Stacked 8-Shaped Inductor Layout for Low Parasitic Capacitance
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Solution Overview
Problem
Existing integrated circuits for inductor and transformer devices face limitations due to high parasitic capacitance and lower quality factor values, particularly in symmetrical structure designs, which restrict their application scope.
Innovation Solution
A novel 8-shaped inductor design with a stack configuration where two coils are partially overlapped without interlacing, allowing for a central symmetrical structure and reduced parasitic capacitance, utilizing a non-interlaced junction to enhance quality factor and symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spiral inductor is used to achieve higher quality factor value and mutual inductance value, then the quality factor is improved, but it is hard to be designed into a symmetrical structure
Solution Approach 1:
The inductor is divided into two separate coils (first coil and second coil) that are stacked vertically on different metal layers. Each coil is designed as an 8-shaped structure with two arms, and the coils are connected through vertical connections at junctions. This segmentation allows each coil to maintain symmetry independently while achieving high quality factor through the stacked configuration.
Solution Approach 2:
The patent transitions from a planar spiral inductor design to a three-dimensional stacked structure by placing coils on different metal layers (e.g., third metal layer and fourth metal layer). This dimensional change enables symmetrical arm configurations in each layer while maintaining high mutual inductance through vertical stacking, resolving the contradiction between symmetry and quality factor.
2Shape
If a stacked transformer with interlacing structure is used to achieve better symmetry, then symmetry is improved, but it needs more area and metal layers and causes more parasitic capacitance
Solution Approach 1:
The patent combines multiple functions into the 8-shaped coil structure: the same coil arms serve both as inductive elements and as symmetrical counterparts. The first and second coils are stacked directly on top of each other, merging the functions of multiple layers into a compact vertical arrangement. This reduces the horizontal area required compared to conventional interlacing structures that require separate winding regions.
Solution Approach 2:
The 8-shaped coils are designed with nested arms where the first arm and second arm of each coil are positioned to overlap or nest together in the planar view. This nesting arrangement achieves symmetry without requiring additional area, as the symmetrical arms share the same spatial footprint when viewed from above, reducing the overall device area.
3Shape
If coils are connected with metal layer with lower conductivity and stacked vertically, then symmetry and compactness are improved, but it causes more parasitic capacitance and lowers quality factor
Solution Approach 1:
The patent applies different design qualities to different parts of the structure: the coil arms use high-conductivity metal layers for maximum inductance and quality factor, while the vertical connections at junctions use through-silicon vias or contact holes to bridge layers. The junction areas are minimized and strategically positioned to reduce parasitic capacitance. This local differentiation allows the majority of the coil structure to maintain high conductivity while achieving vertical stacking for symmetry.
Data Source
AI summary
An integrated circuit includes a first coil and a second coil. The first coil is disposed on the first side of the integrated circuit. The second coil is disposed on the second side of the integrated circuit, and is partially overlapped with the first coil at a junction. The first coil is not interlaced with the second coil at the junction.