Moisture barrier evaluation of SiOx/SiNx stacks on polyimide substrates using electrical calcium test

• The electrical Ca test was used to measure water vapor transmission rate.
• SiOx/SiNx stacks as diffusion barrier of water vapor are effective.
• The optimum barrier structure is 5 pairs of SiOx/SiNx.

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 (SiOx)/silicon nitride (SiNx) stacks were consecutively deposited onto the PI substrate at 350 °C by plasma-enhanced chemical vapor deposition. SiNx and SiOx films show great moisture impermeability while the SiNx film presented higher moisture resistance than the SiOx film. The sample of PI coated with SiOx/SiNx stacks was kept flat by stress compensation of SiNx film and SiOx film. The WVTR value of the optimum barrier structure (5 pairs of SiOx/SiNx) 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 SiOx/SiNx barrier stacks presented on PI have a great potential for flexible electronics applications.