Back-Side-Emitting VCSEL Wafer Bonded to Heat-Dissipation Substrate
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Solution Overview
Problem
Wafer-to-wafer bonding in VCSELs often fails due to interfacial stress and trapped particles, and high-power VCSELs face challenges with heat dissipation and light emission due to the native substrate's low thermal conductivity and absorption of shorter wavelengths.
Innovation Solution
A back-side-emitting VCSEL wafer is bonded to a highly thermally conductive non-native substrate with closely matched coefficients of thermal expansion, and trenches are etched to reduce wafer-to-wafer contact area and provide strain relief, allowing for improved heat dissipation and light emission through the back side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If wafer-to-wafer bonding is used to attach VCSEL wafer to heat-dissipation wafer, then heat dissipation is improved, but bonding failure occurs due to interfacial stress and trapped particles
Solution Approach 1:
The patent introduces trenches that segment the bonding interface into bonded regions and unbonded trench regions. This segmentation reduces the continuous contact area between wafers, thereby reducing interfacial stress and the likelihood of bonding failure while maintaining heat dissipation paths through the bonded regions
Solution Approach 2:
The trenches act as intermediary features that mediate between the conflicting requirements of bonding integrity and stress reduction. By creating controlled unbonded regions, the trenches serve as stress relief zones while allowing the bonded regions to maintain thermal contact
2Illumination intensity
If native substrate is used in VCSEL, then light emission is achieved, but thermal conductivity is low causing heat accumulation
Solution Approach 1:
The patent merges the light emission function of the VCSEL wafer with the heat dissipation function of the separately bonded heat-dissipation wafer. The VCSEL wafer maintains its native substrate for optimal light emission, while the heat-dissipation wafer provides superior thermal conduction through direct thermal contact at the bonding interface
3Power
If VCSELs are configured for high power in small area, then power density is improved, but heat concentration increases causing performance degradation
Solution Approach 1:
The patent extends the heat dissipation path from the traditional in-plane conduction through the substrate to a three-dimensional path that includes vertical conduction through the bonding interface into the heat-dissipation wafer. This dimensional extension provides additional thermal conduction pathways that efficiently remove heat from high-power VCSEL configurations
4Illumination intensity
If back-side emission is implemented, then light emission at shorter wavelengths is enabled, but additional processing complexity is introduced
Solution Approach 1:
The patent performs preliminary actions during wafer fabrication including forming trenches and applying bonding interfaces before final assembly. This preliminary preparation of the wafer structure enables back-side emission functionality while managing processing complexity through staged manufacturing steps
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 configuration reduces the likelihood of bonding failure, enhances heat dissipation by spreading heat through a more conductive path, and enables light emission from the back side even at shorter wavelengths, improving overall VCSEL performance.
Implementation Method 1
Heat generated in the active region of the VCSEL spreads into a larger area in the thermally-conductive substrate at a much shorter distance than a path through the native substrate of lower thermal conductivity
Implementation Method 2
interfacial stress at the bonding interface can lead to bonding failure between the VCSEL wafer and the heat-dissipating wafer
Data Source
AI summary
A wafer-to-wafer bonded arrangement is provided comprising a VCSEL wafer and a highly thermally-conductive (HTC) wafer that are bonded together with the front side of the VCSEL wafer bonded to the HTC wafer. The VCSEL wafer is fabricated to include, at least initially, a native substrate. The HTC wafer includes a thermally-conductive, non-native substrate. All or a portion of the native substrate may be removed after performing wafer-to-wafer bonding. In effect, the HTC wafer becomes the substrate of the bonded pair. During operation of VCSEL dies diced from the bonded wafer, heat generated by the dies flows into the non-native substrate where the heat spreads out and is dissipated. Laser light generated by the VCSEL die is emitted through the back side of the VCSEL die.