GaN HEMT Threshold Voltage Control via Segmented Gate
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Solution Overview
Problem
Semiconductor devices, such as HEMTs, typically face a tradeoff between breakdown voltage and ON resistance, with silicon nearing its limits, necessitating the use of materials like GaN or SiC to reduce ON resistance, but these materials often result in normally-ON elements with negative threshold voltages, requiring a solution for achieving positive threshold voltages for normally-OFF operation and increased ON current.
Innovation Solution
A semiconductor device structure incorporating a first and second nitride semiconductor layer with a third nitride semiconductor layer featuring alternately laminated high- and low-dopant concentration layers, where the low-dopant concentration layer has a larger band gap than the high-dopant concentration layer, is used to increase the gate-on threshold voltage, enabling normally-off operation with high ON current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a HEMT structure with AlGaN/GaN heterojunction is used to achieve low ON resistance, then the ON resistance is reduced, but the threshold voltage becomes negative resulting in normally-ON operation
Solution Approach 1:
The gate electrode is divided into multiple segments (first gate electrode and second gate electrode) separated by a recess portion. This segmentation allows independent control of different gate regions, enabling the first gate to provide high voltage for low ON resistance while the second gate maintains positive threshold voltage for normally-OFF operation.
Solution Approach 2:
Different regions of the gate structure are assigned different functions: the first gate electrode region is optimized for reducing ON resistance through high voltage application, while the second gate electrode region is optimized for maintaining positive threshold voltage. The recess portion creates localized field control zones with different electrical characteristics.
2Ease of operation
If the threshold voltage is increased to achieve normally-OFF operation, then the device safety is improved, but the ON current capability is reduced
Solution Approach 1:
The segmented gate structure enables independent voltage control of different gate regions. The first gate can be biased at high voltage to maximize ON current when the device is conducting, while the second gate maintains the positive threshold voltage for normally-OFF operation, thus resolving the tradeoff between threshold voltage and ON current capability.
Solution Approach 2:
The gate voltages are dynamically controlled with different characteristics: the first gate voltage is optimized for high current conduction state, while the second gate voltage is optimized for threshold control and off-state stability. This dynamic differentiation allows the device to achieve both high ON current and positive threshold voltage.
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 described structure effectively increases the threshold voltage of HEMTs, allowing for normally-off operation while maintaining low ON resistance, by enhancing the potential of the channel layer and suppressing two-dimensional electron gas generation, thus achieving a high gate-on voltage without excessive power consumption or operation failures.
Implementation Method 1
electrons are generated by polarization in the HEMT a high concentration of electrons exist below a gate electrode
Data Source
AI summary
A semiconductor device includes a first and second nitride semiconductor layer. The second nitride semiconductor layer has a band gap larger the first nitride semiconductor layer. Source and drain electrodes are formed spaced from each other on the second nitride semiconductor layer. A third nitride semiconductor layer is formed on the second nitride semiconductor layer between the source and drain electrodes. A gate electrode is formed on the third nitride semiconductor layer. The third nitride semiconductor layer comprises at least two first layers and at least one a second layer which has a lower p-type dopant concentration than the first layer. The second layer also has a band gap larger than the first layer. The lowermost layer and the uppermost layer in the third nitride semiconductor layer stack are the first layers.