III-N Substrate Buffer Structure for Power Devices
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Solution Overview
Problem
III-N material based power devices face challenges in achieving high electrical resistivity and leakage current blocking capability due to lattice mismatch and stress issues when grown on foreign substrates, leading to thick buffer layers that exacerbate substrate warpage and thermal mismatch.
Innovation Solution
A III-N based substrate with a buffer structure featuring a first superlattice laminate with a higher average aluminum content than a second superlattice laminate, which enhances breakdown voltage and controls substrate warpage by introducing additional compressive stress to compensate for tensile stress during cooling, while maintaining acceptable wafer bow limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the buffer thickness is increased to enhance leakage blocking capability, then the breakdown voltage is improved, but the substrate warpage is exacerbated
Solution Approach 1:
The buffer layer is segmented into multiple superlattice laminates (first and second superlattice laminates) with different aluminum contents, rather than using a single thick buffer layer. This segmentation allows each layer to contribute differently to stress management while collectively achieving high breakdown voltage.
Solution Approach 2:
Different regions of the buffer structure have different aluminum contents tailored to specific functions: the first superlattice laminate has higher aluminum content for superior leakage blocking, while the second has lower aluminum content for stress compensation and warpage control.
2Shape
If a single superlattice laminate is used to reduce buffer thickness, then substrate warpage is reduced, but the breakdown voltage is insufficient
Solution Approach 1:
The buffer structure uses a composite of two superlattice laminates with different aluminum compositions (AlGaN layers with varying Al content). This composite structure combines the high breakdown field strength of Al-rich regions with the stress-compensating properties of Al-poor regions, achieving both high voltage blocking and flat substrate morphology.
3Reliability
If the aluminum content is increased to improve breakdown field strength, then the leakage blocking capability is enhanced, but the tensile stress increases leading to greater warpage
Solution Approach 1:
The structure uses the second superlattice laminate with lower aluminum content as a counterweight to the first superlattice laminate with higher aluminum content. The lower-Al layers introduce compressive stress that balances the tensile stress from high-Al layers, achieving stress equilibrium while maintaining high breakdown voltage capability.
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 achieves a breakdown field strength of over 150 V/μm and keeps substrate warpage within acceptable limits, improving leakage blocking capability and reducing the thickness required for the buffer layer structure compared to single superlattice laminates.
Implementation Method 1
a first superlattice laminate with a higher average aluminum content than a second superlattice laminate, which enhances breakdown voltage and controls substrate warpage by introducing additional compressive stress to compensate for tensile stress during cooling
Implementation Method 2
the buffer layer structure is provided to compensate for lattice mismatch and to control wafer bow
Data Source
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AI summary
III-N based substrate for power electronic devices, comprising a base substrate, a III-N laminate above the base substrate and a buffer layer structure between the base substrate and the III-N laminate. The buffer layer structure comprises at least a first superlattice laminate and a second superlattice laminate above the first superlattice laminate. The first superlattice laminate comprises a repetition of a first superlattice unit which consists of a plurality of first AlGaN layers. The second superlattice laminate comprises a repetition of a second superlattice unit which consists of a plurality of second AlGaN layers. An average aluminum content of the first superlattice laminate is a predetermined difference greater than an average aluminum content of the second superlattice laminate, to improve the vertical breakdown voltage.