GaN HEMT Drain Electrode Design for Current Degradation
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Solution Overview
Problem
The design and fabrication of III-N transistors with high figures of merit have proven difficult, leading to challenges in improving size, efficiency, reliability, and output characteristics, which hinders market adaptation.
Innovation Solution
The development of lateral III-N devices, such as AlGaN/GaN HEMTs, with specific structures that include a conductive substrate, a III-N material structure with a buffer layer, channel layer, and barrier layer, and a drain electrode configuration that prevents full depletion of the 2DEG channel at high voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the maximum rated drain-to-source operating voltage is increased to improve power handling capability, then the power handling capability is improved, but current degradation occurs due to full depletion of the 2DEG channel
Solution Approach 1:
The patent applies local quality by creating different aluminum composition regions within the barrier layer. The barrier layer has a first region with a first aluminum composition and a second region with a second aluminum composition that is higher than the first. This compositional variation creates localized differences in band structure and electron confinement, allowing the device to maintain 2DEG channel charge at high voltages while handling high power, thus resolving the contradiction between power handling capability and current degradation.
2Productivity
If the device operates at maximum rated drain-to-source voltage to improve efficiency, then efficiency is improved, but the 2DEG channel becomes fully depleted leading to performance degradation
Solution Approach 1:
The patent employs parameter changes by varying the aluminum composition parameter within the barrier layer. The barrier layer transitions from a first aluminum composition in the first region to a second aluminum composition in the second region. This parameter variation modifies the conduction band offset and polarization effects, enabling the device to maintain adequate 2DEG channel charge even when operated at maximum rated voltage, thereby preserving efficiency while preventing performance degradation.
3Reliability
If the aluminum composition in the barrier layer is increased to improve voltage blocking capability, then voltage blocking capability is improved, but the 2DEG channel charge density decreases
Solution Approach 1:
The patent applies segmentation by dividing the barrier layer into multiple regions with different aluminum compositions. Rather than using a single high-aluminum-composition barrier layer that would deplete the 2DEG channel, the barrier layer is segmented into a first region with lower aluminum composition and a second region with higher aluminum composition. This segmentation allows the device to achieve high voltage blocking capability through the high-composition region while maintaining sufficient 2DEG channel charge density through the low-composition region.
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 enhances the performance of III-N devices by reducing current degradation and maintaining low on-state resistance even at maximum rated operating voltages, thereby improving reliability and efficiency.
Implementation Method 1
a III-N material structure including a III-N buffer layer, a III-N channel layer and a III-N barrier layer where a compositional difference induces a 2DEG channel therein
Implementation Method 2
the 2DEG channel is fully depleted of charge below the second portion of the drain electrode when the III-N device is biased at or above the maximum rated drain-to-source operating voltage
Data Source
AI summary
Lateral III-N devices such as AlGaN/GaN HEMTs can have structures which serve to improve performance and reduce current degradation. The III-N device can include a conductive substrate and a III-N material structure that includes a III-N buffer layer, a III-N channel layer and a III-N barrier layer where a compositional difference induces a 2DEG channel therein. The first portion is in ohmic contact with the 2DEG channel and the second portion extends over a top surface of the III-N barrier layer and is in direct contact with the top surface of the III-N barrier layer. The device further includes a drain-to-substrate pinch-off voltage and a maximum rated drain-to-source operating voltage which is greater than the drain-to-substrate pinch-off voltage, and the 2DEG channel is fully depleted of charge below the second portion of the drain electrode when the III-N device is biased at or above the maximum rated drain-to-source operating voltage.