Reverse HEMT Intermediate Layer Reduces Access Resistance
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Solution Overview
Problem
Reverse HEMTs face a trade-off between gate leak current and access resistance, where reducing gate leak current increases access resistance, and vice versa, due to the direct contact of the gate electrode with the channel layer without a barrier layer, complicating the electrode formation process.
Innovation Solution
A reverse HEMT design with an intermediate semiconductor layer doped at a higher impurity concentration than the channel layer, extending from beneath the source and drain electrodes to the gate electrode, which reduces contact and access resistance without increasing the gate leak current, by interposing the intermediate layer between the non-rectifying electrodes and the channel layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate electrode is placed in direct contact with the channel layer without a barrier layer, then the access resistance is reduced, but the gate leak current increases
Solution Approach 1:
An intermediate layer is introduced between the gate electrode and the channel layer. This intermediate layer serves as a mediator that allows the gate electrode to contact the channel layer while preventing direct contact that would cause excessive gate leak current, thus resolving the contradiction between reducing access resistance and preventing gate leak current.
Solution Approach 2:
The intermediate layer is positioned specifically at the gate electrode contact region, creating local differentiation in the structure. This local modification allows the gate area to have different electrical properties compared to the source/drain regions, enabling reduced gate leak current while maintaining low access resistance through the barrier layer in other areas.
2Object-generated harmful factors
If a barrier layer is placed between the gate electrode and the channel layer, then the gate leak current is reduced, but the access resistance increases
Solution Approach 1:
The barrier layer is segmented into two distinct parts: a first barrier layer between the source/drain electrodes and the channel layer, and a second barrier layer (intermediate layer) between the gate electrode and the channel layer. This segmentation allows each barrier layer to be optimized independently - the first barrier layer minimizes access resistance while the second barrier layer minimizes gate leak current.
Solution Approach 2:
The barrier layers are designed with different parameters - the first barrier layer has specific thickness and composition optimized for low access resistance, while the second intermediate layer has different thickness and composition optimized for low gate leak current. By changing the parameters of different barrier layers, both contradictory requirements are satisfied simultaneously.
3Object-generated harmful factors
If additional layers are added to reduce gate leak current, then the gate leak current is reduced, but the process complexity increases
Solution Approach 1:
The intermediate layer is formed by merging the barrier layer formation process with the existing semiconductor layer fabrication process. By growing the intermediate layer as part of the epitaxial growth sequence along with the channel layer and other semiconductor layers, the process complexity is minimized while still achieving the function of reducing gate leak current.
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 intermediate layer effectively reduces contact and access resistance while maintaining a low gate leak current, simplifying the electrode formation process and improving the transistor's performance across various frequency ranges.
Implementation Method 1
The barrier layer and the GaN channel layer induce a two dimensional electron gas (2DEG) in an interface therebetween, exactly, in the GaN channel layer adjacent to the interface against the barrier layer
Implementation Method 2
The intermediate semiconductor layer, which is provided on the channel layer, is made of nitride semiconductor material and has an N-polar surface in a side opposite to the channel layer. The intermediate semiconductor layer is doped with impurities by a concentration greater than a concentration of impurities in the channel layer
Data Source
AI summary
A high electron mobility transistor (HEMT) made of primarily nitride semiconductor materials is disclosed. The HEMT, which is a type of reverse HEMT, includes, on a C-polar surface of a SiC substrate, a barrier layer and a channel layer each having N-polar surfaces in respective top surfaces thereof. The HEMT further includes an intermediate layer highly doped with impurities and a Schottky barrier layer on the channel layer. The Schottky barrier layer and a portion of the intermediate layer are removed in portions beneath non-rectifying electrodes but a gate electrode is provided on the Schottky barrier layer.