Moisture barrier evaluation of SiO_x/SiN_x stacks on polyimide substrates using electrical calcium test

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/(m² 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/(m² day). The SiO_x/SiN_x barrier stacks presented on PI have a great potential for flexible electronics applications.