High-performance transparent barrier films of SiO_x/SiN _x stacks on flexible polymer substrates

A transparent barrier structure consisting of silicon oxide (SiO _x)/silicon nitride (SiN_x) stacks was deposited on a polycarbonate substrate at 80°C by plasma-enhanced chemical vapor deposition. Details of radio-frequency (rf) power effects on the SiO_x and SiN_x film properties in terms of etching rate, refractive index, internal stress, and water vapor transmission rate (WVTR) were investigated. It was found that the impermeability, flexibility, and optical property of the SiO_x/SiN_x barrier films can be tailored by varying the rf power. A gradual decrease in the compressive internal stress of each stack film was designed to prevent the stress-induced cracks during the multilayer deposition process. The WVTR value of the optimum barrier structure (SiN _x + 6 pairs of SiO_x/SiN_x) can reduce to 3.12 × 10^-6 g/m²/day under a calcium test (100 days at 25°C, 40% relative humidity). After 5000 cyclic bending tests in a compressive mode, the WVTR value can keep below 3.54 × 10^-5 g/m²/day. The performance of the SiO_x/SiN_x, barrier stacks presented has high potential for future flexible electronics applications.