Vertical HEMT Pillar Architecture to Reduce Current Collapse
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Solution Overview
Problem
Existing HEMTs face limitations in high-frequency, high-power, high-temperature, and high-voltage operations due to current collapse and inefficient use of surface area, leading to trade-offs between drain current and breakdown voltage.
Innovation Solution
A vertical HEMT design utilizing a GaN-based material with a heterojunction of AlGaN and GaN layers, featuring a pillar structure with a 2DEG channel, and a current blocking layer to enhance electron mobility and breakdown voltage, while minimizing device size and parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional horizontal HEMT structure is used, then current flow is mediated through 2DEG at heterojunction interface, but device area cannot be effectively downscaled and current collapse occurs at high power operation
Solution Approach 1:
The patent transitions from traditional horizontal planar HEMT structure to a vertical HEMT architecture where the current flow path is reoriented from lateral to vertical direction. The drain contact is positioned at the bottom of the device and source contacts at the top, with the 2DEG channel forming vertical transport paths through the heterostructure. This dimensional change enables improved area utilization and reduces current collapse by distributing current through multiple vertical pillars rather than a single lateral path.
2Area of stationary object
If vertical HEMT structure is implemented, then area downscaling is improved, but manufacturing complexity increases due to multi-layer heterostructure and pillar formation
Solution Approach 1:
The vertical HEMT structure is segmented into multiple discrete vertical pillars arranged in an array, with each pillar containing its own 2DEG channel formed by AlGaN/GaN heterojunction. The pillars are laterally separated and embedded in a supporting matrix layer. This segmentation allows the complex heterostructure to be divided into repeating modular units, facilitating systematic manufacturing while achieving high area density.
Solution Approach 2:
The device employs composite heterostructure materials consisting of alternating layers of AlGaN and GaN with different band gaps. The AlGaN barrier layer forms the heterojunction with the GaN channel layer, creating the 2DEG at the interface. This composite material system enables simultaneous achievement of high electron mobility, high breakdown voltage, and effective area utilization in the vertical architecture.
3Strength
If higher breakdown voltage is achieved through material optimization, then high voltage operation is enabled, but device losses increase and efficiency decreases
Solution Approach 1:
The patent optimizes different regions of the vertical HEMT with locally tailored properties: the AlGaN barrier layer composition and thickness are specifically designed to achieve high breakdown voltage at the heterojunction interface, while the GaN channel layer is optimized for low resistance vertical transport. The drain contact region uses specific metal compositions to minimize contact resistance, and the source contact regions are configured to reduce series resistance. This local optimization enables high breakdown voltage operation with minimized energy losses.
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 vertical HEMT achieves high-frequency, high-power, and high-voltage operations with improved breakdown voltage and reduced transistor losses, enabling efficient use of surface area and reliable performance in power electronics.
Implementation Method 1
a heterostructure mesa (600) arranged on the pillar layer (500), the heterostructure mesa (600) comprising an AlGaN-layer (610) and a GaN-layer (620), together forming a heterojunction (630)
Implementation Method 2
the at least one vertical pillar (510) is forming an electron transport channel between the drain contact (410) and the heterojunction (630)
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A vertical high-electron-mobility transistor, HEMT (100), comprising: a substrate (310); a drain contact (410), the drain contact being a metal contact via through said substrate; a pillar layer (500) arranged above the drain contact (410) and comprising at least one vertical pillar (510) and a supporting material (520) laterally enclosing the at least one vertical pillar (510); a heterostructure mesa (600) arranged on the pillar layer (500), the heterostructure mesa (600) comprising an AlGaN-layer (610) and a GaN-layer (620), together forming a heterojunction (630); at least one source contact (420a, 420b) electrically connected to the heterostructure mesa (600); a gate contact (430) arranged on said heterostructure mesa (600), and above the at least one vertical pillar (510); wherein the at least one vertical pillar (510) is forming an electron transport channel between the drain contact (410) and the heterojunction (630).