Improving insulating film deposition stability with atmospheric pressure plasma jet by post-mixing precursor feedthrough with hollow electrode

•A post-mixing precursor feedthrough is proposed for APPJ film deposition.•The contamination thickness is reduced by 79.9 % for the post-mixing feedthrough.•Contamination increases the breakdown voltage and decreases the discharge strength.•Surface hydrophobic and insulating performances are enhanced after the treatment.•Film deposition stability is remarkably improved for the post-mixing feedthrough. Film deposition with atmospheric pressure plasma jet (APPJ) is an effective approach to enhance surface performances of insulating materials for its high reactivity and flexible operation. However, the plasma-activated precursor will inevitably produce inner-wall contamination in the dielectric tube as it travels through the electrode gap, deteriorating film deposition stability during long-term operation. In this paper, a post-mixing precursor feedthrough is designed to suppress the dielectric tube contamination and improve film deposition stability. The influences of traditional pre-mixing feedthrough and post-mixing feedthrough proposed in this paper on discharge and film deposition stability are compared. The thickness of inner-wall contamination is acquired by image processing technique. The electrical and optical discharge characteristic variations with operation duration are diagnosed to evaluate the discharge stability. The film performance is characterized by the water contact angle (WCA) and flashover voltage. Finally, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) measurements are performed for the film physicochemical property variations to explore the mechanism about the effect of precursor feedthrough on film deposition stability. The results indicate that the thickness of the contamination is reduced by 79.9 % for the post-mixing feedthrough after a 30-minute operation. Contamination growth increases the initial discharge voltage and decreases the discharge strength, which is remarkably inhibited for the post-mixing feedthrough. The degradation of WCA and flashover voltage for the post-mixing feedthrough is