Study On Atomic-scale Fabrication Process And Performance Of The Thin Film Encapsulation Layers With High Barrier Property For Displays

Display technology is developing rapidly towards the direction of high resolution and flexibility,which has attracted interests from the areas of virtual reality（VR）,on-board dis-play,et al.However,flexible displays such as organic light-emitting diodes（OLEDs）are easy to be eroded by moisture and oxygen in the ambient,resulting in the severe degradation of device performance.With the introduction of the applied external strain,the commercial metal/glass lids encapsulation method is not compatible with the next-generation flexible displays,and thin film encapsulation（TFE）is considered as the potential method to solve this problem.To overcome the contradiction between barrier property and ever-increasing flexibility demand of the encapsulation layers for flexible displays,how film thickness and strain condition affect the mechanical stability of the barrier structure is systematically ex-pounded based on the film fracture theory.Furthermore,the atomic-scale fabrication methods including atomic layer infiltration（ALD）are utilized to develop the inorganic-inorganic stack,organic-inorganic nanolaminates,polymer-infiltrated barrier structures,and the application areas of which range from rigid to flexible displays.The main research work is introduced as follow:To suppress the spontaneous cracking of the barriers aroused by the residual stress,Al₂O₃ film with reversal residual stress is introduced on the top of the commercial Si N_x layer,which decreases the overall residual stress of the composite encapsulation films.Besides,the introduced Al₂O₃ layer helps decouple the pinhole defects of Si N_x layer,which prevents the interface degradation caused by the diffused moisture,and the water vapor transmission rate（WVTR）of the Al₂O₃/Si N_x stack reaches 10^-6 g/m²/day.Besides,the lifespan of the blue OLED encapsulated with composite encapsulation films is prolonged to be more than 1000hours when stored in the severe environment（60℃/90%RH（relative humidity））.The critical energy release rate of the interface between composite encapsulation films and OLED im-proves 5 orders of magnitude higher than that of the single Si N_x layer,and the delamination or peeling behaviors of the barriers are hindered completely.The deposition efficiency of the spatial-ALD method improves 2 orders of magnitude than that of the conventional ALD.To overcome the fracturing issue of the inorganic barriers aroused by the applied exter-nal strain,PDMS/Al₂O₃ nanolaminates are developed with a total thickness of～100 nm,and the thinner Al₂O₃ inorganic sublayer contributes to the significant improvement of the bend-ing-resistance of the nano-laminated barrier structure.O₂ plasma pre-treatment is utilized to improve the wettability of the PDMS sublayers,which also creates lots of nucleation sites for the deposition of Al₂O₃ film.The introduction of the organic sublayers helps decouple the defects between the neighbouring inorganic sublayers,and the barrier property of PDMS/Al₂O₃ nanolaminates reaches the magnitude of 10^-5 g/m²/day.Furthermore,the mod-ification layer is used to move the neutral axis（NA）towards the nanolaminates to optimize the strain condition under bending test with a small radius,and the barrier property of the modified encapsulation structure improves 1～2 orders of magnitude than that of the unmod-ified one after bending fatigue test.Furthermore,the operational lifetime of the encapsulated blue OLED improves 60 times than that of the pristine one.The polymer substrates perform poor barrier property due to the existence of free vol-umes between polymer chains.The atomic layer infiltration（ALI）method with the optimized process is utilized to realize the effective diffusion and infiltration of precursors in the sub-surface of PEN substrates,which has been demonstrated by the quartz crystal microbalance（QCM）method.Furthermore,O₂ plasma pre-treatment is utilized to introduce a large amount of oxygen group to the surface of PEN substrate,and the adhesion between Al₂O₃ modifica-tion layer and PEN substrate is improved significantly.The barrier property of PEN substrate modified with O₂ plasma pre-treatment and ALI process reaches the magnitude of 10^-5g/m²/day before and after bending fatigue test,which improves 3～4 orders of magnitude than that of the unmodified ones.When applied to the encapsulation of OLEDs,the normalized luminance remains≥94%after storage of more than 800 hours in the ambient.