LED Electrode Structure Reducing Gold Usage via Alternating Metal Layers
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Solution Overview
Problem
The high cost of gold used in conventional LED electrode structures due to inadequate hardness and electromigration issues with aluminum, which are not reliably addressed by aluminum alloys, necessitates a cost-effective alternative.
Innovation Solution
An electrode structure for LEDs with a bond pad layer comprising alternately stacked first metal layers of aluminum or aluminum alloys and second metal layers of titanium, nickel, chromium, platinum, palladium, titanium nitride, titanium wolfram, wolfram, rhodium, or copper, significantly reducing the amount of gold required while enhancing hardness for improved wire bonding and electromigration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick gold layer is used in the bond pad layer, then wire bonding hardness and electromigration resistance are improved, but production cost increases significantly
Solution Approach 1:
The bond pad layer is segmented into multiple functional sub-layers: a hard mask layer (titanium nitride or tungsten) providing hardness and electromigration resistance, and a gold layer providing good conductivity and bonding properties. This segmentation allows each material to perform its optimal function without requiring excessive gold thickness.
Solution Approach 2:
The invention uses a composite structure combining different materials (titanium nitride/tungsten + gold) in the bond pad layer. The hard mask layer serves as a composite component that provides mechanical hardness and electromigration resistance, while the gold layer provides electrical conductivity, achieving performance optimization with reduced gold content.
2Quantity of substance
If aluminum is used instead of gold in the bond pad layer, then production cost decreases, but wire bonding hardness and electromigration resistance deteriorate
Solution Approach 1:
The hard mask layer acts as an intermediary between the aluminum reflective layer and the wire bonding interface. It provides the necessary hardness and electromigration resistance that aluminum lacks, while allowing the aluminum layer to continue providing cost-effective conductivity and reflectivity.
Solution Approach 2:
Different regions of the electrode structure are assigned different material qualities: the reflective layer uses aluminum for cost-effective conductivity, while the bond pad interface uses titanium nitride or tungsten for hardness and electromigration resistance. This local differentiation optimizes both cost and performance.
3Quantity of substance
If aluminum alloy is used to replace gold, then production cost is reduced, but wire bonding hardness and electromigration resistance are not reliably improved
Solution Approach 1:
The invention uses a thin layer of expensive material (titanium nitride or tungsten) to provide the critical hardness and electromigration resistance functions, while the bulk of the bond pad can use cheaper aluminum. This approach minimizes the use of expensive materials while maintaining reliability.
Solution Approach 2:
The invention changes the material parameter from aluminum or aluminum alloy to titanium nitride or tungsten for the hard mask layer. This parameter change fundamentally improves hardness and electromigration resistance properties that cannot be achieved by aluminum alloying alone.
Data Source
AI summary
An electrode structure of an LED includes an adhesion layer and a bond pad layer. The adhesion layer is stacked on the LED. The bond pad layer is stacked on the adhesion layer. The bond pad layer includes at least two first metal layers, at least two second metal layers and an outermost gold layer sequentially and alternately stacked. The first metal layers are selected from the group consisting Al and an Al alloy, and the second metal layers are selected from the group consisting of Ti, Ni, Cr, Pt, Pd, TiN, TiW, W, Rh and Cu. Thus, the main structure of the bond pad layer is a stacked structure of the first metal layers and the second metal layers. The first metal layers may be selected from a low-cost material, and the second metal layers improve issues of inadequate hardness and electromigration of the first metal layers.