(Invited) TFT Technologies from Commercial Displays to Emerging Immersive Displays
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Thin film transistors (TFTs) are used in displays providing the function of controlling light transmission, such as LCDs, reflection, such as electrophoretic displays, or emission, such as LED or OLED displays, from individual pixels in a 2D array named active matrix flat panel displays (AMFPDs). The advantages of using TFTs in displays include gray-scale, dynamic, crosstalk-free, and uniform images as well as low power consumption over a large area.The first report on the functional TFT and the outline and demonstration of the TFT LCD triggered worldwide research and development activities on AMFPDs. The lack of commercial products on the market is due to the bottleneck in the manufacturing technology, i.e., availability of a large area, low temperature, and high throughput process. The invention of the a-Si: H TFT in 1979 solved the production problem [1]. TFT LCDs were quickly introduced to the market. The size of the commercial displays changed from 4 in the 1980s to 98 in 2023, as shown in Figure 1 [2]. Extremely low power consumption electrophoretic displays were also introduced to the market. The main drawback of the a-Si:H TFT is the low field effect mobility, e.g., 1 cm2/Vs, which limits applications in driver circuits as well as very high speed or high driving current displays. Poly-Si TFTs can have mobilities up to 2 orders of magnitude higher than that of a-Si:H TFT. However, due to the complicated process conditions, their applications have been limited to small-sized displays, such as 20-inch LCDs, OLEDs, and -LEDs. The driver circuits were successfully integrated into the display. The a-IGZO TFT has a field effect mobility between those of a-Si:H TFT and poly-Si TFT. The a-IGZO TFT array can be mass-produced at a low temperature on a large substrate. Therefore, since the first report of the a-IGZO TFT in 2004 [3], it was quickly accepted by the display industry. Commercial OLEDs and -LEDs based on a-IGZO TFTs have been manufactured. Driver circuits have also been demonstrated. However, due to the lack of the p-channel TFT, the CMOS circuit has to be made of the n-channel oxide TFT and the p-channel poly-Si TFT.Recently, due to the advancement in semiconductor technology and software, immersive displays have emerged in areas of entertainment, industry, education, etc. Displays play an important role in this trend because the human interface with the data is critical to these functions [4]. There are some basic requirements on the display concerning image quality, power consumption, response to the environment, and the users physical condition. In many applications, the size, weight, and flexibility of the display are important. In this paper, the authors will discuss these issues based on the existing TFT technology and explore opportunities. Kuo, ECS Interface, 22(1), 55-61, 2013.A commercial TCL 98" LCD downloaded from Google.Nomura, et al., Nature, 432, 488-492, 2004.Kuo, IEEE J. Immersive Displays, 1, 28-40, 2024.Figure 1
