HEMT Gate Overhang and Tapered Cap for Breakdown Voltage
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Solution Overview
Problem
Semiconductor devices using nitride semiconductors face issues with current collapse, gate leakage, and breakdown voltage, which are not adequately addressed by existing technologies.
Innovation Solution
A field effect transistor design with a gate electrode that overhangs the drain electrode and a cap layer with a tapered side surface, where the angle between the substrate and the cap layer's side surface is between 15° and 90°, disperses the electric field and reduces peak electric field intensity, thereby improving breakdown voltage and reducing current collapse and gate leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional HEMT structure is used, then the device can operate with standard characteristics, but current collapse occurs and gate leakage increases while breakdown voltage is limited
Solution Approach 1:
The gate electrode is designed to overhang the drain electrode in the lateral dimension, creating a three-dimensional electric field distribution. This dimensional change allows the electric field to be dispersed not only vertically but also laterally, reducing peak field intensity at critical interfaces and improving breakdown characteristics while suppressing current collapse
Solution Approach 2:
The cap layer is designed with a tapered side surface instead of a vertical wall, creating a curved geometry. This curvature distributes the electric field more evenly across the interface between layers, reducing field concentration at sharp edges and corners, thereby lowering gate leakage and improving overall device reliability
2Ease of operation
If the gate electrode extends further to improve control, then gate control capability increases, but electric field concentration increases leading to higher gate leakage
Solution Approach 1:
The tapered cap layer geometry replaces sharp vertical edges with gradual curves, distributing the electric field generated by the extended gate electrode. This curvature effect allows the gate to maintain enhanced control capability while preventing field concentration that would otherwise cause increased gate leakage
3Ease of manufacture
If the cap layer has a vertical side surface, then manufacturing is simpler, but electric field concentration occurs at the interface leading to reduced breakdown voltage
Solution Approach 1:
The tapered side surface of the cap layer, while requiring slightly more complex manufacturing, creates a gradual transition in geometry that distributes electric field lines. This curvature prevents field concentration at sharp interfaces, significantly improving breakdown voltage to justify the additional fabrication steps
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 effectively suppresses current collapse, reduces gate leakage, and enhances breakdown voltage while maintaining low ON resistance, as demonstrated by leakage current reductions and improved transistor performance.
Implementation Method 1
the cap layer has a tapered side surface, the angle between a main surface of the substrate and a side surface of the cap layer being between 15° and 90°... disperses the electric field and reduces peak electric field intensity
Data Source
Figure 1
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AI summary
A high electron mobility transistor having a channel layer, electron supply layer, source electrode, and drain electrode is included so as to have a cap layer formed on the electron supply layer between the source and drain electrodes and having an inclined side surface, an insulating film having an opening portion on the upper surface of the cap layer and covering the side surface thereof, and a gate electrode is formed in the opening portion and extending, via the insulating film, over the side surface of the cap layer on the drain electrode side. The gate electrode having an overhang on the drain electrode side can reduce the peak electric field.