Thin Film Transistor Substrate With Third Gate Electrode
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Solution Overview
Problem
Existing oxide semiconductor-based thin film transistors face challenges in achieving different threshold voltages, which is essential for high-speed driving and CMOS circuit applications, as most high-mobility oxide semiconductors like amorphous IGZO primarily exhibit n-type conduction, making it difficult to fabricate CMOS inverter circuits with controlled threshold voltages.
Innovation Solution
A thin film transistor substrate configuration with a third gate electrode that can control the threshold voltages of first and second thin film transistors by adjusting the potential of a coupled power supply line, allowing for different threshold voltages and noise reduction through noise shielding, using metal oxide materials like indium tin oxide for the third gate electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a double gate structure is used to suppress hump occurrence, then device reliability is improved, but the ability to individually control threshold voltages of multiple transistors deteriorates
Solution Approach 1:
The invention divides the gate control into independent segments by providing separate gate electrodes (first gate electrode and second gate electrode) for each transistor. This allows individual threshold voltage control for the first and second thin film transistors while maintaining the double gate structure for hump suppression. Each transistor's gate electrodes can be independently biased to achieve desired threshold voltages.
2Speed
If oxide semiconductor materials with high mobility are used, then device speed is improved, but the ability to achieve p-type conduction deteriorates
Solution Approach 1:
The invention changes the electrical parameters (threshold voltage and conduction type) of the oxide semiconductor layer by controlling the potential of the third gate electrode. By adjusting the potential applied to the third gate electrode, the oxide semiconductor can be switched between n-type and p-type conduction modes, enabling both enhancement-mode and depletion-mode transistors while maintaining high mobility.
3Speed
If threshold voltages of multiple transistors are made different for high-speed driving, then device speed is improved, but device complexity increases
Solution Approach 1:
The invention makes the gate electrode structure universal and multi-functional by using identical gate electrode configurations (first and second gate electrodes) for both transistors. The same structural elements serve dual purposes: suppressing humps and enabling independent threshold voltage control. This universality reduces design complexity while achieving different threshold voltages through independent biasing.
Data Source
AI summary
An active matrix substrate (20a) includes: an insulating substrate (10a); a first thin film transistor (5a) including a first gate electrode (11b) located on the insulating substrate (10a) and a first oxide semiconductor layer (13a) having a first channel region (Ca); a second oxide semiconductor layer (13b) including a second gate electrode (11c) located on the insulating substrate (10a) and having a second channel region (Cb); a second gate insulating film (17) covering the first oxide semiconductor layer (13a) and the second semiconductor layer (13b); and a third gate electrode (25) located on the second gate insulating film (17) and facing the first channel region (Ca) and the second channel region (Cb) with the second gate insulating film (17) interposed therebetween.