熱電元件組裝是將成對的p型與n型熱電材料以銲料與金屬導線進行連接，並在元件上下兩端外加陶瓷基板以保護元件結構，而熱電材料與金屬導線間的接觸電阻將會嚴重限制微小型或薄膜型熱電元件的效能。本研究探討在迴銲過程中所產生介金屬化合物對熱電材料與導線接點的接觸電阻影響性。我們分別利用兩種不同銲料Sn-4Ag-05Cu和Sn-37Pb將商用p型或n型碲化鉍熱電材料與金屬銅箔進行接著，而實驗結果呈現此兩接點所產生的主要介金屬化合物分別為SnTe及PbxSn1-xTe。接點接觸電阻經量測後約為10-4~10-5 □cm2，此數值和在接點的介金屬化合物種類與厚度息息相關。另外實驗結果指出，銻和銅元素在迴銲過程中對介金屬化合物的成長機制有重大且相反的影響性，因此我們利用基本的錫-銻或錫-銅銲料與碲基材反應偶實驗來探討銻或銅元素的影響機制。
實驗結果顯示，在錫-銻銲料與碲基材反應偶中，銻元素的添加大幅加速介金屬化合物SnTe的生成，其成長速率甚至達每分鐘24微米，遠大於在電子封裝中常見化合物的成長速率。隨著增加銻元素的含量，SnTe的成長速率會加快並伴隨著晶粒尺寸的縮小。此表示在化合物內部的錫原子有效傳輸面積將因銻原子不斷排入銲料中而減少，進而改變化合物生長的速率決定步驟，從原先的錫和碲元素界面反應轉為錫原子在化合物層中的擴散。而錫-銅銲料與碲基材反應中發現，僅僅只要0.1wt%Cu添加入純錫銲料中，在液態銲料和碲基材反應界面上會生成一層薄薄的CuTe化合物進而有效抑制SnTe化合物劇烈的生長。CuTe化合物會隨著液態銲料中銅含量增加而由不規則分佈的叢集結構(clusters)轉為層狀結構，且在相同反應時間內，CuTe厚度正比於銅含量的二分之ㄧ次方，此表示CuTe成長為擴散控制機制。另外本實驗以Sn-0.1Cu銲料接著碲化鉍化合物與金屬銅箔，並量測其接觸電阻，數值約為10-5 □cm2。經過150 ºC168小時熱處理後，介金屬化合物成長仍然受到明顯的限制，說明CuTe在Sn-0.1Cu/Te反應偶中是個不錯的阻障層。綜合上述結果，我們相信Sn-0.1Cu銲料對於組裝碲化鉍為主的熱電元件是個不錯的選擇。本研究的重要性在於探討碲化鉍材料與銲料的界面反應，並對於適合熱電元件組裝的銲料選擇 提供有效的方針。

Typical thermoelectric modules are made of a number of p- and n-type thermoelements which are jointed to copper conductors by soldering reaction and arranged in a square array between two ceramic plates. Contact resistance of conductors/thermoelements joints may become a serious limitation to the performance of thermoelectric modules with relatively short or thin-film type thermoelements. In this study we have investigated the impact of interfacial compounds on the contact resistivity of bismuth telluride/Cu soldered junctions. Two different solder alloys, Sn-4Ag-0.5Cu and Sn-37Pb, were used to joint both commercial p-type and n-type bismuth telluride onto thin Cu foils. SnTe and Pb1-xSnxTe were identified to be the major interfacial compounds for the Sn-4Ag-0.5Cu and Sn-37Pb soldered junctions, respectively. The contact resistivity measured is around 10-4 ~ 10-5 □cm2, which depends on both the thickness and composition of interfacial compounds. Sb and Cu element are observed to have a strong influence but in an opposite manner on growth kinetics of the interfacial compounds during soldering reaction. The mechanisms for Sb and Cu on SnTe growth were explored using a simple solder/Te reaction couple.
Addition of Sb element in solder considerably enhances the growth rate of SnTe compound, e.g. 24µm/min for 1wt% Sb addition, that is rarely seen in typical soldering reactions. With increasing Sb content in Sn-Sb solder, the growth rate of SnTe may increase accompanied with the reduction in size of SnTe grains. It indicates that the effective channel area for Sn transport in compound may decrease with the consecutive Sb ejection into solder, and hence the rate-limiting step of SnTe formation will change from Sn/Te reaction to the transport of Sn through the compound layer. A dosage of 0.1 wt% Cu in Sn is capable of suppressing the vigorous Sn/Te reaction effectively by forming a thin CuTe at the solder/Te interface. The CuTe morphology changes from irregular clusters into a layered structure with increasing Cu content. With the same reaction time, the CuTe thickness increases proportionally to x1/2 in the Sn-xCu alloys, suggesting a diffusion-controlled growth for CuTe. The contact resistivity of bismuth telluride/Cu soldered junctions using Sn-0.1Cu alloy were measured to ~ 10-5 □cm2. After thermal treatment at 150 ºC for 168 hours, the growth of intermetallic compounds in Sn-0.1Cu/Te couples were still obviously suppressed, indicative of the superior barrier capability for CuTe compound. It is believed that Sn-0.1Cu alloy shall be a good candidate solder for assembly of telluride based thermoelectric modules under the consideration of electrical property and mechanical integrity. This study may be of importance in understanding the interfacial reaction between bismuth telluride and solder, as well as in providing the effective strategy to choose appropriate solder alloys for thermoelectric assembly.

誌謝 I
Abstract II
摘要 IV
Table of Contents VI
List of Figures IX
List of Tables XIII

Chapter 1 Introduction 1
1.1 Introduction and background 1
1.1.1 Concerns of sustainable energy search, and heat dissipation for the integrated circuit 1
1.1.2 A promising solution – Thermoelectric technology 2
1.2 Thermoelectric modules 4
1.2.1 Bismuth telluride based materials 5
1.2.2 Ceramic plates 6
1.2.3 Metallic conductors 6
1.2.4 Solders 7
1.3 Conversion efficiency of thermoelectric modules 10
1.4 Soldering and Intermetallic compounds 14
1.5 Motivation 15
Chapter 2 Literature review 17
2.1 Intermetallics on reliability of thermoelectric modules 17
2.2 Approaches to reliability improvement of thermoelectric module 19
2.2.1 Diffusion barrier 19
2.2.2 Solder recipe 23
2.3 Reaction couples 24
2.3.1 Pure Sn/Te reaction couple 24
2.3.2 Sn-Ag solder alloys/Te reaction couple 25
2.3.3 Sn-Bi solder alloys/Te reaction couple 26
Chapter 3 Experimental procedure 28
3.1 Specimen preparation 28
3.1.1 Bismuth telluride/Cu soldered specimen 28
3.1.2 Sn-Sb solder alloys/Al-patterned Te reaction couple 29
3.1.3 Sn-Cu solder alloys/Te reaction couple 31
3.2 Specimen analysis 31
3.2.1 Microstructure analysis 31
3.2.2 Compositional analysis and phase identification of interfacial compounds 32
3.2.3 Electrical contact resistivity measurement 33
Chapter 4 Interfacial reactions at bismuth telluride/Cu soldered junctions and corresponding electrical contact resistivity 36
4.1 Preface 36
4.2 Interfacial compound formation on solder-jointed junctions 36
4.3 Electrical contact resistivity of solder jointed junctions 39
4.3.1 Electrical contact resistance 39
4.3.2 Intermetallic compounds on electrical contact resistivity 40
4.4 Influence on formation kinetics of intermetallic compounds by the constituents of solder and bismuth telluride 41
4.4.1 Comparison between n/SnAgCu and p/SnAgCu junctions 41
4.4.2 Comparison between p/SnPb and p/SnAgCu junctions 44
4.5 Summary 48
Chapter 5 Effect of trace elements on growth kinetics of tin telluride compound in reaction couple 49
5.1 Preface 49
5.2 Enhanced SnTe growth kinetics for reaction between Sn-Sb alloy and Te substrate 49
5.2.1 Change of SnTe growth by 1wt% Sb addition 51
5.2.2 Microstructure examination of compound layer in Sn-1Sb/Te couple 55
5.2.3 Effect of Sb content on SnTe growth 56
5.3 Mechanism of Sb-enhanced SnTe growth during Sn-Sb/Te soldering reaction 58
5.3.1 Structure examination of SnTe compound 58
5.3.2 Kinetics analysis of SnTe growth 60
5.4 Suppressive SnTe growth kinetics for reaction between Sn-Cu alloy and Te substrate 64
5.4.1 Formation of barrier-like CuTe in Sn-0.1Cu/Te couples 64
5.4.2 Growth kinetics of CuTe in Sn-0.1Cu/Te couples 67
5.5 Effect of Cu content on CuTe growth kinetics in Sn-Cu/Te couples 69
5.5.1 Morphology change with Cu content 69
5.5.2 Kinetic analysis of CuTe growth 72
5.6 Feasibility and efficiency evaluation of Sn-Cu alloys in thermoelectric module assembly 73
5.6.1 Electrical contact property of Sn-0.1Cu soldered junctions 73
5.6.2 Thermal aging treatment on CuTe compound 74
5.7 Summary 77
Chapter 6 Conclusions 78
6.1 Conclusions 78
6.2 Future prospects 79
References 81
Publication List 87

[1] P.K. Bansal, A. Martin, Int. J. Energy Res., 24 (2000) 93.
[2] H. Watanabe, Proceedings of the 17th International conference on thermoelectrics, (1998) 486.
[3] T.M. Ritzer, Proceedings of the 18th International conference on thermoelectrics, (1999) 432
[4] D.M. Rowe: CRC Handbook of Thermoelectrics CRC Press LLC. Boca Raton, FL,1995.
[5] L.E. Bell, Science, 321 (2008) 1457.
[6] G. Min, D.M. Rowe, Applied Energy, 83 (2006) 133.
[7] W. Wang, F.L. Jia, Q.H. Huang, J.Z. Zhang, Microelectron. Eng., 77 (2005) 223.
[8] J.H. Cheng, C.K. Liu, R.M. Tain, C.K. Yu, Proceedings of the 6th world conference on experimental heat transfer, fluid mechanics, and thermodynamics, (2005).
[9] K. Uemura, Journal of Thermoelectricity, 3 (2002) 7.
[10] G. Min, D.M. Rowe, Solid-State Electronics, 43 (1999) 923.
[11] L. Michalski, K. Eckersdorf, J. Kucharski, J. McGhee: Temperature measurement, 2nd e., John Wiley & Sons, New York, 2002.
[12] L.A. Fisk, Science, 309 (2005) 2016.
[13] F.D. Winter, G. Stapfer, E. Medina, Aerospace and electronic systems magazine, IEEE, (2000) 5.
[14] M. Strasser, R. Aigner, C. Lauterbach, T.F. Sturm, M. Franosh, G. Wachutka, Proceedings of the 22th International conference on thermoelectrics, (2003) 45.
[15] M. Kishi, H. Nemoto, T. Hamao, M. Yamamoto, S. Sudou, M. Mandai, S. Yamamoto, Proceedings of the 18th International conference on thermoelectrics, (1999) 301.
[16] D.T. Crane, Proceedings of the 9th Diesel Engine Emissions Reduction (DEER) Conference, (2003) 1.
[17] S. Goktun, Energy Conv. Manag., 36 (1995) 1197.
[18] D.S. Sumida, T.Y. Fan, Opt. Lett., 20 (1995) 2384.
[19] C.T. Elliot, Proceedings of the 4th Advanced Infrared Detectors and Systems, (1990) 61.
[20] G. Maltezos, M. Johnston, A. Scherer, Appl. Phys. Lett., 87 (2005) 3.
[21] B. Yang, H. Ahuja, T.N. Tran, HVAC&R. Res., 14 (2008) 635.
[22] J. Winkler, V. Aute, B. Yang, R. Radermacher, Proceedings of International Refrigeration and Air Conditioning Conference, (2006) 17.
[23] C. Shafai, M.J. Brett, Journal of Vacuum Science & Technology a-Vacuum Surfaces and Films, 15 (1997) 2798.
[24] H.J. Goldsmid, R.W. Douglas, British Journal of Applied Physics, 5 (1954) 386.
[25] T.S. Shilliday, J. Appl. Phys., 28 (1957) 1035.
[26] H.J. Goldsmid, A.R. Sheard, D.A. Wright, British Journal of Applied Physics, 9 (1958) 365.
[27] H.J. Goldsmid, British Journal of Applied Physics, 11 (1960) 209.
[28] C. Wood, Rep. Prog. Phys., 51 (1988) 459.
[29] I.H. Kim, Mater. Lett., 43 (2000) 221.
[30] G.F. Wang, T. Cagin, Phys. Rev. B, 76 (2007) 8.
[31] T. Caillat, M. Carle, P. Pierrat, H. Scherrer, S. Scherrer, J. Phys. Chem. Solids, 53 (1992) 1121.
[32] J. Jiang, L.D. Chen, S.Q. Bai, Q. Yao, Q. Wang, J. Cryst. Growth, 277 (2005) 258.
[33] O. Yamashita, S. Tomiyoshi, K. Makita, J. Appl. Phys., 93 (2003) 368.
[34] M.H.C. Li, A. Al-Refaie, C.Y. Yang, IEEE Trans. Electron. Packag. Manuf., 31 (2008) 126.
[35] J. Ure, R.W., R.R. Heikes: Thermoelectricity : Science and engineering. Interscience Publishers, Inc., New York, 1961.
[36] G.S. Nolas, J. Sharp, H.J. Goldsmid: Thermoelectrics: Basic principles and new materials developments. Springer, New York, 2001.
[37] G. Min, D.M. Rowe, Energy Conv. Manag., 41 (2000) 163.
[38] C.Y. Liu, H.K. Kim, K.N. Tu, P.A. Totta, Appl. Phys. Lett., 69 (1996) 4014.
[39] H.K. Kim, K.N. Tu, P.A. Totta, Appl. Phys. Lett., 68 (1996) 2204.
[40] T.D. Alieva, B.S. Barkhalov, D.S. Abdinov, Inorganic Materials, 31 (1995) 178.
[41] M.L. Huang, T. Loeher, A. Ostmann, H. Reichl, Appl. Phys. Lett., 86 (2005) 3.
[42] S.C. Hsu, S.J. Wang, C.Y. Liu, J. Electron. Mater., 32 (2003) 1214.
[43] T.A. Corser, Proceedings of the 41th Electronic Components and Technology Conference, (1991) 150.
[44] Z.M. Liu, X.L. Wang, X.W. Liu, W.Y. Quan, S.F. Sun, S.C. Ye, J.W. Lui, Proceedings of the 16th International Conference on Thermoelectrics, (1997) 708.
[45] J.H. Kiely, D.V. Morgan, D.M. Rowe, Semicond. Sci. Technol., 9 (1994) 1722.
[46] Y. Hori, D. Kusano, T. Ito, K. Izumi, Proceedings of the 18th International Conference on Thermoelectrics, (1999) 328.
[47] T.M. Ritzer, P.G. Lau, A.D. Bogard, Proceedings of the 16th International Conference on Thermoelectrics, (1997) 619.
[48] Y.L. Chang, W.C. Wang, SEM 11th International Congress & Exposition on Experimental and Applied Mechanics (2008).
[49] K.A. Moores, Y. K. Joshi, G. Miller, Proceedings of the 18th International Conference on Thermoelectrics, (1999) 31.
[50] K. Hasezaki, H. Tsukuda, A. Yamada, S. Nakajima, Mater. Trans. JIM, 38 (1997) 1022.
[51] R.P. Gupta, J.B. White, O.D. Iyore, U. Chakrabarti, H.N. Alshareef, B.E. Gnade, Electrochem. Solid State Lett., 12 (2009) H302.
[52] R.P. Gupta, K. Xiong, J.B. White, K. Cho, H.N. Alshareef, B.E. Gnade, J. Electrochem. Soc., 157 (2010) H666.
[53] O.L. Mengali, M.R. Seiler, Advanced Energy Conversion, 2 (1962) 59.
[54] R.J. Buist, S.J. Roman, Proceedings of the 18th International Conference on Thermoelectrics, (1999) 249.
[55] Y.C. Lan, D.Z. Wang, G. Chen, Z.F. Ren, Appl. Phys. Lett., 92 (2008) 3.
[56] R.P. Gupta, O.D. Iyore, K. Xiong, J.B. White, K. Cho, H.N. Alshareef, B.E. Gnade, Electrochem. Solid State Lett., 12 (2009) H395.
[57] M. Yahatz, J. Harper, U.S. patent 5,817,188, Melcor Corporation, U.S.A., (1998) [58] S.W. Chen, C.N. Chiu, Scr. Mater., 56 (2007) 97.
[59] C.N. Liao, Y.C. Huang, J. Mater. Res., 25 (2010) 391.
[60] C.N. Chiu, C.H. Wang, S.W. Chen, J. Electron. Mater., 37 (2008) 40.
[61] M. Datta, S.A. Merritt, M. Dagenais, IEEE Trans. Compon. Packaging Technol., 22 (1999) 299.
[62] M.K.M. Arshad, I. Ahmad, A. Jalar, G. Omar, U. Hashim, J. Electron. Packag., 128 (2006) 246.
[63] J.E. Huheey, E.A. Keiter, R.L. Keiter: Inorganic Chemistry : Principles of Structure and Reactivity, 4th ed. HarperCollins College Publishers, New York, 1993.
[64] Y. Huang, R.F. Brebrick, J. Electrochem. Soc., 135 (1988) 486.
[65] Y. Huang, R.F. Brebrick, J. Electrochem. Soc., 135 (1988) 1547.
[66] A.E. Abken, Sol. Energy Mater. Sol. Cells, 73 (2002) 391.
[67] N.P. Gorbachuk, A.S. Bolgar, V.R. Sidorko, L.V. Goncharuk, Powder Metall. Met. Ceram., 43 (2004) 284.
[68] K.J. Linden, C.A. Kennedy, J. Appl. Phys., 40 (1969) 2595.
[69] S.W. Liang, Y.W. Chang, C. Chen, Y.C. Liu, K.H. Chen, S.H. Lin, J. Electron. Mater., 35 (2006) 1647.
[70] M. Orihashi, Y. Noda, L.D. Chen, T. Goto, T. Hirai, J. Phys. Chem. Solids, 61 (2000) 919.
[71] P. Villars, Allen Prince, H. Okamoto: Handbook of Ternary Alloy Phase Diagrams. ASM International, 1994.
[72] H.K. Kim, K.N. Tu, Appl. Phys. Lett., 67 (1995) 2002.
[73] J.H. Lee, Y.S. Kim, J. Electron. Mater., 31 (2002) 576.
[74] M.O. Alam, Y.C. Chan, K.N. Tu, J. Appl. Phys., 94 (2003) 7904.
[75] S.J. Wang, C.Y. Liu, J. Electron. Mater., 32 (2003) 1303.
[76] S.J. Wang, C.Y. Liu, Scr. Mater., 55 (2006) 347.
[77] S.W. Chen, A.R. Zi, P.Y. Chen, H.J. Wu, Y.K. Chen, C.H. Wang, Mater. Chem. Phys., 111 (2008) 17.
[78] C.M. Liu, C.E. Ho, W.T. Chen, C.R. Kao, J. Electron. Mater., 30 (2001) 1152
[79] R.F. Brebrick, J. Phys. Chem. Solids, 24 (1963) 27.
[80] R.J. McCabe, M.E. Fine, Metall. Mater. Trans. A-Phys. Metall. Mater. Sci., 33 (2002) 1531.
[81] R.J. McCabe, M.E. Fine, J. Electron. Mater., 31 (2002) 1276.
[82] M.H.N. Beshai, S.K. Habib, A.M. Yassein, G. Saad, M.M.H. El-Naby, Cryst. Res. Technol., 34 (1999) 119
[83] B.B. Alchagirov, A.M. Chochaeva, High Temp., 38 (2000) 44
[84] D.R. Poirier, G.H. Geiger: Transport Phenomena in Materials Processing. Metals & Materials Society, Warrendale, Pa., 1994.
[85] J.H. Yao, K.R. Elder, H. Guo, M. Grant, Phys. Rev. B, 47 (1993) 14110.
[86] R.W. Cahn, P. Haasen: Physical Metallurgy, 3rd rev. North-Holland Physics Pub., New York, 1983.
[87] S.J. Wang, C.Y. Liu, Acta Mater., 55 (2007) 3327.
[88] S.K. Ghandhi: VLSI Fabrication Principles: Silicon and Gallium Arsenide, 2nd ed. John Wiley & Sons, New York, 1994.
[89] B. Chao, S.H. Chae, X.F. Zhang, K.H. Lu, J. Im, P.S. Ho, Acta Mater., 55 (2007) 2805.