Bus Electrode Taper Control in Organic EL Displays
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Solution Overview
Problem
The existing organic electro-luminescence display devices face issues with the inverse taper of the bus electrode, leading to deteriorated step coverage and insulation breakdown due to a large inclination angle of the bus electrode, which results in pinholes and potential shorting of the anode and cathode electrodes.
Innovation Solution
The bus electrode is formed with an inclination angle of 30° to 70° using a modified etchant composition of phosphoric acid, nitric acid, acetic acid, and water, which slows down the etching process and allows for a more controlled taper, preventing insulation breakdown and improving step coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the bus electrode is formed with a large inclination angle (80° to 110°) using conventional etchant, then the etching process is faster and more efficient, but the inverse taper of the bus electrode is deteriorated causing pinholes and insulation breakdown
Solution Approach 1:
The patent changes the chemical composition parameters of the etchant by replacing conventional phosphoric acid with a mixed acid solution containing nitric acid (5-10%), acetic acid (5-10%), and hydrofluoric acid (0.1-1%). This parameter change in etchant chemistry fundamentally alters the etching mechanism to produce a controlled taper angle of 30°-70° instead of the conventional 80°-110°, resolving the contradiction between etching efficiency and taper control.
Solution Approach 2:
The patent uses a composite etchant solution combining multiple acids (nitric acid, acetic acid, and hydrofluoric acid) in specific proportions. This composite chemical system works synergistically to achieve both reasonable etching speed and precise taper control, unlike single-acid etchants that cannot simultaneously satisfy both requirements.
2Ease of manufacture
If the bus electrode has a large inclination angle, then the etching process is simpler and faster, but the step coverage of the insulating film is deteriorated leading to pinholes
Solution Approach 1:
By changing the etchant composition from conventional phosphoric acid-based solutions to a mixed acid solution with controlled concentrations of nitric acid (5-10%), acetic acid (5-10%), and hydrofluoric acid (0.1-1%), the patent achieves a moderate inclination angle (30°-70°) that allows insulating films to properly cover the bus electrode surface without forming pinholes, thereby improving reliability while maintaining manufacturing feasibility.
3Reliability
If the bus electrode inclination angle is reduced to 30° to 70°, then the step coverage and insulation reliability are improved, but the etching process becomes more complex and slower
Solution Approach 1:
The patent employs a composite etchant formulation where nitric acid provides controlled oxidation, acetic acid moderates the etching rate, and hydrofluoric acid selectively attacks metal oxides. This composite system achieves the desired 30°-70° inclination angle with acceptable etching efficiency, resolving the contradiction between reliability improvement and productivity maintenance.
Solution Approach 2:
The patent optimizes the concentration parameters of each acid component in the etchant solution to achieve a balance between etching speed and taper control. By carefully adjusting nitric acid (5-10%), acetic acid (5-10%), and hydrofluoric acid (0.1-1%) concentrations, the process achieves moderate inclination angles that prevent insulation breakdown while maintaining reasonable production efficiency.
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 reduced inclination angle of the bus electrode enhances the step coverage of the insulating film, preventing insulation breakdown and improving the reliability of the electro-luminescence display device by reducing the occurrence of pinholes and electrode shorts.
Implementation Method 1
the bus electrode is formed by etching a chrome Cr, a molybdenum Mo, and a copper Cu, etc. using an etchant consisted of phosphoric acid in a rage of 60 to 65 weight %, nitric acid in a range of 5 to 6 weight %, acetic acid of 10 weight %, and water in a range of 19 to 25 weight %
Data Source
AI summary
This invention relates to an organic electro-luminescence device and a method of fabricating the same that is capable of reducing an inverse taper of a bus electrode.An organic electro-luminescence display device comprises: an anode electrode including a transparent electrode and a bus electrode; a cathode electrode crossing the anode electrode; and an organic layer located at a cross both the anode electrode and the cathode electrode, wherein the bus electrode has an inclination angle of 30° to 70°.