Moisture barrier coating of AlN and Al₂O₃ multilayer film prepared by low-temperature atomic layer deposition

AlN and Al₂O₃ multilayer films intended as moisture barriers were deposited on polyethylene naphthalate films by remote-type plasma-enhanced atomic layer deposition. The deposition temperatures for AlN and Al₂O₃ were 160 and 20 °C, respectively. It was assumed that the AlN and Al₂O₃ interface would suppress the formation of dislocations and pinholes that lead to moisture diffusion. The AlN top layer was expected to act as a water-resistant layer. The surface morphology and the crystallinity of the deposited film were investigated by atomic force microscopy (AFM) and x-ray diffraction, respectively. The gas barrier property of the multilayer film was determined by the water vapor transmission rate, which was measured as 1.3 × 10⁻³ g/m²/day at a temperature of 40 °C and a relative humidity (RH) of 90%. The AFM image showed that the AlN top layer remained unchanged during water vapor contact for 120 h at 40 °C and 90% RH. The applicability of the multilayer film as a moisture barrier coating for compound semiconductor devices is discussed.