Stepped Gate Field Plates for GaN HEMT Electric Field Shaping
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Solution Overview
Problem
Existing GaN HEMT devices with lift-off metallization processes face issues of unwanted metal layers and haloes, leading to electric field crowding and potential dielectric failure in high voltage applications, necessitating improved device structures and fabrication processes for field plates.
Innovation Solution
A semiconductor device structure and fabrication method featuring a stepped field plate in GaN HEMTs, with specific configurations of passivation layers and conductive metal layers to shape the electric field, reducing sensitivity to lift-off process limitations and enhancing device reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a lift-off metallization process is used to form gate metal field plate, then the fabrication process is simplified, but unwanted metal layers and haloes remain on the wafer surface causing electric field crowding and potential dielectric failure
Solution Approach 1:
The patent extracts and removes the harmful unwanted metal layers and haloes from the wafer surface through selective etching processes. The etch selectivity between the gate metal field plate material and the unwanted metal residues enables precise removal of harmful elements while preserving the functional field plate structure, thereby eliminating electric field crowding and dielectric failure risks.
Solution Approach 2:
The patent applies different etching conditions and parameters to different regions of the wafer. By controlling the etch process to affect only specific areas where unwanted metal residues are present, the method achieves localized removal of harmful elements without impacting the overall field plate structure or introducing new defects, thus maintaining device reliability.
2Productivity
If unwanted metal extrusions are present on the wafer surface, then the fabrication process is complete, but electric field crowding occurs leading to dielectric failure
Solution Approach 1:
The patent converts the harmful effect of unwanted metal extrusions into a beneficial etching target. By designing the etch process to specifically target and remove these extrusions, the method transforms a fabrication defect into a controlled removal step, eliminating electric field crowding and preventing dielectric failure while maintaining overall fabrication efficiency.
3Device complexity
If conventional field plate structures are used, then the device structure is simple, but leakage increases and device lifespan decreases
Solution Approach 1:
The patent segments the field plate structure into multiple controlled layers or regions with different properties. This segmentation allows for optimized electric field distribution across different zones, reducing leakage paths and improving overall device performance and lifespan while maintaining reasonable structural complexity.
Solution Approach 2:
The patent introduces additional dimensional control through stepped field plate configurations or vertical layering. By extending the field plate control into the vertical dimension or creating stepped profiles, the method achieves superior electric field management that reduces leakage and extends device lifespan without excessive 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
The stepped field plate structure improves electric field distribution, reduces leakage, and increases the robustness and lifespan of GaN HEMTs, mitigating the risks associated with lift-off metallization processes.
Implementation Method 1
A thickness of the first and second passivation layers under the gate field plate, and a step size of each step of the stepped gate field plate are configured to shape an electric field under the stepped gate field plate between the gate contact and the drain contact.
Data Source
Figure 1~2
Figure 3
Figure 4A~4C
AI summary
A GaN semiconductor power transistor structure with a stepped gate field plate, and a method of fabrication is disclosed. The stepped gate field plate is formed using contact metal and/or interconnect metal. The stepped structure of the gate field plate is defined by dielectric etching to form openings for the stepped gate field plate, and the dielectric thickness under the gate field plate is sized and stepped to shape appropriately the electric field in the region between the gate and drain. The resulting stepped gate field plate structure is less sensitive to limitations of stepped field plates fabricated by a lift-off metal process.