Atmospheric plasma deposition of glass coatings on aluminum

The deposition and properties of glass coatings on aluminum was investigated using atmospheric pressure plasma-enhanced chemical vapor deposition. The plasma, generated with radio frequency power at 27.12 MHz, was fed helium, oxygen and two types of silicon precursors, hexamethyldisilazane and tetraethylorthosilicate. After deposition, the coatings were analyzed for composition, adhesion and dielectric strength. X-ray photoelectron spectroscopy revealed that the glass coatings contained approximately 25% silicon, 50% oxygen and 25% carbon. Scratch tests indicated that the coatings were strongly adherent to the substrates. The glass coatings achieved DC dielectric strengths in between 50 and 250 V for a thickness range of 0.5 to 1.3 μm. The maximum breakdown voltage measured was 400 V. Scanning electron microscopy revealed that breakdown occurred at cracks and other defects in the coatings. These defects appeared to form around areas of surface roughness and contamination.