Parallel Holding Capacitor for OLED Luminance Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In organic electroluminescence (EL) displays, the degradation of current-voltage characteristics over time leads to variations in light-emission luminance due to changes in threshold voltage and mobility of drive transistors, resulting in image quality issues and power consumption increases when trying to maintain constant luminance.
Innovation Solution
A display configuration with a holding capacitor formed by three electrodes connected in parallel, increasing capacitance without expanding the capacitor's size, ensuring a high bootstrap ratio to maintain consistent gate-source voltage and drive current, thus enhancing image quality without increasing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the capacitance of the holding capacitor is increased to maintain constant luminance, then the image quality is improved, but the pixel area increases
Solution Approach 1:
The holding capacitor is constructed by utilizing the vertical dimension (thickness direction) of the pixel structure. Multiple capacitor electrodes are stacked in the thickness direction to increase capacitance without expanding the planar area of the pixel, thereby resolving the contradiction between maintaining image quality and limiting pixel area.
Solution Approach 2:
The holding capacitor electrodes are nested within the pixel structure by stacking them in the thickness direction. This nested arrangement allows multiple capacitor layers to occupy the same footprint area, effectively increasing capacitance while maintaining the original pixel area constraints.
2Reliability
If the drive current is increased to compensate for degradation, then the luminance consistency is improved, but the power consumption increases
Solution Approach 1:
The holding capacitor provides feedback by maintaining a stable gate-source voltage that compensates for degradation effects. This feedback mechanism ensures consistent drive current and luminance output without requiring increased power consumption, as the capacitor stores and releases energy to maintain voltage stability.
Solution Approach 2:
The holding capacitor is charged in advance during the write period to store the gate-source voltage. This preliminary charging action prepares the capacitor to maintain consistent drive current throughout the display period, preventing luminance degradation without requiring increased power consumption during operation.
3Reliability
If the capacitance is increased by expanding the capacitor size, then the bootstrap ratio is improved, but the manufacturing complexity increases
Solution Approach 1:
Instead of increasing capacitance by expanding the planar area of capacitor electrodes, the invention stacks multiple electrodes in the thickness direction. This dimensional change allows the bootstrap ratio to be improved without increasing manufacturing complexity associated with larger electrode areas or more complex planar layouts.
Solution Approach 2:
The stacked capacitor electrodes serve multiple functions: they increase capacitance to improve the bootstrap ratio, maintain stable gate-source voltage, and compensate for degradation effects. This multi-functionality is achieved through a unified stacking structure that simplifies manufacturing compared to alternative approaches requiring separate components or larger areas.
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 configuration maintains consistent light-emission luminance across pixels, improving image quality and reducing power consumption by ensuring the necessary drive current is applied without increasing the drive current's magnitude, even under limited pixel size conditions.
Implementation Method 1
a holding capacitor connected between the gate and source of the drive transistor
Data Source
AI summary
Disclosed herein is a display including: a pixel array part configured to include pixels that are arranged in a matrix and each have an electro-optical element, a write transistor for writing a video signal, a drive transistor for driving the electro-optical element based on the video signal written by the write transistor, and a holding capacitor connected between gate and source of the drive transistor, wherein the holding capacitor includes a first electrode, a second electrode disposed to face one surface of the first electrode for forming a first capacitor, and a third electrode disposed to face the other surface of the first electrode for forming a second capacitor, and the first capacitor and the second capacitor are connected in parallel to each other electrically.