| Summary: | 碩士 === 國立清華大學 === 物理系 === 104 === 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.
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