Pre-charge Voltage Polarity Reversal for OLED Transistor Deterioration
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Solution Overview
Problem
The continuous application of positive voltage to driving thin film transistors in organic electroluminescent display devices leads to deterioration, reducing the lifetime of the transistors and decreasing the brightness of the organic light-emitting diodes.
Innovation Solution
The implementation of a pre-charge voltage with opposite polarity to the data voltage, applied using a third transistor connected to the (n−1)th scan signal, helps prevent deterioration by discharging charges in the capacitors and reducing the storage of previous data voltages, thereby maintaining transistor performance and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If positive voltage is continuously applied to driving thin film transistors to maintain operation, then the transistors can continuously drive the organic light-emitting diodes, but the transistors deteriorate and their lifetime is reduced
Solution Approach 1:
The patent applies periodic voltage polarity reversal to the driving thin film transistors. After a period of positive voltage application for normal operation, a negative voltage is applied in subsequent periods to clear trapped charges. This periodic action allows continuous operation while preventing cumulative damage, thereby extending transistor lifetime without sacrificing productivity.
Solution Approach 2:
The patent applies a negative voltage to the driving transistors in advance of when deterioration would occur during normal positive voltage operation. This preliminary anti-action (negative voltage application) prevents the accumulation of trapped charges that would otherwise lead to threshold voltage shifts and transistor deterioration, counteracting the harmful effects before they accumulate to problematic levels.
2Illumination intensity
If positive voltage is continuously applied to driving thin film transistors, then the organic light-emitting diodes can maintain brightness, but the threshold voltage of transistors changes and brightness decreases over time
Solution Approach 1:
By periodically reversing the voltage polarity applied to driving transistors, the patent prevents cumulative charge trapping that would otherwise cause progressive brightness degradation. The periodic negative voltage pulses reset the transistor electrical characteristics, allowing the display to maintain consistent brightness intensity and duration over extended operational periods.
Solution Approach 2:
The negative voltage application serves as a preliminary corrective action that prevents threshold voltage drift before it affects brightness output. By clearing trapped charges in advance, the patent ensures that transistors maintain their original electrical characteristics, thereby preserving display brightness uniformity throughout the intended operational lifetime.
3Reliability
If a pre-charge voltage with opposite polarity is applied using an additional transistor and scan signal, then transistor deterioration is prevented, but the device structure becomes more complex
Solution Approach 1:
The patent makes the existing (n-1)th scan signal serve a dual function: it activates the third transistor to apply pre-charge voltage to driving transistors, and simultaneously serves as the scan signal for its intended row. This multi-functionality approach integrates the pre-charge function into existing scan infrastructure, preventing transistor deterioration without adding dedicated pre-charge scan signal generation circuitry.
Solution Approach 2:
The existing scan signal infrastructure serves the additional function of controlling pre-charge voltage application. The (n-1)th scan signal automatically triggers the pre-charge operation for the nth row's driving transistors without requiring separate control signals or additional timing circuitry. The system uses its own existing signals to perform the protective function, avoiding additional complexity.
Data Source
AI summary
An organic electroluminescent display device includes an organic light-emitting diode, a first transistor outputting a data voltage by an nth scan signal (n is a natural number), a second transistor providing a current to the organic light-emitting by the data voltage, a capacitor storing the data voltage, and a third transistor supplying the second transistor and the capacitor with a pre-charge voltage by an (n−1)th scan signal, the pre-charge voltage having an opposite polarity to the data voltage.