Composite-Channel GaN HEMT for High-Frequency Power
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Solution Overview
Problem
High electron velocity and high charge density are inversely related in GaN HEMTs, limiting high frequency and high power performance due to reduced electron velocity at high charge densities.
Innovation Solution
A composite channel HEMT structure is formed with multiple channel/barrier layer pairs, each with a separate 2DEG, distributing high total charge density among multiple 2DEGs to sustain high saturated electron velocity and achieve high gain and power operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high charge density is achieved in a single 2DEG, then high power operation is enabled, but saturated electron velocity decreases, limiting high frequency performance
Solution Approach 1:
The patent divides the single high-density 2DEG into multiple separate 2DEGs formed by stacked channel/barrier layer pairs. Each 2DEG maintains lower charge density to preserve high saturated electron velocity, while the parallel combination of multiple 2DEGs achieves the required total charge density for high power operation. This segmentation resolves the contradiction by distributing the charge density burden across multiple channels.
Solution Approach 2:
The patent combines multiple 2DEGs in parallel under a single gate electrode, merging their individual current contributions to achieve high total charge density and high power capability. The merging occurs in the conductive regions where currents from multiple 2DEGs converge, allowing the device to simultaneously maintain high velocity in each channel and high power through combined output.
2Reliability
If a conventional single-channel HEMT structure is used, then the device is simple to manufacture, but it cannot achieve both high electron velocity and high charge density simultaneously
Solution Approach 1:
The conventional single-channel structure is segmented into multiple channel/barrier layer pairs, creating a composite channel with multiple 2DEGs. This segmentation enables each sub-channel to operate at optimal electron velocity while the aggregate provides high charge density, achieving superior high frequency and high power performance.
Solution Approach 2:
The patent employs a composite channel structure made of alternating channel layers and barrier layers, forming a composite semiconductor structure. This composite architecture combines the beneficial properties of multiple interfaces to generate multiple 2DEGs, each contributing to the overall performance while maintaining manufacturability through standard heteroepitaxial growth techniques.
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 composite-channel HEMT operates with high gain and high power at high frequencies, effectively addressing the challenge of achieving both high electron velocity and charge density, resulting in efficient high-frequency performance.
Implementation Method 1
At the heterojunction between GaN and AlGaN layers, the difference in bandgap energies between the higher bandgap AlGaN and the GaN creates a two-dimensional electron gas (2DEG) in the smaller bandgap GaN
Implementation Method 2
the difference in bandgap energies between the higher bandgap AlGaN and the GaN creates a two-dimensional electron gas (2DEG)
Implementation Method 3
the Al content in the AlGaN layer creates a piezoelectric charge at the interface, transferring electrons to the 2DEG in the GaN layer
Data Source
AI summary
A HEMT comprises a composite channel, made up of a plurality of channel/barrier layer heterojunctions. That is, two or more channel/barrier layer pairs are deposited on a substrate, under a gate contact. A separate 2DEG is formed in each channel layer at the heterojunction with the barrier layer. The HEMT channel is effectively divided among a plurality of parallel 2DEGs. A high total charge density—required for high power operation—is divided among the plurality of 2DEGs. Since each 2DEG does not have a large charge density, it can sustain the high saturated electron velocity required for very high frequency operation. The composite-channel HEMT thus operates with high gain, at high power levels, and at high frequencies.