GaN HEMT Field Plate and P-Type Layer for Normally-Off Operation
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Solution Overview
Problem
High electron mobility transistors (HEMTs) face challenges in achieving a normally-off operation and efficient electric field distribution due to the limitations of conventional heterojunctions, particularly with AlGaN and GaN materials, which affect the breakdown voltage and device reliability.
Innovation Solution
A semiconductor device design incorporating a p-type doped layer, a gate electrode, and a field plate with a field dispersion portion, where the passivation layer thickness varies to effectively disperse the electric field, ensuring a normally-off operation and enhanced breakdown voltage by strategically positioning the field plate between the gate and drain electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional heterojunction structure with AlGaN and GaN is used, then high electron mobility is achieved, but normally-off operation cannot be achieved and breakdown voltage is limited
Solution Approach 1:
The device is segmented into multiple functional regions: a first region with higher Al content in the AlGaN barrier layer forming a 2DEG channel for high electron mobility, and a second region with lower Al content forming a high-resistance region that enables normally-off operation. This spatial segmentation allows each region to fulfill its specific function while working together to achieve both high breakdown voltage and normally-off characteristics
Solution Approach 2:
Different regions of the AlGaN barrier layer are assigned different local qualities through varying aluminum content. The first region has high Al content (30-50%) to create strong band offset and high electron mobility, while the second region has low Al content (5-20%) to provide high resistance and enable off-state operation. This local quality variation resolves the contradiction between achieving high mobility and enabling normally-off operation
2Reliability
If the passivation layer thickness is uniform, then manufacturing is simplified, but electric field distribution is not optimized and breakdown voltage is limited
Solution Approach 1:
The passivation layer is designed with non-uniform thickness, having a first thickness over the first region and a second thickness over the second region. This local quality variation in thickness optimizes the electric field distribution, with the thinner region allowing better field control and the thicker region providing enhanced insulation, thereby increasing breakdown voltage while maintaining manufacturing feasibility through standard deposition techniques
Solution Approach 2:
The solution moves from a one-dimensional uniform thickness parameter to a two-dimensional thickness profile by varying the passivation layer thickness across different regions. This dimensional change allows optimization of electric field distribution in the vertical dimension while maintaining horizontal coverage, achieving higher breakdown voltage without fundamentally complicating the manufacturing process
3Reliability
If a field plate is added to improve electric field distribution, then breakdown voltage increases, but device complexity increases
Solution Approach 1:
The field plate function is merged with the existing gate electrode structure. The gate electrode extends over both the first region and the second region, combining the gate control function with the field plate function. This integration achieves improved electric field distribution and higher breakdown voltage without adding separate field plate structures, thereby avoiding increased device 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 design achieves a normally-off operation and improved electric field distribution, leading to increased breakdown voltage and device reliability by effectively shifting the electric field, thus addressing the limitations of conventional HEMTs.
Implementation Method 1
a p-type doped layer, disposed on the active layer and between the source electrode and the drain electrode
Implementation Method 2
The field plate includes a field dispersion portion disposed between the gate electrode and the drain electrode. The first passivation layer has a second thickness between the field dispersion portion and the active layer. The second thickness is smaller than the first thickness.
Data Source
AI summary
A semiconductor device includes a substrate, an active layer, a source electrode, a drain electrode, a p-type doped layer, a gate electrode, a passivation layer, and a field plate. The active layer is disposed on the substrate. The source electrode, the drain electrode and the p-type doped layer are disposed on the active layer. The p-type doped layer is disposed between the source electrode and the drain electrode, and has a first thickness. The gate electrode is disposed on the p-type doped layer. The passivation layer covers the gate electrode and the active layer. The field plate is disposed on the passivation layer and is electrically connected to the source electrode. The field plate includes a field dispersion portion disposed between the gate electrode and the drain electrode. The passivation layer between the field dispersion portion and the active layer has a second thickness smaller than the first thickness.