HEMT Device with Tapered AlGaN Layer for Uniform Electric Field
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Solution Overview
Problem
Existing III-Nitride HEMT devices with uniform 2DEG profiles suffer from reduced breakdown voltage and increased on-state resistance due to triangular electric field distribution, leading to suboptimal figure of merit and increased device complexity and cost with multi-step field plates.
Innovation Solution
Implementing a non-uniform two-dimensional electron gas profile by tapering the AlGaN charge supplying layer from the gate to the drain, resulting in a monotonically increasing 2DEG profile that achieves a uniform electric field distribution and maximizes the device's figure of merit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a uniform 2DEG profile is used in the drift region, then the device structure is simple, but the electric field distribution becomes triangular resulting in reduced breakdown voltage and increased on-state resistance
Solution Approach 1:
The patent applies local quality by creating a non-uniform 2DEG profile through selective removal of AlGaN material in the drift region. The AlGaN layer thickness is varied laterally, being thicker near the gate and thinner toward the drain, which creates localized differences in charge density. This results in a trapezoidal electric field distribution that maintains high breakdown voltage while keeping the device structure relatively simple.
Solution Approach 2:
The patent changes the physical parameter of AlGaN layer thickness in the drift region to control the 2DEG profile. By adjusting the thickness parameter of the AlGaN layer (from thicker near gate to thinner near drain), the charge density and electric field distribution are modified. This parameter change transforms the electric field shape from triangular to trapezoidal, improving breakdown voltage without adding complex multi-step field plate structures.
2Reliability
If multi-step field plates are used to improve electric field distribution, then breakdown voltage improves, but device complexity and manufacturing cost increase
Solution Approach 1:
Instead of adding multi-step field plates that increase device complexity, the patent changes the parameter of AlGaN layer thickness in the drift region. This single-structure approach with varied thickness creates the desired trapezoidal electric field distribution, achieving high breakdown voltage without the complexity of multiple field plate steps.
Solution Approach 2:
The patent extracts the field shaping function from separate field plate structures and integrates it into the AlGaN layer itself. By removing AlGaN material selectively in the drift region, the charge supplying layer itself becomes the field-shaping element, eliminating the need for additional field plate structures and reducing device complexity.
3Reliability
If the AlGaN layer thickness is increased monotonically from gate to drain, then a uniform electric field distribution is achieved maximizing figure of merit, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements a monotonic change in AlGaN layer thickness from gate to drain, creating a controlled gradient in charge density. This parameter change achieves uniform electric field distribution and maximizes figure of merit. The manufacturing precision is managed by using standard semiconductor fabrication techniques to control the thickness profile.
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 breakdown voltage per unit length and improves immunity to dynamic on-state resistance degradation, while reducing device complexity and cost by eliminating the need for multiple field plates.
Implementation Method 1
HEMTs utilize two semiconductor materials with different band-gaps, forming an electron potential well at a heterointerface between the two semiconductor materials, which materials might be, for example, AlGaN and GaN
Implementation Method 2
The potential well confines electrons and defines a two-dimensional electron gas (2DEG) conduction channel
Implementation Method 3
By implementing a non-uniform two-dimensional electron gas profile between the gate and drain electrodes... one can obtain a monotonically increasing 2DEG profile that results in a uniform electric field distribution
Data Source
Figure 1a~1c
Figure 2
Figure 3~4
AI summary
A HEMT device has a substrate; a buffer layer disposed above the substrate; a carrier supplying layer disposed above the buffer layer; a gate element penetrating the carrier supplying layer; and a drain element disposed on the carrier supplying layer. The carrier supplying layer has a non-uniform thickness between the gate element and the drain element, the carrier supplying layer having a relatively greater thickness adjacent the drain element and a relatively thinner thickness adjacent the gate element. A non-uniform two-dimensional electron gas conduction channel is formed in the carrier supplying layer, the two-dimensional electron gas conduction channel having a non-uniform profile between the gate and drain elements.