Study of Gas Permeation Through Thin ta-C:H Films

Protective ultra-thin barrier lms gather increasing economic interest for controlling permeation and di usion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was the investigation of the lm thickness in uence on the gas permeation barrier of ultra-thin, cytocompatible tetrahedral amorphous carbon (ta-C:H) lms on polyimide (PI) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit these diamond-like carbon lms. The results indicate high barrier to hydrogen gas permeation by all lm thicknesses (<0.2% H2 permeation compared to uncoated PI). While the thickness of the ta-C:H layers has minor in uence, the number of layers, realized by oneor double-side deposition strongly impacts the barrier e ect. Finally, tests under tensile stresses showed minor impact in the elasto-plastic deformation regime, but the expected strong increase of gas permeation after exceeding the tensile strength and lm fracture.