OLED Cathode and Pad Electrode Structure for Voltage Drop
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Solution Overview
Problem
Top emission type OLED display devices face issues with voltage drop due to high resistance of the cathode, leading to non-uniform luminance and image quality, and pad electrodes are prone to corrosion from moisture and etchants, affecting device reliability.
Innovation Solution
A three-layered pad electrode structure is implemented, with a low resistive material for the second layer and an etch stopper function for the third layer, and a semi-transparent cathode with a low work function to reduce resistance and prevent corrosion, along with a barrier layer to protect the pad electrodes from etchants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the cathode is made thin to be semi-transparent for top emission, then light transmission is improved, but resistance increases causing voltage drop
Solution Approach 1:
The cathode is divided into multiple thin layers (e.g., LiF, Alq3, Al) to achieve semi-transparency while maintaining electrical conductivity. Each layer contributes differently to light transmission and electron transport, resolving the contradiction between transparency and conductivity.
Solution Approach 2:
The cathode uses composite material structure combining different materials (alkali metal, organic compound, aluminum) to achieve both semi-transparency and low resistance. The composite structure allows optimization of both optical and electrical properties simultaneously.
2Ease of operation
If pad electrodes are made exposed for connection, then electrical connection is improved, but corrosion from moisture and etchants increases
Solution Approach 1:
The pad electrode structure has different properties in different regions: the upper layer is resistant to etchants for protection, while the lower layer provides good electrical connection. This local differentiation resolves the contradiction between connection quality and corrosion resistance.
Solution Approach 2:
An intermediate protective layer is introduced between the pad electrode and the external environment (moisture, etchants). This intermediary layer protects the electrical connection points from corrosion while maintaining electrical functionality.
3Manufacturing precision
If etchant is used to pattern the anode, then manufacturing precision is improved, but corrosion of pad electrodes worsens
Solution Approach 1:
The etchant that could harm the pad electrode is converted into a beneficial tool by using a protective layer that is selectively resistant to the etchant. The harmful etchant process is retained for precise anode patterning while the harm to pad electrodes is eliminated through the protective barrier.
Solution Approach 2:
A protective layer is introduced as an intermediary between the etchant and the pad electrode. This intermediary allows the etching process to proceed with high precision while protecting the pad electrode from corrosion.
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 minimizes voltage drop and corrosion, enhancing the uniformity of luminance and image quality, and improving the reliability and manufacturing simplicity of OLED display devices.
Implementation Method 1
When the excitons transit from an excited state into a base state, namely, a stable state, light with a predetermined wavelength is emitted.
Data Source
AI summary
An organic light-emitting diode (OLED) display device and a method of fabricating the same can reduce resistance of a cathode by forming an auxiliary electrode. Also, such OLED display device and method can prevent damage on a pad electrode due to an etchant during patterning of an anode by applying a protective structure to the pad electrode of a pad area and by including the pad electrode exposed from a plurality of pad electrode layers.