HEMT Stress-Inducing Layer for Flat Electric Field
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Solution Overview
Problem
Type III-nitride HEMT devices face a design trade-off between on-state resistance and breakdown voltage, with uniform 2DEG profiles leading to suboptimal electric field distribution and limited figure of merit (FOM), and existing field plate techniques increase complexity and cost while not achieving ideal flat field distribution.
Innovation Solution
A high electron mobility transistor (HEMT) with a non-uniform lateral two-dimensional electron gas profile is achieved by incorporating a stress-inducing layer with varying piezoelectric effect in the drift region between the gate and drain, modulated through etched openings or gray scale photolithography, to achieve a flat electric field distribution.
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 non-optimal (triangular shape) resulting in reduced breakdown voltage per unit drift region length
Solution Approach 1:
The patent applies local quality by creating a non-uniform 2DEG density distribution in the drift region through a graded AlGaN barrier layer. The aluminum composition ratio varies laterally from the gate towards the drain, generating different piezoelectric field strengths in different regions. This local variation in material composition achieves optimal electric field distribution (trapezoidal shape) without adding complex structural elements like field plates.
2Reliability
If field plate techniques are used to improve electric field distribution, then breakdown voltage is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the material parameter (aluminum composition ratio) of the AlGaN barrier layer to achieve the desired electric field distribution. By varying the aluminum content laterally, the piezoelectric effect is modulated to create the optimal trapezoidal electric field profile. This parameter-based approach replaces the need for additional field plate structures, reducing device complexity while maintaining breakdown voltage performance.
3Reliability
If field plate techniques are used to improve electric field distribution, then breakdown voltage is improved, but gate to drain capacitance increases
Solution Approach 1:
The graded AlGaN barrier layer creates localized variations in piezoelectric field strength along the drift region. This local quality approach shapes the electric field distribution to be trapezoidal, which improves breakdown voltage without requiring extended field plates that would increase gate-to-drain overlap area and thus reduce parasitic capacitance.
4Reliability
If multiple field plate steps are implemented, then electric field distribution is improved, but manufacturing process complexity and cost increase
Solution Approach 1:
The patent implements the electric field shaping function within the AlGaN barrier layer itself by changing the aluminum composition parameter during growth. This can be achieved in a single growth process step using conventional MOCVD or MBE techniques, avoiding the need for multiple deposition and etching steps required for multistep field plates. The parameter change approach simplifies manufacturing while achieving the desired electric field distribution.
5Ease of manufacture
If a uniform 2DEG profile is used, then manufacturing is simple, but on-state resistance and figure of merit are limited
Solution Approach 1:
The graded AlGaN barrier layer creates a non-uniform 2DEG density distribution where the electron concentration varies laterally from gate to drain. This local variation optimizes both the on-state resistance (by maintaining adequate 2DEG density) and the breakdown voltage (by shaping the electric field), thereby improving the overall figure of merit without significantly complicating the manufacturing process.
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 significantly improves the figure of merit (FOM) by enhancing breakdown voltage and reducing on-state resistance, achieving a flat electric field distribution and increasing the maximum oscillation frequency and cut-off frequency.
Implementation Method 1
a stress inducing layer on the barrier layer, the stress inducing layer varying the piezo-electric effect in the barrier layer in a drift region between a gate and a drain
Data Source
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Figure 3A
AI summary
A high electron mobility field effect transistor (HEMT) having a substrate, a channel layer on the substrate and a barrier layer on the channel layer includes a stress inducing layer on the barrier layer, the stress inducing layer varying the piezo-electric effect in the barrier layer in a drift region between a gate and a drain. A two dimensional electron gas (2DEG) has a non-uniform lateral distribution in the drift region between the gate and the drain.