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The rise of LTPS-TFT: Why is it the future star of OLED displays?
With the rapid development of science and technology, display technology continues to evolve, and low-temperature polycrystalline silicon (LTPS) has become a rising star in the display industry. The key to LTPS is its ability to synthesize polysilicon at low temperatures, no more than 650 degrees Celsius, which is particularly important for the production of large panels, as traditional high-temperature methods may cause the glass panel to deform, thus affecting the quality of the final product.
The use of LTPS materials has significantly improved the resolution and production cost of displays. This technology is rapidly changing the display market landscape.
The development of polysilicon
Polycrystalline silicon (p-Si), as an important conductive material, consists of many highly ordered lattice structures. As early as 1984, researchers discovered that amorphous silicon (a-Si) is an excellent precursor material that can form p-Si films with stable structure and low surface roughness. By using low-pressure chemical vapor deposition (LPCVD) technology, the surface roughness can be effectively reduced to achieve better thin film effects. With further development of the technology, the researchers succeeded in lowering the temperature during the annealing process, thereby improving conductivity. Advances in these technologies continue to impact the microelectronics, photovoltaics, and display industries.
Application in LCD
Currently, amorphous silicon TFTs are widely used in liquid crystal display (LCD) flat panels because they can form complex high-current drive circuits. The emergence of LTPS-TFT has brought new opportunities to display technology, such as higher device resolution, lower synthesis temperature and enhanced cost-effectiveness. However, LTPS-TFT also faces challenges. For example, the large area of TFT in traditional a-Si devices leads to a small aperture ratio and cannot effectively integrate complex circuits.
As LTPS continues to expand its use in the display field, will future displays be able to achieve higher performance and better dynamic response?
Laser annealing technology processing
XеCl laser annealing (ELA) is a key method for producing p-Si. This technology melts the a-Si material through laser irradiation, eventually forming polycrystalline silicon with excellent conductive properties. This process can crystallize a-Si without heating the substrate, thereby producing larger particles of p-Si and reducing the resistance to electron movement due to grain boundary scattering. This is crucial for complex circuit integration in LCD displays.
Development of LTPS-TFT equipment
In addition to the improvement of TFT technology itself, the key to the successful application of LTPS in graphic displays lies in innovative circuit technology. Among them, a new pixel circuit design can make the output current of the transistor independent of the threshold voltage, thereby achieving uniform brightness. LTPS-TFT is also widely used to drive OLED displays, which have high resolution and large panel compatibility. However, changes in the LTPS structure still lead to non-uniform threshold voltage, resulting in uneven brightness. To solve this problem, the new pixel circuit uses four n-type TFTs, one p-type TFT, a capacitor and a control element to control the image resolution, and display technology is constantly making breakthroughs.
The rise of LTPO technology
Low-temperature polycrystalline oxide (LTPO) is an OLED display backplane technology that combines LTPS TFTs and oxide TFTs such as indium gallium zinc oxide. The driving circuit of LTPO uses LTPS, while the driving TFT uses IGZO material, which has better adjustments for the efficient use of power. This means that the screen can operate at a lower refresh rate when displaying static images, but can achieve the high refresh rate requirements when displaying dynamic content. LTPO technology improves battery life and is used in mobile devices such as mobile phones and smart watches.
Technological development has made LTPS-TFT technology mainstream in the display industry, with both potential and challenges. With further research and technological application, what heights can LTPS reach in future display technology?
