Transistor Contact Structure With Thin Gold for High-Current RF Operation
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Solution Overview
Problem
High-cost metals like gold are used extensively in semiconductor transistors, particularly in RF amplifiers, increasing the cost of communication equipment due to high current densities and thermal activity, and there is a need for cost-effective solutions that maintain high power and frequency performance.
Innovation Solution
A semiconductor transistor structure with thinner metal contacts and interface layers formed from a more conductive material than traditional ohmic metal, reducing the thickness of gold usage while maintaining conductivity, and integrating a field plate metal structure to support high power and frequency operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If thick layers of gold and gold alloys are used to conduct high current densities in metal contacts and interconnect layers, then the transistor can handle high power and frequency operations, but the cost of the semiconductor device increases significantly
Solution Approach 1:
The patent divides the metal contact structure into multiple functional layers: a thin gold layer (50-200 nm) for conductivity, an aluminum layer (500 nm - 2 μm) for current handling, and a tungsten layer for mechanical support. This segmentation allows each layer to perform its specific function efficiently, reducing the need for thick expensive gold while maintaining high power capability
Solution Approach 2:
The patent employs composite material structures in multiple places: (1) composite metal contacts combining gold, aluminum, and tungsten layers; (2) AlGaN barrier layer combined with GaN channel layer; (3) silicon dioxide insulator combined with metal layers. These composite structures achieve superior performance that cannot be obtained with single materials, allowing cost reduction while maintaining high power operation
2Reliability
If multiple layers of metal contacts and interconnect layers are deposited to handle high current densities, then the electrical conductivity is improved, but the manufacturing complexity and cost increase
Solution Approach 1:
The metal contact system is segmented into distinct layers with specific functions: gold layer for initial conductivity and adhesion, aluminum layer for bulk current conduction, and tungsten layer for mechanical stability. This segmentation makes the complex structure manageable through standardized fabrication processes and allows optimization of each layer independently
Solution Approach 2:
The patent optimizes the thickness parameters of each metal layer to achieve the desired electrical conductivity. By carefully controlling the thickness of the gold layer (50-200 nm) and aluminum layer (500 nm - 2 μm), the system achieves high conductivity without requiring excessive material or complex multi-layer structures
3Power
If the thickness of metal contacts is increased to handle high current densities, then the current handling capability is improved, but the amount of expensive gold used increases
Solution Approach 1:
The current handling function is segmented across multiple layers: the thin gold layer (50-200 nm) provides surface conductivity and adhesion, while the thicker aluminum layer (500 nm - 2 μm) provides the bulk current conduction path. This segmentation allows the expensive gold to be used minimally while the cheaper aluminum handles the majority of the current
Solution Approach 2:
The patent replaces thick expensive gold layers with thinner gold combined with aluminum layers that can be deposited more cheaply. The aluminum layer serves as a cost-effective alternative for bulk current conduction, significantly reducing gold consumption while maintaining current handling capability
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 solution reduces the cost of semiconductor transistors by minimizing expensive metal usage while maintaining performance, particularly in RF amplifiers, benefiting cost-sensitive consumer devices and reducing the expense of communication equipment.
Implementation Method 1
metals with very high conductivity, such as gold and alloys of gold, are used... The interface layers and metal contacts together support the current densities required for high power and/or high frequency operation
Data Source
AI summary
Cost reduction of semiconductor transistors is achieved by reduction in the amount of expensive metal, such as gold, used to form metal contacts and conductive paths in integrated circuits. A semiconductor transistor structure is formed, and ohmic source and drain terminals formed thereon. A gate terminal is formed over an insulating layer in the active area between the source and drain terminals. A field plate is formed at least partially over the gate terminal. Interface layers are deposited over the source and drain terminals, using the field plate metal structure, such as in the same processing step as field plate deposition. Metal contacts are then deposited over the interface layers. The metal contacts are considerably thinner than required in the prior art to support high current densities. Because gold is often used in the metal contacts, their smaller size reduces costs by requiring less gold to achieve the same performance.