OLED Pixel Circuit Layout for Leakage-Stable Luminance
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Solution Overview
Problem
Existing display devices experience issues with leakage currents from the gate electrode of driving transistors, leading to undesired brightness variations and deterioration of light emitting elements due to IR drops in the driving power source.
Innovation Solution
A display device design incorporating specific transistor configurations and capacitors to minimize leakage currents, utilizing N-type transistors and capacitors to stabilize node voltages, and employing alternating scan signal polarities to enhance driving reliability and power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a liquid crystal display device is miniaturized, then the size is reduced, but the aperture ratio decreases leading to insufficient luminance
Solution Approach 1:
The pixel electrode is divided into multiple segments (first pixel electrode and second pixel electrode) arranged in different directions. This segmentation allows each electrode to collect charges more effectively in its specific direction, improving overall aperture ratio and luminance while maintaining the miniaturized display size.
Solution Approach 2:
Different electrode structures are applied in different regions of the pixel. The first pixel electrode extends in a first direction while the second pixel electrode extends in a second direction, creating local optimizations for charge collection in various areas of the pixel to enhance overall aperture ratio.
2Illumination intensity
If the aperture ratio is increased to improve luminance, then the luminance increases, but the pixel structure becomes more complex
Solution Approach 1:
Multiple pixel electrodes are merged into a single integrated structure where the first and second pixel electrodes are electrically connected. This merging achieves a high aperture ratio equivalent to having multiple electrodes while simplifying the overall structure by reducing the number of separate components.
Solution Approach 2:
The pixel electrode structure serves multiple functions simultaneously: it acts as both the first pixel electrode extending in the first direction and the second pixel electrode extending in the second direction, while also functioning as the common electrode. This multi-functionality increases aperture ratio without proportionally increasing structural complexity.
3Ease of manufacture
If organic light-emitting materials are used, then the device can be manufactured, but they deteriorate due to oxidation and emit unwanted wavelengths
Solution Approach 1:
A hole blocking layer is introduced as an intermediary between the hole transport layer and the organic light-emitting material. This intermediary layer prevents direct contact between the organic material and oxygen/moisture from the environment, thereby preventing oxidation and deterioration while allowing the device to be manufactured with organic materials.
4Device complexity
If the hole blocking layer is positioned between the anode and hole transport layer, then the structure is simple, but the electron-hole recombination efficiency is insufficient
Solution Approach 1:
The hole blocking layer is repositioned from the traditional position between the anode and hole transport layer to a new position between the hole transport layer and the organic light-emitting material. This dimensional repositioning in the layer stack allows the hole blocking layer to effectively control charge distribution at the critical interface where electron-hole recombination occurs, improving recombination efficiency without significantly increasing structural complexity.
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
The solution effectively reduces leakage currents, maintains desired brightness, and prevents deterioration of light emitting elements by stabilizing voltage levels and compensating for threshold voltage changes in the organic light emitting diodes.
Implementation Method 1
a light-emitting diode that emits blue light
Implementation Method 2
a color conversion layer that converts a wavelength of the light emitted from the light-emitting diode into another wavelength
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
In a pixel, a display device including the pixel, and a method of driving the display device, the pixel includes a first transistor connected between a first power source and a fourth node and having a gate electrode connected to a first node, a second transistor connected between a third node and a data line and turned on in response to a scan signal supplied to an i-th first scan line, where i is a natural number, a third transistor connected between the first node and the fourth node and turned on in response to a scan signal supplied to an i-th third scan line, a fourth transistor connected between the second node and an initialization voltage and turned on in response to a scan signal supplied to an i-th second scan line, a first capacitor connected between the third node and the first node, a second capacitor connected between the first node and the second node, and an organic light emitting diode connected between the second node and a second power source, wherein the third transistor is an N-type transistor.