Bi-Sb-Te/Te複合濺鍍薄膜熱電性質與微結構之研究

Thermoelectric Properties and Microstructure of Sputtered Bi-Sb-Te/Te Multilayered Thin Films

朱菀翎(Chu, Wan Ling)

指導教授 ： 廖建能

國立清華大學/工學院/材料科學工程學系/碩士(2016年)

摘要

碲化鉍系化合物在室溫區段具有優秀的熱電優值。但在室溫鍍製的熱電薄膜內有較多缺陷，性質通常不佳，常需經後續退火熱處理來改善性質。在碲化鉍系統中，碲為一高蒸汽壓的元素，易於退火製程中揮發。為補足在退火製程中揮發掉的碲元素，本實驗以磁控濺鍍法製備Bi0.4Sb1.6Te3/Te複合多層膜於聚亞醯胺基板，以抑制薄膜內部Te元素的揮發。首先，本實驗先針對濺鍍製程參數與聚亞醯胺基板之選擇進行研究。結果顯示調高濺鍍製程壓力將使薄膜鍍率降低。調高鍍膜功率將影響成份元素濺鍍效率進而影響薄膜內的元素比例。具有高熱膨脹係數的聚亞醯胺基板會在熱退火製程中產生額外的熱應力（張應力），使熱電膜在高溫退火後表面出現微細孔洞，影響薄膜致密性。低熱膨脹係數的聚亞醯胺基板則無此情形產生。在薄膜電性及微結構部分，所有試片經350 C以上退火處理後皆觀察到富銻析出相，而無多層膜結構的Bi0.4Sb1.6Te3薄膜之析出相尺寸與數量皆多於Bi0.4Sb1.6Te3/Te多層膜結構。在相同退火條件下Bi0.4Sb1.6Te3/Te多層膜較純Bi0.4Sb1.6Te3薄膜擁有較高的載子濃度、較低的電阻率、較高的熱電功率因子與較好的結晶性。且其差異隨著Te層數的增加而變得更加顯著。此結果顯示額外添加的Te層抑制Te孔隙VTe的生成。我們可在含有15層Te經400 C退火的Bi0.4Sb1.6Te3/Te多層膜中得到最高的熱電功率因子約為9.2×10-3 W/mK2。

關鍵字

熱電材料 ； 碲化鉍 ； 多層膜結構

並列摘要

Bismuth telluride-based compounds have superior thermoelectric properties at room temperature regime. The thermoelectric thin films deposited at room temperature usually have many crystal defect. A post thermal treatment is required to eliminate the defects and improve the thermoelectric properties of the thermoelectric thin films. However, Te atoms have high vapor pressure and easily to evaporate during the annealing process, resulting in the variation of composition. In this study, a Bi0.4Sb1.6Te3/Te multilayered structure has been deposited on a polyimide substrate by RF/DC magnetron sputtering. The extra Te layers inserted in between the Bi0.4Sb1.6Te3 films is used to compensate the Te loss during thermal annealing. First, the effects of sputtering parameters and polyimide substrate on the characteristics of Bi0.4Sb1.6Te3 were investigated. The results show that a high process pressure reduces the deposition rate of the Bi0.4Sb1.6Te3 thin film. The composition will vary by changing the sputtering power due to different elemental sputter yield. Moreover, the polyimide substrate of high coefficient of thermal expansion possesses a high tensile thermal stress at annealing temperature and is susceptible to the formation of micro voids in the Bi0.4Sb1.6Te3 thin films. As for the microstructure and thermoelectric properties, we observed that some Sb-rich phases precipitate at the film surface after the specimen annealed at the temperature higher than 350 C. Interestingly, the Bi0.4Sb1.6Te3/Te films exhibits less and smaller Sb-rich precipitates than the Bi0.4Sb1.6Te3 films. The Bi0.4Sb1.6Te3/Te films were found to have a higher carrier concentration, a lower electrical resistivity and better crystallinity than the Bi0.4Sb1.6Te3 films. The discrepancy appears to increase with the increasing number of Te layers in the sample. It is suggested that the excess Te layers in the Bi0.4Sb1.6Te3/Te films are able to compensate the Te loss and suppress the formation of Te vacancies VTe during the high temperature annealing. A high thermoelectric power factor of 9.2×10-3 W/mK2 is obtained for the Bi0.4Sb1.6Te3/Te samples with 15 Te intersection layers after annealed at 400 C.

並列關鍵字

thermoelectric materials ； bismuth telluride ； multilayer structure

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