Evaluation of gas permeation through barrier layers for organic electronic devices by helium detector method

Evaluation of gas permeation properties through barrier layers is important for the development of flexible organic light-emitting devices (FOLEDs). In this reported work, an helium (He) leak detector was used in a novel permeation test for metallic barrier layers. Aluminium (Al) or chromium (Cr) film was deposited as a barrier layer onto a polyethylene terephthalate (PET) substrate using a magnetron sputtering system. For the samples of PET substrates with Al and Cr films at thicknesses of 200 nm, the He pressures were 3.1 × 10^-6 and 1.3 × 10^-5 Torr, respectively, as measured via He detector testing. The poor permeation blocking by the Cr film was because of microcracks. The He pressure for samples with 1 000 nm thick Al coating and for Al foil (30 μm) showed different values of 3.2 × 10^-8 and 1.1 × 10^-10 Torr, respectively, which indicated high sensitivity in a low permeation range. The high sensitivity in permeation properties measured by He detector testing reflected the qualities of He that include one of the lightest weights known to science and a very small size. This He detector test will be useful in the development of long-life FOLEDs, as it will aid the measuring of the gas permeation properties of barrier layers that are highly effective in blocking water vapour.