LTPS Display Panel Dual Crystallization for Defect Control
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Solution Overview
Problem
Existing display panel technologies face challenges in achieving high-quality polysilicon layers for both display and peripheral circuit areas, with low-temperature polysilicon (LTPS) processes like solid-phase crystallization (SPC) and laser annealing resulting in defects, non-uniformity, and reduced throughput, while high-temperature methods compromise on quality and throughput.
Innovation Solution
A method utilizing two distinct LTPS processes: solid-phase crystallization for the display area and laser annealing for the peripheral circuit area, producing a uniform polysilicon layer in the display area and high electron mobility in the peripheral circuit area by converting amorphous silicon into polysilicon, with interconnection via electrically conductive connectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If solid-phase crystallization is carried out at low temperature, then the polysilicon grain quality is improved, but the annealing time becomes very long reducing throughput
Solution Approach 1:
The patent applies a preliminary low-temperature solid-phase crystallization process to convert amorphous silicon into polysilicon with good grain quality, followed by a subsequent laser annealing step to further improve electron mobility. This two-stage approach allows the first stage to establish a solid foundation of crystalline structure while the second stage optimizes electrical properties, thereby resolving the contradiction between achieving high quality and maintaining throughput.
Solution Approach 2:
The patent replaces the conventional prolonged thermal annealing process with laser annealing technology. The laser provides localized, rapid heating that achieves the desired polysilicon quality improvement in much shorter time compared to traditional furnace annealing, thus resolving the throughput issue while maintaining quality standards.
2Productivity
If rapid thermal annealing is used to increase throughput, then the production efficiency is improved, but the TFT performance deteriorates
Solution Approach 1:
The patent performs preliminary low-temperature solid-phase crystallization to establish a baseline polysilicon structure with adequate grain quality. This preliminary action creates a foundation that can be subsequently enhanced by laser annealing, allowing the process to achieve both high throughput and high TFT performance that neither method could achieve alone.
Solution Approach 2:
The patent changes the temperature and time parameters of the annealing process by using laser annealing instead of conventional rapid thermal annealing. The laser provides extremely rapid heating and cooling cycles with precise control, achieving parameter optimization that simultaneously improves throughput and maintains superior TFT performance.
3Reliability
If laser annealing is applied to convert amorphous silicon to polysilicon, then the electron mobility is improved, but non-uniformity known as laser mura occurs
Solution Approach 1:
The patent applies low-temperature solid-phase crystallization as a preliminary action before laser annealing. This first stage creates a uniform polysilicon base structure that is less susceptible to laser-induced non-uniformity. By establishing this foundation first, the subsequent laser annealing can improve electron mobility without creating severe laser mura effects.
Solution Approach 2:
The preliminary solid-phase crystallization process acts as a cushioning step that protects the polysilicon layer from the harmful effects of direct laser annealing. This beforehand cushioning reduces the susceptibility to laser mura while still allowing the laser to achieve its beneficial effect of improving electron mobility in the already-crystallized structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a uniform polysilicon layer in the display area with reduced defects and high electron mobility in the peripheral circuit area, enhancing the overall performance and quality of the display panel.
Implementation Method 1
solid-phase crystallization (SPC) is a promising technique for converting amorphous silicon (a-Si) into polysilicon. The crystallization from an amorphous phase to a poly-crystalline phase occurs through a nucleation process and a grain growth process.
Implementation Method 2
The crystallization from an amorphous phase to a poly-crystalline phase occurs through a nucleation process and a grain growth process.
Implementation Method 3
Laser annealing is another low-temperature annealing technique for converting a-Si into poly-Si. With laser annealing, the electron mobility is high and the overall quality of poly-Si is good.
Implementation Method 4
Voutsas et al. (U.S. Patent Publication No. 2004/0180481 A1) discloses a method for producing TFTs on a flexible substrate, wherein high-temperature oxidation is applied to a SPC poly-Si material in order to achieve poly-Si of a higher quality.
Data Source
AI summary
A display panel comprising at least one display area and one peripheral circuit area having electronic components for driving the display components in the display area. The electronic components in the display area are fabricated substantially on a polysilicon layer converted from amorphous silicon by a solid phase crystallization process, whereas the electronic components in the peripheral circuit area are fabricated substantially on a polysilicon layer converted from amorphous silicon first by the solid phase crystallization process and then by laser annealing. As such, display area has a more uniform poly-Si layer substantially free of defects associated with laser annealing, and the peripheral circuit has a poly-Si layer with higher electron mobility.