N-polar AlGaN/GaN HEMT for Threshold Voltage Uniformity
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Solution Overview
Problem
Existing Ga-polar AlGaN/GaN enhancement mode field effect transistors face challenges with threshold voltage uniformity, repeatability, gate leakage, and dispersion, particularly in high breakdown and high-frequency applications, due to difficulties in etching and p-type material growth.
Innovation Solution
The N-polar orientation uses polarization fields to deplete the 2DEG under the gate, eliminating the need for gate recess etching and p-type doping, and incorporates a graded AlGaN cap and delta-doped n-type layers to suppress dispersion and reduce gate leakage, while maintaining low on-resistance and high breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate recess etching is used to achieve enhancement mode operation in Ga-polar AlGaN/GaN HEMTs, then E-mode operation is achieved, but threshold voltage uniformity and repeatability deteriorate
Solution Approach 1:
The patent inverts the conventional Ga-polar orientation approach by using N-polar AlGaN/GaN HEMT structure. Instead of etching the AlGaN barrier layer to achieve E-mode operation, the N-polar structure inherently provides E-mode operation through its polarization field characteristics, eliminating the need for gate recess etching and achieving both E-mode operation and uniform threshold voltage control.
Solution Approach 2:
The patent changes the fundamental material orientation parameter from Ga-polar to N-polar growth direction. This parameter change fundamentally alters the polarization field distribution, enabling enhancement mode operation without requiring aggressive etching processes, thereby simultaneously achieving E-mode operation and improved threshold voltage uniformity.
2Reliability
If fluorine-based plasma is used to expose AlGaN under the gate region, then threshold voltage shift is achieved, but threshold voltage uniformity and repeatability deteriorate
Solution Approach 1:
Instead of using fluorine-based plasma treatment on Ga-polar structures to achieve threshold voltage shift, the patent inverts to N-polar orientation where the threshold voltage is naturally controlled by the epitaxial structure design. This eliminates the need for plasma treatment and its associated uniformity problems.
3Ease of manufacture
If conventional Ga-polar structures are used, then device structure is established, but gate leakage increases and breakdown voltage decreases
Solution Approach 1:
The patent inverts the conventional Ga-polar structure to N-polar orientation. This inversion fundamentally changes the polarization field direction and distribution, creating a more effective barrier against gate leakage and enabling higher breakdown voltages while maintaining manufacturability.
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 enables the development of enhancement mode FETs with improved threshold voltage control, reduced dispersion, and low gate leakage, enhancing reliability and performance for power switching and high-frequency applications.
Implementation Method 1
the proposed device structure in the opposite N-polar direction provides E-mode devices without using a gate recess etch. Threshold voltage is these devices will be controlled by the epitaxial-structure and will not be affected by the processing steps. Furthermore, since the polarization fields are used to deplete the 2-dimensional electron gas (2DEG)
Data Source
AI summary
A novel enhancement mode field effect transistor (FET), such as a High Electron Mobility Transistors (HEMT), has an N-polar surface uses polarization fields to reduce the electron population under the gate in the N-polar orientation, has improved dispersion suppression, and low gate leakage.