GaN Transistor Structure With Substrate Removal for Heat Dissipation
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Solution Overview
Problem
Traditional GaN transistors on silicon substrates face issues with high thermal and structural mismatch, leading to defects, poor heat dissipation, back-gating, and limitations in vertical current flow, which impede the development of high-power, high-electron mobility transistors with enhanced electrical power and thermal conductivity.
Innovation Solution
A method involving the growth of an epitaxial layer on a removable flat substrate, complete removal of the substrate, and application of a thermally conducting layer that contacts at least 80% of the bottom side of the epitaxial layer, allowing for improved heat dissipation and mechanical stability, and enabling the creation of transistors with high electron mobility and vertical structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon substrate is used for GaN transistor production, then cost-effectiveness is improved, but thermal conductivity and structural matching deteriorate
Solution Approach 1:
The patent extracts and removes the silicon substrate from the final transistor structure. The substrate is used only temporarily during epitaxial growth and is completely removed before final device assembly, eliminating its harmful thermal and electrical effects while maintaining the cost benefits of silicon-based manufacturing processes
Solution Approach 2:
The patent introduces a sacrificial substrate as an intermediary that facilitates low-cost epitaxial growth but is subsequently removed. This intermediary enables the use of inexpensive silicon processing techniques while avoiding the permanent presence of silicon in the final device, allowing replacement with superior thermal conductivity materials
2Stability of the object's composition
If buffer layers are added to accommodate lattice mismatch on Si substrates, then structural compatibility is improved, but vertical current flow and electron mobility deteriorate
Solution Approach 1:
The patent removes the substrate entirely before final device assembly, eliminating the need for thick buffer layers that would otherwise be required to accommodate silicon-GaN lattice mismatch. This extraction approach allows direct growth on lattice-matched substrates or suspension of the epitaxial layer
Solution Approach 2:
The patent performs substrate removal as a preliminary action before final device assembly and electrical contact formation. This preliminary removal eliminates lattice mismatch issues that would otherwise require buffer layers, enabling direct vertical current flow through the GaN structure
3Strength
If the substrate is kept in place, then mechanical support is improved, but heat dissipation and electrical performance deteriorate
Solution Approach 1:
The patent applies a temporary support structure or suspension technique as a preliminary measure to maintain mechanical integrity during substrate removal and subsequent processing steps. This preliminary support enables complete substrate removal while maintaining device structural integrity throughout manufacturing
Solution Approach 2:
The patent extracts and removes the silicon substrate completely from the final device structure, eliminating it as a thermal barrier. The epitaxial layer is suspended or supported by alternative means that do not impede heat flow, enabling direct heat dissipation pathways through the GaN structure
4Reliability
If substrate removal is performed, then heat dissipation and electron mobility are improved, but mechanical stability and manufacturing complexity deteriorate
Solution Approach 1:
The patent performs substrate removal as a preliminary step before final device assembly and electrical contact formation. This timing choice simplifies subsequent processing by eliminating the need to work around substrate constraints, despite adding an initial complex step
Solution Approach 2:
The patent uses temporary support structures or suspension techniques as intermediaries during the substrate removal process. These intermediaries maintain mechanical stability during manufacturing while allowing complete substrate removal, and are subsequently removed or integrated into the final device 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
This method results in transistors with enhanced electrical power, improved heat dissipation, and increased mechanical stability, enabling higher vertical breakdown voltage and integration of complex circuit structures without back-gating issues, while reducing defects and thermal resistance.
Implementation Method 1
an epitaxial layer, which comprises or consists of a semiconductor material, is grown onto a front side of a flat substrate
Implementation Method 2
a thermally conducting layer is applied to the bottom side of the epitaxial layer... improved heat dissipation
Data Source
AI summary
The invention relates to a method for producing a transistor with a high degree of electron mobility and to a transistor with a high degree of electron mobility. The method is characterized in that an epitaxial layer is first grown on a flat substrate, and the flat substrate is then completely removed from the bottom of the epitaxial layer, wherein a thermally conductive layer is applied onto the bottom of the epitaxial layer such that the thermally conductive layer contacts at least 80%, preferably at least 90%, particularly preferably at least 95%, in particular 100%, of the bottom of the epitaxial layer. The method is simple and inexpensive to carry out and provides a transistor which has a high degree of electron mobility, an improved electric output without backgating, and an improved heat dissipation. The method additionally allows a transistor to be provided with a vertical transistor structure.