OLED Pixel Circuit Light Blocking for Threshold Voltage Stability
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Solution Overview
Problem
Existing organic light emitting display devices suffer from characteristic deviations in threshold voltage of driving transistors due to process differentials, leading to differential deterioration and image quality degradation over time, with existing solutions either inadequately addressing light-induced shifts or not effectively shielding all transistors from light.
Innovation Solution
The implementation of a light blocking unit with a light blocking layer that selectively blocks light input to the driving transistor while allowing light to input to the switching transistors, thereby controlling the threshold voltage shift and enhancing reliability, by forming the light blocking layer under the driving transistor and creating openings under the switching transistors to prevent positive polarity shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light blocking layer is formed under the driving transistor to prevent positive polarity threshold voltage shifts, then the threshold voltage stability is improved, but the device complexity increases due to additional light blocking units and openings
Solution Approach 1:
The light blocking layer is segmented into different regions: a first light blocking unit under the driving transistor and a second light blocking unit under the switching transistor, with openings strategically placed to allow light exposure only where needed. This segmentation enables selective threshold voltage control for different transistor types within the same pixel circuit.
Solution Approach 2:
Different regions of the pixel circuit receive different light exposure conditions: the driving transistor region is blocked from light to prevent positive polarity shifts, while the switching transistor region has openings that allow light exposure to induce negative polarity shifts. This local differentiation optimizes threshold voltage characteristics for each transistor's specific functional requirements.
2Reliability
If openings are provided under switching transistors to allow light exposure for negative polarity shifts, then the compensation capability is improved, but uncontrolled light exposure may cause harmful effects on other circuit elements
Solution Approach 1:
The light blocking layer is segmented into functional units with precisely positioned openings that allow light exposure only to the switching transistor region. This segmentation ensures that light-induced negative polarity shifts occur only where needed for compensation, while other circuit elements remain protected from harmful light exposure.
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 effectively adjusts and stabilizes the threshold voltage of transistors, reducing image quality degradation by selectively managing light exposure, thereby improving the reliability and longevity of the organic light emitting display device.
Implementation Method 1
a light blocking unit LS, including a light blocking layer 110 which is formed for blocking light input to the pixel circuit unit CA
Implementation Method 2
the solution disclosed centers on a 'light blocking film 33' which prevents light from entering two switching transistors (Tr11, Tr12) but which is not provided at a driver transistor (Tr13) (paragraphs 0071, 0079, 0080). The resulting selective irradiation of the driver transistor (Tr13) shifts its threshold voltage to the minus side
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An organic light emitting display device including an emission unit (OA) and a pixel circuit unit (CA). The emission unit (OA) includes an organic light emitting diode (OLED). The pixel circuit unit (CA) includes a driving transistor (DT), at least one or more switching transistors (ST1, ST2), a capacitor (Cst), a light blocking unit (LS), and an opening (OP) in which a light blocking layer (110) is not formed. The light blocking unit (LS) includes the light blocking layer (110) which blocks light input to the pixel circuit unit (CA). The pixel circuit unit (CA) is configured to drive the emission unit and selectively block the light input to the pixel circuit unit (CA).