Defect-permeation correlation for ultrathin transparent barrier coatings on polymers

Abstract

We begin this article by presenting a model for gas permeation through defects in barrier coatings, which is based on a very simple geometrical approach. This model allows us to evaluate permeation through a single- or through multiple circular defects in the coating, and also in special cases of size distributions and noncircular geometries. The model agrees well with published results based on complex computer simulations, and it has proven very useful in the analysis of our permeation measurements for barrier-coated plastic films. We then present correlations between measured O2 transmission rate (OTR) values and the number densities and size distributions of defects in SiO2 and SiN barrier coatings on polyester (PET), results which we compare with published data for aluminized PET. We also show the temperature dependence of OTR and H2O vapor transmission rate for SiO2 and SiN coatings deposited on one and on both sides of PET films. The apparent activation energies evaluated from these measurements support the model of defect-dominated mass transport, but suggest different mechanisms for oxygen and water vapor transmission: Excellent agreement is found between measured and calculated OTR values; these, and the apparent activation energy for OTR through single or double side SiO2 and SiN coatings on PET films, confirm that the observed residual OTR is indeed controlled by the presence of (pinhole) defects in the coatings.

Modelling water vapour permeability through atomic layer deposition coated photovoltaic barrier defects

“…It is known that barrier film permeability can be affected by the chemical and physical structures of the barrier, concentration of the permeant, temperature and humidity [7,8] as well as surface defects on the barrier coating that may be induced during the deposition processes [9,10]. Da Silva Sobrinho et al [11] stated that the source of defect-driven permeation has been primarily attributed to pinhole defects [12,13] though more recent studies have shown that in the absence of pinhole defects permeation rates are still reduced by three orders of magnitude over the substrate material [14]. The remaining permeation is shown to be the result of defects in the sub-micromere to several micrometre range, produced by the surface microstructure [15] and/or low density of the films [14][15][16].…”

The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films

“…7. Based on the pinhole calculation model of A.S. da Silva Sobrinho et al [47] the pinhole size is estimated to be > 20 μm in the bilayer architecture assuming pinhole controlled moisture permeation.…”

Defect prevention in silica thin films synthesized using AP-PECVD for flexible electronic encapsulation

“…It is known that single layer encapsulation performance is limited by the presence of defects, such as cracks or pinholes in the inorganic layer [1][2][3][4]9,24,25]. Studies have shown that the use of multilayer encapsulation barriers [1,[3][4][5][6][7][10][11][12]24], deposited using techniques such as sputtering, atomic layer deposition and molecular layer deposition processes, can prevent the formation [1,[3][4][5], and propagation [3], of such defects.…”

“…Studies have shown that the use of multilayer encapsulation barriers [1,[3][4][5][6][7][10][11][12]24], deposited using techniques such as sputtering, atomic layer deposition and molecular layer deposition processes, can prevent the formation [1,[3][4][5], and propagation [3], of such defects. Water vapour transmission rate (WVTR) values for multilayer encapsulation barriers have been reported within the region of 10 -5 g m -2 day -1 (at 30 o C, 90% relative humidity (RH)) [1,6,7], and hence almost achieve the OLED protection requirement of 1×10 -6 g m -2 day -1 (at 25 o C, 40% RH) [4,5,8,12].…”