Moisture Permeation through Ultrathin TiO₂ Films Grown by Atomic Layer Deposition

We report on moisture permeation through ultrathin TiO 2 barrier layers grown by atomic layer deposition (ALD). The steady-state water vapor transmission rate (WVTR) was as low as 6 × 10 -4 g/(m 2 ·day) as determined by electrical Ca test at 60 °C and 85% relative humidity (RH). These Ca test measurement results confirmed the existence of a critical thickness at which the WVTR changes abruptly. In addition, the results revealed that the moisture permeation through the layer occurred via two distinctly different mechanisms. The time to failure of the barrier film, rather than the steady-state WVTR, was proposed in order to evaluate the barrier property more accurately.