Stacked TFT Channel Extension for OLED Gradation
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Solution Overview
Problem
High-resolution organic light-emitting display devices face challenges in achieving sufficient gradation and reliability due to the saturation of current in driving thin-film transistors with a single gate structure, especially in smaller pixel sizes, where the linear section of the IDS-VG graph is excessively short and the kink effect worsens, making it difficult to supply current reliably to organic light-emitting diodes.
Innovation Solution
A stack-type driving thin-film transistor is designed with a first and second active layer overlapping each other, featuring protruding portions and a connection electrode that penetrates both layers, allowing electrons to pass through dual channels, thereby increasing the channel length without expanding the transistor's area, reducing the kink effect, and enhancing gradation capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a single gate structure is used in thin-film transistors for high-resolution displays, then the transistor area can be minimized, but the linear section of the IDS-VG graph becomes excessively short and the kink effect worsens, making sufficient gradation difficult
Solution Approach 1:
The patent transitions from a planar single-gate structure to a three-dimensional stacked dual-gate structure. By stacking two active layers vertically with gate electrodes positioned between them, the invention increases the effective channel length without expanding the planar footprint, thereby maintaining small transistor area while improving gradation capability through extended linear section in IDS-VG characteristics
Solution Approach 2:
The patent divides the single channel into two separate channels by stacking active layers. Each active layer has its own channel region, and the total effective channel length becomes the sum of both channels. This segmentation allows the transistor to achieve longer effective channel length for better gradation control while maintaining compact planar dimensions
2Measurement precision
If the sub-pixel size is reduced to achieve high resolution, then more pixels can be displayed, but the driving thin-film transistor undergoes current saturation quickly and sufficient gradation becomes difficult to realize
Solution Approach 1:
By stacking active layers vertically, the invention increases the effective channel length within the confined planar area of small sub-pixels. This vertical dimension expansion allows sufficient gradation control through extended linear section without increasing the sub-pixel footprint, enabling high resolution while maintaining current control stability
Solution Approach 2:
The patent changes the structural parameters of the thin-film transistor by introducing a stacked configuration with multiple active layers and dual gate electrodes. This structural parameter change increases the effective channel length and modifies the electrical characteristics to extend the linear section of IDS-VG graph, enabling sufficient gradation in miniaturized sub-pixels
3Device complexity
If a general single gate structure is used, then the transistor structure is simple, but the kink effect is worsened which causes increased ID after saturation, making it difficult to secure reliability
Solution Approach 1:
The patent segments the channel into two separate channels through stacked active layers, each controlled by the gate electrode. This segmentation creates dual-channel conduction paths that reduce the kink effect by distributing current flow, thereby improving current supply reliability to OLED while maintaining relatively simple structure through shared gate electrode
Solution Approach 2:
The patent combines two active layers and their channels into a single integrated transistor structure with a shared gate electrode. This merging approach achieves the kink effect reduction benefit of dual-channel structure while avoiding the complexity of completely separate transistor structures, as both channels share common source and drain electrodes
Data Source
AI summary
A driving thin-film transistor can include a substrate; a first active layer disposed on the substrate and including a first protruding portion; a second active layer overlapping with the first active layer and including a second protruding portion; a gate electrode disposed between the first active layer and the second active layer; a source electrode connected to the first protruding portion of the first active layer; and a drain electrode connected to the second protruding portion of the second active layer, in which the first protruding portion of the first active layer and the second protruding portion of the second active layer are located at different positions.