OLED Display Transistor Segmentation for Current Stability
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Solution Overview
Problem
OLED displays face issues with display characteristics deterioration due to high off current in switching thin film transistors and low mobility/stability in driving thin film transistors, leading to reduced current transmission, image sticking, and reduced operating life.
Innovation Solution
The OLED display employs different types of crystalline silicon for switching and driving semiconductors, with specific transistor structures and gate insulating layers to optimize performance, including amorphous silicon for switching and microcrystalline or polycrystalline silicon for driving, and overlapping control electrodes to enhance current flow and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the same type of thin film transistor is used for both switching and driving functions, then device complexity is reduced, but display characteristics deteriorate due to inability to optimize for different functions
Solution Approach 1:
The patent applies local quality by using different thin film transistor structures in different locations: switching TFTs with one gate electrode for low off-current, and driving TFTs with two gate electrodes for high mobility and stability. This allows each transistor to be optimized for its specific function while maintaining overall device performance.
2Object-generated harmful factors
If switching thin film transistor off current is reduced, then cross-talk between pixels is reduced, but manufacturing precision requirements increase to achieve low off current characteristics
Solution Approach 1:
The patent changes the structural parameter of the switching TFT by using a single gate electrode configuration with specific dimensional ratios (channel width to length ratio) to achieve low off-current characteristics. This parameter optimization allows reduction of cross-talk without requiring excessive manufacturing precision.
3Productivity
If driving thin film transistor mobility is increased, then sufficient driving current is achieved, but threshold voltage stability may be compromised due to higher current stress
Solution Approach 1:
The patent uses composite material structures for the driving TFT, combining two gate electrodes with different functions: a first gate for controlling threshold voltage and a second gate for enhancing mobility. This composite structure allows simultaneous achievement of high driving current and stable threshold voltage.
4Reliability
If different types of thin film transistors are used for switching and driving functions, then performance is optimized, but device complexity and manufacturing process difficulty increase
Solution Approach 1:
The patent segments the display device into two functional zones: switching TFT regions with one-gate structure and driving TFT regions with two-gate structure. This segmentation allows independent optimization of each transistor type while maintaining clear manufacturing process separation.
Solution Approach 2:
The patent employs universal manufacturing processes that can accommodate both switching and driving TFT structures. The same base fabrication steps are used for both transistor types, with additional processing only where needed for the second gate electrode in driving TFTs, thereby reducing overall manufacturing complexity.
Data Source
AI summary
An organic light emitting diode (“OLED”) display includes; a substrate, first and second signal lines which intersect each other and are disposed on the substrate, a switching control electrode connected to the first signal line, a switching input electrode connected to the second signal line, a switching output electrode disposed substantially opposite the switching input electrode with respect to the switching control electrode, a switching semiconductor which partially overlaps the switching input electrode and the switching output electrode, first and second driving control electrodes connected to the switching output electrode, a driving semiconductor disposed between the first and second driving control electrodes, a driving input electrode and a driving output electrode which partially overlap the driving semiconductor and are disposed substantially opposite each other with respect to the driving semiconductor, a first electrode connected to the driving output electrode, a second electrode which faces the first electrode, and a light emitting member disposed between the first electrode and the second electrode.