Group III-N HEMT Multi-Layered Substrate Thermal Management
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Solution Overview
Problem
Group III-N high electron mobility transistors (HEMTs) face limitations due to the requirement for a floating substrate, which complicates packaging, leads to thermal conductivity issues, crosstalk, and unregulated voltages, and restricts the breakdown voltage, necessitating alternative approaches for forming these devices.
Innovation Solution
A multi-layered substrate structure is formed with a p-type lower layer and an n-type upper layer, allowing the upper portion to electrically float while the lower portion is grounded, enabling the use of conductive epoxy for better thermal conductivity and reducing crosstalk and EMI radiation, while achieving the full breakdown voltage of 600V.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a floating substrate is used to increase buffer breakdown voltage, then the breakdown voltage is doubled to 600V, but thermal conductivity deteriorates due to the need for non-conductive epoxy in packaging
Solution Approach 1:
The substrate is segmented into two distinct layers: a first substrate layer (e.g., SiC) that is electrically floated to provide high breakdown voltage, and a second substrate layer (e.g., Si) that is grounded and provides excellent thermal conductivity for heat dissipation. This segmentation allows each layer to fulfill its specific function independently, resolving the contradiction between electrical isolation requirements and thermal management needs.
Solution Approach 2:
The first substrate layer acts as an intermediary between the floating buffer structure required for high breakdown voltage and the grounded, thermally conductive second substrate layer. This intermediate layer enables the use of conductive epoxy in packaging while maintaining the electrical floating condition necessary for achieving 600V breakdown voltage.
2Strength
If a floating substrate is used to achieve higher breakdown voltage, then the voltage is doubled to 600V, but packaging complexity increases due to the requirement for non-conductive epoxy
Solution Approach 1:
By segmenting the substrate into floating and grounded layers, the patent eliminates the need for complex non-conductive epoxy packaging solutions. The grounded second substrate layer provides a straightforward thermal path to the heat sink, simplifying the packaging structure while the floating first substrate layer maintains the high breakdown voltage capability.
3Strength
If a floating substrate is used to increase breakdown voltage, then the full 600V is achieved, but crosstalk and EMI radiation increase
Solution Approach 1:
The patent segments the substrate electrical configuration into floating and grounded regions. The grounded second substrate layer serves as a reference plane that shields against EMI radiation and reduces crosstalk between devices, while the floating first substrate layer maintains the high breakdown voltage. This segmentation allows simultaneous achievement of high voltage capability and electromagnetic compatibility.
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 solution allows for improved thermal conductivity, reduced crosstalk and EMI radiation, and maintains the full breakdown voltage of 600V, addressing the challenges posed by the floating substrate requirement in conventional Group III-N HEMTs.
Implementation Method 1
a p-n junction is formed between a p-type lower layer and an n-type upper layer
Data Source
AI summary
The Si substrate of a group III-N HEMT is formed in layers that define a p-n junction which electrically isolates an upper region of the Si substrate from a lower region of the Si substrate. As a result, the upper region of the Si substrate can electrically float, thereby obtaining a full buffer breakdown voltage, while the lower region of the Si substrate can be attached to a package by way of a conductive epoxy, thereby significantly improving the thermal conductivity of the group III-N HEMT and minimizing undesirable floating-voltage regions.