Stacked Spiral Inductor Structure for High-Frequency ICs
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Solution Overview
Problem
Integrated inductors in high-frequency integrated circuits face challenges in optimizing their quality factor due to substrate and metal losses, particularly because the metal layers in the crossover regions differ from those in the windings, restricting conductivity and increasing parasitic resistance.
Innovation Solution
A stacked structure for spiral inductors is introduced, utilizing multiple metal layers with specific segment connections and via configurations to create shunt windings and crossover regions, optimizing the quality factor by aligning metal layer thickness and layout for symmetry and improved conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the top metal layer is used as winding and the next metal layer as crossover region, then the inductor structure is simple, but the parasitic resistance increases and quality factor deteriorates
Solution Approach 1:
The patent transitions from a planar single-layer inductor structure to a three-dimensional stacked structure utilizing multiple metal layers. The inductor winding is formed across different metal layers (e.g., first metal layer and second metal layer) connected by vias, creating a vertical stacking arrangement that increases the effective winding area without increasing chip footprint, thereby reducing parasitic resistance and improving quality factor.
Solution Approach 2:
The patent merges the functions of multiple metal layers to form a unified inductor structure. The first and second metal layers are combined to create the inductor winding, with vias providing electrical connection between layers. This merging of multiple layers into a single functional inductor structure increases the effective conductor cross-section and reduces overall parasitic resistance.
2Reliability
If increasing widths of the winding is used to improve quality factor, then parasitic resistance decreases, but chip area increases
Solution Approach 1:
The patent exploits the vertical dimension by stacking metal layers to increase the effective winding area. Instead of expanding the inductor width in the planar direction (which would increase chip area), the design uses multiple metal layers stacked vertically, connected by vias, to increase the conductor cross-section and reduce parasitic resistance without increasing the horizontal chip footprint.
Solution Approach 2:
The patent implements a nested structure where the inductor winding is formed by nesting multiple metal layers vertically. The first metal layer contains portions of the winding, and the second metal layer contains additional winding portions, with vias connecting them. This nested vertical arrangement effectively increases the total winding area while maintaining a compact chip footprint.
3Reliability
If multiple metal layers in parallel are used, then series resistance decreases, but the crossover region conductivity cannot be optimized
Solution Approach 1:
The patent uses vertical stacking of metal layers to create parallel current paths for the inductor winding. The first and second metal layers are positioned at different vertical levels and connected by vias, forming a multi-layer parallel structure that reduces series resistance. Additionally, the crossover region is also implemented across multiple layers, allowing optimization of conductivity in both the winding and crossover regions simultaneously.
Data Source
AI summary
A stacked structure of a spiral inductor includes a first metal layer, a second metal layer, a first set of vias, and a second set of vias. The first metal layer includes a first segment, a second segment, and a third segment, wherein the layout direction of the third segment is different from the layout direction of the first and second segments. The second metal layer includes a fourth segment, a fifth segment, and a sixth segment connected to the fifth segment, wherein the layout direction of the sixth segment is different from the layout direction of the fourth and fifth segments. The first set of vias connects the first and fourth segments, and they construct a first shunt winding. The second set of vias connects the second and fifth segments, and they construct a second shunt winding. The third and sixth segments construct a crossover region.