RF-FET Comb-Shaped Electrodes for RF Performance
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Solution Overview
Problem
The challenge in manufacturing scaled-down channel length transistors for RF-FETs is maintaining acceptable parasitic capacitance and electro-migration while achieving improved RF characteristics, especially for large gate widths needed in RF products.
Innovation Solution
The design incorporates a comb-shaped gate, source, and drain electrodes with thin metal routing layers and a multi-level interconnect scheme where each thin metal layer is connected to the previous one with a specific retraction dimension, maximizing vias between layers to reduce electro-migration and balancing current density across fingers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If scaled-down channel length transistors are manufactured, then intrinsic RF characteristics are improved, but parasitic capacitance and electro-migration increase
Solution Approach 1:
The gate electrode is divided into multiple gate fingers arranged in parallel, which segments the current path and reduces current density in each individual finger. This segmentation allows the transistor to achieve large effective gate width while maintaining acceptable current density levels in each finger, thereby reducing electro-migration and parasitic capacitance effects.
Solution Approach 2:
The patent transitions from a planar single-layer electrode structure to a multi-level three-dimensional interconnect structure. By stacking multiple thin metal routing layers vertically and connecting them with vias, the design achieves large gate width in the horizontal plane while distributing current through multiple vertical layers, thereby reducing current density and electro-migration in each individual layer.
2Reliability
If large gate widths are used in RF products, then RF performance is improved, but electro-migration and parasitic capacitance worsen
Solution Approach 1:
The gate electrode is divided into multiple gate fingers arranged in parallel, which segments the current path and reduces current density in each individual finger. This segmentation allows the transistor to achieve large effective gate width while maintaining acceptable current density levels in each finger, thereby reducing electro-migration and parasitic capacitance effects.
Solution Approach 2:
The patent transitions from a planar single-layer electrode structure to a multi-level three-dimensional interconnect structure. By stacking multiple thin metal routing layers vertically and connecting them with vias, the design achieves large gate width in the horizontal plane while distributing current through multiple vertical layers, thereby reducing current density and electro-migration in each individual layer.
3Manufacturing precision
If thin metal routing layers are used, then manufacturing precision is improved, but electro-migration increases
Solution Approach 1:
The patent transitions from a planar single-layer electrode structure to a multi-level three-dimensional interconnect structure. By stacking multiple thin metal routing layers vertically and connecting them with vias, the design achieves large gate width in the horizontal plane while distributing current through multiple vertical layers, thereby reducing current density and electro-migration in each individual layer.
Solution Approach 2:
Multiple thin metal routing layers are combined vertically to form a stacked interconnect structure. By merging several layers with smaller individual current capacities into a unified multi-layer system, the total current capacity increases while each individual layer maintains thin dimensions for manufacturing precision, effectively distributing the electro-migration stress across multiple layers.
Data Source
AI summary
A Field Effect Transistor (FET) capable of operating at high frequencies and includes comb-shaped source and drain electrodes. The comb-shaped drain electrode includes a plurality of thin comb-shape drain electrode layers at corresponding levels of the FET, each comb-shaped drain electrode layer including a plurality of drain electrode fingers having substantially the same width as the comb-shaped drain electrodes of each other layer. The comb-shaped source electrode includes a plurality of comb-shape source electrode layers at the corresponding levels, each comb-shaped drain electrode layer including a plurality of drain electrode fingers having substantially the same width as the comb-shaped source electrodes of each other layer. In addition, the inter-level retraction of adjacent drain electrode layers is the same or substantially the same. Similarly, the inter-level retraction of adjacent source electrode layers is the same or substantially the same.