Self-Aligned VCSEL Microlens Structure for Beam Divergence Control
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Solution Overview
Problem
The alignment of microlenses with DBR stacks in VCSEL devices is often imprecise, leading to misalignment, reduced laser power, defocusing, and misdirection of emitted light due to bonding materials and misalignment issues.
Innovation Solution
A self-aligned microlens process forms a microlens stack with additional reflector layers over DBR stacks, utilizing oxidation to create lens layers with varying refractive indices that automatically align with the DBR stacks, eliminating misalignment errors and ensuring focused laser emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If microlenses are manufactured separately and bonded to DBR stacks, then the VCSEL device can be assembled, but misalignment and reduced laser power occur
Solution Approach 1:
The microlens stack and DBR stack are merged into a single integrated structure where the microlens stack is formed directly over the DBR stack in a unified manufacturing process. This eliminates the separate bonding step that causes misalignment, as the microlens layers are deposited and patterned in direct registration with the underlying DBR layers throughout the entire fabrication sequence.
2Strength
If bonding materials are used to attach microlenses, then the structure is held together, but interference with laser focusing occurs
Solution Approach 1:
The bonding material layer is completely removed from the structure. Instead of using external bonding agents to attach the microlens to the DBR stack, the microlens stack is grown epitaxially in direct contact with the DBR stack, creating a bond-free interface that eliminates optical interference while maintaining structural integrity through the integrated growth process.
3Device complexity
If conventional alignment processes are used, then manufacturing is simplified, but misalignment errors reduce laser power
Solution Approach 1:
The manufacturing process is made self-aligning through the sequential formation of structures. The microlens stack is formed directly over the DBR stack using the same wafer and alignment references, with each subsequent layer automatically registering to the underlying layers. This self-aligned approach eliminates the need for separate alignment operations and ensures optimal optical coupling without adding 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
The self-aligned microlens process ensures precise alignment and focused laser emission by integrating the microlens with the DBR stacks, enhancing the reliability and performance of VCSEL devices.
Implementation Method 1
The microlens stack comprises lens layers laterally surrounded by oxidized lens layers that laterally contact a sidewall spacer directly over the reflector stack... a difference in refractive indices between the lens layers and the oxidized lens layers causes the lens layers to collectively act as a lens
Data Source
AI summary
A method of making a microlens for a VCSEL device includes forming a first lens layer over a second reflector layer. The first lens layer has a first average concentration of a first element. A first additional reflector layer is formed over the first lens layer. A second lens layer is formed over the first additional reflector layer. The second lens layer has a second average concentration of the first element greater than the first average concentration. A second additional reflector layer is formed over the second lens layer.An oxidation process is performed to oxidize peripheral portions of the first and second lens layers to form oxidized peripheral portions of the first and second lens layer. The oxidized peripheral portions of the second lens layer are wider than the oxidized peripheral portions of the first lens layer.