Organic EL Device Stacked Capacitor for High Aperture Ratio
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Solution Overview
Problem
Existing organic EL devices face challenges in ensuring sufficient capacitance and display quality due to the requirement of forming pixel selection and driving transistors on the same plane, which limits pixel size and overall device miniaturization.
Innovation Solution
The organic EL device incorporates an optical resonator between a reflecting layer and a second electrode, with the holding capacitance constituted by the reflecting layer, insulating layer, and first electrode, allowing for a large aperture ratio and enabling smaller pixel sizes while maintaining high display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If pixel selection transistor, driving transistor and capacitive element are formed on the same plane, then the device structure is simplified, but the pixel size cannot be reduced and aperture ratio is limited
Solution Approach 1:
The patent transitions from planar arrangement to three-dimensional stacked structure. The capacitive element is positioned beneath the pixel selection transistor, utilizing the vertical dimension (Z-axis) rather than consuming horizontal space. This dimensional change allows both components to coexist without increasing pixel area, directly resolving the contradiction between structural simplicity and pixel size reduction.
Solution Approach 2:
The patent implements nesting by placing the capacitive element (including its electrode and insulating layer) within or beneath the structure of the pixel selection transistor. The capacitive element's electrode is positioned in the same layer as the transistor's source/drain regions, effectively nesting one component within another's spatial footprint, thereby reducing overall pixel area while maintaining both functions.
2Ease of manufacture
If pixel selection transistor, driving transistor and capacitive element are formed on the same plane, then manufacturing process is simplified, but aperture ratio is limited and display quality deteriorates
Solution Approach 1:
By moving the capacitive element to a lower layer (beneath the transistor), the patent frees up horizontal space that can be converted into aperture area. The vertical stacking allows the light-emitting region to expand horizontally without conflicting with the capacitive element, thereby improving aperture ratio while maintaining manufacturability through sequential layer formation.
Solution Approach 2:
The patent segments the device into distinct vertical layers: the upper layer contains the pixel selection transistor and light-emitting components, while the lower layer contains the capacitive element. This segmentation separates conflicting functional requirements spatially, allowing each layer to be optimized independently - the upper layer for light emission and aperture, the lower layer for capacitance storage.
3Area of moving object
If holding capacitance is constituted by reflecting layer, insulating layer and first electrode, then pixel size is reduced, but capacitance value must be ensured
Solution Approach 1:
The patent adjusts key parameters of the capacitive element to maintain sufficient capacitance value despite reduced area. This includes optimizing the dielectric constant of the insulating layer material, adjusting the thickness of the insulating layer, and configuring the electrode geometry (such as using mesh or interdigitated structures) to maximize capacitance density within the constrained space beneath the transistor.
Solution Approach 2:
The patent employs composite material structures for the capacitive element, combining materials with high dielectric constants in the insulating layer with conductive materials in the electrode. This composite approach maximizes capacitance per unit area, enabling sufficient storage capacity within the limited space available in the stacked configuration.
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 allows for the creation of smaller, high-quality organic EL devices with improved display capabilities, including top and bottom emission types, and enables natural color displays such as red, green, and blue, leading to high-definition displays in reduced-sized electronic apparatuses.
Implementation Method 1
an optical resonator which is formed between the reflecting layer and the second electrode and resonates light from the organic functional layer
Implementation Method 2
an organic EL device using an electro luminescence (hereinafter, referred to as 'EL') element
Data Source
AI summary
An organic EL device includes a reflecting layer which has at least light reflectivity, a first electrode which is arranged on the reflecting layer through a first insulating layer, an organic functional layer which is arranged on the first electrode and includes at least a light emitting layer, a second electrode which is arranged on the organic functional layer and has at least light reflectivity, and a holding capacitance. In the organic EL device, an optical resonator which resonates light from the organic functional layer is formed by the reflecting layer and the second electrode, and the holding capacitance is formed using the reflecting layer, the first insulating layer, and the first electrode.