Oxide TFT Pixel Circuit Structure for Low-Leakage Grayscale Control
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Solution Overview
Problem
Existing organic light emitting display devices using hybrid-type thin film transistors face challenges with high leakage current and fluctuation in current due to the use of different semiconductor materials, particularly polycrystalline and oxide semiconductor patterns, which complicates processing and limits grayscale expression.
Innovation Solution
The implementation of a thin film transistor (TFT) structure with an oxide semiconductor pattern, including a dummy electrode and specific insulating layers, to reduce leakage current and control parasitic capacitance, thereby stabilizing current fluctuations and enhancing grayscale expression. This structure incorporates a bottom gate configuration to protect the active layer and simplifies the manufacturing process by using a single mask for multiple layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If hybrid-type thin film transistors using different semiconductor materials (polycrystalline and oxide) are used, then driving speed is improved, but leakage current increases and processing becomes complicated
Solution Approach 1:
The patent uses oxide semiconductor patterns uniformly for all TFTs in the pixel circuit portion and GIP circuit portion, eliminating the need for hybrid structures. This homogeneous approach maintains low leakage current characteristics while simplifying the manufacturing process by using the same semiconductor material throughout.
2Speed
If hybrid-type thin film transistors using different semiconductor materials are used, then driving speed is improved, but processing complexity increases
Solution Approach 1:
The patent employs oxide semiconductor patterns for all TFTs uniformly, eliminating the need for separate formation processes for polycrystalline and oxide semiconductors. This reduces processing complexity while maintaining the low leakage current advantage of oxide semiconductors.
Solution Approach 2:
The oxide semiconductor pattern serves multiple functions: it provides low leakage current characteristics and can be formed using a single mask process for all TFTs in the pixel circuit and GIP circuit, universalizing the manufacturing approach across different circuit regions.
3Speed
If polycrystalline semiconductor pattern is used for driving TFT, then driving speed is improved, but grayscale expression deteriorates due to large current fluctuation
Solution Approach 1:
The patent uses oxide semiconductor patterns for all TFTs including driving TFTs, which provides stable current characteristics and low fluctuation rates. This enables reliable grayscale expression while maintaining adequate driving speed through the uniform oxide semiconductor structure.
Data Source
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AI summary
Provided is an organic light emitting display device in which a driving thin film transistor TFT (DT) includes an oxide semiconductor pattern. The driving thin film transistor includes a gate electrode (305) disposed under an oxide semiconductor pattern, and a dummy electrode (315), a source electrode (319S) and a drain electrode (319D) over the oxide semiconductor pattern, and the dummy electrode (315) is electrically connected to the source electrode (319S) to increase the S-factor of the driving TFT (DT). In addition, the organic light emitting display device of the present disclosure includes a plurality of switching TFTs (ST-n) including an oxide semiconductor pattern, and the plurality of switching TFTs (ST-n) includes a plurality of switching thin film transistors (ST-n) having different distances between the oxide semiconductor pattern and the gate electrode so as to have different threshold voltages.