Active-Matrix Display Bilayer Electrode Planarization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing active-matrix displays face issues with parasitic electrical contacts and leakage currents due to the thickness and application method of the insulation layer, which degrades the performance of electrooptic elements like organic electroluminescent diodes, and there is a compromise between planarization and light extraction.
Innovation Solution
Incorporating a bilayer lower electrode structure with an organic conducting layer and a metal layer, where the organic conducting layer provides planarization and the metal layer optimizes electrical properties, while keeping the insulation layer thin to avoid interfering with the optical cavity and light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the insulation layer is made thick to completely fill the features formed by circuit components, then the planarization function is improved, but the volume of material required increases and the application process becomes more complex
Solution Approach 1:
The lower electrode is segmented into two functional layers: an organic conducting layer that provides planarization by filling via features, and a metal layer that provides electrical conductivity. This segmentation allows each layer to be optimized for its specific function, with the organic layer being thin enough to avoid optical interference while still providing adequate planarization.
Solution Approach 2:
The lower electrode uses a composite structure combining organic conducting material and metal material. The organic conducting layer (e.g., PEDOT:PSS) provides planarization and fills via features, while the metal layer (e.g., aluminum, silver, or transparent conductive oxide) provides electrical conductivity. This composite approach resolves the contradiction by allowing the organic layer to be thin (avoiding optical cavity interference) while still achieving planarization.
2Reliability
If the lower electrode provides contact with the TFT transistor through vias in the insulation layer, then the electrical connection is improved, but parasitic electrical contacts and leakage currents are generated due to replicas formed on the electrode surface
Solution Approach 1:
The organic conducting layer is deposited first to fill the via features and create a planar surface before the metal layer is applied. This preliminary action prevents the formation of hollow replicas that would cause parasitic contacts, as the organic layer completely fills the via spaces and creates a uniform surface for subsequent metal deposition.
Solution Approach 2:
The organic conducting layer acts as an intermediary between the insulation layer and the metal layer. It fills the via features and provides a planarizing interface that prevents the metal layer from replicating the via hollows, thereby eliminating the source of parasitic electrical contacts while maintaining electrical connectivity.
3Manufacturing precision
If a thick insulation layer is used for planarization, then the planarity of the lower electrode surface is improved, but the optical cavity tuning and light extraction are compromised
Solution Approach 1:
The planarization function is segregated from the optical function by using an organic conducting layer specifically for planarization. This layer can be kept thin (e.g., 50-200 nm) to avoid optical cavity interference while still providing adequate planarization for the metal electrode layer, thus preserving light extraction efficiency.
Solution Approach 2:
The use of composite materials (organic conducting layer + metal layer) allows the organic layer to provide planarization with minimal thickness, avoiding the optical interference problems associated with thick insulating layers. The metal layer then provides the electrical function without interfering with light extraction.
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 enhances the planarity of lower electrodes, improves the performance of electrooptic elements, and maintains optimal light extraction without compromising the tuning of the optical cavity, offering better electrical and optical performance.
Implementation Method 1
this insulating material must be suitable for being applied so as to fill the features, for example by spin coating
Implementation Method 2
a metal layer (162) covering the organic conducting layer
Implementation Method 3
the electrooptic elements are organic electroluminescent diodes
Data Source
Figure 1~2
Figure 3
AI summary
In this display, an upper electrical insulation layer (14') covers the active matrix; each electrooptic element comprises a lower supply electrode (16") that is applied to this insulation layer (14'). According to the invention, this lower electrode includes an organic conducting layer (161') applied directly to said insulation layer (14') and a metal layer (162) covering the organic conducting layer. Such a structure makes it possible to optimize both planarization and light extraction by an optical cavity effect thereby improving the performance of the display.