Driving TFT Stress Current for OLED Brightness Stability
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Solution Overview
Problem
Flexible OLED display devices on polyimide substrates experience significant initial brightness changes due to current drift in thin-film transistors (TFTs) caused by moisture, leading to instability and reduced brightness over time.
Innovation Solution
Applying a stress current higher than the maximum current for the OLED element to the driving TFT during non-light-emitting periods to reduce current instability and minimize brightness changes, thereby stabilizing the TFT characteristics and maintaining brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stress current higher than maximum current is applied to the driving TFT during non-light-emitting periods, then current drift is reduced and brightness stability is improved, but power consumption increases
Solution Approach 1:
The stress current is applied periodically during non-light-emitting periods (horizontal blanking period and vertical blanking period) rather than continuously. This timing-based approach allows the TFT characteristics to be stabilized when not displaying images, while avoiding continuous power consumption. The control circuit switches between normal display mode and stress application mode based on the timing signal, implementing periodic action to resolve the contradiction between reliability improvement and energy consumption.
2Reliability
If the driving TFT operates at higher current levels, then TFT characteristics are stabilized faster, but the risk of TFT degradation increases
Solution Approach 1:
The stress current is applied in advance during non-light-emitting periods to proactively stabilize TFT characteristics before the next display period begins. This preliminary stabilization action prevents current drift from accumulating during operation, thereby maintaining TFT reliability without requiring continuous high-current operation that would accelerate degradation. The stress application is preventive rather than corrective.
Solution Approach 2:
High stress current is applied intermittently during blanking periods rather than continuously, allowing the TFT to experience stabilization stress only when not actively displaying images. This periodic high-stress application stabilizes characteristics while minimizing cumulative degradation exposure, as the TFT spends most time operating at normal, lower current levels during actual display periods.
3Reliability
If stress current is applied during light-emitting periods, then TFT characteristics are stabilized, but image quality deteriorates due to current interference
Solution Approach 1:
The control circuit applies stress current only during non-light-emitting periods (horizontal blanking period and vertical blanking period) when no image is being displayed. During light-emitting periods, the control circuit switches to normal display mode and stops applying stress current, ensuring that image quality is not affected. This temporal separation between stress application and image display resolves the contradiction between stabilization effectiveness and image quality.
Data Source
AI summary
A display device includes a pixel circuit and a control circuit configured to control the pixel circuit. The pixel circuit includes a light-emitting element, and a driving thin-film transistor configured to control the amount of current to the light-emitting element. The control circuit is configured to apply a stress current higher than a maximum current for the light-emitting element to display images to the driving thin-film transistor but not to supply current to the light-emitting element in a period other than light-emitting periods of the light-emitting element to display an image.