VCSEL Substrate Design for Low Thermal Resistance and Parasitic Inductance
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Solution Overview
Problem
Existing substrates for VCSEL chips face challenges with high thermal resistance and parasitic inductance due to dielectric materials used, which hinder heat dissipation and high-speed signal quality, especially in time-of-flight camera applications where both heat and electrical current flow vertically.
Innovation Solution
A substrate design featuring a metal core separated by thin dielectric layers with thicknesses under 60 μm, made from materials like AlON, AlN, or AlPO4, which provide low thermal resistance and parasitic inductance, allowing for efficient heat dissipation and high-speed signal transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional dielectric materials are used in substrate design, then electrical insulation is provided, but thermal resistance increases and heat dissipation is hindered
Solution Approach 1:
The patent employs composite material structures combining metal layers with dielectric materials in a multi-layer substrate design. The metal layers provide thermal conduction pathways while dielectric materials provide electrical insulation, creating a composite structure that simultaneously addresses both thermal management and electrical isolation requirements in VCSEL assemblies
Solution Approach 2:
The substrate introduces intermediary metal layers and thermal vias between the VCSEL chip and the external environment. These intermediary structures serve as thermal conduits that bridge the thermal gap created by conventional dielectric materials, enabling efficient heat transfer from the VCSEL chip without compromising electrical insulation
2Reliability
If conventional dielectric layers are used between metal layers, then electrical isolation is achieved, but parasitic inductance increases and signal quality deteriorates
Solution Approach 1:
The patent changes the physical parameters of the dielectric layers, specifically reducing their thickness to minimize the vertical distance that current must travel through high-inductance paths. This parameter optimization reduces parasitic inductance while maintaining adequate electrical isolation, thereby improving high-speed signal integrity in VCSEL driver circuits
Solution Approach 2:
The substrate design transitions from planar signal routing to three-dimensional vertical routing through multiple metal layers separated by thin dielectric coatings. This dimensional approach allows current loops to be minimized by routing signals directly above or below ground planes in adjacent layers, reducing parasitic inductance while maintaining electrical isolation
3Temperature
If thick dielectric layers are used for heat dissipation, then thermal management is improved, but parasitic inductance increases and high-speed signal performance decreases
Solution Approach 1:
The substrate implements local quality differentiation by creating regions with different dielectric thicknesses and material properties. Areas directly beneath VCSEL chips feature thin dielectric layers for low inductance signal routing, while peripheral regions utilize thicker dielectric layers for enhanced heat dissipation. This spatially varying design optimizes both thermal management and signal performance in their respective locations
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 substrate design achieves low thermal resistance and parasitic inductance, enhancing heat dissipation and high-speed signal quality in VCSEL-based time-of-flight camera applications by using thin dielectric layers with low thermal resistance, thereby improving optical output and signal modulation performance.
Implementation Method 1
a dielectric layer separating the top metal layer and the bottom metal layer, wherein the dielectric layer has a thickness under sixty (60) micrometers (μm) and a thermal resistance under fifteen (15) degrees Celsius per watt (C/W), wherein a current loop flowing vertically across the dielectric layer has a low self-inductance based on the thickness of the dielectric layer, and wherein the bottom metal layer is arranged to dissipate heat generated by the current loop flowing vertically across the dielectric layer
Implementation Method 2
a dielectric layer separating the top metal layer and the bottom metal layer, wherein the dielectric layer has a thickness under sixty (60) micrometers (μm) and a thermal resistance under fifteen (15) degrees Celsius per watt (C/W), wherein a current loop flowing vertically across the dielectric layer has a low self-inductance based on the thickness of the dielectric layer
Data Source
AI summary
A circuit (e.g., for use in a time-of-flight camera projector module) may include a top metal layer having an anode and a cathode, one or more capacitors connected to the anode, a vertical-cavity surface-emitting laser connected to the anode and the cathode, and a driver connected to the cathode. The circuit may further include a bottom metal layer connected to ground and arranged below the top metal layer, and a dielectric layer separating the top metal layer and the bottom metal layer. In some implementations, the dielectric layer has a thickness under sixty micrometers and a thermal resistance under fifteen degrees Celsius per watt. Accordingly, a current loop flowing vertically across the dielectric layer has a low self-inductance based on the thickness of the dielectric layer and the bottom metal layer is arranged to dissipate heat generated by the current loop flowing vertically across the dielectric layer.