Nitride Semiconductor Buffer Layer Design for Crack Mitigation
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Solution Overview
Problem
Group III nitride semiconductor HEMTs face limitations due to lattice constant differences between AlGaN and GaN layers, leading to lattice relaxation, stress-induced cracks, and substrate warping, constraining device design and performance.
Innovation Solution
A nitride semiconductor element with a Si substrate, a buffer layer comprising an AlN layer and multiple AlGaN layers with decreasing Al component proximity to the GaN electron transfer layer, reducing lattice constant differences and mitigating stress through gradual lattice constant adjustment and strain transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a GaN layer with large thickness is laminated to improve voltage tolerance, then voltage withstanding performance is improved, but lattice relaxation occurs and tensile stress generates fine cracks (alligator cracks) on the GaN layer
Solution Approach 1:
The buffer layer is segmented into multiple AlGaN sub-layers with different Al components (first AlGaN layer with higher Al component, second AlGaN layer with lower Al component), allowing gradual lattice constant adjustment and stress distribution across layers, enabling thick GaN electron transfer layers without crack formation
Solution Approach 2:
Different regions of the buffer layer have different Al components tailored to local stress requirements: the first AlGaN layer closer to AlN has higher Al component to match lattice constants, while the second AlGaN layer closer to GaN has lower Al component to reduce lattice mismatch, optimizing stress distribution locally
2Stability of the object's composition
If the Al component of AlGaN layer is increased to reduce lattice mismatch with AlN, then lattice relaxation is reduced, but the difference in lattice constant between AlGaN and GaN layers increases, causing tensile stress and cracks
Solution Approach 1:
The buffer layer is divided into multiple AlGaN layers with progressively decreasing Al components, creating a gradient structure that gradually transitions from AlN lattice constant to GaN lattice constant, reducing both lattice relaxation and tensile stress simultaneously
Solution Approach 2:
The Al component parameter is varied across different AlGaN layers (first layer: higher Al component, second layer: lower Al component), allowing continuous adjustment of lattice constants to match both AlN and GaN layers, eliminating both lattice relaxation and excessive tensile stress
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 allows for a wide range of GaN electron transfer layer thicknesses, enhancing device design freedom, voltage tolerance, and reliability by alleviating cracks and substrate warping.
Implementation Method 1
the lattice constant of the AlGaN layer can gradually increase from an initial value close to the lattice constant of AlN to a value close to the lattice constant of the Group III-nitride electron transfer layer
Implementation Method 2
the compression stress applied on the GaN layer disappears, and a tensile stress is generated... the compression stress applied on the GaN layer disappears
Data Source
AI summary
A nitride semiconductor element capable of accommodating GaN electron transfer layers of a wide range of thickness, so as to allow greater freedom of device design, and a nitride semiconductor element package with excellent voltage tolerance performance and reliability. On a substrate, a buffer layer including an AlN layer, a first AlGaN layer and a second AlGaN layer is formed. On the buffer layer, an element action layer including a GaN electron transfer layer and an AlGaN electron supply layer is formed. Thus, an HEMT element is constituted.