Optimization Of Thin Film Encapsulation For Flexible AMOLED Display

In recent years,the application of OLED display becomes more and more popular in mobile phone and TV Flexible OLED displays have been widely studied because of their lightweight and foldable characteristics.Since the first commercialization of OLED,the material properties and lifetime of OLED devices have been developed rapidly.Exposure to moisture and oxygen leads to serious degraded of OLED material because of its extremely sensitive to vapor and oxygen,so OLED encapsulation has become the most important step in manufacturing process.At present,flexible OLED displays with curved surfaces have already presented in the market,while the real sense of flexible OLED display is still remain in the initial stage of research.The main research directions for improving the flexibility of OLED display are as follows:the selection and optimization of flexible substrates,the design of bending resistance TFT array substrate,the development of thin film encapsulation(TFE)technology,and the investigation of good bending modulus material such as polarizers.In TFE technology,several layers of inorganic and organic layer stacking structure are adopted to obtain the barrier and flexural property at the same time.In this paper,wide-used AMOLED display is selected as the research object,and the TFE technology and structure are optimized.The main contents include the following two aspects:Firstly,the properties of Al2O3,PMMAand SiNx,single layer were studied,which were deposited by PEALD,Inkjet printing and PECVD respectively.The results show that:(?)In PEALD process,the main influence factors of properties of Al2O3 film included the TMA pulse time,RF pulse time,RF power and cycle number.The refractive index,deposition rate and optical transmittance of Al2O3 thin film showed the best performance when the RF power is 100w,the TMA pulse time is 150ms,the RF pulse time is 3s.The thickness of Al2O3 film is proportional to the cycle number.When the film thickness is above 33nm,the average stress is low,and the stress reaches the lowest value at 160Mpa at 203nm.(?)PMMA organic layer was prepared by inkjet printing,and the thickness of the thin film was investigated and characterized.The results show that the interference effect of the first layer of SiNx film was smoothed by PMMA organic layer,and the thicker of the organic layer,the more obvious smooth.The increase of thickness caused the red shift of the interference wave.When the thickness of the organic layer is 8um,the transmittance of the PMMA film is higher than others,and its surface morphology and uniformity reach to the best as well.(?)The property of inorganic layer SiNx film,including the refractive index,thickness and uniformity,were optimized by adjusting the PECVD parameters of radio frequency power,SiH4 and NH3 flow.And the top conditions were obtained:RF power is 600W,SiH4 flow is 360sccm and NH3 flow is 318 sccm in the process window of which pressure is 1550 mTorr,spacing is 1218mils,N2 flow is 4800 sccm,H2 flow is 3000 sccm,substrate temperature is 85? and the deposition time is 240s.Secondly,based on the best performance of each single layer,three different laminated structures were designed and applied to the AMOLED display.The aging test was carried out to study the encapsulation performance and flexural performance.The results showed that the optical transmittance of the three structures at 550nm is above 90%.The encapsulation performance and flexural reliability of Al2O3/SiNx/PMMA/SiNx is relatively best,after bended in r=7mm and 60?/90%RH 240h,there is no visible failure,which provides an important reference for improvement the performance of thin film encapsulation.