Segmented Nanowire Active Regions for RF Transistor Heat Dissipation
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Solution Overview
Problem
RF transistors tend to heat up during operation, reducing device lifetime due to self-heating phenomena, particularly in gallium nitride high electron mobility transistors (HEMTs) where high thermal boundary resistances at interfaces between epitaxial layers contribute to elevated active region temperatures.
Innovation Solution
A semiconductor device with segmented active regions is developed, featuring miscut substrates, epitaxially grown intermediate layers with surface steps, nanowire channels, and a cap layer, which reduces thermal boundary resistance by allowing effective heat transfer through the device. The nanowire channels are grown on surface steps, and the structure includes materials like aluminum nitride and gallium nitride, with crystallographic orientations such as N-polar, Ga-polar, and semipolar, and is constructed using metalorganic chemical vapor deposition (MOCVD) to minimize impurities and interface damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high power density is used in RF transistors, then power output is improved, but thermal boundary resistance causes self-heating and reduces device lifetime
Solution Approach 1:
The active region is divided into multiple segments separated by air gaps, creating a segmented structure. This segmentation allows heat to be dissipated through multiple pathways and reduces thermal boundary resistance by eliminating continuous material interfaces that trap heat, thereby enabling high power density operation while maintaining device lifetime
Solution Approach 2:
Material is removed to create air gaps between active region segments. These air gaps extract the thermal boundary resistance problem from the device structure, providing thermal isolation and reducing heat accumulation in the active regions, which allows high power operation without self-heating damage
2Ease of manufacture
If continuous epitaxial layers are used, then manufacturing is simplified, but thermal boundary resistance increases and heat dissipation is reduced
Solution Approach 1:
The continuous epitaxial layer is segmented by removing portions to create air gaps. This segmentation improves heat dissipation by eliminating thermal boundary resistance at material interfaces while maintaining relative manufacturing simplicity through selective removal processes followed by epitaxial regrowth of cap layers
Solution Approach 2:
The device structure transitions from uniform continuous layers to a non-uniform segmented structure with air gaps in specific locations. This local modification creates regions of low thermal boundary resistance where needed, improving heat dissipation from active regions without complicating the overall epitaxial manufacturing process
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 enables rapid heat dissipation without interfacial thermal boundary resistance, reducing operating temperatures and increasing device lifetimes, allowing for higher power densities in RF applications while maintaining performance metrics.
Implementation Method 1
rapid heat dissipation without interfacial thermal boundary resistance
Implementation Method 2
intermediate layers epitaxially grown on the miscut substrate
Implementation Method 3
epitaxially growing of the intermediate layers, the cap layer and the nanowire channels includes metalorganic chemical vapor deposition (CVD)
Data Source
AI summary
A semiconductor device is provided and includes a miscut substrate, intermediate layers epitaxially grown on the miscut substrate such that an uppermost surface of the intermediate layers includes surface steps, segmented active regions including nanowire channels, each of which is epitaxially grown on a corresponding one of the surface steps and a cap layer epitaxially grown on the nanowire channels and exposed portions of the uppermost surface.