Scalable MEMS Inductor with Laminated Magnetic Core

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Solution Overview

Problem

Existing MEMS inductors face challenges in scalability to frequencies above 10 MHz at high currents greater than a few hundred mA, requiring a solution for forming a scalable MEMS inductor.

Innovation Solution

A scalable MEMS inductor is formed on a semiconductor wafer with a stress relief layer, multiple magnetic laminations, and thick copper wiring to reduce DC resistance, utilizing materials like permalloy and SU-8 epoxy to minimize eddy currents and absorb dimensional changes, thereby preventing stress transmission to underlying structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional MEMS inductor structures are used, then fabrication is simpler, but scalability to frequencies above 10 MHz at high currents is limited

Engineering Contradiction:

Improvescalability to frequencies above 10 MHzVSAvoidinductor structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The magnetic core is divided into multiple thin laminations (first magnetic lamination, second magnetic lamination, third magnetic lamination) stacked together. This segmentation reduces eddy current losses by increasing electrical resistance between layers while maintaining magnetic permeability, enabling scalability to higher frequencies above 10 MHz.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inductor uses composite material construction combining magnetic laminations (permalloy or nickel-iron alloy) with non-magnetic spacer layers (SU-8 epoxy or silicon dioxide). This composite structure optimizes both magnetic properties and electrical isolation, achieving high inductance values with reduced eddy currents for high-frequency operation.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If thin magnetic laminations are used to reduce eddy currents, then eddy current losses decrease, but manufacturing precision requirements increase

Engineering Contradiction:

Improveeddy current lossesVSAvoidlamination thickness control

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

Non-magnetic spacer layers (SU-8 epoxy or silicon dioxide) are deposited beforehand to define precise thickness and positioning of the magnetic laminations. This preliminary action establishes accurate spacing and alignment before magnetic material deposition, reducing manufacturing precision requirements for the thin laminations themselves.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent specifies lamination thickness parameters (e.g., 1-10 micrometers) and material composition parameters (permalloy or nickel-iron alloy with specific magnetic permeability) to optimize the balance between eddy current reduction and manufacturability. These parameter changes enable thin laminations to be produced with acceptable precision using standard semiconductor fabrication processes.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If thick copper wiring is used to reduce DC resistance, then operational current capability increases, but device area increases

Engineering Contradiction:

Improveoperational current capabilityVSAvoidinductor device area

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The inductor design transitions from planar winding to a three-dimensional stacked configuration with vertical magnetic laminations and copper traces. This dimensional change allows thick copper wiring for high current capability while confining the device footprint to a compact area by utilizing the vertical dimension for magnetic flux path.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

Thick copper wiring is applied locally only where high current capability is needed (in the windings and connections), while other areas use thinner traces. This local quality approach minimizes overall device area while maintaining high operational current capability at critical locations.

Inventive Principle:

Principle #3Local quality

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 solution enables high inductance values and high maximum operational currents, achieving scalability and reducing eddy currents, thus addressing the limitations of existing MEMS inductors.

Implementation Method 1

Core structures formed from laminated Ni—Fe have been shown to have low eddy current losses

Methodology Applied

Scientific EffectEddy currents: Eddy Currents

Implementation Method 2

Methodology Applied

Scientific EffectStress relief: Stress Relaxation

Data Source

PatentUS8443511B2Method of forming a MEMS power inductor

Publication Date: 2013.05.21 NAT SEMICON CORP

AI summary

A scalable MEMS inductor is formed on the top surface of a semiconductor die. The MEMS inductor includes a plurality of magnetic lower laminations, a circular trace that lies over and spaced apart from the magnetic lower laminations, and a plurality of upper laminations that lie over and spaced apart from the circular trace.