LTPS and Oxide TFT Gate Line Overlap for Display Resolution
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Solution Overview
Problem
Conventional display devices face challenges in achieving high resolution, low power consumption, and uniformity due to limitations in carrier mobility and threshold voltage variations of silicon-based TFTs, which necessitate complex compensation circuits and increased manufacturing costs, especially for flexible displays.
Innovation Solution
A display device that combines oxide TFTs and LTPS TFTs on a substrate, with overlapping gate lines to reduce circuit size and utilize parallel capacitors to increase capacitance without increasing size, allowing for higher resolution and improved transmittance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LTPS TFTs are used to achieve high carrier mobility, then driving speed is improved, but threshold voltage variations increase causing display non-uniformity
Solution Approach 1:
The patent divides the TFT population into two segments: LTPS TFTs for high-speed driving circuits and a-Si TFTs for pixel switching circuits. This segmentation allows each TFT type to be optimized for its specific function, with LTPS providing high mobility for fast switching and a-Si providing uniform threshold voltage for consistent pixel operation, thereby resolving the contradiction between driving speed and threshold voltage uniformity.
2Manufacturing precision
If a-Si TFTs are used to achieve uniform threshold voltage, then display uniformity is improved, but carrier mobility decreases limiting driving speed
Solution Approach 1:
The patent segments the TFT backplane into two functional zones: pixel circuits using a-Si TFTs for uniform threshold voltage and high display uniformity, and driving circuits using LTPS TFTs for high carrier mobility and fast switching speeds. This spatial segmentation resolves the contradiction by assigning each TFT type to its optimal application.
3Manufacturing precision
If complex compensation circuits are added to correct threshold voltage variations, then display uniformity is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the compensation function from the pixel circuit level and implements it at the driving circuit level using LTPS TFTs with higher mobility. By taking out the complex compensation circuitry from each pixel and centralizing it in the driving circuits, the patent achieves display uniformity while reducing overall device complexity and manufacturing cost.
4Reliability
If fabrication temperature is lowered to protect flexible substrates, then substrate degradation is prevented, but TFT performance deteriorates
Solution Approach 1:
The patent applies local quality by using a-Si TFTs in pixel circuits where low-temperature fabrication protects the flexible substrate, while using LTPS TFTs in driving circuits where higher performance is needed and can be achieved through localized laser annealing. This local differentiation resolves the contradiction between substrate protection and TFT performance.
Data Source
AI summary
Provided is a display device. A poly-Si layer is disposed on a substrate. A first metal layer is disposed on the poly-Si layer, and a metal oxide layer is disposed on the first metal layer. A second metal layer is disposed on the metal oxide layer. The first metal layer is overlapped with the second metal layer. The first metal layer and the second metal layer may be gate lines connected to different TFTs.