![]() Over the past decade, the direction of progress in this technology has been clearly divided into subjects of study. Amorphous oxide semiconductors began to gain attention because of their higher µ and reliability compared to a-Si TFT, and they were commercialized in active matrix organic light-emitting diode (AMOLED) backplanes. However, in 2003, the use of indium-gallium-zinc-oxide (IGZO) was reported and its applications have rapidly expanded. The first transistors equipped with oxide semiconductors used binary oxides such as ZnO, SnO, and their results were not noteworthy. ![]() It mainly discusses the current technical level and prospects for amorphous metal oxide, semiconducting CNT, TMDCs, and organic TFTs(Figure 2). This review article provides a technical roadmap and recent progress update in the development of backplane TFTs for OLED flat panel displays and next-generation flexible displays. ![]() Therefore, organic semiconductors, TMDCs, and CNT are promising candidate materials due to their high mechanical flexibility (Figure 1). The backplane TFTs of a display that has true form freedom should include flexible semiconducting materials. However, many challenges such as optimization of materials, process, and device must be met before such materials can be used in backplane TFTs of commercial OLEDs and next generation displays.įlexible displays have high form freedom and are therefore considered to constitute the next generation of displays. For this purpose, research is being conducted on new semiconductor materials such as 2D transition metal dichalcogenides (TMDCs) and semiconducting carbon nanotubes (CNTs). Therefore, applications to large, high-resolution OLED TVs require development of methods to overcome this limitation. However, LTPS is fabricated using laser annealing, but this process cannot easily achieve a high yield of uniform backplane TFT for a large OLED TV. Low-temperature polycrystalline silicon (LTPS) has been commercialized as a backplane for high-resolution mobile OLED displays due to its high µ. Various metal oxide materials have been evaluated to obtain higher µ than IGZO TFTs can, but the materials have not achieved the stability, reliability, and large-area uniformity that IGZO provides, so further development is required before they can be commercialized. To increase the resolution and speed of OLED display applications, however, the carrier mobility of metal oxide must be increased further. IGZO has been commercialized for OLED TVs. Indium gallium zinc oxide (IGZO), the prototypical amorphous metal oxide TFT, has µ ∼ 10 cm 2 Semiconducting materials for the backplane TFTs in the flat panel displays have a range of achieved and possible µ (Figure 1). To minimize brightness differences under the same gate bias, the driving TFTs of OLEDs require a very stringent operation reliability, including threshold voltage shift < 0.5 V. To achieve dynamic current-driving mode and low off-state current for low power consumption, the driving TFTs for OLEDs require high carrier mobility ( µ) > 10 cm 2 Semiconducting materials that are currently being used as the active layer of backplane TFTs or are being developed for flat-panel displays include polycrystalline silicon, amorphous metal oxides, semiconducting carbon nanotubes (CNTs) and two-dimensional semiconductors for OLEDs, and amorphous silicon and organic semiconductors for LCDs or e-paper displays. Recently, interest in form-free displays is increasing with the introduction of foldable and rollable OLED displays. Currently, the display market is divided into a high-end market with organic light emitting diodes (OLEDs) and a general and low-end market based on liquid crystal display (LCD). In the past 40 years, flat panel displays have greatly improved as a result of development of new display modes, improved electrical characteristics of backplane thin film transistors (TFTs), and optimization of materials and manufacturing processes.
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