Thermal Conductivity Analysis of Diamond Films.

Thermal Conductivity Measurement;Textured Diamond;3 omega method;Heated Bar method;Nucleation Layer

Govindaraju, Nirmal ; Prof. Zlatko Sitar, Committee Chair,Govindaraju, Nirmal ; Prof. Zlatko Sitar ; Committee Chair

University:North Carolina State University

关键词: Thermal Conductivity Measurement;    Textured Diamond;    3 omega method;    Heated Bar method;    Nucleation Layer;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/3152/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

Thermal conductivity is a fundamental material property which governs heat transport in solids. A basic material property like thermal conductivity is influenced by the structure of the material, and hence the method of synthesis and the defects present in the material. With the advent of high speed microelectronics with extremely large device densities, there is an ever increasing need to find solutions for effective heat dissipation, especially in the context of Silicon On Insulator (SOI) technology. One solution to this problem would be to use diamond as the buried dielectric. Therefore, for the effective use of diamond films, it is essential that the thermal properties, especially the thermal conductivity, of the material be characterized.A brief background of the structure, properties and synthesis of diamond is presented. This is followed by a review of some of the experimental methods used for measuring the thermal conductivity of diamond. In order to measure the thermal conductivity of CVD diamond, two different measurement approaches are used. The first is the 3ω technique, which uses thermal waves generated by a heater/thermometer to probe the underlying material and extract the thermal conductivity from the measured temperature rise. Measurements on bulk substrates of different materials, including diamond, yield results consistent with values found in literature. However, in the case of diamond thin films, the method proves to be unreliable since there is significant deviation from the assumption of one dimensional heat transportthrough the solid. An alternative method, known as the heated bar technique, is therefore employed to measure the thermal conductivity of the sample.The heated bar technique employs one dimensional steady state heat transfer to measure the thermal conductivity of the material. An assembly of thin film heaters and thermocouples is deposited on a free standing substrate. A known quantity of heat is input into the material and the resulting temperature profile is measured using thin film thermocouples. From the measured temperature profile and the applied heat flux, the thermal conductivity of the material is extracted.Thermal conductivity measurements are performed on diamond films as a function of morphology and thickness. It is found that there is a significant difference in the measured value of the thermal conductivity between highly oriented diamond (HOD) samples and samples having fiber texture. This is attributed to the presence of low angle grain boundaries in the HOD films, which serve to refract rather than scatter phonons which are the dominant heat carriers in the case of diamond. The effect of the nucleation layer on the lateral thermal conductivity of the material is ascertained by performing thermal conductivity measurements before and after etching of 10 μm of diamond from the nucleation side of a textured substrate. It is found that the removal of the thermally poor quality material does not significantly affect the lateral thermal conductivity of thick diamond films.