Roll-to-Roll Atmospheric Atomic Layer Deposition of Al2O3 Thin Films on PET Substrates†

The conventional atomic layer deposition (ALD) technologies are capable of fabricating supreme quality thin films of a wide variety of materials, but sequential introduction and purging of precursors and inert gases prevent its application in the mass production of thin films under atmospheric conditions. In this study, we introduce a novel technique of roll-to-roll atmospheric (R2R-A)ALD using a multiple-slit gas source head. Thin films of Al₂O₃ are developed on a movable web of polyethylene terephthalate (PET) substrate at 50 °C. The Al₂O₃ deposition is carried out under a working pressure of 740 Torr, which is very near to atmospheric pressure (760 Torr). An appreciable growth rate of 0.98 Å per cycle is observed at a carefully optimized web velocity of 7 mm s⁻¹. Good morphological, chemical, electrical, and optical characteristics are shown by the Al₂O₃ films produced at a large scale. Low root mean square roughness (R_q) values of 1.85 nm and 1.75 nm are recorded for the Al₂O₃ films deposited at 50 °C over 75 and 125 ALD cycles, respectively. The appearance of Al 2p, Al 2s, and O 1s peaks at the binding energies of 74 eV, 119 eV, and 531 eV, respectively, in the X-ray photoelectron spectroscopy (XPS) analysis confirms the fabrication of Al₂O₃ films, which is also supported by Fourier transform infrared spectroscopy (FTIR). The films show excellent insulating properties, and optical transmittance of more than 85% is recorded in the visible region.