Thermal Analysis of Parylene Thin Films for Barrier Layer Applications

Biocompatible polymer films demonstrating excellent thermal stability are highly desirable for high-temperature (>250 degrees C) applications, especially in the bioelectronic encapsulation domain. Parylene, as an organic thin film, is a well-established polymer material exhibiting excellent barrier properties and is often the material of choice for biomedical applications. This work investigated the thermal impact on the bulk properties of four types of parylene films: parylene N, C, VT4, and AF4. The films, deposited using the standard Gorham process, were analyzed at varying annealing temperatures from room temperature up to 450 degrees C. Thermal properties were identified by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods, while X-ray diffraction (XRD) analysis showed the effect of high-temperature exposure on the structural properties. In addition to thermal and structural analysis, the barrier properties were measured through the helium transmission rate (HTR) and the water vapor transmission rate (WVTR). Fluorinated parylene films were confirmed to be exceptional materials for high-temperature applications. Parylene AF4 film, 25um thick, demonstrated excellent barrier performance after 300 degrees C exposure, with an HTR and a WVTR of 12.18 x 10(3) cm(3) (STP) m(-2) day(-1) atm(-1) and 6.6 g m(-2) day(-1), respectively.