Double Gate Thin-Film Transistor for OLED Aperture Ratio
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Solution Overview
Problem
Thin-film transistors (TFTs) in display apparatuses face challenges with carrier mobility and threshold voltage uniformity, particularly when using amorphous silicon, which limits high-speed operation, and polysilicon, which requires additional compensation circuits.
Innovation Solution
A double gate TFT structure is implemented, featuring a first gate electrode, an active layer of oxide semiconductor, source and drain electrodes, and a second gate electrode that can function as a cathode in OLED displays, with specific voltage configurations to adjust the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon is used as the active layer, then the manufacturing process is simpler, but the carrier mobility decreases making high-speed operation difficult
Solution Approach 1:
The gate electrode is divided into two separate gates (first gate electrode and second gate electrode) positioned at opposite sides of the active layer. This segmentation allows independent control of threshold voltage and carrier mobility, enabling high-speed operation while maintaining manufacturing simplicity through the use of amorphous silicon active layer
Solution Approach 2:
The invention transitions from a conventional single-plane gate structure to a three-dimensional double gate structure where gates are positioned on opposite sides of the active layer. This dimensional change enhances carrier mobility through improved electric field control while maintaining compatibility with amorphous silicon manufacturing processes
2Speed
If polysilicon is used as the active layer, then the carrier mobility increases, but the threshold voltage becomes non-uniform requiring additional compensation circuits
Solution Approach 1:
The invention extracts the threshold voltage control function from the material selection and implements it through the second gate electrode. This separation allows the active layer to focus on providing high carrier mobility while the second gate independently adjusts threshold voltage uniformity, eliminating the need for compensation circuits
Solution Approach 2:
The invention changes the control parameter for threshold voltage from material composition (polysilicon crystallinity) to electrical parameter (voltage applied to second gate electrode). This parameter change enables precise control of threshold voltage uniformity while maintaining high carrier mobility through the active layer material
3Manufacturing precision
If a separate compensation circuit is added to polysilicon TFTs, then threshold voltage uniformity is improved, but the device complexity increases
Solution Approach 1:
The invention merges the threshold voltage control function with the second gate electrode that is already part of the basic TFT structure. This integration eliminates the need for separate compensation circuits while achieving uniform threshold voltage control, thereby reducing device complexity
Solution Approach 2:
The second gate electrode serves multiple functions: it controls threshold voltage uniformity, enables high-speed operation through improved electric field control, and can function as a cathode in OLED displays. This multi-functionality eliminates the need for dedicated compensation circuits
Data Source
AI summary
A double gate thin-film transistor (TFT), and an organic light-emitting diode (OLED) display apparatus including the double gate TFT, includes a double gate thin-film transistor (TFT) including: a first gate electrode on a substrate; an active layer on the first gate electrode; source and drain electrodes on the active layer; a planarization layer on the substrate and the source and drain electrodes, and having an opening corresponding to the active layer; and a second gate electrode in the opening.