AlN Inter-layer Mitigates GaN Substrate Bowing
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Solution Overview
Problem
Gallium nitride (GaN) transistor devices face issues with cracking and bowing due to the high coefficient of thermal expansion (CTE) difference between the GaN layer and the underlying semiconductor substrate, which affects device performance and breakdown voltage.
Innovation Solution
A composite GaN layer with alternating layers of GaN and aluminum nitride (AlN) is used, where AlN inter-layers are introduced between GaN layers to increase the thickness of the GaN layer, reducing bowing and cracking, and improving breakdown voltage by adjusting the doping concentration and V/III ratio of the AlN inter-layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the GaN layer is increased to improve breakdown voltage, then the breakdown voltage is improved, but substrate bowing and cracking worsen due to high CTE difference
Solution Approach 1:
The patent divides the continuous GaN layer into multiple thinner GaN sub-layers separated by AlN interlayers. This segmentation reduces the thermal stress accumulation in each individual GaN layer while maintaining the total thickness needed for high breakdown voltage. The AlN interlayers act as stress relief barriers that prevent crack propagation between GaN layers.
Solution Approach 2:
The patent creates a composite structure consisting of alternating GaN and AlN layers. The AlN interlayers have different thermal expansion properties compared to GaN, which helps to mitigate the thermal stress caused by CTE mismatch with the silicon substrate. This composite approach allows the structure to accommodate thermal expansion differences while maintaining mechanical integrity and achieving high breakdown voltage.
2Reliability
If AlN inter-layers are introduced to reduce bowing and cracking, then substrate reliability is improved, but device complexity increases
Solution Approach 1:
The patent optimizes specific parameters of the AlN interlayers including thickness (5 nm to 50 nm), doping concentration (1×10^16 to 1×10^18 atoms/cm³), and V/III ratio (50 to 500) during metal-organic chemical vapor deposition. By carefully controlling these parameters, the structure achieves stress relief functionality while maintaining manufacturability and avoiding excessive complexity.
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 effectively mitigates substrate bowing and cracking while enhancing the breakdown voltage of GaN transistor devices to greater than 600 V, improving their reliability and performance.
Implementation Method 1
The GaN layer 104 has a relatively high coefficient of thermal expansion (CTE) in comparison to the underlying semiconductor substrate 102. The AlN inter-layer 206 has a lower CTE in comparison to the GaN layer 104.
Implementation Method 2
acts 408-412 may be iteratively performed to form the composite GaN layer 202. In some embodiments, the composite GaN layer 202 is deposited by metal-organic chemical vapor deposition (MOCVD)
Implementation Method 3
a first GaN layer 204a is deposited onto the graded layer 306 by way of a MOCVD process... an AlN inter-layer 206 is deposited onto the first GaN layer 204a
Data Source
AI summary
The present disclosure relates to a gallium-nitride (GaN) transistor device having a composite gallium nitride layer with alternating layers of GaN and aluminum nitride (AlN). In some embodiments, the GaN transistor device has a first GaN layer disposed above a semiconductor substrate. An AlN inter-layer is disposed on the first GaN layer. A second GaN layer is disposed on the AlN inter-layer. The AlN inter-layer allows for the thickness of the GaN layer to be increased over continuous GaN layers, mitigating bowing and cracking of the GaN substrate, while improving the breakdown voltage of the disclosed GaN device.