| Atomic layer deposition（ALD）is a thin film preparation technique based on substrate surface chemistry,which establishes surface chemistry reactions that occur independently and alternately for each precursor material.Each precursor material exhibits self-limiting properties,and the corresponding self-limiting surface half-reaction grows the material as a single atomic layer on the substrate surface.The continuous self-limiting surface reactions satisfy the requirements of atomic-level control and co-deposition,and the dense and conformal films can achieve excellent moisture barrier performance with low film thickness.Therefore,ALD technology has a great development prospect in the field of flexible thin film encapsulation,and it will be an effective means to reduce the overall thickness of the device at the encapsulation part.In recent years,the barrier film prepared by ALD has become one of the main approaches to solve the poor stability of flexible organic light emitting diodes（OLEDs）.However,ALD is currently used only as a thin film fabrication tool to grow specific materials,and the precise atomic-level control characteristics do not realize its true potential and value.With the upgrading of display technology,the corresponding thin film encapsulation process is gradually becoming more efficient and advanced.Confronted with the future development for foldable and wearable display technology,the existing level of film preparation technology and encapsulation performance cannot satisfy the requirements.Research can no longer be limited by traditional processes and empirical structures,the development of novel processes,materials,and structures is critical to achieving future standards for flexible encapsulation.This thesis contains a complete and systematic study on flexible encapsulation solutions and corresponding performance for ALD technology,focusing on the future application requirements of flexible OLEDs.First,the flexible encapsulation performance of mono-layer and laminated-layer film are well studied,and the“functional independence”between each single layer in the current encapsulation structure is revealed,which is the technical barriers that make it hard to break through the upper limit of flexible encapsulation performance.For this purpose,a“functional homo-layer”idea is proposed that aim to integrates the moisture barrier performance and flexibility in a mono-layer.Second,the effect of precursor partial pressure and steric hindrance on the surface activity of substrates during the ALD process is thoroughly studied to achieve precise modulation of the precursor surface half-reaction saturation degree,and combined with the surface reaction characteristics of O2 plasma,a film in-situ hybridization growth process is successfully developed,which establishes the technical basis for the“functional homo-layer”idea.Finally,the mechanism of O2 plasma on the integration of moisture barrier performance and flexibility of barrier films is investigated thoroughly,and this hybridization growth process with sequential pulses of EG,O2 plasma,and TMA is called plasma enhanced molecular layer deposition（PEMLD）.As consequence,an Al CO film with excellent barrier performance and flexibility is successfully prepared by PEMLD,and can be applied to flexible OLEDs encapsulation as a moisture barrier without any damage.This novel hybridization growth process breaks the traditional perception of ALD technology,and the film growth achieves precise modulation within a single atomic layer.It is a breakthrough in ALD and an important beginning of thin film encapsulation technology from rigid to flexible.The main research contents and results of this thesis are summarized as follows:（1）The changes of moisture barrier performance of ALD barrier films before and after bending were analyzed by electrical calcium corrosion testing and the moisture permeation behavior was observed by optical calcium corrosion testing.The flexible encapsulation performance of inorganic encapsulation films was analyzed thoroughly.Subsequently,an organic/inorganic laminated-layer structure using MLD-alucone film as an intermediate layer was designed and prepared,and the mechanism and prerequisites for defect coupling effect in the laminated-layer structure were investigated,pointing out the“functional independence”between each single layer,which was considered to be the limitation of the current encapsulation technology to achieve ultra-flexibility.（2）The steric hindrance during the film growth process was analyzed by in-situ quartz crystal microbalance（QCM）and in-situ quadrupole mass spectrometry（QMS）.The precise modulation of the substrate surface activity state was successfully achieved by regulating the partial pressure time of different precursor materials during the film growth process,which broke the traditional process,and realized the in-situ hybridization growth process of ALD film called“component tailoring process”.Finally,the properties of organic and inorganic components are successfully integrated within a single atomic/molecular layer by“component tailoring process”,and the film properties could be modulated as desired.（3）The film hybridization growth process was carried out by the sequential pulses of EG,O2 plasma,and TMA.The oxidation of carbon backbone in EG by O2 plasma resulted O-Al-O bonds cross-link otherwise parallel and independent C-C backbone,significantly improved barrier performance due to the reduction of moisture permeation paths.Moreover,the cross-linked structure enhanced the film toughness and maximized the flexibility of the organic backbone.As consequence,an Al CO film with excellent barrier performance and flexibility was successfully prepared by this film growth process,which was called PEMLD.The optimal encapsulation film prepared by PEMLD exhibited excellent barrier performance with a WVTR of 1.44×10-5 g·m-2·day-1,as well as preserved 95%of the initial barrier performance after 10,000 bends with a3mm bending radius due to its potent crack-inhibition characteristics.Due to the low process temperature of 40°C and the absorption of O2 plasma by the residual active sites-CH3,the encapsulation process was performed without any damage to the device.The flexible OLEDs encapsulated with a 50 nm-Al CO maintained 98.1%of its initial luminance after 600 hours when placed at 60°C and 90%relative humidity. |
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