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

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was the investigation of the film thickness influence on the gas permeation barrier of ultra-thin, cytocompatible tetrahedral amorphous carbon (ta-C:H) films on polyimide (PI) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit these diamond-like carbon films. The results indicate high barrier to hydrogen gas permeation by all film thicknesses (<0.2% H₂ permeation compared to uncoated PI). While the thickness of the ta-C:H layers has minor influence, the number of layers, realized by one- or double-side deposition strongly impacts the barrier effect. 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 film fracture.