OLED TFT Thickness Variation for Mura Reduction
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Solution Overview
Problem
Conventional electroluminescent devices suffer from the 'mura' effect due to uniform semiconductor layer thickness, leading to inconsistent electric field effect mobility among sub-pixels, which affects driving current distribution and luminescent efficiency.
Innovation Solution
An active matrix organic electroluminescent device with a pixel area comprising sub-pixels having switching TFTs with a first silicon layer thickness and driving TFTs with a second silicon layer thickness, where the thickness difference exceeds 10%, allowing adjustable electric field effect mobility and uniform light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform thickness semiconductor layers are formed for simplicity of process, then manufacturing complexity is reduced, but electric field effect mobility becomes inconsistent among sub-pixels causing mura effect
Solution Approach 1:
The patent applies local quality by forming semiconductor layers with different thicknesses in different regions: the channel formation region has a first thickness while the source/drain region has a second thickness greater than the first. This local thickness variation optimizes electric field effect mobility in the channel region while maintaining manufacturability through selective thinning processes.
Solution Approach 2:
The semiconductor layer is segmented into distinct regions with different thicknesses - the channel formation region is thinned to a first thickness while the source/drain region maintains a second thickness. This segmentation allows independent optimization of electrical properties in different functional regions, resolving the contradiction between uniform manufacturing and performance consistency.
2Reliability
If semiconductor film is thinned to reduce channel thickness for performance optimization, then electric field effect mobility is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by first forming a uniformly thick semiconductor layer across the entire substrate before selectively thinning the channel formation region. This preliminary uniform formation simplifies the overall manufacturing process while the subsequent selective thinning is achieved through standard photolithography and etching techniques, avoiding the need for complex thickness control throughout the entire layer.
Solution Approach 2:
Instead of controlling thickness uniformly across the entire semiconductor layer, the patent applies local quality by selectively thinning only the channel formation region to the first thickness while maintaining the source/drain region at the second thickness. This localized approach reduces manufacturing precision requirements compared to controlling the entire layer at a thin dimension.
3Reliability
If different poly-Si thicknesses are formed in switching and driving TFTs, then driving current distribution is improved and mura effect is reduced, but device complexity increases
Solution Approach 1:
The patent applies local quality by forming semiconductor layers with different thicknesses in different functional regions: switching TFTs have a channel region with a first thickness while driving TFTs have a channel region with a second thickness. This local thickness variation optimizes the driving current distribution and reduces mura effect while using the same fabrication process sequence for all TFTs.
Solution Approach 2:
The patent achieves universality by using a single fabrication process sequence that forms semiconductor layers with different thicknesses for both switching and driving TFTs. The same deposition, crystallization, and etching processes are applied universally across the substrate, with thickness differentiation achieved through region-specific patterning rather than separate process lines.
Data Source
AI summary
The invention discloses a system for displaying images comprising an organic electroluminescent device. The organic electroluminescent device comprises a pixel area including a plurality of sub-pixels, a switching TFT having a first silicon layer with a first thickness and a driving TFT having a second silicon layer with a second thickness. Each sub-pixel includes a switching region with a switching TFT thereon and a driving region with a driving TFT thereon. Specifically, a difference between the first thickness and the second thickness at least exceeds 10%. Fabrication methods of the system are also provided.