Thermal diffusivity of highly conductive thin films
Abstract
This thesis is concerned with the problems associated with the development of experimental techniques for the measurement of thermal diffusivity of highly conductive thin films. Two experimental methods were investigated in detail: a gas-photoacoustic method for the through thickness measurement, and a step heating method for the in-plane measurement. The gas-photoacoustic technique is a periodic heat-flow method. Signals are analyzed in the frequency domain. The results of preliminary experiments coupled with theoretical analysis for metallic thin samples show that this approach is not readily adaptable for highly conductive thin films. However, analysis of phase signals obtained in the Front Surface Illumination more is a feasible approach for the measurement of low conductive, free standing thin films or two-layer specimens. The step heating technique is a transient heat flow method. Transient temperature are generated in a strip-shaped sample by step heating one end of the sample while clamping the other end to a heat sink. Three detectors along the heat path are used to obtain transient temperature data. Satisfactory results over a wide temperature range were obtained for both low conductive and highly conductive thin specimens including free standing CVD diamond films. Experiments demonstrated that the step heat technique is a fast, simple and inexpensive approach compared with other techniques proposed for thin films. In determining the thermal diffusivity of the measured specimen through transient temperature measurements, prior knowledge of the specimen's properties and those of a reference material are unnecessary. If the density/specific heat product for the material is known, the thermal conductivity may be determined from the diffusivity results. The results of step heating indicate that this technique has a large potential in the measurement of highly conductive thin films deposited on a low conductive substrate. The simulation shows that the diffusivity of thin films can be estimated providing the specimen geometry factors and the properties of the substrate are known. Further improvements of the technique are suggested.
Degree
Ph.D.
Advisors
Taylor, Purdue University.
Subject Area
Mechanical engineering|Materials science
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