OLED Pixel Supplemental Electrode Voltage Control for Parasitic Capacitance
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Solution Overview
Problem
In OLED display devices, the presence of a supplemental electrode can create parasitic capacitors that result in step efficiency issues, where the pixel emits light with lower than desired luminance at the start of light emission and only reaches desired luminance after a predetermined period.
Innovation Solution
A supplemental electrode is used that applies a first voltage for a predetermined time period when the emission control signal is on and switches to a second voltage after that period, effectively reducing the impact of parasitic capacitors and ensuring consistent luminance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a supplemental electrode is disposed under the driving transistor, then light blocking capability is improved and driving current is increased, but parasitic capacitors are formed causing step efficiency issues
Solution Approach 1:
The supplemental electrode applies a first voltage (e.g., negative voltage) during a predetermined time period before normal operation to preliminarily counteract the parasitic capacitor effects. This preliminary action prevents the accumulation of charges that would otherwise cause step efficiency, ensuring the pixel reaches desired luminance immediately without delay.
Solution Approach 2:
The supplemental electrode changes its voltage parameter dynamically: applying a first voltage (negative or different polarity) during the predetermined time period, then switching to a second voltage (positive or normal operating voltage) afterward. This parameter change allows the system to adapt to different operational phases and eliminate luminance inconsistency caused by parasitic capacitors.
2Power
If a supplemental electrode is used to increase driving current, then OLED brightness is improved, but step efficiency occurs due to parasitic capacitor effects
Solution Approach 1:
Before the OLED emits light, the supplemental electrode applies a first voltage during a predetermined time period to preliminarily neutralize the parasitic capacitor charges. This preliminary action ensures that when the driving current increases, the pixel immediately achieves desired luminance without the time loss associated with step efficiency.
Solution Approach 2:
The supplemental electrode applies a voltage with opposite polarity (first voltage) to counteract the harmful effect of parasitic capacitors before they can cause step efficiency. This preliminary anti-action prevents the time delay by opposing the charge accumulation that would otherwise slow down the luminance response.
3Ease of manufacture
If a supplemental electrode is disposed under the gate electrode, then manufacturing simplicity is maintained, but parasitic capacitors between supplemental electrode and gate electrode cause performance issues
Solution Approach 1:
The supplemental electrode uses different voltage parameters at different times: a first voltage during a predetermined time period to counteract parasitic capacitor effects, then a second voltage for normal operation. This parameter change approach maintains the simple overlapping structure while eliminating the harmful effects of parasitic capacitors formed between the supplemental electrode and gate electrode.
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 approach prevents step efficiency issues by ensuring the pixel emits light with desired luminance from the start, improving the display's performance and consistency.
Implementation Method 1
a first parasitic capacitor between the supplemental electrode and the gate electrode of the driving transistor and an effect of a second parasitic capacitor between the supplemental electrode and an active region of the driving transistor
Data Source
AI summary
A pixel of an organic light emitting diode (“OLED”) display device includes a switching transistor which transfers a data voltage, a storage capacitor which stores the data voltage transferred by the switching transistor, a driving transistor which generates a driving current based on the data voltage stored in the storage capacitor, an emission control transistor which selectively forms a path for the driving current in response to an emission control signal, an OLED which emits light based on the driving current, and a supplemental electrode overlapping a gate electrode of the driving transistor, the supplemental electrode having a first voltage for a predetermined time period from a time point at which the emission control signal has a turn-on level, and having a second voltage after the predetermined time period.