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|Dielectric,Thermal and Structural Characterization of Fluorinated Parylene Films for High Temperature Power Device Surface Insulation|
|Keywords: Fluorinated parylene, Dielectric properties, Power Device Surface Insulation|
|The demand for operating high junction temperature power devices has been increasing for several years, evolving with the availability of SOI (Silicone On Insulator), and more recently, of wide band gap semiconductors. Though the latter ability at elevated temperatures can be very high (up to 300 °C for SOI, above 400 °C for SiC, …) the power device maximum junction temperature remains restricted at lower temperatures, mainly due to the packaging material properties. The insulating surface required for high voltage semiconductor die, is currently made of polyimide (PI) films, thanks to their very good electrical and mechanical characteristics, and their high thermal stability. However, even the most thermally stable polyimides reported up to now (as the HD Microsystems PI 2600 series for instance) exhibit a limit around 300 °C for long use term under air atmosphere. A newly commercially available fluorinated parylene material, the poly(tetra-fluoro-p-xylylene) (PTFPX) appears as a better candidate for one chip (even multi-chip) device surface insulating purpose above 300 °C. The aim of this paper is to evaluate the dielectric properties (i.e. permittivity å’, loss factor tanä, dc conductivity ódc and dielectric strength EBR) between 25 and 400 °C and the thermal properties (i.e. thermal stability, transition temperature) of PTFPX films. Both a broadband dielectric relaxation spectroscopy and a Weibull statistical analysis have been used for measuring the dielectric parameters versus temperature. In addition, differential scanning calorimetry and thermal gravimetric analysis experiments have been performed for evaluating the thermal properties such as the glass transition temperature and the decomposition temperature respectively. The influence of a 400 °C-1 hour post-annealing under N2 atmosphere on the material properties will be presented. Structural characterisation was also performed using X-ray Diffraction analysis. The PTFPX properties will be compared to the PI 2610 ones previously obtained in term of maximum operating temperature limit.|
|Mireille Bechara, Ph.D. Student
Université Paul Sabatier