AlGaN Cap Layer Passivation for HEMT Gate Leakage
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Solution Overview
Problem
Conventional semiconductor materials like silicon and gallium arsenide are not well-suited for high power and high frequency applications due to their small bandgaps and breakdown voltages, necessitating the use of wide bandgap materials such as silicon carbide and Group III nitrides for improved performance in devices like High Electron Mobility Transistors (HEMTs).
Innovation Solution
The development of Group III-nitride high electron mobility transistors with a non-uniform composition AlGaN cap layer and doped regions, along with passivation layers like graphitic and amorphous BN or SiC, to enhance robustness, reduce gate leakage, and improve operational characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional semiconductor materials (silicon, gallium arsenide) are used, then manufacturing cost and ease of manufacture are maintained, but breakdown voltage and power handling capability are insufficient for high power applications
Solution Approach 1:
The patent employs composite material structures including AlGaN/GaN heterostructures with multiple functional layers (buffer layer, active layer, cap layer) and integrated passivation layers (SiN, SiO2, Al2O3). This composite approach enables high breakdown voltage (>100V) and high electron mobility while maintaining manufacturability through established semiconductor fabrication processes.
2Power
If wide bandgap materials (silicon carbide, Group III nitrides) are used to achieve high breakdown voltage, then power handling capability improves, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The device is segmented into distinct functional layers: semi-insulating substrate, buffer layer, active layer, cap layer, and passivation layers. Each layer performs a specific function (substrate for mechanical support, buffer for dislocation management, active layer for electron transport, cap for surface passivation). This segmentation enables high power handling while simplifying the manufacturing process by allowing independent optimization and fabrication of each layer.
Solution Approach 2:
Different regions of the device have locally optimized properties: the buffer layer has specific doping concentrations to manage dislocations, the active layer has high electron mobility characteristics, the cap layer has high dielectric constant for surface passivation, and the passivation layers have tailored thickness and material composition (SiN, SiO2, Al2O3) to address specific surface states. This local quality approach enables high power performance without excessive overall device complexity.
3Reliability
If passivation layers are applied to reduce gate leakage, then reliability improves, but manufacturing steps and process complexity increase
Solution Approach 1:
The patent combines multiple passivation functions into an integrated passivation structure where SiN, SiO2, and Al2O3 layers are deposited in sequence to provide both electrical passivation (reducing gate leakage) and mechanical protection. The cap layer and passivation layers are formed as part of the same fabrication sequence, merging surface preparation and passivation steps. This approach achieves reliable gate leakage reduction (<10^-15 A) while maintaining reasonable manufacturing complexity through combined process steps.
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
These transistors exhibit improved robustness, reduced gate leakage, and enhanced performance in high power and high frequency applications by utilizing a non-uniform AlGaN cap layer and doped regions, as well as effective passivation layers, which address the limitations of conventional materials.
Implementation Method 1
forming a graphitic and/or amorphous BN layer on at least a portion of a surface of a region of wide bandgap semiconductor material
Implementation Method 2
forming a SiC layer on at least a portion of a surface of a region of Group III-nitride semiconductor material
Implementation Method 3
a non-uniform composition AlGaN based cap layer on the barrier layer. The non-uniform composition AlGaN based cap layer has a higher concentration of Al adjacent a surface of the cap layer that is remote from the barrier layer
Data Source
AI summary
High electron mobility transistors are provided that include a non-uniform aluminum concentration AlGaN based cap layer having a high aluminum concentration adjacent a surface of the cap layer that is remote from the barrier layer on which the cap layer is provided. High electron mobility transistors are provided that include a cap layer having a doped region adjacent a surface of the cap layer that is remote from the barrier layer on which the cap layer is provided. Graphitic BN passivation structures for wide bandgap semiconductor devices are provided. SiC passivation structures for Group III-nitride semiconductor devices are provided. Oxygen anneals of passivation structures are also provided. Ohmic contacts without a recess are also provided.