中溫熱電材料Zn4Sb3模組之擴散阻障層及緩衝層之設計

Abstract

近年來，隨著環境環保意識的倡導，石化能源的消耗的問題必須被解決的情況下，熱電材料的應用已漸漸的被大眾發揚。熱電材料模組將環境中的熱源抑或是廢熱轉換成可以被利用的電力。然而就目前商業化的熱電材料模組中，Bi2Te3是最被廣泛使用的，然而他所能提供最完美的轉換效率僅能在工作溫度攝氏200度之下，所以在工業廠區中較高的溫度的熱源，即無法被有效使用。因此β-Zn4Sb3中溫熱電材料被選用來應用在較高的溫度區間，他是一個極具有研究潛力的中溫熱電材料，其具有低的毒性、製備簡易、耗費低，此外，他的熱導率在1 W/mK 之下接近非晶的值。 本實驗的目是探討在電鍍焊料Ag和熱電材料β-Zn4Sb3之間漸鍍擴散阻擋層和緩衝層Ti/W-Ti/Ti的可行性，作為熱電模組化的先行研究。介面的擴散行為藉由掃描式電子顯微鏡以及歐傑電子能譜儀觀察，Ag、Ti、Zn穿過緩衝層Ti之後，可以觀察到成功地被阻擋在W-Ti層。此外，薄膜的片電阻也隨著退火溫度的上升而下降，說明了在較高的溫度，其結晶性上升因而提供了更好的電的性質，我們也實驗了經過固液擴散接合Cu電極的熱電模組，在經過了24小時攝氏400度的環境下，可以完整地呈現擴散被有效抑制的結果。

As the public awareness in environmental issues has arisen in recent years, the applications of thermoelectric (TE) modules are becoming widespread for reducing fuel consumption. TE modules convert heat from the environment into electricity to meet the goal of waste heat recycle. While commercialized TE modules Bi2Te3 provide its best conversion efficiency below 200 ℃, it wouldn’t considered as a proper candidate for higher working temperature in the industry environment. Therefore β-Zn4Sb3 is chosen as a promising mid-temperature TE due to their low toxicity and low-cost for fabrication. In addition, β-Zn4Sb3 has quite low thermal conductivity close to the amorphous limit of below 1 W/mK. The purpose of this work was to investigate the feasibility of using sputtered Ti/W-Ti/Ti multilayer as a diffusion barrier and buffer layer stack between β-Zn4Sb3 bulk material and electroplated Ag layer for mid-temperature thermoelectric (TE) module applications. Interdiffusion at the interface was examined by both scanning electron microscope and Auger electron spectroscopy. After penetrating the Ti buffer layer, Ag, Zn and Sb were successfully blocked by the W-Ti diffusion barrier layer. We also proved that the TE module with diffusion barrier and buffer layers showed phase stability after high temperature aging. Also, the sheet resistance decreased as the temperature increased and it indicated good electrical properties at high working temperatures. In addition, the solid-liquid interdiffusion method was used to join the TE module, and the bonding remained stable at the TE module working temperature of 400 °C for 24 hours.