Slanted Gate Field Plate in GaN HEMTs for Leakage Control
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Solution Overview
Problem
Existing GaN semiconductor power transistors with gate metal field plates face challenges such as increased process complexity and compatibility issues with existing fabrication processes, leading to potential dielectric failure due to unwanted metal extrusions causing electric field crowding in high voltage applications.
Innovation Solution
A semiconductor device structure and fabrication method for GaN HEMTs featuring a slanted gate field plate, where a graded composition dielectric layer with a denser bottom and less dense top enables controlled etching to form a slanted gate metal field plate, optimizing electric field distribution and reducing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lift-off metallization process is used to form gate metal field plate, then device fabrication is simplified, but unwanted metal extrusions remain causing electric field crowding and dielectric failure
Solution Approach 1:
The patent removes the harmful metal extrusions and haloes from the device structure by replacing the lift-off process with a deposition and etch-back process. This extraction of the unwanted metal portions eliminates the source of electric field crowding while preserving the beneficial gate metal field plate function.
Solution Approach 2:
The patent converts the potential harm of metal extrusions into a benefit by using the etch-back process to selectively remove only the unwanted portions while retaining the functional metal field plate. The controlled etching transforms what would be a defect into a precision feature.
2Reliability
If stepped or tapered field plate structures are implemented, then device breakdown voltage increases, but process complexity increases significantly
Solution Approach 1:
The patent changes the geometric parameter of the gate metal field plate from a simple planar structure to a slanted structure with a specific angle (e.g., 45 degrees). This parameter change achieves the electric field shaping effect that increases breakdown voltage while being implemented through a relatively simple deposition and etch-back process rather than complex multi-step patterning.
Solution Approach 2:
The patent performs the metal deposition before the etch-back step, establishing the complete gate metal field plate structure first. This preliminary action allows the subsequent etch-back to precisely define the slanted profile without requiring complex real-time control during deposition.
3Productivity
If gate metal field plate is used to reduce dynamic on-resistance, then device performance improves, but unwanted metal haloes cause electric field crowding
Solution Approach 1:
The patent extracts and removes the harmful metal haloes and extrusions that surround the gate metal field plate by replacing the lift-off process with deposition followed by etch-back. This elimination of unwanted metal portions removes the source of electric field crowding while preserving the functional gate metal field plate that reduces dynamic on-resistance.
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 electric field distribution, resulting in a lower and smoother Coss curve, enhancing the Figure of Merit (FOM) and increasing the robustness and lifespan of the device.
Implementation Method 1
a third dielectric layer having a graded composition wherein a bottom of the third dielectric layer has a denser composition than a top layer of the third dielectric layer
Implementation Method 2
The composition of the third dielectric layer is varied from the bottom to the top to control the etch rate and forms tapered sidewalls
Implementation Method 3
a field plate may be used to engineer or shape the electric field between electrodes, e.g. in the region around the gate and between the gate and the drain
Data Source
Figure 1
Figure 2A~2C
Figure 2D~2F
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.