無電鍍鈷擴散阻障層應用於中溫碲化鉛熱電模組之研究;Investigation of Electroless Cobalt as Diffusion Barrier for Medium-Temperature PbTe Thermoelectric Modules

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Title:	無電鍍鈷擴散阻障層應用於中溫碲化鉛熱電模組之研究;Investigation of Electroless Cobalt as Diffusion Barrier for Medium-Temperature PbTe Thermoelectric Modules
Authors:	謝弦謙;Hsieh, Hsien-Chien
Contributors:	化學工程與材料工程學系
Keywords:	熱電材料;無電鍍鈷;擴散阻障層;界面反應;推力測試;熱電性質;熱電模組;Thermoelectric materials;Electroless cobalt;Diffusion barrier;Interfacial reaction;Shear test;Thermoelectric property;Thermoelectric module
Date:	2018-08-22
Issue Date:	2018-08-31 11:34:16 (UTC+8)
Publisher:	國立中央大學
Abstract:	因應大幅增加的綠色替代性能源需求，可將廢熱進行回收發電的中溫型熱電模組，為近年來備受重視的開發項目。在200至600 C溫度下，碲化鉛合金組成之n型與p型熱電材料，皆具有優異的熱電表現。然而，在熱電模組封裝時，卻遇到與模組電極或中間層發生劇烈界面反應，致使模組熱電轉換效率下降或整體模組失效。本研究旨在應用無電鍍鈷擴散阻障層技術，開發新式中溫碲化鉛模組接合，並對其界面穩定度、接觸電阻與模組機械性質進行探討，最後更進一步評估模組中添加層對熱電材料本身性質之影響。在界面反應研究中，n型碲化鉛熱電材料與銅基板直接接合，發生劇烈共晶反應，造成碲化鉛母材融化，界面生成大量Cu2Te，進而使模組失效；而p型與銅基板接合後，則生成大量的Cu3Sn介金屬化合物，使銅電極被完全消耗。在試以鎳基板直接結合後，n型發現鉛與碲元素擴散進鎳電極，造成電極損壞與母材消耗，而p型與電極界面則產生大量針狀Ni3-xSnTe2介金屬化合物。而在應用無電鍍鈷擴散阻障層於碲化鉛及電極中間後，不僅避免上述劇烈界面反應，更有效阻擋原子之交互擴散。在接觸電阻研究中，應用擴散阻障層之n型與p型熱電模組，皆僅顯示微幅上升，對照文獻中其他模組數值發現，本研究之模組接觸電阻皆在可接受數值內。此外，n型與p型模組之機械性質，皆因添加無電鍍鈷擴散阻障層而優化，證明本研究提出之碲化鉛模組在冶金角度、電性接觸、機械行為皆具有良好的表現。最後則是進一步研究模組添加層對碲化鉛母材本身熱電表現之影響，研究發現不論在n型與p型模組中，添加層將有效提升席貝克係數及降低電阻率，進而使熱電材料具有更優異的熱電表現。而經多次量測後發現，模組亦具有良好的熱電性質熱穩定性。此結果表示，中溫型碲化鉛熱電模組，在熱電母材與電極間添加無電鍍鈷擴散阻障層，不僅有效阻擋劇烈界面反應，其模組亦具有良好的電性與強度表現與可靠度，更可提升熱電母材本身之熱電表現，進而增加模組熱電轉換效率，期以貢獻於商用熱電發電模組之開發與研究。;Because of the increasing demand for alternative sources of energy, the development of medium-temperature thermoelectric modules has gained much attention in recent decades. Lead telluride (PbTe) alloy is known for its high thermoelectric performance in both n-type and p-type compounds at temperatures ranging from 200–600 C; however, the performance and stability of the thermoelectric modules during applications are critical concerns in developing practical products. Severe reactions between PbTe alloy, the electrode, and the joining interlayers greatly affect the efficiency of thermoelectric modules. This study investigated the interfacial stability, electrical contact, and mechanical reliability for both n- and p-types PbTe materials on Cu and Ni electrodes with and without Co–P diffusion barrier layer, considering utilization in microelectronics packaging. Severe reactions occurred between medium-temperature thermoelectric PbTe alloys and the Cu or Ni electrodes when they were in contact. When a Cu electrode was used, a eutectic reaction resulted in the formation of molten PbTe and large Cu2Te phases, leading to failure of the Cu/n-PbTe module, and massive Cu3Sn formation caused Cu foil depletion in Cu/p-Pb0.6Sn0.4Te module. When a Ni electrode was used, Pb and Te penetrated into the electrode, and thick needle-like Ni3-xSnTe2 phases formed in n- and p-types PbTe modules, respectively. The severe interfacial problems were avoided by utilizing a Co–P diffusion layer. The mechanical strength was improved because of the insertion of Co–P layer in PbTe joints, and acceptable electrical contacts were measured. In addition, the influence of the added layers on Seebeck coefficient and resistivity enhanced the performance and thermal stability of the tested n- and p-types PbTe thermoelectric materials within the entire temperature range. These results provide new insights for developing highly efficient and reliable n- and p-PbTe thermoelectric power-generation devices using Ni or Cu electrodes suitable for working temperatures.
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