(iTers News) - The steady growth of high resolution FPDs, such as full HD smartphone panels, is increasing the demand for TFT (thin-film transistor) technologies with performance levels exceeding that of conventional a-Si (amorphous silicon). As the pixel density increases, LCD transmission decreases and power consumption increases, both of which are challenges for mobile LCDs. To minimize these concerns panel makers are increasing production of high performance LTPS (low temperature polysilicon) and oxide TFT based displays. Furthermore, these technologies are also being applied to the production of AMOLED displays.


With FPD makers adding larger generation LTPS fabs, capacity devoted to LTPS production is forecast to double from around 9 million square meters in 2013 to 18 million square meters in 2016. Over the same period, capacity for oxide TFT production is expected to grow even more rapidly, from 3.5 million square meters to over 19 million square meters, thus exceeding that of LTPS by 2016.



Source: 2013 NPD DisplaySearch TFT LCD Process Roadmap Report


Despite the very high growth rate, the oxide TFT ramp up is about two years behind previous expectations and there are concerns about remaining manufacturing challenges. According to the latest analysis from the 2013 NPD DisplaySearch TFT LCD Process Roadmap Report, oxide TFTs offer the promise of high mobility and low leakage current at lower cost than LTPS TFTs, with scalability to any glass size, and can thus improve performance and lower costs of both LCDs and AMOLEDs. However, oxide TFTs suffer from several limitations in mass production.


“Although many panel makers have achieved encouraging oxide TFT results in development, most have struggled to replicate those in mass production,” stated Charles Annis, NPD DisplaySearch Vice President of Manufacturing Research. “Stable, high-yield production of oxide TFT based FPDs requires optimization of the TFT design, dielectric and passivation materials, oxide film deposition uniformity, annealing conditions, and more. Solving one issue often means trading-off performance of another. For example, most panel makers have adopted etch-stopper type TFTs as they provide comparatively good stability. But the design limits how short the TFT channel can be, adds process complexity, and suffers from high parasitic capacitance that detracts from device performance.”

These types of problems have limited mass production of oxide based FPDs to date. Currently, Sharp is the only maker offering oxide LCDs and LGD is the only company selling oxide type AMOLED TVs. Even these market leaders have increased oxide output slower than previously expected, however.


On the other hand, LTPS is a more mature process for TFTs. In spite of higher factory costs and process complexity, LTPS will likely continue to be the leading backplane semiconductor material for ultra-high resolution smartphone displays and gain share in the tablet market for both LCDs and AMOLEDs. Continuous productivity improvements also mean that LTPS remains a viable technology even for AMOLED TVs. However, due to the fact that oxide TFTs have become the major focus of development for the entire FPD industry and have wide applicability to both LCDs and AMOLEDs, oxide TFT production is predicted to eventually surpass that of LTPS.


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