Thermal conductivity and interfacial effect of parylene C thin film using the 3-omega method
Résumé
Parylene has attracted a great interest in the last years because of its potential use in many fields. Among all kinds of parylene, parylene C seems the most interesting one for a large range of applications. In this paper, we are interested in its thermal properties, and in particular the thermal conductivity of thin films. This later is determined by the so-called three-omega method. This technique makes use of a thin conducting strip, in contact with the material under test. The metal wire serves both as a heat source for applying a heat flux and a sensitive thermometer for measuring the surface temperature. The thermal conductivity of parylene C films of different thicknesses (210, 440 and 760 nm) deposited by CVD process on borosilicate substrates is investigated. It is demonstrated that the effective thermal conductivity increases as a function of the thickness of thin film (81.20 x 10(-3), 88.37 x 10(-3) and 92.81 x 10(-3) W m(-1) K-1 are measured, respectively). This effect is produced by the phonon scattering boundary at the interface between substrate/film and film/heater. To highlight the presence of contact thermal resistances and to estimate their value, a numerical approach, based on a finite element method using the software COMSOL(R) Multiphysics, is also proposed. This study shows that the main part (97%) of the interfacial thermal resistance is due to the contact between the parylene C film and the substrate.