Low Density Drain HEMTs via Plasma Field Modification
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Solution Overview
Problem
Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) face challenges with lower maximum drain current and breakdown voltage, leading to current collapse and increased device size, while existing solutions like field plates introduce additional capacitance and degrade device performance.
Innovation Solution
The method involves modifying the surface field distribution between the gate and drain by converting part or all of the region between the gate and drain into a low-density 2DEG (two-dimensional electron gas) using CF4 plasma treatment, forming a Low-Density Drain (LDD) HEMT, which enhances breakdown voltage and suppresses current collapse without degrading gains or cutoff frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a field plate is used to enhance breakdown voltage, then breakdown voltage is improved, but additional gate capacitances are introduced which reduce device gain and cutoff frequencies
Solution Approach 1:
The patent extracts the field plate structure from the device, replacing it with a low-density drain region formed by CF4 plasma treatment. This removes the source of additional gate capacitances while preserving the breakdown voltage enhancement function through modified surface field distribution in the drain region.
Solution Approach 2:
The patent introduces a low-density drain region as an intermediary between the gate and the drain contact. This intermediate region with reduced 2DEG density acts as a field-modifying layer that enhances breakdown voltage without requiring direct field plate connections to the gate, thereby avoiding additional gate capacitances.
2Strength
If the gate-to-drain distance is increased to improve breakdown voltage, then breakdown voltage is enhanced, but device size increases
Solution Approach 1:
The patent applies local quality modification by creating a low-density drain region with specific plasma treatment parameters that concentrate the field-enhancing effect in a localized area near the drain contact. This allows breakdown voltage improvement without extending the overall gate-to-drain distance, maintaining compact device dimensions.
3Strength
If CF4 plasma treatment is applied to create low-density drain region, then breakdown voltage is improved and current collapse is suppressed, but process complexity increases
Solution Approach 1:
The patent merges the breakdown voltage enhancement function with the existing drain region formation process. The CF4 plasma treatment is applied to the drain-side AlGaN layer during the standard fabrication sequence, combining the low-density region creation with the drain contact formation step rather than adding a completely separate process module.
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 improves off-state breakdown voltage by 50% and completely suppresses current collapse in LDD-HEMTs, maintaining or improving device performance metrics like gain and cutoff frequencies, and does not require additional process steps or increase device size.
Implementation Method 1
Part or all of the region between gate and drain can be transformed into a region with low density of 2DEG using a CF4 plasma treatment
Implementation Method 2
The off-state breakdown voltage can be improved and current collapse can be completely suppressed in LDD-HEMTs
Data Source
AI summary
Methods and devices for fabricating AlGaN/GaN normally-off high electron mobility transistors (HEMTs). A fluorine-based (electronegative ions-based) plasma treatment or low-energy ion implantation is used to modify the drain-side surface field distribution without the use of a field plate electrode. The off-state breakdown voltage can be improved and current collapse can be completely suppressed in LDD-HEMTs with no significant degradation in gains and cutoff frequencies.