Embedded Inductor Trenches Block Eddy Currents
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Solution Overview
Problem
Integrated circuits with embedded inductor coils and transformers suffer from low quality factor (Q) due to parasitic eddy currents induced in the silicon substrate, leading to reduced power transfer efficiency and limited frequency of operation.
Innovation Solution
The implementation of trenches filled with a replacement dielectric in the semiconductor substrate underlying the embedded inductor coils and transformers, which blocks the path of eddy currents and improves the quality factor by reducing parasitic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If embedded inductor coils are used in RFICs, then the circuits can operate at radio frequencies, but the quality factor is reduced due to parasitic eddy currents in the silicon substrate
Solution Approach 1:
The continuous silicon substrate beneath the inductor coil is segmented by introducing trenches that divide it into separate regions. These trenches are filled with dielectric material to create electrically isolated zones, thereby blocking the path of parasitic eddy currents and reducing energy losses while maintaining the inductor's operational functionality.
Solution Approach 2:
Dielectric material is introduced as an intermediary substance filling the trenches in the silicon substrate. This dielectric layer acts as a mediator that blocks the flow of parasitic eddy currents between different regions of the substrate, thereby reducing energy losses without interfering with the magnetic field generation by the inductor coil.
2Ease of manufacture
If the silicon substrate is conductive, then it provides good electrical connection, but it induces parasitic eddy currents that reduce power transfer efficiency
Solution Approach 1:
The conductive silicon substrate is segmented into isolated regions by etching trenches and filling them with dielectric material. This segmentation maintains the inherent conductivity of the silicon regions for electrical connections while preventing the formation of continuous eddy current paths, thereby reducing power losses.
Solution Approach 2:
The harmful conductive paths in the silicon substrate are extracted by removing silicon material to form trenches. These removed regions are then filled with non-conductive dielectric material, effectively taking out the problematic eddy current pathways while preserving the necessary electrical connectivity in the remaining silicon regions.
3Quantity of substance
If the embedded inductor coil size is increased, then the inductance value increases, but the parasitic eddy current losses increase proportionally
Solution Approach 1:
The substrate beneath larger inductor coils is divided into multiple isolated regions by trenches filled with dielectric material. This segmentation allows the inductor to maintain a larger size for higher inductance while the trenches prevent the proportional increase in parasitic losses by blocking eddy current paths that would otherwise scale with coil size.
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 enhances the quality factor of the coils, leading to improved power transfer efficiency and increased operational frequency in RF circuits.
Implementation Method 1
The time varying magnetic field induces an electric field (E) in the substrate. The electric field induces a parasitic eddy current in the substrate.
Implementation Method 2
When current flows through the windings of an embedded inductor coil or an embedded transformer coil, the magnetic fields induced around the coil extend into the underlying semiconductor substrate
Implementation Method 3
trenches filled with a replacement dielectric in the portion of a semiconductor substrate underlying the embedded inductor coil
Data Source
AI summary
In a described example, an integrated circuit includes: a semiconductor substrate having a first surface and an opposite second surface; at least one dielectric layer overlying the first surface of the semiconductor substrate; at least one inductor coil in the at least one dielectric layer with a plurality of coil windings separated by coil spaces, the at least one inductor coil lying in a plane oriented in a first direction parallel to the first surface of the semiconductor substrate, the at least one inductor coil electrically isolated from the semiconductor substrate by a portion of the at least one dielectric layer; and trenches extending into the semiconductor substrate in a second direction at an angle with respect to the first direction, the trenches underlying the inductor coil and filled with dielectric replacement material.