Transparent barrier coatings on polyethylene terephthalate by single- and dual-frequency plasma-enhanced chemical vapor deposition

Abstract

Transparent barrier coatings on polymers are receiving much attention in industry, for pharmaceutical, food and beverage packaging applications. Plasma-enhanced chemical vapor deposition (PECVD) is among several competing techniques which can produce thin layers of inorganic glassy barrier materials. In this article we describe the performance of silicon compounds (SiO2 and Si3N4) on 13 μm polyethylene terephthalate (PET) substrates, the barrier coatings being deposited in a dual-frequency (microwave/radio frequency) pilot-scale PECVD reactor for continuously moving flexible webs up to 30 cm in width. The volatile silicon compound used for SiO2 deposition is HMDSO (C6H18Si2O), while SiH4 serves to deposit Si3N4. Coating thicknesses, d, in the range 8 nm⩽d⩽200 nm, are measured using a variety of techniques, namely stylus profilometry, continuous wavelength optical interferometry, x-ray fluorescence, variable angle spectroscopic ellipsometry, and transmission electron microscopy, while film compositions are determined by x-ray photoelectron spectroscopy. Oxygen transmission (OTR) and water vapor transmission (WVTR) measurements are carried out with MOCON “Oxtran” and “Permatran-W” instruments, respectively. As also reported by other workers, we typically find OTR values of about 0.5 scc/m2 day and WVTR about 0.3 g/m2 day, for barrier thicknesses exceeding a “critical” value (dc, about 15 nm), but the minimum permeation values depend upon the concentration of defect sites in the coating (mostly related to substrate microroughness). In order to confirm this correlation, we have developed a technique combining reactive ion etching through the PET, followed by optical and transmission electron microscopies, to characterize the types and number densities of coating defects. On the basis of these, we find good agreement between measured and calculated values of OTR.

Al2O3/ZrO2 Nanolaminates as Ultrahigh Gas‐Diffusion Barriers—A Strategy for Reliable Encapsulation of Organic Electronics

“…Plasma-assisted processes, such as sputtering or plasma-enhanced chemical vapor deposition (PECVD), provide high quality films, but their typically reported OTR and WVTR values of about 0.5 cm 3 m À2 day À1 and 0.3 g m À2 day À1 , respectively, limited by imperfections in the films, are not sufficient for OLED applications. [5,6] Moreover, efficient step coverage and conformal coating are not straightforward with these techniques.…”

Non-Heat Assistance Plasma-Enhanced Chemical Vapor Deposition of SiCxNyOzFilm Using Monomethylsilane, Nitrogen and Argon

“…1 Well-known suitable coating materials are silicon carbide, silicon nitride, silicon dioxide and their mixtures, such as the SiC x N y O z film. [1][2][3] In order to apply a suitable coating to the various material surfaces, particularly to low melting point metals, such as aluminum, the coating film should be formed at temperatures as low as possible, desirably at room temperature without any heating assistance. Additionally, the SiC x N y O z film is widely studied for developing the highly functional films of low k, diffusion barrier, cupper capping layer and etch stop, for the advanced electronics device fabrication.…”

SiOx‐Based Multilayer Barrier Coatings Produced by a Single PECVD Process

“…Therefore in order to obtain a continuous barrier, ceramic layers should be thicker at least twice the interface thickness plus a certain critical value in the range 15-60 nm as reported in literature. [13][14] The results of the CO 2 permeability measurements are shown in Figure 4. The best result shows a BIF of about 65 with the ML design: four dyads C50/P50.…”