- 學位論文
電流輔助熱處理對Bi0.5Sb1.5Te3薄膜平行膜面熱傳導性質影響之研究
Effect of current-assisted thermal treatment on in-plane thermal transport properties of Bi0.5Sb1.5Te3 thin films
摘要
傳統熱電塊材經常應用在大尺度的熱管理，而薄膜型熱電材料則常應用在微電子學中小尺度的熱管理。碲化鉍系化合物因其有在室溫下高熱電優質(ZT)的優點，許多研究以此化合物作為基礎來開發高效率的熱電材料。先前的研究已經證明電流輔助熱退火處理能夠改善碲化鉍系薄膜的熱電性質。然而此種薄膜材料的熱性質卻未被完全了解。 本研究延伸了傳統的 3omega量測技術，並發展出一套考慮介面熱阻效應的方法來量測平行於膜面的熱傳導係數。我們藉由量測二氧化矽薄膜來驗證此方法的可行性，爾後用此方法來量測熱電薄膜的平行膜面熱傳導係數。本研究使用濺鍍法沉積 p 型 Bio.5Sb1.5Te3 薄膜在含有氧化層的矽基板上。在熱退火過程中，我們施加一個密度為2500A/cm2 的電流到熱電薄膜，並將溫度控制在 300◦C。相對於單純熱退火試片，電流輔助退火試片擁有較高的 Seebeck 係數與載子遷移率，以及較低的載子濃度。此外，電流輔助退火試片的平行 kx 與垂直膜面 ky 的熱傳導係數都比熱退火試片的還要高。本研究發現電流輔助退火試片呈現出一個熱傳導的高非均向性，且此非均向比例值 kx/ky 為 1.8。根據微結構與熱電性質分析，此非均向性主要由 (00l) 晶面成長所貢獻，而其他因素則對此結果影響不大。
並列摘要
As traditional bulk thermoelectric (TE) materials are usually applied to large-scale heat management, thin film thermoelectric materials are often used to manage small-scale heat in the field of microelectronics. Bismuth telluride based compound materials are well-known for its high ZT value at room temperature regime. Previous studies have shown that a current-assisted thermal annealing was able to improve thermoelectric properties of Bi-Te based thin films. Yet, the thermal conductivity of such thin film materials is not fully investigated. In this research, we extended the conventional 3omega technique and developed a method, which considers the interfacial thermal resistance, to measure the in-plane thermal conductivity of thermoelectric thin films. Silicon dioxide thin films were used to verify the feasibility of our method, and subsequently, we measured the in-plane thermal conductivity of TE thin films. P-type Bio.5Sb1.5Te3 thin films were deposited by sputtering on a thermally oxidized silicon substrate. A current-assisted thermal annealing is applied to the thin films at a current density of 2500A/cm2 when annealed at 300 ◦C. The electrically stressed Bio.5Sb1.5Te3 thin films have higher Seebeck coefficient, higher mobility and lower carrier concentration than the thermally annealed films. In addition, both cross-plane (ky) and in-plane (kx) thermal conductivities of the electrically stressed TE films were found to be larger than those of the thermally annealed films. The electrically stressed films shows a high anisotropy in thermal conductivity with a ratio kx/ky equal to 1.8. According to the microstructural and thermoelectric analysis, the measured anisotropy is mostly attributed to the development of (00l) film texture, as other factors show little impact on such results.