LTPS Process

LTPS (Low Temperature Poly-Silicon) is a silicon-based material made up of numerous silicon crystals between 0.1 and several microns in size. In the semiconductor industry, poly-silicon is usually formed by annealing at temperatures over 900°C. This method is known as SPC (Solid Phase Crystallization). Glass however starts distorting at 650°C, so SPC is not suitable for manufacturing flat panel displays. LTPS is a poly-silicon coating technique designed for manufacturing flat panel displays.


Figure - Silicon Structure and Mobility




LTPS Features

The LTPS process is far more complex than a-Si but the mobility of LTPS TFT is 100 times higher than a-Si TFT (>100 cm2/V‧s). The CMOS process can be applied directly on the glass substrate as well. The key characteristics of LTPS TFT-LCD include:

  • Low power consumption and ultra high resolution: High mobility means that smaller transistors can provide the necessary charge. The capacitance is also higher than conventional a-Si. When the effective area of light transmittance becomes bigger (high aperture rate), the same brightness can be achieved using fewer backlights or less power while still achieving high resolutions.
  • Super Narrow Border: A conventional a-Si TFT-LCD requires driver ICs on two to three sides, making it difficult to make the border narrower. LTPS TFT-LCD can integrate the driver IC directly onto the glass substrate to achieve both super narrow border and high image quality. The integrated circuit of LTPS TFT-LCD requires fewer external signal connections, reducing the number of module parts.
  • Super Thin: Since some of the driver IC can be placed on the glass substrate, the PCB can be simplified and reduced in size. Meanwhile, as the module becomes smaller, the displays can also be made lighter and thinner.
  • Vehicle of OLED: OLED uses a special current-driven architecture. A compensation circuit for gray-level and panel consistency requires 2 to 6 thin-film transistors per pixel. The high density layout of LTPS makes realizing OLED display with high brightness and high image quality easier. The lifetime of OLED display is also increased. High mobility means a higher driving current can be provided to OLED display, making LTPS a more suitable substrate for Active-Matrix OLED display.



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