Ohmic Contact Geometry for Lower Resistance GaN HEMT Transistors
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Solution Overview
Problem
Conventional High Electron Mobility Transistors (HEMTs) face challenges with high ohmic contact resistance, which contributes to increased on-resistance, particularly in GaN HEMT devices, due to the adverse effect of straight edges of ohmic contacts adjacent to the channel region, leading to current crowding and elevated total contact resistance.
Innovation Solution
The introduction of ohmic contacts with interface regions featuring indentations or irregular shapes, such as teeth or jagged patterns, increases the interface length between the ohmic contacts and doped contact regions, reducing current crowding and total contact resistance by enhancing the periphery of the contact edge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If straight edges of ohmic contacts are used adjacent to the channel region, then the device structure is simple and easy to manufacture, but current crowding occurs leading to elevated total contact resistance
Solution Approach 1:
The patent applies curvature by replacing straight edges with curved or rounded contact edges. Specifically, the ohmic contacts are designed with rounded corners or curved perimeters adjacent to the channel region, which eliminates current crowding at sharp corners and reduces total contact resistance while maintaining manufacturing feasibility
Solution Approach 2:
The patent extends the contact interface from a simple linear edge to a two-dimensional interface region by creating an interface region with both length and width dimensions. This is achieved through rounded corners and curved edges that create a larger contact perimeter, effectively adding dimensional complexity to reduce resistance without significantly complicating manufacturing
2Speed
If the channel region dimensions are decreased to improve device performance, then higher frequency operation is enabled, but total contact resistance becomes more significant and degrades performance
Solution Approach 1:
As channel dimensions are scaled down for higher frequency operation, the rounded corner design becomes even more critical. The curved edges maintain larger effective contact areas relative to the smaller channel dimensions, ensuring that contact resistance does not become the dominant loss mechanism in miniaturized high-frequency devices
Solution Approach 2:
The patent incorporates the curved edge design and interface region formation as preliminary structural features before the device operates. This pre-engineered contact geometry ensures optimal current distribution is established from the outset, preventing contact resistance from degrading performance as the device is scaled for higher frequencies
Data Source
AI summary
A transistor includes a semiconductor layer and a channel region. The transistor further includes a first doped contact region in the semiconductor layer and adjacent the channel region. The transistor further includes a first ohmic contact including an interface region comprising a first interface length between the first ohmic contact and the first doped contact region larger than a length of the interface region.