Multi-Cell RF Transistor Isolation Structure for Lower Gate Coupling
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Solution Overview
Problem
High-power, high-frequency transistors face challenges in maintaining performance due to mutual coupling between gate fingers, which degrades power handling capabilities and DC to RF power conversion efficiency when increasing the number of gate fingers or widening them.
Innovation Solution
The implementation of a multi-cell transistor design with increased physical spacing and isolation structures between groups of unit cell transistors, using metal pads and wall structures with conductive or lossy dielectric materials to reduce mutual coupling, allowing for more gate fingers without degrading performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of gate fingers is increased or their width is widened to enhance power handling capabilities, then the gate periphery increases and power handling capability improves, but mutual coupling between gate fingers increases and DC to RF power conversion efficiency degrades
Solution Approach 1:
The transistor structure is divided into multiple unit cells with gate fingers spaced apart and isolated from each other. This segmentation reduces mutual coupling between adjacent gate fingers, allowing increased gate periphery without proportional increase in mutual coupling effects, thereby maintaining DC to RF power conversion efficiency while enhancing power handling capability.
Solution Approach 2:
Dielectric materials are introduced as intermediary substances between adjacent gate fingers and between the gate fingers and drain region. These dielectric intermediaries reduce capacitive coupling and electromagnetic interference between gate fingers, enabling higher gate periphery while preserving power conversion efficiency.
2Power
If the number of gate fingers is increased or their width is widened to enhance power handling capabilities, then the gate periphery increases and power handling capability improves, but device performance degrades due to mutual coupling
Solution Approach 1:
The transistor is segmented into multiple isolated unit cells with gate fingers separated by dielectric materials. This segmentation allows each gate finger to operate more independently, reducing mutual coupling effects and maintaining device performance reliability even as gate periphery and power handling capability increase.
Solution Approach 2:
Dielectric intermediaries are placed between gate fingers and between gate fingers and drain region to reduce capacitive coupling and electromagnetic interference. This mediation preserves device performance and reliability while enabling increased gate periphery for higher power handling capability.
3Loss of energy
If physical spacing between unit cell transistors is increased to reduce mutual coupling, then DC to RF power conversion efficiency is maintained, but device area increases
Solution Approach 1:
Instead of increasing horizontal spacing between gate fingers, dielectric materials are introduced in the vertical dimension between gate fingers and between gate fingers and drain region. This dimensional approach reduces mutual coupling without significantly increasing device footprint, maintaining power conversion efficiency while controlling device area.
Solution Approach 2:
Dielectric intermediaries are introduced between adjacent gate fingers and between gate fingers and drain region, enabling reduced mutual coupling without requiring increased physical spacing. This mediation allows maintenance of power conversion efficiency while minimizing device area expansion.
Data Source
AI summary
A multi-cell transistor includes a semiconductor structure, a plurality of unit cell transistors that are electrically connected in parallel, each unit cell transistor extending in a first direction in the semiconductor structure, wherein the unit cell transistors are spaced apart from each other along a second direction, and an isolation structure that is positioned between a first group of the unit cell transistors and a second group of the unit cell transistors and that extends above the semiconductor structure.