Fig. 4-4 The forming I − V curve of Cu/TiW/IWZO/Pt at 10 nm thick IWZO with 20% oxygen partial [66]. 54
Fig. 4-5 Impact of the temperature on the LRS which is allowed by the R=R0 (1+α∆T). 55
Fig. 4-6 The TEM image of Cu/TiW/IWZO/Pt device. The thickness of IWZO is about 7.5 nm and the thickness of TiW is about 1.5 nm. 55
Fig. 4-7 Typical IV transient characteristics of Cu/TiW/IWZO/Pt device during forming operations at the different oxygen flow rate. 56
Fig. 4-8 Typical I-V curve of Cu/TiW/IWZO/Pt device during set and reset operations at the different oxygen partial. 56
Fig. 4-9 The distribution of the Vset and Vreset with different oxygen partial. 58
Fig. 4-10 The endurance characteristics of 10 nm IWZO CBRAM with different oxygen flux (a) 13 % oxygen partial, (b) 20 % oxygen partial, (c) 26 % oxygen partial and (d) 33 % oxygen partial. 60
Fig. 4-11 The resistance distribution of IWZO device with different oxygen partial (a) 13 % oxygen partial, (b) 20 % oxygen partial, (c) 26 % oxygen partial and (d) 33 % oxygen partial. 62
Fig. 4-12 The O 1s XPS spectra for a-IWZO with oxygen partial pressures (a) 0 %, (b) 13 %, (c) 20 %, (d) 26%. 64
Fig. 4-13 Typical I-V transient characteristics of Cu/TiW/IWZO/Pt device during forming operations at the different thickness. 65
Fig. 4-14 Typical I-V transient characteristics of Cu/TiW/IWZO/Pt device during set and reset operations at the different thickness. 65
Fig. 4-15 Endurance cycles of IWZO CBRAM with the different thickness (a) 5 nm, (b) 7.5 nm and (c) 10 nm. 67
Fig. 4-16 The cumulative probability of the resistance states of (a) 5 nm, (b) 7.5 nm and (c) 10 nm thick IWZO of device. 69
Fig. 4-17 The schematic diagram of different thickness IWZO CBRAM. 69
Fig. 4-18 The resistance switching time of the IWZO device at 10 μA compliance current. 70
Fig. 4-19 The resistance switching time of the IWZO device at 100 μA compliance current. 71
Fig. 4-20 The resistance switching time of the IWZO device at 1 mA compliance current. 72
Fig. 4-21 The retention of IWZO CBRAM with (a) 5 nm, (b) 7.5 nm and (c) 10 nm thick at 85℃ measurement. 74
Fig. 4-22 The AC endurance of IWZO CBRAM 74
 
Table captions
Chapter 1
Table 1- 1 Compare the emerging NVMs technologies properties [21]. 12
Table 1-2 Overview advantage of ReRAM technologies [22]. 12
Chapter 3
Table 3- 1 The detail parameters of IWZO deposition. 36
Chapter 4
Table 4- 1 Comparison of the resistance temperature coefficient (

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