Double Gate Sampling Transistor for Display Devices
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Solution Overview
Problem
In active-matrix display devices with organic EL elements, the change in signal writing time due to varying threshold voltage of sampling transistors affects image quality and light-emission luminance, especially as screen definition increases, leading to issues like image lag and luminance variations.
Innovation Solution
The implementation of a double gate structure for sampling transistors, where a pair of transistor elements are connected in series with a common gate connection, and a capacitor between the gate and an intermediate node, stabilizes the threshold voltage and signal writing time, ensuring consistent light-emission luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the screen definition is increased, then the image quality is improved, but the signal writing time varies due to threshold voltage changes, causing luminance variations and image defects
Solution Approach 1:
The patent applies parameter changes by modifying the transistor structure from a single gate to a double gate configuration. This structural parameter change enables independent control of threshold voltage and channel formation, allowing the sampling transistor to maintain stable threshold voltage even as screen definition increases, thereby resolving the contradiction between high resolution and signal writing time stability
Solution Approach 2:
The patent introduces an intermediary mechanism by adding a second gate to the sampling transistor. This intermediate control element (the second gate) acts as a mediator that can independently adjust and stabilize the threshold voltage, preventing the threshold voltage variations that would otherwise occur with increased screen definition, thus maintaining consistent signal writing time
2Device complexity
If a single gate structure is used for the sampling transistor, then the device complexity is reduced, but the threshold voltage varies, affecting signal writing time and light-emission luminance
Solution Approach 1:
The patent changes the structural parameter of the transistor from single gate to double gate configuration. This parameter change enables independent control of threshold voltage through the second gate, stabilizing the threshold voltage without significantly increasing overall device complexity, as the double gate structure can be integrated into the existing pixel circuit architecture
Solution Approach 2:
The patent segments the gate control function into two independent gates. The first gate controls the channel formation while the second gate independently controls the threshold voltage. This segmentation allows each gate to perform its specific function optimally, stabilizing the threshold voltage without requiring a complete redesign of the transistor structure
3Ease of manufacture
If the sampling transistor threshold voltage varies, then the manufacturing process is simpler, but the signal writing time changes, causing image lag and luminance variations
Solution Approach 1:
The patent applies parameter changes by implementing a double gate structure that enables independent threshold voltage control. This parameter change stabilizes the signal writing time by preventing threshold voltage variations, without significantly complicating the fabrication process, as the double gate can be formed using standard thin-film transistor manufacturing techniques
4Device complexity
If the threshold voltage of the sampling transistor is not stabilized, then the device structure is simpler, but the light-emission luminance varies, affecting image quality
Solution Approach 1:
The patent changes the transistor structure parameter from single gate to double gate, enabling independent control of threshold voltage. This parameter change stabilizes the light-emission luminance by maintaining consistent signal writing time, while the double gate structure can be integrated into the existing device architecture without significantly increasing overall complexity
5Reliability
If a double gate structure is implemented, then the threshold voltage and signal writing time are stabilized, but the device complexity increases
Solution Approach 1:
The patent segments the gate control function into two independent gates, where the first gate controls channel formation and the second gate controls threshold voltage. This segmentation allows each gate to perform its specific function, stabilizing signal writing time while maintaining a modular structure that can be integrated into existing pixel circuits with minimal increase in overall device complexity
Data Source
AI summary
A sampling transistor in embodiments of the present invention is kept at the on-state with a time width shorter than one horizontal cycle, during the period from the rising of a control pulse supplied from a scanner to the falling of the control pulse, and samples a video signal Vsig from a signal line SL to write the video signal Vsig to a hold capacitor. A sampling transistor T1 has a double gate structure in which a pair of transistor elements are connected in common. This suppresses change in the threshold voltage of the sampling transistor.