Driving Substrate Layout With Polysilicon Frame TFT Channels
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Solution Overview
Problem
Existing display technologies using the amorphous silicon (a-Si) process face challenges in achieving sufficient mobility for thin film transistors in frame regions, leading to increased costs and complexity when replacing these transistors with those made using the IGZO process.
Innovation Solution
A driving substrate is designed with a pixel region and a frame region, where the first thin film transistors in the pixel region have an active layer comprising a stacked amorphous silicon and microcrystalline silicon layer, and the second thin film transistors in the frame region have a channel made of polysilicon, formed by crystallizing the amorphous and microcrystalline silicon layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform amorphous silicon is used as channels of thin film transistors in both pixel region and frame region, then the fabrication process is simple and cost is low, but the mobility of thin film transistors in frame region is insufficient
Solution Approach 1:
The patent applies local quality by using different semiconductor material compositions in different regions: amorphous silicon for pixel region thin film transistors and polysilicon for frame region thin film transistors. This allows each region to have optimized properties for its specific function while maintaining a unified fabrication process flow.
Solution Approach 2:
The patent changes the material parameter (semiconductor layer composition) from uniform amorphous silicon to region-specific materials (amorphous silicon + microcrystalline silicon for pixel, polysilicon for frame). This parameter change enables higher mobility in frame region transistors while keeping the overall process compatible with existing a-Si manufacturing lines.
2Reliability
If thin film transistors in frame region are replaced with IGZO process transistors to improve mobility, then the mobility requirement is met, but the cost increases and fabrication process becomes more cumbersome
Solution Approach 1:
Instead of switching to a completely different IGZO material system, the patent changes the silicon crystallinity parameter within the existing silicon-based process. By forming polysilicon from amorphous silicon through in-situ crystallization, the patent achieves high mobility while maintaining process compatibility and avoiding the complexity of IGZO fabrication.
Solution Approach 2:
The patent uses the existing amorphous silicon layer as a precursor that self-transforms into polysilicon through controlled crystallization. This self-service approach eliminates the need to introduce entirely new semiconductor materials and their associated complex deposition and processing steps required by IGZO technology.
3Ease of manufacture
If polysilicon is formed by crystallizing amorphous silicon layer, then additional semiconductor materials are avoided and cost is reduced, but the process complexity increases
Solution Approach 1:
The patent performs preliminary action by forming the amorphous silicon layer first, which then serves as the precursor for in-situ polysilicon crystallization. This preliminary deposition step simplifies the overall process compared to depositing polysilicon directly, as it allows the use of standard low-temperature a-Si deposition equipment followed by controlled crystallization in the same or subsequent processing steps.
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
This solution improves the mobility of thin film transistors in the frame region while reducing costs, as the polysilicon channel is formed through a simplified process that avoids the need for additional semiconductor materials.
Implementation Method 1
the second channel comprises polysilicon formed by crystallizing an amorphous silicon layer and a microcrystalline silicon layer as a monolithic crystal
Data Source
AI summary
A driving substrate, a manufacturing method thereof and a display panel are provided. First thin film transistors are provided in a pixel region and second thin film transistors are provided in a frame region, in which a first active layer of the first thin film transistor includes an amorphous silicon layer and a microcrystalline silicon layer stacked, and a channel of the second active layer of the second thin film transistor includes polysilicon, so that mobility of the second thin film transistor is greater than that of the first thin film transistor. Also, the polysilicon can be formed by crystallizing the amorphous silicon layer and the microcrystalline silicon layer, which are stacked, as a monolithic crystal.