Abstract
Plasma-enhanced chemical vapor deposition (PECVD) was used to deposit SiOx thin films of varying thicknesses on parylene C substrates, using hexamethyldisiloxane (HMDSO) as a precursor. The microstructure of SiOx coatings was analyzed using X-ray photoemission spectroscopy (XPS), nanoindentation, and spectroscopic ellipsometry. The composition ranged from oxygen-rich oxides with large silanol OH content to hybrid oxides with larger organic content, while refractive index varied from 1.45 to 1.5 depending on the specimen. Reduced moduli of coatings obtained by nanoindentation varied between 15 and 59 GPa and could be correlated with permeability to oxygen and water vapor through the existence of porosity in a broader sense. It can be concluded that the barrier properties are the result of a complex interplay of microstructural features, with porosity, silanol and carbon content playing important roles in the final thin film properties.
Highlights
Thin metal oxide films are extensively used as gas and water vapor diffusion barriers for polymer substrates in a variety of fields due to their interesting permeability range, transparency and dielectric properties, adaptability to industrial practice, and low relative costs
X-ray photoemission spectroscopy (XPS) studies reveal that SiOx can be considered to be a combination of different oxides in which silicon displays different oxidation states (Bell and Ley, 1988; Finster et al, 1990; Alfonsetti et al, 1993, 1994; Vasquez et al, 2002; Clergereaux et al, 2007)
This explanation is especially suited for oxygen deficient oxides, as the occurrence of lower oxidation states can be linked to a shift of the Si 2p peak to lower energies
Summary
Thin metal oxide films are extensively used as gas and water vapor diffusion barriers for polymer substrates in a variety of fields due to their interesting permeability range, transparency and dielectric properties, adaptability to industrial practice, and low relative costs. This includes applications in the food packaging industry (Dole et al, 2006; Duncan, 2011; Siracusa, 2012), selective drug delivery in biomedical applications (Fu and Kao, 2010; Kumari et al, 2010), and microelectronics encapsulation (Anderson et al, 1988; Birkelund et al, 2011). SiOx thin films have been widely used for this purpose
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