GaN Power Transistor Stepped Field Plates for Electric Field Crowding
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Solution Overview
Problem
Existing GaN semiconductor power transistors, such as GaN HEMTs, face issues with unwanted metal layers and electric field crowding due to lift-off metallization processes, leading to potential dielectric failure in high voltage applications.
Innovation Solution
A GaN semiconductor power transistor structure with a stepped field plate and a method of fabrication that includes an epitaxial layer structure, passivation layers, and conductive metal filling stepped openings to shape the electric field, reducing sensitivity to lift-off process limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lift-off metallization process is used to form gate metal field plate, then the field plate structure can be created, 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 unwanted metal layers and haloes that remain after the lift-off process through additional cleaning steps, specifically using selective etching processes to remove residual metal from the wafer surface while preserving the desired field plate structure
Solution Approach 2:
The patent applies preliminary protective actions by forming a protective dielectric layer before the lift-off process that prevents unwanted metal deposition in certain areas, and uses preliminary patterning steps to define precise metal deposition regions that minimize extrusions
2Shape
If a stepped gate metal field plate is fabricated by lift-off process, then the field plate structure is formed, but the process is sensitive to unwanted metal remnants that cause electric field crowding
Solution Approach 1:
The patent introduces intermediary dielectric layers between the metal field plate structures that act as mediators to define precise stepped configurations. These dielectric layers with controlled thicknesses enable the formation of accurate stepped structures while providing a buffer that reduces sensitivity to metal deposition variations
Solution Approach 2:
The patent replaces reliance on purely mechanical lift-off process precision with a combination of dielectric layer thickness control and selective etching processes. This substitution reduces sensitivity to the mechanical limitations of lift-off by using more controllable thin-film deposition and etching techniques
Data Source
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.