Thermal properties of thin insulating layers using pulse transient hot strip measurements

A transient method for measuring thermal conductivity and thermal diffusivity has been developed for studies of insulating solid surface layers with thicknesses down to a few micrometers. The method is based on a procedure by which a string of square pulses, via an ac-coupled circuit, is applied to the hot strip (deposited thin film), which is acting both as a heat source and a sensor of the temperature increase of the substrate. By performing transient experiments over short times (selecting a short pulse duration), it is possible to limit the depth under the hot strip beyond which the thermal properties of the substrate does not influence the recorded thermal properties. A series of experiment with probing depths ranging from 4 to 10 μm has shown that the thermal properties measured with this technique agree very well with independently measured values provided the pulse duration is small compared to the pulse period. Because of the small probing depth and the size of the thermal probe this novel technique should open up possibilities for studying thermal properties of evaporated and sputtered layers of insulators, a kind of solids which up to now has not been accessable for direct measurements of thermal properties.