Hybrid Oxide and LTPS TFT Backplane Design
Solution Overview
Problem
Conventional TFT backplanes face challenges in achieving high resolution and low power consumption due to limitations in carrier mobility and threshold voltage uniformity, particularly in silicon-based TFTs, which also restrict their use in flexible displays.
Innovation Solution
A TFT backplane design that combines oxide TFTs and LTPS TFTs on a single substrate, where oxide TFTs are used in pixel circuits and LTPS TFTs in driving circuits, optimizing carrier mobility and threshold voltage uniformity to enhance display performance and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If LTPS TFTs are used in the backplane to achieve high carrier mobility, then the driving speed and resolution are improved, but the threshold voltage uniformity deteriorates due to grain boundaries causing display non-uniformity (mura)
Solution Approach 1:
The patent applies different TFT types to different functional regions: LTPS TFTs are used in driving circuits where high speed is critical, while a-Si TFTs are used in pixel circuits where uniformity is more important. This local differentiation allows each region to optimize for its specific requirements without compromising the other.
2Ease of manufacture
If a-Si TFTs are used in the backplane to achieve simple fabrication, then the manufacturing process is simplified, but the carrier mobility is insufficient for high-speed drive circuits
Solution Approach 1:
The patent differentiates TFT types by functional region: a-Si TFTs are deployed in pixel circuits where simple fabrication is acceptable, while LTPS TFTs are deployed in driving circuits where high speed is essential. This resolves the contradiction by matching material properties to functional requirements.
3Temperature
If the fabrication temperature is lowered to protect flexible substrates, then the substrate integrity is maintained, but the TFT performance deteriorates
Solution Approach 1:
The patent changes the material parameter from conventional silicon-based semiconductors to oxide semiconductor materials that can be processed at low temperatures (below 200°C) while maintaining high carrier mobility and good TFT performance, thus protecting flexible substrates without sacrificing device performance.
4Manufacturing precision
If higher resolution is achieved by increasing pixel density, then the display quality is improved, but the power consumption increases due to more TFTs required
Solution Approach 1:
The patent uses LTPS TFTs with high carrier mobility in driving circuits to reduce leakage current and improve switching efficiency, while using a-Si TFTs in pixel circuits with low off-current characteristics. This combination reduces overall power consumption even at high resolutions by optimizing each circuit's TFT selection for minimal power loss.
Data Source
AI summary
There is provided a TFT backplane having at least one TFT with oxide active layer and at least one TFT with poly-silicon active layer. In the embodiments of the present disclosure, at least one of the TFTs implementing the circuit of pixels in the active area is an oxide TFT (i.e., TFT with oxide semiconductor) while at least one of the TFTs implementing the driving circuit next to the active area is a LTPS TFT (i.e., TFT with poly-Si semiconductor).