GaN HEMT Stepped Through-Hole Contacts for Lower Ohmic Resistance
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Solution Overview
Problem
Current GaN-based high electron mobility transistors (HEMTs) face challenges in achieving low ohmic contact resistance, which affects their performance and reliability in high-frequency and high-temperature applications, particularly in reducing series resistance and improving amplification capability and efficiency.
Innovation Solution
The design includes a GaN-based HEMT with through holes in the AlGaN barrier layer having a stepped structure, allowing for a multi-step contact between the ohmic metal and the barrier layer, reducing ohmic contact resistance, and using a Ti/Al/Ni/Au metal system for improved ohmic contact formation, along with a nucleation and buffer layer stack for stress reduction and epitaxial growth optimization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional ohmic contact structure is used, then the device structure is simple, but the ohmic contact resistance is high
Solution Approach 1:
The patent transforms the conventional planar ohmic contact into a three-dimensional stepped contact structure by etching through-holes through the AlGaN barrier layer and forming metal contacts that extend through multiple depth levels. This dimensional transformation increases the contact area with the GaN channel layer while maintaining structural feasibility, thereby reducing ohmic contact resistance without excessive complexity increase
Solution Approach 2:
The contact structure is divided into multiple stepped levels within the through-hole, creating sequential contact interfaces at different depths. Each step provides an additional contact area with the GaN channel layer, and the segmented structure allows optimized metal layer deposition (Ti/Al/Ni/Au system) at each level to progressively reduce contact resistance
2Reliability
If the contact area is increased, then the ohmic contact resistance is reduced, but the barrier shape is affected and tunneling current formation becomes more complex
Solution Approach 1:
The stepped contact structure concentrates the increased contact area locally at specific depth levels within the through-hole, rather than uniformly distributing it. Each step creates a localized contact region with optimized geometry, allowing the barrier shape to be maintained in non-contact regions while achieving enhanced contact properties where needed
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 effectively reduces ohmic contact resistance, enhances the performance of the GaN-based HEMT, enabling improved power amplification and switching efficiency in radio frequency and millimeter-wave applications, and is suitable for use in power amplifiers and switches.
Implementation Method 1
increasing a possibility of forming a tunneling current, reducing an ohmic contact resistance
Data Source
AI summary
The technology of this application relates to a high electron mobility transistor, including a substrate and a GaN channel layer and an AlGaN barrier layer that are sequentially stacked on the substrate. Two through holes that are spaced apart from each other are opened in the AlGaN barrier layer. Each of the through holes penetrates the AlGaN barrier layer along a thickness direction of the AlGaN barrier layer, and a hole wall of each of the through holes has at least one stepped structure. Each of the through holes has an upper opening away from the substrate and a lower opening close to the substrate. The high electron mobility transistor further includes a source and a drain, where the source and the drain each fill up a through hole and are directly in contact with and connected to the GaN channel layer.