VCSEL Array Layout With Mesa Tabs for Small-Pitch Density
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Solution Overview
Problem
Current technologies face challenges in achieving small pitch vertical-cavity surface-emitting lasers (VCSELs) and VCSEL arrays with low resistance and good yield, due to limitations in photolithography and microelectronic process techniques, making it difficult to minimize the dimension of metal contacts and deeply etched mesas.
Innovation Solution
The design incorporates a VCSEL element with an oxide aperture and a concentric mesa, featuring mesa tabs and a nitride via, where ohmic metal is applied on the tabs extending towards the oxide aperture, and a trench surrounds the mesa portion, allowing for reduced pitch without decreasing the oxide aperture size, and enabling overlapping mesa tabs in arrays for higher density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pitch of VCSELs in an array is reduced to increase density, then the number of VCSELs per unit area increases, but the minimum dimension for metal contacts and deeply etched mesas becomes difficult to achieve with current photolithography and microelectronic process techniques
Solution Approach 1:
The VCSEL structure is segmented into distinct functional regions: a round mesa portion for current confinement and a separate mesa tab for electrical contact. This segmentation allows the contact area to be optimized independently from the aperture size, enabling smaller pitch while maintaining manufacturability with current photolithography techniques.
Solution Approach 2:
The electrical contact is extended into a tab dimension that protrudes from the round mesa portion. This dimensional extension provides additional area for metal contacts and via formation without increasing the footprint of the active laser region, thereby reducing the pitch required between adjacent VCSELs while maintaining adequate contact dimensions for manufacturing.
2Reliability
If the oxide aperture size is maintained to ensure efficient current confinement, then the laser performance is preserved, but the overall device area cannot be reduced for small pitch arrays
Solution Approach 1:
The device is segmented into a compact round mesa portion containing the oxide aperture for current confinement, and a separate mesa tab for electrical contact. This allows the aperture size to be maintained for reliable current confinement while the overall device area is reduced by concentrating the active region and extending contact functionality to the tab structure.
Solution Approach 2:
The electrical contact functionality is moved to the mesa tab dimension, allowing the round mesa portion to remain compact with a small oxide aperture for efficient current confinement. The tab extends the contact area without increasing the aperture size, thereby maintaining reliability while reducing the area occupied by the active laser region.
3Quantity of substance
If traditional VCSEL structures are used with small pitch, then device density increases, but alignment tolerances become more stringent and yield decreases
Solution Approach 1:
The separation of the round mesa portion from the mesa tab creates distinct alignment targets for different fabrication steps. The tab provides a larger, more tolerant target for metal contact deposition and via formation, reducing the stringency of alignment tolerances compared to traditional compact structures, thereby improving yield at high device density.
Solution Approach 2:
By extending the electrical contact into the tab dimension, the structure provides a larger effective target area for subsequent fabrication steps such as metal deposition and via formation. This dimensional extension relaxes alignment tolerances and improves manufacturing yield while maintaining small pitch and high device density.
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 approach enables the fabrication of VCSEL arrays with smaller pitch and higher density, reducing alignment tolerances and eliminating the need for isolation layers, while maintaining efficient current confinement and electrical contact.
Implementation Method 1
an oxide aperture and a mesa concentrically surrounding the oxide aperture
Implementation Method 2
A nitride via is etched on the mesa tab and extending towards the oxide aperture
Data Source
AI summary
Vertical-cavity surface-emitting lasers (VCSELs) and VCSEL arrays having small size and small pitch are provided. Particularly, the present disclosure relates to novel and advantageous chip layouts for ensuring low resistance devices with good yield for small pitch arrays. More particularly, the present disclosure describes approaches for reducing the area consumed by a VCSEL structure so that a higher density VCSEL device may be achieved.