| AVS 60th International Symposium and Exhibition | |
| Thin Film | Wednesday Sessions |
| Session TF+VT-WeM |
| Session: | Thin Film Permeation Barriers and Encapsulation |
| Presenter: | A. Perrotta, Eindhoven University of Technology, Netherlands |
| Authors: | A. Perrotta, Eindhoven University of Technology, Netherlands G. Aresta, Eindhoven University of Technology, Netherlands W. Keuning, Eindhoven University of Technology, Netherlands M.C.M. van de Sanden, Eindhoven University of Technology; DIFFER, Netherlands W.M.M. Kessels, Eindhoven University of Technology, Netherlands M. Creatore, Eindhoven University of Technology, Netherlands |
| Correspondent: | Click to Email |
Although satisfactory results in term of moisture permeation barrier performance have been achieved for the encapsulation of organic electronic devices, a deeper understanding of the relation between barrier properties and permeation pathways is still necessary. This contribution focuses on the role of the residual nanoporosity in the inorganic layer in controlling its barrier performance.
Plasma-assisted atomic layer deposition (PA-ALD) and plasma-enhanced chemical vapor deposition (PECVD) inorganic (i.e. Al2O3 and SiO2) barrier layers have been extensively analyzed by means of IR spectroscopy, spectroscopic ellipsometry, Rutherford backscattering spectroscopy and elastic recoil detection. The calcium test has been performed to determine the intrinsic water vapor transmission rate (WVTR), i.e. by excluding the local white spot development, as well as the effective WVTR values. Ellipsometric porosimetry (EP) has been applied to determine the open porosity and pore size range of the layers. Two different adsorptives have been adopted as probe molecules, i.e. trivinyltrimethylcyclotrisiloxane (dV3D3 = 1 nm) and water (dH2O = 0.3 nm). A correlation between the residual nanoporosity and the intrinsic barrier properties of moisture barriers has been found, regardless the chemistry of the layer and deposition technique used. Pores larger than 1 nm with a relative content above 1% have been found responsible for poor barrier layers characterized by a WVTR in the range of 10-2-10-3 gm-2day-1. Furthermore, the pore size range of [0.3-1] nm and its relative content have been found to drive the transition in WVTR from 10-4 to 10-5-10-6 gm-2day-1, highlighting the role of the residual nanoporosity in controlling the intrinsic barrier properties.
Electrochemical impedance spectroscopy (EIS) has also been adopted as novel technique in the evaluation of the moisture barrier properties. Water diffusion through the barrier has been followed as a function of the variation of the electrochemical properties and related to the layer porosity.
The control at nanoporosity level has also been addressed by coupling a mediocre PECVD SiO2 barrier layer with an ultra-thin (2 nm) PA-ALD Al2O3 layer. The decrease in WVTR by three orders of magnitude in the SiO2/Al2O3 system has been attributed to the filling of the residual nanoporosity in the SiO2 layer by Al2O3. This result is supported by angle-resolved XPS analysis and explained on the basis of the molecular dimension of the Al2O3 deposition precursor, i.e. trimethylaluminum (dTMA = 0.65 nm), able to penetrate pores larger than 1 nm.