OLED Driving Transistor Double-Gate Structure for Threshold Voltage Compensation
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Solution Overview
Problem
The threshold voltage variations in driving transistors of organic light emitting displays cause luminance differences across pixels, affecting display quality due to process errors and pixel degradation over time.
Innovation Solution
The implementation of a double-gate structure for the driving transistor, with a first gate electrode under and overlapping the active layer, and a second gate electrode overlapping the active layer, coupled through contact holes, along with a storage capacitor to compensate for threshold voltage fluctuations, ensuring consistent drain-to-source current and luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional single-gate structure is used for the driving transistor, then the device complexity is low, but the threshold voltage varies from pixel to pixel causing luminance differences
Solution Approach 1:
The gate electrode is divided into two separate gates (first gate and second gate) that can be independently controlled. This segmentation allows independent optimization of each gate's function: the first gate controls threshold voltage compensation while the second gate controls current driving, thereby resolving the threshold voltage consistency issue without excessive complexity
Solution Approach 2:
The dual-gate structure enables the driving transistor to perform multiple functions simultaneously: threshold voltage compensation, current control, and luminance stabilization. This multi-functionality addresses the threshold voltage variation problem while maintaining reasonable device complexity through integrated design
2Object-affected harmful factors
If the first gate electrode overlaps part of the anode of the OLED, then parasitic capacitance is reduced improving contrast ratio, but the manufacturing precision requirements increase
Solution Approach 1:
The first gate electrode is positioned to overlap only part of the anode rather than the entire anode area. This local overlap approach reduces parasitic capacitance to acceptable levels while minimizing the impact on manufacturing precision requirements by limiting the critical alignment area
3Reliability
If a double-gate structure with contact holes is implemented, then threshold voltage compensation is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The contact holes are formed and configured in advance during the manufacturing process to establish proper electrical connections between the gates and control electrodes. This preliminary configuration ensures reliable threshold voltage compensation while streamlining the manufacturing process by planning connections upfront rather than adding complex routing later
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution minimizes luminance differences between white grayscale display periods, improves picture quality by stabilizing the drain-to-source current, and reduces parasitic capacitance, preventing color shifts and enhancing contrast ratio.
Implementation Method 1
an organic light emitting diode (OLED) configured to emit light depending on the drain-to-source current of the driving transistor
Data Source
AI summary
A pixel includes a driving transistor to control an amount of drain-to-source current flowing from a first electrode to a second electrode based on a voltage applied to a first gate electrode. The current is used to control light emitted from an organic light emitting diode. The pixel also includes a first transistor coupled between the first gate electrode and second electrode of the driving transistor. The first gate electrode is under an active layer of the driving transistor, and the first gate electrode overlaps the active layer of the driving transistor.