GaN Transistor Buffer Stack for Current Collapse and Leakage Control
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Solution Overview
Problem
Gallium nitride (GaN) transistors face challenges with current collapse performance due to non-uniform intrinsic carbon doping across wafers, leading to reduced production yield and increased costs, and surface oxidation issues from exposed AlGaN layers causing leakage problems.
Innovation Solution
The implementation of a dual superlattice buffer structure with extrinsic carbon doping using ethene as a carbon source gas, along with a silicon nitride cap layer to enhance carbon uniformity and reduce surface oxidation, allowing for improved epitaxial deposition at higher temperatures while maintaining breakdown voltage performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If intrinsic carbon doping is increased to improve current collapse performance, then current collapse performance is improved, but epitaxial deposition process temperature must be decreased which adversely affects GaN material quality
Solution Approach 1:
The patent changes the carbon doping method from intrinsic to extrinsic doping, allowing carbon incorporation at higher epitaxial deposition temperatures. This parameter change enables simultaneous achievement of improved current collapse performance and maintained GaN material quality by decoupling the temperature constraint from carbon doping effectiveness
Solution Approach 2:
The patent introduces an extrinsic carbon source as an intermediary to deliver carbon atoms to the GaN layer during epitaxial growth. This intermediary carbon source enables controlled carbon incorporation without requiring temperature reduction, thus maintaining both current collapse performance and material quality
2Reliability
If intrinsic carbon doping is used to improve current collapse performance, then current collapse performance is improved, but carbon doping is non-uniform across the wafer which reduces production yield
Solution Approach 1:
The patent changes from intrinsic carbon doping to extrinsic carbon doping using a controlled carbon source gas during epitaxial growth. This parameter change achieves uniform carbon distribution across the entire wafer surface, ensuring consistent current collapse performance and eliminating the production yield reduction caused by spatial non-uniformity
3Ease of operation
If AlGaN layer is exposed during processing to enable transistor functionality, then transistor operation is enabled, but surface oxidation and micro-pitting occur which cause leakage performance issues
Solution Approach 1:
The patent introduces a silicon nitride cap layer as an intermediary protective coating over the exposed AlGaN surface. This cap layer acts as a barrier that prevents oxidation and micro-pitting during subsequent processing steps, thereby maintaining leakage performance while still enabling transistor functionality
Solution Approach 2:
The patent applies a silicon nitride cap layer beforehand to protect the AlGaN surface from oxidation and damage during processing. This prior protective measure prevents the formation of leakage paths, ensuring reliable transistor operation without sacrificing surface integrity
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 approach achieves uniform carbon doping across the wafer, mitigates current collapse, and reduces surface leakage, resulting in improved production yield and reduced costs by maintaining high-quality GaN material with enhanced breakdown voltage and reduced vertical leakage.
Implementation Method 1
performing an epitaxial deposition process that deposits at least one layer of the buffer structure using an extrinsic carbon source gas
Implementation Method 2
intrinsic carbon doping due to use of a metal organic source, and the intrinsic carbon doping helps current collapse performance
Implementation Method 3
some GaN transistor designs include an epitaxially deposited top aluminum gallium nitride (AlGaN) layer that is exposed during subsequent processing, leading to oxidation and surface micro-pitting
Data Source
AI summary
Fabrication methods and gallium nitride transistors, in which an electronic device includes a substrate, a buffer structure, a hetero-epitaxy structure over the buffer structure, and a transistor over or in the hetero-epitaxy structure. In one example, the buffer structure has an extrinsically carbon doped gallium nitride layer over a dual superlattice stack or over a multilayer composition graded aluminum gallium nitride stack, and a silicon nitride cap layer over the hetero-epitaxy structure.