Vertical GaN Device with Trenches for Current Distribution
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Solution Overview
Problem
Current gallium nitride semiconductor devices face challenges in achieving high-speed switching with large current capacity due to non-uniform current distribution and high resistance issues, particularly when grown on silicon substrates, which lead to crystalline defects and increased on-voltage.
Innovation Solution
A gallium nitride semiconductor device is developed with a silicon substrate and buffer layers, including an aluminum nitride layer and a gallium nitride layer, where trenches are formed to allow vertical current flow, and a metal sulfide layer is used between the buffer and silicon substrate to enhance crystal quality and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a GaN layer is grown directly on a silicon substrate, then manufacturing cost is reduced and wafer diameter can be enlarged, but crystalline defects and dislocation occur due to lattice constant difference
Solution Approach 1:
An aluminum nitride (AlN) buffer layer is introduced as an intermediary between the silicon substrate and the GaN layer. This buffer layer serves as a mediator that gradually transitions the lattice constant from silicon to GaN, reducing the abrupt lattice mismatch and minimizing dislocation formation while enabling the use of inexpensive silicon substrates for large-diameter wafers
2Manufacturing precision
If a buffer layer such as aluminum nitride is provided between silicon substrate and GaN layer, then crystal quality is improved and dislocation is reduced, but manufacturing complexity increases
Solution Approach 1:
The thickness of the AlN buffer layer is optimized to 5-50 nm to achieve the right balance between reducing dislocation and maintaining manufacturability. Additionally, the lattice constant transition is managed by controlling the buffer layer properties, enabling crystal quality improvement without excessive manufacturing complexity
3Strength
If a lateral device structure is used with sapphire substrate, then breakdown voltage resistance is improved, but current distribution becomes non-uniform and wiring resistance increases
Solution Approach 1:
The patent inverts the conventional lateral device structure by adopting a vertical device architecture where the current flows perpendicular to the substrate surface. This inversion allows current to be extracted from both top and bottom surfaces, enabling uniform current distribution while maintaining high breakdown voltage resistance through the vertical field effect transistor structure
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 device achieves efficient vertical current flow with reduced on-voltage and improved crystal quality, enabling high-speed operation with low resistance and large current capacity, surpassing existing silicon-based semiconductor devices.
Implementation Method 1
a buffer layer provided on one of the principal surfaces of the silicon semiconductor substrate for either one or both of crystal structure conversion and crystal quality improvement
Implementation Method 2
an epitaxial gallium nitride semiconductor layer layered on the buffer layer
Data Source
AI summary
A gallium nitride semiconductor device is disclosed that can be made by an easy manufacturing method. The device includes a silicon substrate, buffer layers formed on the top surface of the silicon substrate, and gallium nitride grown layers formed thereon. The silicon substrate has trenches 12 formed from the bottom surface, each trench having a depth reaching the gallium nitride grown layer through the silicon substrate and the buffer layers. The inside surface of each of the trenches and the bottom surface of the silicon substrate is covered with a drain electrode as a metal film. The vertical gallium nitride semiconductor device with this structure allows an electric current to flow in the direction of the thickness of the silicon substrate regardless of the resistance values of the gallium nitride grown layers and the buffer layers.