GaN HEMT Non-Uniform 2DEG via Stress Layer
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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 density leading to suboptimal electric field distribution and limited figure of merit (FOM), and existing field plate techniques increase complexity and cost while introducing non-ideal electric field profiles.
Innovation Solution
A high electron mobility transistor (HEMT) with a stress inducing layer varying the piezo-electric effect in the barrier layer to achieve a non-uniform lateral distribution of 2DEG in the drift region, using varying size openings or height profiles to modulate the electric field and improve electric field distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a uniform 2DEG density is used in the drift region, then the device structure is simple, but the electric field distribution becomes non-ideal (triangular shape) resulting in reduced breakdown voltage
Solution Approach 1:
The patent applies local quality by creating a non-uniform 2DEG density distribution in the drift region through a stress-inducing layer with varying thickness. The stress-inducing layer is thinner near the gate and thicker near the drain, locally modifying the piezoelectric effect to achieve desired electric field shaping without complex multi-step field plates
Solution Approach 2:
The patent changes the physical parameter of 2DEG density from uniform to non-uniform by exploiting the piezoelectric effect. By varying the thickness of the stress-inducing layer, the piezoelectric stress is modulated, which directly changes the 2DEG density profile in the drift region, transforming the electric field shape from triangular to trapezoidal
2Reliability
If multiple field plates are used to improve electric field distribution, then breakdown voltage improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the field-shaping function from complex multi-step field plate structures and implements it through a single stress-inducing layer with varying thickness. This eliminates the need for multiple field plate steps while achieving the desired electric field distribution, thereby reducing device complexity and manufacturing cost
Solution Approach 2:
The stress-inducing layer acts as an intermediary between the barrier layer and the drift region. It mediates the piezoelectric effect to locally modulate the 2DEG density, thereby shaping the electric field profile without requiring direct complex field plate structures
3Reliability
If field plates are added to shape the electric field, then breakdown voltage improves, but gate to drain capacitance increases
Solution Approach 1:
The patent extracts the field-shaping function from traditional field plates and implements it through piezoelectric stress modulation. This eliminates the need for physical field plate extensions that would increase gate-to-drain capacitance, achieving field shaping without the capacitive penalty
4Reliability
If the drift region length is increased to improve breakdown voltage, then breakdown voltage improves, but on-state resistance increases quadratically
Solution Approach 1:
The patent changes the 2DEG density parameter from uniform to non-uniform, creating higher electron concentration near the drain region. This allows the device to achieve higher breakdown voltage without increasing drift region length, thereby avoiding the quadratic increase in on-state resistance that would result from lengthening the drift 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
The non-uniform 2DEG distribution results in a flat electric field profile, significantly enhancing the device's figure of merit (FOM) by improving breakdown voltage for a given drift region length, reducing device complexity and cost.
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
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.