OLED Pixel Capacitor Bent Electrodes for Brightness Uniformity
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Solution Overview
Problem
The existing organic light emitting displays suffer from uneven brightness due to variations in the threshold voltage of transistors during manufacturing, leading to inconsistencies in image quality across pixels.
Innovation Solution
The solution involves a pixel structure with a first transistor, a second transistor, a first capacitor, and a second capacitor, where the outer portions of the capacitors have bents, allowing for controlled voltage application and reduced capacitance, thereby compensating for threshold voltage differences and improving brightness uniformity. The manufacturing method includes depositing and etching poly silicon and metal layers to form these capacitors with bents, which helps in reducing the capacitance and kickback voltage differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional capacitor structures are used in OLED manufacturing, then the manufacturing process is simple, but capacitance differences and kickback voltage variations cause uneven brightness across pixels
Solution Approach 1:
The capacitor electrode patterns are designed with asymmetric bent shapes instead of conventional symmetric rectangular structures. The bent portions extend in specific directions to increase the electrode area and adjust capacitance values, allowing precise control over capacitance differences between first and second capacitors to compensate for kickback voltage variations
Solution Approach 2:
Different regions of the capacitor electrodes have different geometries - straight portions for basic connectivity and bent portions for area adjustment. The bent portions are strategically placed to locally increase capacitance where needed, enabling fine-tuning of capacitance ratios between different capacitors in the pixel circuit
2Manufacturing precision
If transistor threshold voltage variations are not compensated, then the device structure remains simple, but image quality deteriorates due to brightness unevenness
Solution Approach 1:
The capacitor network is designed to provide feedback compensation for kickback voltage variations. By carefully controlling the capacitance ratios between first and second capacitors through geometric design, the circuit automatically compensates for threshold voltage variations without requiring additional active compensation circuits
Solution Approach 2:
The capacitance values are precisely controlled by changing the geometric parameters of the electrode patterns - specifically the area and shape of bent portions. This allows adjustment of capacitance ratios to optimize kickback voltage compensation while maintaining a relatively simple passive circuit structure
3Manufacturing precision
If capacitor area is increased to reduce capacitance differences, then capacitance uniformity improves, but the device area increases
Solution Approach 1:
The electrode patterns incorporate bent portions with curved geometries instead of straight lines, allowing more efficient use of space. The bent shapes increase the effective electrode area within a compact footprint, achieving the required capacitance values without proportionally increasing the overall pixel area
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 effectively reduces the unevenness of brightness and image quality deterioration caused by capacitance differences between capacitors, resulting in improved image quality by compensating for threshold voltage variations and aligning design and actual kickback voltages.
Implementation Method 1
An organic light emitting display is a flat panel display device that displays an image using an organic light emitting diode (OLED) to generate light by utilizing the recombination of electrons-holes
Implementation Method 2
a first capacitor for storing a voltage corresponding to the data signal and for applying the voltage corresponding to the data signal to the gate of the first transistor
Data Source
AI summary
A pixel including: an organic light emitting diode for emitting light in accordance with a received driving current; a first transistor including a gate for receiving a voltage corresponding to a data signal, the first transistor being for transferring the driving current in a direction from a source of the first transistor to a drain of the first transistor; a second transistor for transferring the data signal in accordance with a scan signal; a first capacitor for storing a voltage corresponding to the data signal and for applying the voltage corresponding to the data signal to the gate of the first transistor; and a second capacitor for controlling the voltage stored in the first capacitor, wherein an outside portion of the first capacitor has a plurality of bents.