Dual-Channel Thin Film Transistor for Gray Scale and ON-Current
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Solution Overview
Problem
Thin film transistors used in display apparatuses have a small sub-threshold swing (s-factor), making it difficult to represent gray scales effectively, and they also lack excellent current characteristics in the ON-state.
Innovation Solution
A thin film transistor design featuring a two-channel structure formed by partially stacking two different types of oxide semiconductor layers, with a specific overlap and non-overlap area configuration between the active layers and a gate electrode, enhancing the s-factor and ON-current characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thin film transistor is designed with a conventional single-channel structure, then the manufacturing process is simple, but the s-factor is small and gray scale representation is poor
Solution Approach 1:
The active layer is segmented into two distinct channels: a first channel with lower mobility and a second channel with higher mobility. This segmentation allows each channel to contribute differently to the overall transistor characteristics, enabling improved gray scale representation through the high mobility channel while maintaining manufacturing simplicity
Solution Approach 2:
The patent employs a composite active layer structure combining two different oxide semiconductor materials with different mobility characteristics. This composite structure enables the transistor to achieve both a large s-factor for gray scale representation and good on-off characteristics, resolving the contradiction between measurement precision and device complexity
2Reliability
If the mobility of the active layer is increased to improve ON-current, then the ON-current characteristics improve, but the s-factor decreases making gray scale representation difficult
Solution Approach 1:
The patent applies local quality by assigning different mobility characteristics to different channels within the same active layer. The first channel has lower mobility while the second channel has higher mobility, allowing each region to optimize for its specific function: the high mobility second channel improves ON-current characteristics while the overall structure maintains a large s-factor for gray scale representation
3Measurement precision
If the interval between gate electrode and active layer is increased to improve s-factor, then the s-factor increases, but the ON-current characteristics deteriorate
Solution Approach 1:
Instead of adjusting the vertical interval between gate electrode and active layer, the patent introduces a horizontal dimension by creating a dual-channel structure within the active layer. The second channel with higher mobility compensates for the reduced gate control effect, allowing the transistor to maintain both a large s-factor and good ON-current characteristics without increasing the gate-active layer interval
Data Source
Figure 1A
Figure 1B~1C
Figure 1D~2
AI summary
A thin film transistor including an active layer; and a gate electrode at least partially overlapped with the active layer. Further, the active layer includes a first active layer and a second active layer on the first active layer; a channel; a first connection portion contacting a first side of the channel; and a second connection portion contacting a second side of the channel. In addition, the channel includes a first overlap area in which the first active layer and the second active layer overlap each other based on a plan view; and a first non-overlap area in which the first active layer and the second active layer do not overlap each other based on the plan view. Also, in the channel of the active layer, each of the first active layer and the second active layer extends from the first connection portion to the second connection portion. The second active layer also has a mobility greater than a mobility of the first active layer.