VCSEL Pad Layout for Higher Emitter Density
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Solution Overview
Problem
The density of emitters in vertical cavity surface emitting lasers (VCSELs) is limited by the structural arrangement, resulting in a relatively sparse distribution due to minimum spacing requirements between common pads, which restricts further reduction in spacing and increases the distance between emitters.
Innovation Solution
The implementation of a VCSEL design with multiple first sub-pads connected through first vias and at least one second sub-pad connected through second vias, allowing for independent placement of sub-pads without covering spacing regions, enabling closer emitter placement and increased density without short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple emitters share one common pad, then the device complexity is reduced, but the emitter density becomes sparse due to minimum spacing requirements between common pads
Solution Approach 1:
The common pad is segmented into multiple first sub-pads, with each sub-pad corresponding to a specific emitter. This segmentation allows each emitter to have its own dedicated pad region, eliminating the need for large spacing between shared common pads and enabling higher emitter density while maintaining simple pad structure.
2Quantity of substance
If the spacing between common pads is reduced to increase emitter density, then the emitter density increases, but photoresist inclination occurs during manufacturing
Solution Approach 1:
By segmenting the pad structure into first sub-pads and second sub-pads with distinct functions, the design allows closer spacing between emitter-associated pads while the second sub-pads provide stable reference regions that prevent photoresist inclination during manufacturing processes.
Solution Approach 2:
The second sub-pads act as intermediary elements that provide stable reference regions between the first sub-pads. These intermediary structures prevent photoresist inclination by providing stable reference points during manufacturing, enabling closer spacing between functional pad regions.
3Device complexity
If one common pad covers multiple emitters and spacing regions, then the pad structure is simplified, but the minimum spacing between emitters cannot be reduced further
Solution Approach 1:
The pad structure is segmented into first sub-pads that directly correspond to individual emitters and second sub-pads that serve as shared reference structures. This segmentation allows the spacing between emitters to be reduced since each emitter has its own dedicated first sub-pad region, eliminating the need for large spacing required by shared common pads.
Solution Approach 2:
The pad structure transitions from a two-dimensional planar arrangement to a multi-layered three-dimensional structure with first sub-pads and second sub-pads at different levels. This dimensional change allows overlapping projections in the planar view while maintaining physical separation, enabling reduced emitter spacing without compromising pad functionality.
Data Source
AI summary
Provided VCSEL includes emitters arranged in an array disposed on a surface of a substrate, a first passivation layer disposed on a surface of the emitters facing away from the substrate and provided with a first via, a second passivation layer provided with a second via, and a first pad. The first pad includes first sub-pads and at least one second sub-pad, a number of the first sub-pads is equal to a number of the emitters, the first sub-pads are disposed on a side of the first passivation layer facing away from the substrate and connected to the emitters through the first via, the second passivation layer covers the first sub-pads and the first passivation layer, and the at least one second sub-pad is connected to the first sub-pads through the second via.