GaN HEMT Stress Inducing Layer for Breakdown Voltage
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Solution Overview
Problem
Type III-nitride high electron mobility transistor (HEMT) devices face a design trade-off between on-state resistance and breakdown voltage, with existing field plates resulting in non-ideal electric field distribution and increased device complexity and cost, limiting the figure of merit (FOM) defined as BV2/Ron.
Innovation Solution
A stress inducing layer with a non-uniform lateral distribution of two-dimensional electron gas (2DEG) is introduced in the drift region between the gate and drain, achieved by varying the size or height of the stress inducing layer, which modulates the piezoelectric effect and electric field distribution, resulting in a flat electric field profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If field plates are used to improve electric field distribution, then breakdown voltage is improved, but device complexity and gate to drain capacitance 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 non-uniform thickness. This layer is integrated into the existing heterostructure without adding separate field plate components, thereby achieving electric field control while reducing device complexity and gate-to-drain capacitance.
Solution Approach 2:
The stress inducing layer is merged with the barrier layer or drift region, combining the field shaping function with the existing device structure. This integration eliminates the need for separate field plate structures and their associated fabrication steps, reducing both device complexity and parasitic capacitance while maintaining breakdown voltage enhancement.
2Strength
If multiple field plates are used to improve electric field distribution, then breakdown voltage is improved, but manufacturing cost and process complexity increase
Solution Approach 1:
The patent extracts the field shaping function from multiple field plate structures and implements it through a single stress inducing layer with spatially varying thickness. This approach eliminates multiple fabrication steps and materials, significantly reducing manufacturing cost and process complexity while achieving the desired electric field distribution for enhanced breakdown voltage.
Solution Approach 2:
The patent changes the thickness parameter of the stress inducing layer spatially to achieve different stress magnitudes across the drift region. This single parameter variation (thickness gradient) replaces the need for multiple field plates with different geometries, simplifying the manufacturing process and reducing costs while maintaining the electric field control necessary for improved breakdown voltage.
3Device complexity
If uniform 2DEG density is used in the drift region, then device structure is simple, but electric field distribution is non-ideal with peak under the gate region
Solution Approach 1:
The patent applies local quality by creating a stress inducing layer with non-uniform thickness specifically in the drift region. This local variation in layer thickness produces spatially varying piezoelectric stress that generates the desired non-uniform 2DEG density profile, achieving ideal electric field distribution (trapezoidal shape) only where needed without complicating the overall device structure.
Solution Approach 2:
The patent changes the physical state and distribution of the stress inducing layer to modulate the piezoelectric effect. By varying the thickness parameter of this layer across the drift region, the patent creates a controlled gradient in 2DEG density that transforms the electric field distribution from triangular to trapezoidal, improving breakdown voltage without significantly increasing device complexity.
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 for a given drift region length, achieving a more efficient electric field distribution and reducing device complexity and cost.
Implementation Method 1
the stress inducing layer varying a 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 a piezo-electric effect in the barrier layer in a drift region between a gate and a drain, wherein a two dimensional electron gas (2DEG) has a non-uniform lateral distribution in the drift region between the gate and the drain, wherein the stress inducing layer comprises a material having a height that decreases linearly and monotonically in the drift region in the direction from the gate towards the drain, and wherein the 2DEG decreases in density in the drift region between the gate and the drain.