When an FMM is used repeatedly during the continuous manufacturing of a full color OLED, evaporated organic materials accumulate on the surface and interface of the FMM as well as inside the gap between the metal sheet and the stainless steel frame. 1b which is an enlarged cross-sectional view of a portion surrounded by the circle on line A–A′ in Fig. However, due to the technical limitation of FMM fabrication, a gap is created between the thin metal sheet and the stainless steel frames as shown in Fig. Due to its limited ductility and low thickness, it is extremely difficult to keep the FMM aligned and attached to the TFT back plane with high positional accuracy, so the thin metal sheet needs to be stretched and supported by a thick metal frame using laser welding. The thin metal sheet of the FMM is only 30–200 μm. The thin metal sheet includes tiny openings formed by electroforming or micro photo etching of stainless steel or Invar (64% Fe-36% Ni alloy). The FMM is typically fabricated by laser welding of a thin metal sheet onto a stainless steel frame as the schematic of Fig. To form pixels emitting red(R), green(G) and blue(B) colors, pixels patterns are selectively deposited onto a thin film transistor (TFT) backplane panel with pixel bank array by evaporation of organic light emitting materials through a fine metal shadow mask (FMM) with tiny pixel-shaped apertures after highly precise alignment of the FMM to the TFT backplane. A typical OLED display structure consists of multi-organic layers such as an electron injection layer, an electron transport layer, a hole transport layer, and a hole injection layer which are sandwiched between a transparent indium-tin-oxide anode and a reflective metallic cathode. In the manufacture of flat panel displays for television screens, cell phone displays, computer monitors, and so on, organic electroluminescent displays (OLEDs) have attracted attention due to their large angle visibility, high brightness, wide range of working temperature, fast response time, high contrast and vivid color compared with traditional flat panel displays such as liquid crystal displays. The developed FMM-mimic microstructure proves very convenient for inspecting the residual contaminant inside the gap through the transparent glass by general optical and fluorescence microscopy. We analyzed the residual contaminants on the FMM-mimic microstructure using a fluorescence microscope. The Alq 3-deposited FMM-mimic microstructure was cleaned by N-methyl-2-pyrrolidone (NMP) with changing cleaning time. To demonstrate the proposed cleanliness analytical method, a 1.4 μm-thick Tris-(8-hydroxyquinoline) aluminum (Alq 3) film was deposited on the FMM-mimic microstructure as a contaminant by vacuum thermal evaporation. The FMM-mimic microstructure was fabricated using a combination of photolithography, reactive ion etching, anodic bonding and sand blasting processes. We developed a FMM-mimic microstructure as a substitute for the FMM, which can be used for the evaluation of cleaning efficiency. This study proposes the unique method to analyze the cleanliness of the fine metal mask (FMM) used in OLED display manufacturing after FMM cleaning process.
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