ITO/Ag/ITO Pixel Electrode Etching for Galvanic Corrosion Control
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Solution Overview
Problem
Galvanic corrosion between metal layers in organic light emitting display devices leads to particle defects and corrosion issues during the manufacturing process, particularly due to the reaction between silver and aluminum, resulting in short circuits and other defects.
Innovation Solution
A display device with a pixel electrode structure of ITO/Ag/ITO, where the upper ITO layer is first patterned, followed by a two-step etching process to pattern the Ag layer and lower ITO layer, reducing silver particle generation and preventing corrosion with aluminum in the pad electrode by forming an undercut that collects silver ions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single-step etching process is used to pattern the pixel electrode, then the manufacturing process is simpler and faster, but silver particles are generated causing defects and short circuits
Solution Approach 1:
The etching process is divided into two sequential steps: first etching the ITO layer, then etching the Ag layer. This segmentation prevents silver particles from being generated during the etching of the Ag layer, as the ITO layer is already removed and cannot react with etched Ag to form particles.
Solution Approach 2:
The ITO layer is etched and removed before etching the Ag layer. This preliminary action eliminates the source of galvanic corrosion (the ITO/Ag interface) before the Ag layer is patterned, preventing particle formation during the subsequent Ag etching step.
2Device complexity
If the ITO layer completely covers the Ag layer, then the pixel electrode structure is simpler, but galvanic corrosion occurs between ITO and Ag causing particle defects
Solution Approach 1:
The ITO layer is selectively removed in a preliminary etching step before the Ag layer is etched. This creates a structure where the Ag layer is exposed and can be patterned without the ITO layer present to cause galvanic corrosion during etching.
Solution Approach 2:
The ITO layer is extracted (removed) from the stacked structure before the Ag layer patterning step. This extraction eliminates the galvanic couple between ITO and Ag that would otherwise cause corrosion and particle formation during the Ag etching process.
3Ease of manufacture
If aluminum is used in the pad electrode for low cost and good conductivity, then the device is more economical, but the aluminum reacts with silver causing corrosion of the pad electrode side surface
Solution Approach 1:
The undercut structure extracts or removes the vulnerable aluminum side surface from contact with silver ions. By creating a recessed undercut geometry, the aluminum is physically separated from the silver-containing layers, preventing galvanic corrosion while maintaining the cost-effective aluminum material choice.
Solution Approach 2:
The undercut structure acts as an intermediary physical barrier between the aluminum pad electrode and silver ions. This geometric feature mediates the interaction by providing physical separation, preventing direct contact and thus preventing corrosion while allowing the pad electrode to maintain its simple aluminum construction.
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 two-step etching process significantly reduces silver particle-related defects and prevents corrosion of the pad electrode's side surface, enhancing manufacturing reliability and reducing the occurrence of short circuits.
Implementation Method 1
a metal line and the metal layer may react with the etchant to cause galvanic corrosion. Galvanic corrosion is a phenomenon in which electrons move and the metal ions are reduced by an oxidation-reduction reaction when two metals having different corrosion potentials are connected to an electrolyte.
Data Source
AI summary
A display device includes an insulating layer disposed on a substrate, a pixel electrode including a first conductive layer, a second conductive layer, and a third conductive layer sequentially stacked on the insulating layer, a pixel defining layer covering the pixel electrode and partially exposing the pixel electrode through an opening, an organic light emitting layer disposed in the opening of the pixel defining layer, and an opposing electrode disposed on the organic light emitting layer and overlapping the pixel electrode. A length of the first conductive layer is less than a length of the second conductive layer.