Embedded Inductor Design for Eddy Current Reduction
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Solution Overview
Problem
Conventional on-chip spiral inductors suffer from low Q-factor at high frequencies due to magnetic coupling with the silicon substrate, leading to eddy currents and restrictive placement limitations, which are not adequately addressed by existing techniques such as higher substrate resistance or larger inductor-substrate distances.
Innovation Solution
The development of horizontal inductors formed using alternating metal and via layers, where the magnetic field is aligned parallel to the substrate plane, reducing eddy currents and allowing for flexible placement of devices underneath, while maintaining a smaller footprint and lower series resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planar spiral inductors are used, then inductance is achieved, but magnetic coupling with substrate causes eddy currents and low Q-factor
Solution Approach 1:
The patent transitions from a conventional planar spiral inductor configuration to a three-dimensional stacked inductor structure utilizing multiple metal layers and via contacts. This vertical stacking approach changes the geometric dimensionality, allowing magnetic flux to be directed vertically through the substrate rather than horizontally within a single plane, thereby reducing eddy current losses in the substrate and improving Q-factor.
Solution Approach 2:
The patent employs composite conductive structures formed by combining multiple metal layers with via contacts to create stacked inductor configurations. These composite structures enable optimized magnetic field distribution and reduced substrate coupling by distributing the inductive function across multiple conductive layers and materials, thereby minimizing eddy current effects.
2Reliability
If larger inductor to substrate distance is used, then magnetic coupling is reduced, but semiconductor area increases
Solution Approach 1:
Instead of increasing horizontal distance between inductor and substrate, the patent utilizes the vertical dimension by stacking metal layers and via contacts to create a three-dimensional inductor structure. This allows the magnetic flux to be directed vertically through the substrate, achieving reduced magnetic coupling without increasing the horizontal footprint on the semiconductor chip.
3Reliability
If conventional placement restrictions are applied, then device behavior is maintained, but semiconductor area increases
Solution Approach 1:
The patent's vertical stacking configuration directs magnetic flux vertically through the substrate, which minimizes interference with devices placed in the horizontal plane beneath the inductor. This dimensional change allows devices to be placed directly underneath the inductor structure without suffering from adverse magnetic field effects, thereby improving area utilization while maintaining device behavior.
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
This approach significantly reduces eddy current losses, enhances Q-factor at high frequencies, and allows for more flexible device placement without increasing semiconductor area, thereby improving inductor performance and integration efficiency.
Implementation Method 1
inductors generate magnetic fields
Implementation Method 2
The magnetic coupling of the magnetic flux generated by an inductor with such substrate promotes eddy currents, which may lead to a low gain ('Q-factor') at high frequencies
Data Source
AI summary
An embedded inductor and a method for forming an inductor are described. Spaced apart first stripes are formed substantially parallel with respect to one another as part of a first metal layer. First contacts, second contacts, and third contacts in respective combination provide at least portions of posts. Spaced apart second stripes substantially parallel with respect to one another and to the first stripes are formed as part of a second metal layer located between the first metal layer and the second metal layer. The first stripes, the posts, and the second stripes in combination provide turns of a coil.