Effective Thin Film Permeation Barrier for Organic Electronic Devices
- Effective Thin Film Permeation Barrier for Organic Electronic Devices
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- Chapter 1
Thin film permeation barrier deposition technique is one of the crucial factors for the commercialization of promising organic electronic devices because organic electronic devices exhibit environmental vulnerability. With a long history of passivation technique started from food packaging, various mechanisms and deposition methods are suggested and those products are closely related to the modern life. These relatively well established backgrounds are still applicable to the passivation for the organic electronic devices. Therefore, in order to make proper thin film barrier films, the understanding about the basic mechanism and background technology is essential. For this reason, in chapter 1, general permeation mechanisms and methods will be introduced as well as the state of the art for the passivation technology for organic electronic devices.
Silicon monoxide (SiO) thin films were introduced as an efficient interlayer for achieving plasma-based organic light-emitting diode (OLED) surface passivation. The SiO thin films could be consecutively formed via thermal evaporation, without breaking the vacuum, after deposition of the OLED cathode. The plasma resistivity and UV-blocking characteristics of the SiO interlayer protected the OLED devices against electrical and optical degradation during the plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) passivation processes. In addition, the non-conformal deposition and hydroxyl group-rich surface characteristics of the SiO thin films yielded enhanced surface pinhole coverage and a higher initial film density in the subsequently deposited PEALD-based Al2O3 barrier film. As a result, the OLEDs with a SiO/Al2O3 bilayer passivation layer displayed a remarkably increased device shelf-life compared to devices prepared using Al2O3-only passivation. A MOCON test showed that the water vapor transmission rate (WVTR) of the SiO/Al2O3 bilayer film was 0.0033 g/m2day, 2.3 times lower than the rate of a single Al2O3 barrier film. The results of our study demonstrated the multi-purpose role of a SiO interlayer in plasma-based OLED passivation. The layer acted as a damage-free protective layer for the underlying OLED devices and an assistant layer to improve the upper barrier film performance.
Polymeric zinc acrylate (pZA) was introduced as an organic interlayer for the inorganic/organic multilayer passivation of flexible organic thin film transistors (OTFTs). The pZA film was deposited by thermally evaporating a zinc diacrylate (ZDA) monomer under high vacuum (< 10-5 Torr) and applying UV irradiation. The conversion of ZDA into a polymeric phase was confirmed by FTIR analysis, breakdown voltage measurements and the photopatternability of the film before and after UV irradiation. Vacuum-thermally evaporated pZA film showed good surface smoothness and a high permeation activation energy (53kJ/mol) compared to a conventional polymeric films. As an interlayer for multilayer passivation, vacuum-thermal evaporated silicon monoxide (SiO) was introduced as inorganic counterparts of pZA interlayer. A multilayer film comprising 6.5 pairs of layers showed water vapor transmission rate (WVTR) of 0.055 g/m2day, a 25-fold improvement over the WVTR of a single SiO film (1.207 g/m2day). OTFTs encapsulated with 6.5 pairs of polymeric zinc acrylate/silicon monoxide layers showed prolonged stability over 97 days. In addition, the passivation layer did not show crack formation, and sustained barrier characteristics, even after 500 times of bending test.
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