Two-step sputtering for depositing smooth and thin ZnO films on non-heated, non-epiready PET substrates
DOI:
https://doi.org/10.55713/jmmm.v36i2.2461Keywords:
Oxide material, Flexible substrate, Sputtering, Surface, CrystallinityAbstract
Highly crystalline, smooth-surface, and thin zinc oxide (ZnO) films have been successfully deposited on flexible polyethylene terephthalate (PET) substrates using an optimized two-step RF magnetron sputtering technique at ambient temperature. The PET used in this study was a commercially available overhead projector film, which was not epiready-grade and had a lower melting point (~150℃). This issue made high-quality deposition more challenging. In the first step, a thin ZnO buffer layer was deposited at low RF power to provide a smooth and thermally stable surface. This layer served as both a structural template and a thermal barrier during the subsequent high-power deposition of the main ZnO film. Structural analysis confirmed that the buffer layer suppressed lattice mismatch and reduced residual stress. The resulting film showed low surface roughness and no cracking. These features exceeded those of films grown directly at high power, which suffered from poor surface morphology due to substrate deformation. Although the use of a polycrystalline buffer layer led to a reduction in optical transmittance from increased light scattering, the fine-grained structure contributed to improved mechanical stability and dielectric loss suppression. These characteristics made films particularly suitable for piezoelectric applications on flexible substrates. This proposed two-step technique effectively balanced between surface smoothness and structural quality and offered practical solution for the fabrication of high-performance films on thermally sensitive substrates.
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