VCSEL Array Layout With Isolated Cathodes and Common Anode
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Solution Overview
Problem
Current VCSEL arrays with common anodes or cathodes face limitations in circuit design and transistor type restrictions, especially when multiple sections are involved, leading to increased fabrication complexity and costs, and p-type substrates have higher defect density and optical loss compared to n-type substrates.
Innovation Solution
A VCSEL array design featuring a common n-type substrate as the anode and isolated cathodes for each sub-array, with a tunnel junction within the bottom mirror structure to facilitate independent electrical connections and reduce voltage drop, allowing for superior performance and manufacturability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a common anode or cathode is used in VCSEL arrays, then fabrication is simplified, but circuit design flexibility is restricted and transistor type choices are limited
Solution Approach 1:
The patent segments the cathode into multiple isolated cathodes (first cathode, second cathode, etc.) while maintaining a common anode. This allows different sections of the VCSEL array to be independently controlled by different transistor types (e.g., first section with n-type transistors, second section with p-type transistors), thereby improving circuit design flexibility without complicating the overall fabrication process.
2Adaptability or versatility
If p-type substrates are used in VCSEL arrays, then certain circuit configurations are enabled, but defect density and optical loss increase
Solution Approach 1:
Instead of using a p-type substrate with isolated anodes (the conventional approach), the patent inverts the approach by using an n-type substrate with isolated cathodes. This inversion maintains circuit configuration flexibility while avoiding the high defect density and optical loss associated with p-type substrates, as n-type substrates have superior material quality.
3Adaptability or versatility
If multiple sections with isolated anodes and cathodes are created, then circuit design flexibility is improved, but fabrication complexity and costs increase
Solution Approach 1:
The patent merges the anodes of multiple VCSEL sections into a single common anode structure, while only isolating the cathodes. This reduces fabrication complexity compared to fully isolated anode-cathode configurations, as it requires fewer isolation trenches and contact holes, while still achieving the desired circuit design flexibility through cathode isolation.
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 design enables flexible circuit configurations, reduces fabrication complexity, and improves reliability and performance by utilizing n-type substrates, which have lower defect density and optical loss, making it suitable for high-density emitter arrays.
Implementation Method 1
a tunnel junction to reverse a carrier type within the bottom mirror structure
Implementation Method 2
an oxidation layer to provide optical and electrical confinement of VCSELs of the VCSEL array
Data Source
AI summary
A vertical-cavity surface-emitting laser (VCSEL) array may include an n-type substrate layer and an n-type metal on a bottom surface of the n-type substrate layer. The n-type metal may form a common anode for a group of VCSEL. The VCSEL array may include a bottom mirror structure on a top surface of the n-type substrate layer. The bottom mirror structure may include one or more bottom mirror sections and a tunnel junction to reverse a carrier type within the bottom mirror structure. The VCSEL array may include an active region on the bottom mirror structure and an oxidation layer to provide optical and electrical confinement. The VCSEL array may include an n-type top mirror on the active region, a top contact layer over the n-type top mirror, and a top metal on the top contact layer. The top metal may form an isolated cathode for the VCSEL array.