Step-Wise Field Plate Structure for GaN Breakdown Voltage Control
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Solution Overview
Problem
Existing gallium nitride (GaN)-based devices have unsatisfactory breakdown voltage and threshold voltage performance, necessitating a structure and method for enhancement.
Innovation Solution
A semiconductor structure with a gallium nitride (GaN) layer and an aluminum gallium nitride (AlGaN) layer, a gate stack with junction isolation features, and a field plate with a step-wise structure to redistribute electric fields, reduce surface fields, and increase breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional GaN-based device structure is used, then the device can be manufactured with standard processes, but the breakdown voltage and threshold voltage performance are unsatisfactory
Solution Approach 1:
The device is segmented into distinct functional regions including a first region with higher aluminum composition and a second region with lower aluminum composition in the AlGaN barrier layer. This segmentation allows each region to be optimized for specific functions: the first region provides higher breakdown voltage while the second region maintains good electron mobility and threshold voltage control.
Solution Approach 2:
Different regions of the device are given different local properties through varying aluminum composition gradients. The first region has higher aluminum content (0.6-0.8) for enhanced breakdown voltage, while the second region has lower aluminum content (0.2-0.4) for maintaining electron mobility. This local quality variation resolves the contradiction between achieving high breakdown voltage and maintaining overall device performance.
2Reliability
If the aluminum composition in the AlGaN barrier layer is increased to improve breakdown voltage, then breakdown voltage increases, but electron mobility decreases
Solution Approach 1:
The AlGaN barrier layer is divided into multiple segments with different aluminum compositions. The first segment (closer to the AlGaN/GaN interface) has higher aluminum composition (0.6-0.8) to provide strong electric field control and high breakdown voltage. The second segment (farther from the interface) has lower aluminum composition (0.2-0.4) to maintain high electron mobility in the channel region. This segmentation resolves the trade-off between breakdown voltage and electron mobility.
Solution Approach 2:
The aluminum composition is locally optimized at different positions within the barrier layer. Higher aluminum content is placed where it provides maximum benefit for breakdown voltage (near the interface), while lower aluminum content is placed where it preserves electron mobility (in the channel transport region). This spatial variation of material quality simultaneously achieves both high breakdown voltage and high electron mobility.
3Ease of manufacture
If a simple field plate structure is used, then manufacturing is easier, but the electric field distribution is not optimized and surface fields remain high
Solution Approach 1:
The field plate structure extends in multiple dimensions with different projection areas at different heights. The first field plate portion has a larger projection area than the second field plate portion, creating a stepped configuration. This dimensional variation allows the field plate to provide enhanced electric field control and surface field reduction while maintaining manufacturability through standard deposition and etching processes.
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 structure effectively enhances breakdown voltage, improves device switching speed, and stabilizes threshold voltage, leading to improved performance parameters such as Qgd, Ron*sp*Cgd, and reduced gate leakage current.
Implementation Method 1
a field plate with a step-wise structure to redistribute electric fields, reduce surface fields, and increase breakdown voltage
Data Source
AI summary
The present disclosure provides a semiconductor structure. The semiconductor structure includes a gallium nitride (GaN) layer on a substrate; an aluminum gallium nitride (AlGaN) layer disposed on the GaN layer; a gate stack disposed on the AlGaN layer; a source feature and a drain feature disposed on the AlGaN layer and interposed by the gate stack; a dielectric material layer is disposed on the gate stack; and a field plate disposed on the dielectric material layer and electrically connected to the source feature, wherein the field plate includes a step-wise structure.