Multi-Channel HEMT With Stepped Electrodes
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Solution Overview
Problem
High electron mobility transistors (HEMTs) face challenges with resistivity and strain issues due to varying aluminum content in AlGaN barrier layers, which can lead to wafer breakage and inverse piezo-electric effects, and obtaining a good ohmic contact is difficult, especially with high Al content.
Innovation Solution
The design incorporates a HEMT with two channel layers, where the lower channel layer has a lower aluminum content and the upper channel layer has a higher aluminum content, allowing for a significant difference in pinch-off voltages, enabling independent control of current flow between the layers, and uses stepped source and drain electrodes to reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the aluminum content in the AlGaN barrier layer is increased to reduce resistivity, then the resistivity becomes lower, but the strain increases leading to wafer breakage and inverse piezo-electric effects
Solution Approach 1:
The device is divided into multiple channel layers (first channel layer, second channel layer, third channel layer) with different aluminum content barrier layers. This segmentation allows each layer to have optimized aluminum content for its specific function, reducing overall strain while maintaining low resistivity in critical regions.
Solution Approach 2:
Different aluminum content barrier layers are used in different regions: the first and third barrier layers have lower aluminum content (reducing strain), while the second barrier layer has higher aluminum content (reducing resistivity). This local quality approach optimizes both strain and resistivity in their respective regions.
2Device complexity
If a single channel layer is used, then the device structure is simpler, but the ability to independently control current flow in different regions is limited
Solution Approach 1:
The channel region is segmented into three distinct channel layers, each with different aluminum content barrier layers. This enables independent control of current flow in each layer through selective gating, providing superior adaptability for multi-mode operation while maintaining a relatively simple overall structure.
Solution Approach 2:
The multiple channel layers enable dynamic control of current flow characteristics. By applying different gate voltages to each layer, the device can dynamically switch between different operating modes (e.g., single-channel mode, dual-channel mode, or all channels active), enhancing versatility without excessive complexity.
3Strength
If AlN spacer is used to reduce strain, then the strain is reduced, but obtaining a good ohmic contact becomes difficult
Solution Approach 1:
Instead of using AlN spacer throughout, the invention uses lower aluminum content barrier layers (which are more conducive to ohmic contact) in the first and third positions, while using higher aluminum content (better for strain reduction) in the second position. This local quality approach maintains good ohmic contact interfaces while still reducing strain.
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
This configuration allows for effective control of current flow in HEMTs by ensuring that current for one channel layer can be turned off or on without significantly affecting the adjacent layer, achieving lower contact resistance and higher reliability.
Implementation Method 1
High electron mobility transistors (HEMTs) can have a two dimensional electron gas (2DEG) with a relatively low resistivity, and such resistivity can be affected by the amount of aluminum within and AlGaN barrier layer.
Implementation Method 2
when the Al content is too high, more strain can result, thus increasing the risk of wafer breakage and inverse piezo-electric effect.
Data Source
AI summary
An electronic device can include a HEMT including at least two channel layers. In an embodiment, a lower semiconductor layer overlies a lower channel layer, wherein the lower semiconductor layer has an aluminum content that is at least 10% of a total metal content of the lower semiconductor layer. An upper semiconductor layer overlies the upper channel layer, wherein the upper semiconductor layer has an aluminum content that is greater as compared to the lower semiconductor layer. In another embodiment, an electronic device can include stepped source and drain electrodes, so that lower contact resistance can be achieved. In a further embodiment, an absolute value of a difference between pinch-off or threshold voltages between different channel layers is greater than 1 V and allows current to be turned on or turned off for a channel layer without affecting another channel layer.