銻化鈷薄膜熱電熱時效之研究

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Title:	銻化鈷薄膜熱電熱時效之研究
Authors:	陳映竹;Chen, Ying-Chu
Contributors:	化學工程與材料工程學系
Keywords:	銻化鈷;薄膜熱電
Date:	2020-08-17
Issue Date:	2020-09-02 15:14:09 (UTC+8)
Publisher:	國立中央大學
Abstract:	隨著能源與環保議題興起，熱電材料近年來備受矚目。科技的進步，使得人們開始追求微型化且具有高輸出功率的熱電裝置。本實驗選擇對環境無害的CoSb3作為主要探討的中溫熱電材料，藉由射頻磁控濺鍍製備厚度300 nm的CoSb3熱電薄膜於SiO2/Si上，測試試片分別為單層CoSb3與Cu/Ti/CoSb3，而Cu/Ti/CoSb3中的Ti作為Cu與CoSb3之間的接著層。對單層CoSb3熱電薄膜進行不同的熱時效溫度於不同時間下之熱時效分析，以TGA、SEM、EDS以及GIXRD分別進行薄膜的熱重損失、元素組成分析以及相鑑定，藉由單層CoSb3所得之熱時效結果再進一步以Cu/Ti/CoSb3進行熱時效測試。經熱重損失分析結果得知，本實驗製備的CoSb3約於480 oC時會發生Sb昇華之現象，因此本實驗將以低於480 oC進行熱時效測試。經400 oC時效48小時之單層CoSb3熱電薄膜，其SEM影像觀察到CoSb3會發生晶粒成長，使得薄膜中生成孔洞且令薄膜不連續；於450 oC時效120小時後，由於Sb昇華導致CoSb3完全轉變為CoSb2，並且有部分CoSb2轉變成CoSb，因此適合此CoSb3熱電薄膜的環境溫度需低於400 oC，故選擇300 oC作為熱時效溫度，並對Cu/Ti/CoSb3進行不同時間之熱時效測試，觀察Cu/Ti/CoSb3中金屬電極的Cu原子於CoSb3熱電薄膜表面擴散情形，可推得300 oC時，Cu於CoSb3的擴散係數約為{10}^{-7}\ ({cm}^2/s)，並且量測熱時效前後Cu/Ti/CoSb3之接觸電阻，可知Ti雖可作為Cu與CoSb3的接著層，但隨著熱時效時間拉長，Cu/Ti/CoSb3的接觸電阻率會隨之增大，因此，需選擇另一有效接著層用以接著Cu與CoSb3。;Thermoelectric materials have attracted great attention in recent years due to sharp increase of energy consumption and environmental protection purpose. Thermoelectric (TE) devices which have shrinking dimensions and high output efficiencies are developed with the advance of materials science and technology. CoSb3 thin film, the eco-friendly medium-temperature TE material, is chosen as the material in this study. CoSb3 thin films with a thickness of 300 nm were deposited on SiO2/Si substrate by radio-frequency (RF) magnetron sputtering method. There were two types of testing samples which were single CoSb3 layer and Cu/Ti/CoSb3 respectively, and Ti acted as the adhesion layer of Cu and CoSb3. The investigation focused on thermal aging results of single CoSb3 layer at different temperatures and various aging durations of time. TGA, SEM-EDS, and GIXRD were used to investigate the thermal weight loss, elemental composition and phase characterization of CoSb3thin films, respectively; furthermore, the aging conditions of Cu/Ti/CoSb3 were determined by the results of single CoSb3 layer after aging tests. The result of TGA showed that there was a weight loss at 480 oC due to sublimation of Sb. SEM observation indicated that grain growth of the CoSb3 film occurred at 400 oC after aging for 48 hours, and voids appeared on the thin film and resulted in discontinuity of thin film. Besides, because of Sb sublimation, CoSb3 phase totally transformed to CoSb2, and partial CoSb2 became CoSb at 450 oC for 120 hours. The proper operating temperature of CoSb3 thin films should be less than 400 oC; therefore, the module of Cu/Ti/CoSb3 was aged at 300 oC for different durations of time to discuss the Cu diffusion on CoSb3 surface. The diffusivity of Cu in CoSb3 at 300 oC is about {10}^{-7}(cm^2/s). The contact resistivities of unaged and aged Cu/Ti/CoSb3 were measured. The contact resistivities of Cu/Ti/CoSb3 increased with prolonging aging durations. Consequently, another alternative adhesion layer should be chosen between Cu and CoSb3.
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