-A robust methodology is established to predict the critical bending radius of a flexible AMOLED. According to the methodology, the critical bending radius of display manufactured by the same process could be reduced from 7 mm to 4 mm by modulating the layer stack thickness.Keywords -flexible, neutral plane, stress, strain, simulation, AMOLED. DOI # 10.1002/jsid.443 Objective and backgroundRecently, there are many significant investments in the development of flexible display technology. Several flexible AMOLED products are already available in the display market. But, these products are only slightly curved and remain rigid, which are not as much different from the present glass-based portable device as one could anticipate from a flexible display. In order to realize flexible display applied to the rollable or foldable device of next generation, it is necessary to reduce the critical bending radius.The structure of a flexible AMOLED display can be divided into several parts: the flexible substrate, TFT backplane, OLED, and encapsulation layers. The AMOLED display contains functional brittle inorganic layers that have different purposes and could easily fail during bending. A number of literatures have pointed out that we can place the mechanically vulnerable components (TFT backplane and OLED) close to the zero-strain plane (the neutral plane) to improve the reliability and flexibility of flexible displays.1-4 But, the inorganic layers used for encapsulation layers would be far away from neutral plane and easily fail during bending.OLED materials are extremely sensitive to ambient water vapor and oxygen, which causes oxidation of cathode and results in the formation of black spots in electroluminescence. [5][6][7][8] Therefore, keeping the performance of encapsulation layers during bending is important. The most common technique of encapsulation for flexible AMOLED is the thin-film encapsulation (TFE) 9-12 that is fabricated by alternative stacks of inorganic and organic layers. In order to protect the TFE layer, we modulate the thickness of organic layers. In our structure configuration, we maintain the neutral plane located on TFT and OLED layers but change the thicknesses of organic layers. The inorganic layers in TFE component could get closer to the neutral plane and take lesser strain. Experiment and process flowA robust methodology consisting of a mechanical model of multi-films under bending loads and experiment of bending test is proposed to predict the critical bending radius of a flexible AMOLED display. Figure 1 shows the process flow. We apply this methodology in different layer stack structure configuration and try to reduce the critical bending radius.The flexible AMOLED interpreted below is fabricated by PI substrate with SiNx bottom barrier to perform the IGZO TFT process, then, deposit the OLED material and encapsulated by thin-film encapsulation (TFE) process. The TFE layer is made by stacks of SiNx layers and "organic coating for planarization (OCP)" layers, alternately. SiNx is dep...

The 2.7 inch flexible AMOELD is successfully demonstrated through FTIR analysis and mechanical simulation. Through FTIR analysis we can optimize the CVD parameter to realize the SiNx of WVTR~10 -5 (60Ԩ/90% R.H.). According to the simulation result, the curvature radius can be reduced to 10mm by modulating the Organic Coating for Planarization(OCP) layer thickness.

Although laser seal frit encapsulation owns great ability of protecting OLED from moisture and oxygen oxidation, the bonding strength is too weak to resist machenical force, which is easy to result in peeling the top and bottom substrates of OLED display. In this paper, we improve the bonding strength and production yield ratio by optimizing TFT array structure and process.

Applying a high performance thin-film barrier to OLED products conventionally needs high temperature process, but OLED devices would be damaged by heat. In this paper, we apply a low temperature encapsulation process to 6-inch VGA IGZO AMOLED display, and get through the 60℃/90% RH over 500 hrs environment test, and WVTR is about 10 -5 g/m 2 ·day.

A robust methodology is established to predict the critical bending radius of a flexible AMOLED. According to the methodology, the critical bending radius of display manufactured by the same process could be reduced from 7 mm to 4mm by modulating the layer stack thickness.