GaN Power Transistor Slanted Gate Field Plate for Electric Field Shaping
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Solution Overview
Problem
Existing GaN semiconductor power transistors with field plates face challenges such as increased process complexity and compatibility issues with existing fabrication processes, and the lift-off metallization process can lead to unwanted metal layers causing electric field crowding and dielectric failure in high voltage applications.
Innovation Solution
A GaN semiconductor power transistor structure with a slanted gate metal field plate and a method of fabrication that includes an epitaxial layer structure, passivation layers, and a graded composition dielectric layer to form a slanted gate field plate, which shapes the electric field and reduces leakage by optimizing the electric field distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lift-off metallization process is used to form gate metal field plate, then fabrication process is simplified, but unwanted metal layers remain causing electric field crowding and dielectric failure
Solution Approach 1:
The patent extracts and removes the problematic unwanted metal layers and haloes that remain after lift-off processing through additional etching steps. The method specifically targets and eliminates these residual metal structures that cause electric field crowding, while preserving the functional gate metal field plate structure.
Solution Approach 2:
The patent converts the harmful effect of residual metal layers into a beneficial process feature by using the same lift-off approach but adding controlled etching steps that selectively remove only the unwanted metal remnants. This transforms the previously harmful residual metal into a manageable intermediate state that can be cleanly eliminated.
2Reliability
If stepped or tapered field plates are used to shape electric field, then device breakdown voltage increases, but process complexity increases significantly
Solution Approach 1:
The patent segments the field plate formation into distinct functional zones: a gate metal field plate portion and a separate slanted field plate portion. This segmentation allows each portion to be optimized independently - the gate metal portion provides basic field shaping while the slanted portion (formed with graded composition dielectric) provides enhanced breakdown voltage without requiring complex multi-step patterning.
Solution Approach 2:
The patent applies local quality by creating a slanted field plate structure with specific geometric characteristics in the high-stress region near the drain, while maintaining a simpler gate metal field plate structure in other regions. The slanted portion is formed only where maximum electric field control is needed, using localized graded composition dielectric layers.
3Productivity
If gate metal field plate is used to reduce dynamic on-resistance, then device performance improves, but unwanted metal extrusions cause electric field crowding
Solution Approach 1:
The patent extracts and removes the harmful metal extrusions and haloes that accompany gate metal field plate formation through selective etching processes. These unwanted metal structures are eliminated while the functional gate metal field plate remains intact, preserving the low on-resistance benefit without the electric field crowding penalty.
Solution Approach 2:
The patent introduces an intermediary graded composition dielectric layer that mediates between the gate metal field plate and the underlying structures. This intermediary layer prevents metal extrusions from directly contacting sensitive regions, thereby eliminating electric field crowding while maintaining the field plate's beneficial low-resistance characteristics.
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 slanted gate field plate structure improves the Figure of Merit (FOM) by providing a lower and smoother Coss curve, enhancing the robustness and lifespan of the device while avoiding the issues of unwanted metal extrusions and electric field crowding.
Implementation Method 1
The thickness of the third passivation layer and the slant angle of the slanted gate field plate are configured to shape an electric field under the slanted gate field plate between the gate contact and the drain contact
Data Source
AI summary
A GaN semiconductor power transistor structure with a slanted gate field plate, and a method of fabrication are disclosed. The gate field plate comprises a gate metal field plate and slanted gate field plate structure formed using contact metal and/or interconnect metal. The slanted structure of the gate field plate is defined by etching of a dielectric layer having a graded composition, to form a slanted opening that is filled with conductive metal. The dielectric thickness under the gate field plate and the slant angle are configured to shape appropriately the electric field in the region between the gate and drain.