Mechanically robust silica-like coatings deposited by microwave plasmas for barrier applications

Dense and flexible silicon dioxide-like barrier coatings were deposited by microwave postdischarge (downstream plasma). The optical transparency, recyclability, and compatibility with microwave usage are some of the advantages of SiO_x offers as compared to thin metallic coatings. Generally, porous silicon dioxide coatings with poor barrier properties are obtained by microwave downstream plasmas, because of limited ion bombardment. Here, we demonstrate that by using very high powers, mechanically robust, barrier coatings deposit both by pulsed and continuous microwave downstream discharges. These SiO_x coatings exhibit hardness comparable to Al ₂O₃, but have higher elasticity. Thus, the SiO_x have superior cohesion and the ability to recover after cracking. The high critical tensile and compression strain for crack formation demonstrates that these coatings are very resistant and flexible. Correspondingly, a two orders of magnitude barrier improvement is obtained with 100-nm-thick-coating deposited by continuous discharge. The films deposited by pulsed discharges show better elasticity and flexibility but slightly lower barrier performances compared to the coatings deposited by continuous discharges.