EL Display Panel Reverse Bias Drive Transistor Threshold Drift
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Solution Overview
Problem
In organic EL display panels using an active matrix drive system, the change in threshold voltage of drive transistors over time leads to luminance non-uniformity and potential burn-in issues, especially when P-channel transistors are replaced with N-channel transistors due to limitations in thin film processes, causing variations in drive current and emission luminance across pixels.
Innovation Solution
An EL display panel with a pixel structure that includes a reverse bias potential generating portion to generate a reverse bias potential reflecting gradation values and applies this potential to the gate electrode of the drive transistor during non-emission periods, balancing the positive and negative changes in threshold voltage to maintain consistent luminance, and using a voltage applying portion to apply this reverse bias potential.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If P-channel thin film transistors are used as drive transistors in organic EL display panels, then the drive transistor can operate as a constant current source with stable gate-to-source voltage, but the thin film process cannot fabricate P-channel transistors in some cases
Solution Approach 1:
The invention changes the operating parameters of the N-channel drive transistor by applying reverse bias potential during non-emission periods. This parameter change compensates for the threshold voltage drift that occurs over time, enabling N-channel transistors to achieve stable constant current source operation similar to P-channel transistors, thus resolving the contradiction between manufacturing compatibility and operational stability
2Ease of manufacture
If N-channel thin film transistors are used as drive transistors to replace P-channel transistors, then the display panel can be manufactured with available thin film processes, but the gate-to-source voltage changes with temporal change of I-V characteristics causing luminance non-uniformity
Solution Approach 1:
The invention applies reverse bias potential to the gate electrode during non-emission periods as a preliminary counter-action to prevent threshold voltage drift. This pre-compensation mechanism counteracts the temporal changes in I-V characteristics before they cause luminance non-uniformity, allowing N-channel transistors to maintain manufacturing precision comparable to P-channel transistors
3Stability of the object's composition
If the gate-to-source voltage is held constant using a simple pixel circuit configuration, then the emission luminance can be held constant, but the threshold voltage changes over time leading to luminance non-uniformity and burn-in
Solution Approach 1:
The invention implements periodic application of reverse bias potential during non-emission periods in each frame cycle. This periodic action continuously compensates for threshold voltage drift that accumulates over time, maintaining both gate-to-source voltage stability and luminance uniformity across the display panel throughout its operational lifetime
Data Source
AI summary
Disclosed herein is an electro luminescence display panel having a pixel structure corresponding to an active matrix drive system, including: a reverse bias potential generating portion configured to generate a reverse bias potential in which corresponding one of gradation values of pixels is reflected; and a voltage applying portion configured to apply the reverse bias potential to a gate electrode of a drive transistor composing a pixel circuit adapted to operate for a non-emission time period.