Silver Electrode Protection in Semiconductor Light Emitting Devices
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Solution Overview
Problem
Silver electrodes in semiconductor light emitting devices are prone to migration, oxidation, and sulfidation due to exposure to moisture and impurity ions, leading to decreased emission intensity, lifetime, and breakdown voltage, especially under energization and high-energy wavelengths.
Innovation Solution
A semiconductor light emitting device structure is developed with a silver-containing metal film covered by a second metal film made of a non-silver metal, such as Pt/Au, which is in electrical contact with the silver film and extends to cover the dielectric film, reducing exposure to ambient air and impurity ions, and alleviating electric field concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a silver electrode is used to reflect light efficiently, then light extraction efficiency and brightness are improved, but the electrode becomes susceptible to migration, oxidation, and sulfidation, reducing reliability and lifetime
Solution Approach 1:
The silver electrode is segmented into two functional parts: a lower silver layer for light reflection and an upper protective metal layer for environmental barrier. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
A protective metal layer (Al, Ti, Pt, or Pd) is introduced as an intermediary between the silver electrode and the external environment. This intermediary layer prevents direct contact between silver and harmful substances like moisture, oxygen, and sulfur, while maintaining electrical conductivity.
2Ease of manufacture
If the silver electrode is exposed to ambient air and moisture, then ease of manufacture is improved, but migration and oxidation occur, decreasing emission intensity and lifetime
Solution Approach 1:
The protective metal layer is formed preliminarily over the silver electrode during the fabrication process, creating a permanent barrier before the device is exposed to ambient conditions. This preliminary protection prevents migration and oxidation throughout the device's operational life.
Solution Approach 2:
The electrode structure uses composite materials combining silver with another metal (Al, Ti, Pt, or Pd). The composite structure leverages silver's high reflectivity and the protective metal's resistance to oxidation and migration, achieving both ease of manufacture and long lifetime.
3Reliability
If a protective metal layer is added to cover the silver electrode, then reliability and resistance to migration are improved, but device complexity increases
Solution Approach 1:
The protective metal layer is applied locally only where needed - specifically covering the silver electrode and extending to the dielectric film. This localized application provides maximum protection with minimum additional complexity.
Solution Approach 2:
The protective metal layer serves multiple functions simultaneously: it prevents oxidation, blocks migration, provides electrical contact, and extends coverage to the dielectric film for enhanced protection. This multi-functionality reduces the need for additional separate components.
4Reliability
If the protective metal film extends to cover the dielectric film, then insulation and breakdown voltage are improved, but manufacturing precision requirements increase
Solution Approach 1:
The protective metal layer is designed to extend beyond the silver electrode boundary onto the dielectric film, creating a cushioning effect that prevents edge effects and enhances insulation. This over-extension provides a safety margin that compensates for manufacturing variations.
Solution Approach 2:
The protective metal layer transitions from a two-dimensional electrode pattern to a three-dimensional structure by extending vertically onto the dielectric film surface. This dimensional change provides additional insulation path length without significantly increasing planar manufacturing complexity.
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 significantly reduces leakage current, improves insulation and breakdown voltage characteristics, enhances emission intensity, and increases the device's lifetime while maintaining high light extraction efficiency and reflection properties.
Implementation Method 1
Silver efficiently reflects the light emitted from the light emitting layer, and hence is suitable to realize a semiconductor light emitting device with high brightness
Implementation Method 2
there is a proposal for protecting a silver electrode by covering it with a metal other than silver or a protection film to prevent migration and reduce degradation
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
A semiconductor light emitting device includes a first semiconductor layer (1), a second semiconductor layer (2), a light emitting layer (3) provided between the first semiconductor layer and the second semiconductor layer, a first electrode (7) provided on the first semiconductor layer, a second electrode (4) including a first metal film (5) provided on the second semiconductor layer and containing at least one of silver and a silver alloy, and a second metal film (6) provided on the first metal film and made of a metal substantially not containing silver, and a dielectric film (8) spaced from the first metal film on the second semiconductor layer. The second metal film covers the first metal film, at least part of the dielectric film, and a surface of the second semiconductor layer exposed between the first metal film and the dielectric film.