Moisture barrier evaluation of SiO /SiN stacks on polyimide substrates using electrical calcium test

Abstract Electrical calcium (Ca) test was used to measure water vapor transmission rate (WVTR) through polyimide (PI) substrate with barrier films. The WVTR was obtained by measuring the resistance of the Ca as a function of time. Barrier films consisted of silicon oxide (SiO x )/silicon nitride (SiN x ) stacks were consecutively deposited onto the PI substrate at 350 °C by plasma-enhanced chemical vapor deposition. SiN x and SiO x films show great moisture impermeability while the SiN x film presented higher moisture resistance than the SiO x film. The sample of PI coated with SiO x /SiN x stacks was kept flat by stress compensation of SiN x film and SiO x film. The WVTR value of the optimum barrier structure (5 pairs of SiO x /SiN x ) is 5.58 × 10 − 6 g/(m 2 day) under an electrical Ca test (25 °C, 40% relative humidity). After 500 times cyclic bending in a compressive mode, WVTR value keeps below 4.32 × 10 − 5 g/(m 2 day). The SiO x /SiN x barrier stacks presented on PI have a great potential for flexible electronics applications.