Enhanced Impermeability To Moisture-vapor Of Poly(Chloro-p-xylylene) Film By Hyperthermal Hydrogen Induced Cross-linking Technique

Parylene C membrane(poly chlorinated p-xylyene, hereinafter referred to the PC film) is widely used in fields of semiconductor devices, sensors, microelectronics and material moisture protection because of its excellent moisture impermeability, anticorrosive, electric insulation, physical and mechanical properties, optical and biological compatibility. However, PC film is difficult to meet the enhanced requirement on the moisture impermeability in some application fields. Therefore, it needs to be modified or composite with other coating materials to obtain more excellent barrier performance for water vapor. Nevertheless, it is difficult to obtain an excellent coating bonding strength for some coating materials(such as Si O2) on the surface of PC membrane due to its low surface energy. Many surface modification methods, such as chemical oxidation, plasma surface treatment and ultraviolet irradiation have been studied extensively with aims to enhance the surface energy of PC membrane and improve its bonding strength with other materials. But these techniques will damage PC membrane and degrade its integrate properties. Therefore, it is very necessary to find new surface modification methods to increase the bonding strength between the PC membrane with other coating materials and improve the barrier performance of the composite film.In this study, a new type of surface modification technique, that is the Hyperthermal Hydrogen Induced Cross-linking(HHIC), was used to modify the surface of PC membrane in order to enhanced the impermeability to moisture and the bonding strength with other coating materials. In HHIC system, hydrogen protons with proper kinetic energy are produced. Those molecules with kinetic energy larger than 10 eV are called hyperthermal hydrogen, which can selectively fracture hydrocarbon bonds when colliding with the molecular chain on surface of PC film and produce carbon free radicals which will crosslink subsequently. Because the kinetic energy of hyper thermal hydrogens can be controlled easilyable, the bond-cracking and cross linking process can also be regulated feasibly. Therefore, it is a kind of environmental friendly and mild surface modification method.The main results are list as followed:(1) The surface molecular chains of PC film can be cross linked with HHIC technique, which results in the decrease of water vapor transmittance of PC thin film from the original 0.48 g/(m2·day) down to 0.12 g/(m2·day), but still keeps its light transmittance and mechanical strength.(2) Polyacrylic acid(PAA) can easily be grafted on surface molecular chains of PC film using HHIC technique, which is beneficial to improving its surface wettability(the water contact angle on the surface of PC film reduces from the initial the 84 to 23 degrees) and enhancing bonding strength with other coating materials, such as SiO2.(3) Composite films of PC-SiO2 and PC/PAA(HHIC grafting)-SiO2 with the SiO2 coating thickness of both 150 nm are prepared using plasma enhanced chemical vapor deposition(PECVD) method in order to further improve the water vapor barrier performance of PC film. The results show that these composite films present excellent water vapor barrier properties with the water vapor transmittance dropped from 0.48 g/(m2·day) to 0.01 g/(m2·day). And the grafting of PAA can significantly improve the adhesion strength between the PC membrane and the SiO2 coating.