3D Multipath Inductor with Cross-overs for RF Loss Reduction
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Solution Overview
Problem
In integrated circuits, on-chip inductors face challenges in achieving high quality factor (Q-factor) and self-resonance frequency (fSR) due to proximity and skin effect losses, which complicate the design of efficient transformers and inductors, especially in high-frequency radio frequency (RF) applications.
Innovation Solution
A three-dimensional multipath inductor structure with lateral and vertical cross-overs is designed, where turns on multiple layers are divided into segments with varying positions to equalize path lengths, reducing skin and proximity effect losses by employing lateral and vertical cross-overs and connecting segments in parallel to increase conductive area, thereby optimizing Q-factor and fSR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional single-layer inductor structures are used, then manufacturing is simple, but Q-factor is low due to proximity and skin effect losses
Solution Approach 1:
The patent transitions from conventional single-layer planar inductors to multi-layer three-dimensional inductor structures. By stacking multiple metal layers vertically and implementing lateral cross-overs within layers plus vertical cross-overs between layers, the design creates equal-length current paths that eliminate proximity and skin effect losses, achieving Q-factor greater than 10 at 2.4 GHz while maintaining manufacturability through standard CMOS processes.
Solution Approach 2:
The inductor structure is divided into multiple segments across different metal layers with lateral cross-overs creating multiple parallel current paths. Each layer is segmented into distinct path groups that are laterally separated and vertically stacked, allowing current to distribute across multiple equal-length paths rather than following a single spiral trajectory, thereby reducing resistive losses.
2Reliability
If turn-width is increased to reduce coil resistance, then Q-factor improves, but occupied chip area increases
Solution Approach 1:
The patent utilizes the vertical dimension by stacking multiple metal layers to increase the effective conductive cross-section without expanding the planar footprint. Current flows through multiple vertically-stacked paths connected by lateral and vertical cross-overs, effectively increasing the turn-width equivalent while maintaining a compact chip area, achieving Q-factor > 10 at 2.4 GHz with small occupied area.
Solution Approach 2:
Multiple metal layers are merged into a unified inductor structure through lateral cross-overs within layers and vertical cross-overs between layers. The parallel current paths across different layers are electrically combined to function as a single equivalent inductor with reduced resistance, achieving Q-factor improvement without requiring increased individual layer dimensions.
3Reliability
If multi-layer crisscross winding is used to reduce proximity effect, then Q-factor improves, but device complexity increases
Solution Approach 1:
The patent implements a systematic multi-layer architecture where current paths are organized into distinct lateral groups within each layer and connected through vertical cross-overs. This structured approach to three-dimensional routing achieves crisscross-like current distribution that reduces proximity effects, while the modular design with repeating lateral and vertical cross-over patterns maintains relative simplicity compared to conventional multi-layer crisscross windings.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The 3D multipath inductor structure achieves reduced DC resistance, higher inductance density, and improved Q-factor at lower frequencies, with simulations showing a 22% reduction in DC resistance and a 40% increase in Q-factor at 500 MHz, supporting enhanced performance in high-frequency applications.
Implementation Method 1
Skin effect is the tendency for high-frequency currents to flow on the surface of a conductor. Proximity effect is the tendency for current to flow in other undesirable patterns, e.g., loops or concentrated distributions, due to the presence of magnetic fields generated by nearby conductors.
Implementation Method 2
Proximity effect is the tendency for current to flow in other undesirable patterns, e.g., loops or concentrated distributions, due to the presence of magnetic fields generated by nearby conductors. In transformers and inductors, proximity effect losses typically dominate over skin effect losses.
Implementation Method 3
connecting segments in parallel to increase conductive area, thereby optimizing Q-factor and fSR
Data Source
AI summary
Fabrication methods for a 3D multipath inductor, including forming a metal layer to form spiral turns about a center region, the spiral turns including segments that extend length-wise along the turns and having positions that vary from an innermost position and an outermost position relative to the center region; forming a lateral cross-over configured to couple portions of lateral segments in different relative positions from the center region to form lateral segment paths that have a substantially same length for all lateral segment paths in a grouping thereof; forming an additional metal layer to form spiral turns about the center region including corresponding geometry to the first metal layer; and forming a vertical cross-over configured to couple portions of segments on different metal layers to form vertical segment paths that have a substantially same length for all vertical segment paths in a grouping thereof.