Abstract: Al2 O3 film and SiO2 film were deposited on PET substrates by magnetron sputtering , and SiO2/Al2 O3/PET composite films were prepared .The surface morphology and the water vapor transmission ( WVT ) rates of the composite films were characterized by scanning electron microscopy ( SEM ) and moisture permeability instrument respectively . The influences of Al 2 O3 film preparation parameters , including radio-frequency(RF) power, argon flow, vacuum degree and sputtering time on the WVT rates of SiO2/Al2 O3/PET composite films were investigated .The results show that the WVT rates decrease with the increase in vacuum degree , and firstly decreases and then increases with the increase in RF power , argon flow and sputtering time .Among the four process parameters , vacuum degree had the greatest effect on WVT rates, followed by argon flow , RF power and sputtering time .The optimal process parameters were obtained as the vacuum degree of 0.5 ×10 -3 Pa, RF power of 300 W, sputtering time of 6 min and argon flow of 70 mL· min-1 .

Key words: Al2 O3 film and SiO2 film were deposited on PET substrates by magnetron sputtering , and SiO2/Al2 O3/PET composite films were prepared .The surface morphology and the water vapor transmission ( WVT ) rates of the composite films were characterized by scanning electron microscopy ( SEM ) and moisture permeability instrument respectively . The influences of Al 2 O3 film preparation parameters , including radio-frequency(RF) power, argon flow, vacuum degree and sputtering time on the WVT rates of SiO2/Al2 O3/PET composite films were investigated .The results show that the WVT rates decrease with the increase in vacuum degree , and firstly decreases and then increases with the increase in RF power , argon flow and sputtering time .Among the four process parameters , vacuum degree had the greatest effect on WVT rates, followed by argon flow , RF power and sputtering time .The optimal process parameters were obtained as the vacuum degree of 0.5 ×10 -3 Pa, RF power of 300 W, sputtering time of 6 min and argon flow of 70 mL· min-1 .