Abstract
Gas barrier films are widely used in electronic and packaging applications. They are also critical components of flexible organic light-emitting diodes (FOLEDs) that require high gas barrier performance. Among the various film manufacturing techniques, solution-processed thin-film encapsulation (TFE) represents a low-cost FOLED fabrication method. The nanometer-thick SiN films produced following the vacuum ultraviolet (VUV)-induced densification of solution-processed perhydropolysilazane (PHPS) films in a N2 atmosphere can potentially serve as TFE barrier films. However, the nanometer-thick PHPS densification process has not been examined in sufficient detail. We investigated and discussed the effects of the Si–N bond number, PHPS film composition, and free volume (present in the produced Si–N network) on the VUV-induced PHPS densification process. It was found that VUV irradiation caused rapid hydrogen release and film densification through the formation of Si–N bonds. The results obtained using the X-ray photoelectron spectroscopy and dynamic secondary ion mass spectrometry techniques, and the calculated residual hydrogen ratios, revealed that the film composition was strongly related to the number of residual hydrogen atoms and Si–N bonds. Notably, nanometer-thick PHPS film densification was a relatively slow process, in which the free volume in the Si–N network was considerably reduced by the atomic rearrangement induced by the simultaneous cleavage of several Si–N bonds during VUV irradiation. We believe that the results presented herein can potentially serve as a guideline for developing solution-processed nanometer-thick SiN films with relatively high density and excellent gas barrier performance (that is comparable to that exhibited by vacuum-processed barrier films).
Highlights
Gas barrier films are essential components of electronic and packaging applications because they can effectively protect various products such as flexible organic light-emitting diodes (FOLEDs) from water vapor and atmospheric oxygen
The water vapor transmission rate (WVTR) of 10−3 g/m2/day was achieved by the PHPS derived silicon nitride (PDSN) films after VUV irradiation for 5 min,[18] the maximum irradiation time was 2500 min to analyze the VUV densification process in detail
We investigated the VUV irradiation-induced densification of solution-processed nanometer-thick PHPS films in an inert atmosphere to determine the applicability of the all-solution-processed Thin-film encapsulation (TFE) method for FOLED manufacturing
Summary
Gas barrier films are essential components of electronic and packaging applications because they can effectively protect various products such as flexible organic light-emitting diodes (FOLEDs) from water vapor and atmospheric oxygen. Densities higher than those of SiOx films fabricated by vacuum processes such as plasma-enhanced chemical vapor deposition (PECVD) and atomic layer deposition exhibited high barrier performance with WVTRs of approximately 10−6 g/m2/ day.[25,26] In 2019, we obtained nanometer-thick PHPS derived silicon nitride (PDSN) barrier films and poly-. We successfully obtained the guidelines for the fabrication of nanometer-thick PDSN (SiOxNy:Hz) films, with high density and barrier performance from solution-processed PHPS films, whose performance is comparable to that of films fabricated following the vacuum processes and an amorphous dense Si3N4 film (Si/N = 1:1.33) with the maximum amount of Si− N bonds and the minimum free volume (Figure 1)
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