Photo-acoustic measurement of thermal conductivity of thin films and bulk materials

The photoacoustic (PA) technique is one of many techniques for measuring thermal conductivity of thin films. Compared with other techniques for thermal conductivity measurement, the photo acoustic method is relatively simple, yet is able to provide accurate thermal conductivity data for many types of thin films thin films and bulk materials. In this work, the PA measurement in a high frequency range is made possible by a newly developed PA apparatus, which extends the limit of the PA technique. Thermal conductivities of SiO2 with thicknesses from 0.05 to 0.5 mum on Si wafer, e-beam evaporated thin nickel film on Si wafer, and thermal barrier coatings are obtained. In addition to the commonly used phase shift fitting, which is only appropriate for thermally-thin films, an amplitude fitting method is developed and employed for measuring both thin films and bulk materials with smooth or rough surfaces. Comparing results by amplitude fitting to those obtained by other methods and reference values shows good agreements. Applications and limitations of the photoacoustic technique are discussed.