Patterned Deep Trench Isolation for Low-Loss RF Passive Devices
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Solution Overview
Problem
Conventional deep trench isolation techniques in semiconductor integrated circuits lead to undesirable capacitive coupling and current leakage due to highly-doped regions forming conductive paths under large passive devices like inductors and transmission lines, causing RF signal attenuation.
Innovation Solution
Patterned deep trench isolation with disjoint trenches and alternating doped regions to disrupt eddy currents, using insulating materials and selective doping to minimize conductive loops and reduce resistive losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional deep trench isolation with interconnected trenches is used, then thermal expansion mismatch is managed, but eddy currents form under passive devices causing RF signal attenuation
Solution Approach 1:
The patent segments the continuous trench pattern into disjoint, isolated trenches. Instead of interconnected trenches forming a lattice, the isolation trenches are separated from each other, which breaks the conductive paths that would otherwise form eddy currents under passive devices. This segmentation maintains thermal expansion management while eliminating the harmful current loops.
Solution Approach 2:
The patent applies different properties to different regions: under passive devices, disjoint trenches are used to prevent eddy currents, while in other regions, conventional interconnected trenches may be used for standard isolation. The doped body portion is selectively positioned to provide local electrical properties that prevent current leakage only where needed beneath passive devices.
2Reliability
If highly-doped regions are formed around trenches to prevent charge accumulation, then charge trapping is reduced, but conductive paths form enabling eddy currents
Solution Approach 1:
By segmenting the trench structure into disjoint, isolated trenches rather than continuous interconnected trenches, the patent prevents the formation of closed conductive loops. Even with highly-doped regions present to prevent charge accumulation, the segmented structure breaks potential eddy current paths, eliminating the harmful effect while preserving the beneficial charge management.
Solution Approach 2:
The insulating material lining the trenches acts as an intermediary that prevents direct conductive contact between the highly-doped regions and the substrate beneath passive devices. This intermediary layer allows the highly-doped regions to prevent charge accumulation at trench interfaces while blocking the formation of conductive eddy current paths through the substrate.
3Reliability
If lattice-like interconnected trench patterns are used, then complete substrate isolation is achieved, but current leakage occurs under large passive devices
Solution Approach 1:
The patent transitions from a continuous lattice-like interconnected trench pattern to segmented, disjoint trenches. This segmentation maintains the isolation function by preventing current leakage paths, while specifically addressing the problem under large passive devices where interconnected trenches would create eddy current loops. The disjoint trenches provide isolation without forming closed conductive paths.
Data Source
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AI summary
An electronic device and related method of fabricating such a device includes an electrically-conductive passive device (e.g., an inductor or transmission line) fabricated above an upper surface of a semiconductor substrate that has a body portion disposed between the upper surface and a lower surface of the substrate. The body portion is doped n-type or p-type and the passive device is separated from the upper surface by one or more layers of electrically insulating material. The substrate includes a set of electrically-insulating isolation trenches disposed beneath the passive device that extend from the upper surface of the substrate toward the lower surface of the substrate and the isolation trenches are disjoint from each other.