Shielding Electrode in Transparent OLED TFTs
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Solution Overview
Problem
Conventional transparent organic light emitting display devices suffer from light leakage currents when exposed to external light, leading to changes in the S-factor and threshold voltage of TFTs, which degrade gray-level expressiveness and result in inconsistent gray-level representation across a frame.
Innovation Solution
Incorporating a shielding electrode between the transparent substrate and the active layer of TFTs in the pixel circuit, including the driving, sampling, and initializing TFTs, to block external light and maintain stable gray-level expression by ensuring constant driving currents at both start and end timings of a frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a transparent substrate is applied to the organic light emitting display device, then transparency and light weight are improved, but light leakage current is generated in the TFT active layer when external light is irradiated
Solution Approach 1:
A shielding electrode is introduced as an intermediary component between the transparent substrate and the TFT active layer. This shielding electrode blocks external light from reaching the active layer, preventing light leakage current while maintaining the overall transparency of the display device. The shielding electrode acts as a mediator that resolves the conflict between transparency and light interference.
2Illumination intensity
If external light is irradiated onto the TFT active layer through the transparent substrate, then the display device maintains transparency, but the S-factor and threshold voltage of the TFTs change, degrading gray-level expressiveness
Solution Approach 1:
The shielding electrode serves as a protective intermediary that prevents external light from altering the electrical characteristics of the TFTs. By blocking light exposure to the active layer, the shielding electrode stabilizes the S-factor and threshold voltage, ensuring consistent gray-level expressiveness while the transparent substrate maintains optical transparency.
3Illumination intensity
If external light irradiates the TFTs through the transparent substrate, then transparency is maintained, but driving current changes occur within one frame, preventing constant gray-level expression
Solution Approach 1:
The shielding electrode acts as a stable protective barrier between external light and the TFT active layer. This intermediary structure prevents light-induced variations in driving current throughout the frame period, ensuring that the driving current remains constant and enabling stable gray-level expression while transparency is preserved.
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
The shielding electrode effectively suppresses light leakage currents, stabilizing the S-factor and threshold voltage of TFTs, thereby enhancing gray-level expressiveness and maintaining consistent gray-level representation across a frame even under external light exposure.
Implementation Method 1
a shielding electrode disposed between the substrate and the respective active layer of the various transistors... block a light leakage current of the plurality of TFTs
Data Source
AI summary
The pixel circuit which controls the driving of the organic light emitting diode includes a driving TFT which supplies a driving current to the organic light emitting diode; a sampling TFT which samples a threshold voltage of the driving TFT; a first initializing TFT which supplies an initialization voltage to one electrode of the organic light emitting diode; and a storage capacitor which stores a voltage applied to the driving TFT, and at least one of the driving TFT, the sampling TFT, and the first initializing TFT includes a shielding electrode disposed between the substrate and the active layer. Therefore, even though the external light is irradiated onto a transparent substrate, a full white gray-level and a full black gray-level can be expressed so that the gray-level expressiveness may not be degraded.