熱電材料可以直接將熱能和電能相互轉換，這種有用的材料可以被加工串聯成更復雜的熱電模組，如能利用廢熱發電的熱電發電機，或作為小型熱泵的熱電致冷器，能替電子元件散熱，傳遞掉其產生的積聚熱量。中溫型熱電材料的傳統接合技術需在真空條件下進行接合，並且會形成介金屬化合物，導致其接合強度降低。本研究中對Ge0.87Pb0.13Te（GPT）熱電塊材和銅電極間在大氣中進行了低溫銀銀直接接合。首先，通過磁控濺鍍在Ni/GPT熱電塊材和銅電極上製備細晶粒銀薄膜，並在250 ℃和40 MPa的接合壓力下，在大氣中接合30分鐘，形成GPT/Ni/Ag/Cu熱電接腳，但卻發現存在銀薄膜塑性變形的問題，接合比例也只達到79%至84.5%。接下來，通過兩步驟沉積法用鈦擴散阻障層取代了原本的鎳擴散阻障層，並在Ti/GPT熱電塊材和Ti/Cu電極上成功製備了（111）優選的奈米雙晶銀薄膜，在相同結合條件的情況下成功接合出改良的熱電接腳GPT/Ti/Ag/Ti/Cu。不僅解決了塑性變形的問題，接合比例也明顯上升到85.3%至93.3%。最後，將接合好的熱電接腳進行接合強度的分析。GPT/Ti/Ag/Ti/Cu的結合強度能達到 6 MPa，且其銀銀對接層在薄膜對薄膜剪力測試後依然能維持高接合強度。

Thermoelectric materials can directly convert heat and electricity into each other, such useful materials can be processed into much complex thermoelectric modules, like thermoelectric generators that generate electric power from waste heat, or thermoelectric coolers, which function as a small heat pump, transferring heat accumulation between electronic components. However, the traditional bonding technology for medium-temperature thermoelectric bulk usually requires bonding process in a vacuum condition and will form intermetallic compounds that lower the bonding strength. In this study, we performed low-temperature Ag-to-Ag direct bonding technology for Ge0.87Pb0.13Te (GPT) thermoelectric bulk and Cu electrode in the atmosphere. First, fine grain Ag thin film was deposited by magnetron sputtering on Ni/GPT thermoelectric material with Ni diffusion barrier and Cu electrode to form GPT/Ni/Ag/Cu thermoelectric leg under atmospheric bonding process at 250 °C with a bonding pressure of 40 MPa for 30 minutes. However, it had issue of Ag thin film plastic deformation and the bonding ratio was only 79% to 84.5%. Next, improved thermoelectric leg GPT/Ti/Ag/Ti/Cu was formed by a two-step deposition method, replacing Ni diffusion barrier with Ti diffusion barrier and successfully deposited highly (111) oriented nanotwinned Ag film on both Ti/GPT thermoelectric material and Ti/Cu electrode, while the bonding condition was the same as above. Not only did it solve the plastic deformation problem, the bonding ratio significantly increased into 85.3% to 93.3%. In addition, the bonding strength was also analyzed. The highest GPT/Ti/Ag/Ti/Cu bonding strength is 6 MPa, and the Ag-to-Ag direct bonding layer remains well bonded after shear strength test.

Chapter 1 Introduction 1
Chapter 2 Literature Review 3
2.1 Thermoelectric Materials 3
2.1.1 Thermoelectric module 4
2.1.2 Thermoelectric figure of merit 5
2.1.3 Bonding method 6
2.2 Nano-twinned Structure 6
2.2.1 Coincident Site Lattice 8
2.2.2 Stacking Fault Energy 9
2.2.3 Deformation Twin and Growth Twin 10
2.3 Deposition Method 10
2.4 Characteristics of Nano-twinned Silver 12
2.4.1 Ultrahigh strength and ductile 12
2.4.2 High electrical conductivity 14
2.4.3 Superior thermal stability 16
2.5 Direct Silver to Silver Bonding 17
2.5.1 Dissociation of Ag oxide 18
2.5.2 Surface diffusivity 19
2.5.3 Roughness 20
2.5.4 Nabarro-Herring Creep 21
2.5.5 Thermal expansion coefficient (CTE) 21
Chapter 3 Experimental processes 22
3.1 Sputtered Deposition System and Coating process 24
3.2 Specimen Preparation and Structure 26
3.3 Bonding Process 28
3.3.1 Grounding and polishing 30
3.4 Characterization methods 32
3.4.1 Cross-sectional Images and Thickness Measurement: FIB/SEM 32
3.4.2 Preferred Orientation: EBSD 34
3.4.3 Crystal Structure and Preferred Orientation: XRD 35
3.4.4 Surface Roughness: AFM 36
3.4.5 Electrical Resistivity: Four-Point Probe 37
3.4.6 Shear strength test 39
Chapter 4 Results 41
4.1 Microstructure observation and property analysis of As-Deposited Silver Thin Film 41
4.1.1 Ag/Ni/Si 43
4.1.2 Ag/Cu 45
4.1.3 Ag/Ni/GPT 49
4.1.4 Ag/Ti/Cu 53
4.1.5 Ag/Ti/GPT 58
4.2 Microstructure observation and property analysis of the as-bonded samples 63
4.2.1 Cross-sectional observation 63
4.2.2 Electrical resistivity 68
4.2.3 Shear strength 69
Chapter 5 Discussion 79
5.1 Bonding mechanism 79
5.1.1 Dissociation of Silver oxide 81
5.1.2 Diffusivity 81
5.1.3 Surface diffusion 82
5.1.4 Grain boundary diffusion 83
5.2 Properties 86
5.2.1 Electrical performance 86
5.2.2 Bonding strength 86
Chapter 6 Conclusion 88
References 89

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