Magnetic MEMS and Micropower Systems

1Magnetic MEMS & Micropower Systems April 27, 2006

Magnetic MEMS and Micropower Systems

David P. Arnold

Assistant ProfessorInterdisciplinary Microsystems Group

Department of Electrical and Computer EngineeringUniversity of Florida

229 Benton HallPO Box 116200

Gainesville, FL 32611-6200

(352) 392-4931 phone (352) 392-1104 [email protected]

http://www.img.ufl.edu


Overview

Microscale Magnetics Advantages Challenges Applications

Magnetic MEMS Applications Microactuators Vibrational Energy Harvesting Micromotors/Generators Magnetic Self-Assembly


MEMS Overview

Microelectromechanical Systems (MEMS) - integration of mechanical elements, sensors, actuators, and/or electronics on a common silicon substrate through microfabrication technologies

Ultrasonic Proximity Ultrasonic Proximity Transducer/SensorTransducer/Sensor

Capacitive MicrophoneCapacitive Microphone

Packaged Piezoresistive Packaged Piezoresistive MicrophoneMicrophone

3-Axis Capacitive Accelerometer3-Axis Capacitive Accelerometer

Electroosmotic PumpElectroosmotic Pump

1mm

Thermally Actuated MicromirrorThermally Actuated Micromirror


Microscale Magnetics


MEMS Transduction Schemes

Various energy-transduction mechanisms for MEMS Piezoelectric Thermal Electrostatic

Electromagnetic (Electrodynamic and Magnetic) Relatively large forces over large displacements High magnetic fields without material damage Joule heating of conductors Magnetic forces are body forces (electrostatic are surface forces)


Types of “Magnets”

Soft Magnet(“back iron”)

Hard Magnet(“magnet”, “permanent magnet”)

Ferromagnetic Materials Electromagnet


Electrodynamic Actuation

1. Electrodynamic: motor action produced by the current in an electric conductor located in a fixed transverse magnetic field (e.g., voice coil).

N S

F

i

1

2

BliF

Cone

Coil

Flexible Diaphragm Magnet

Coil

Diaphragm

Magnet

Cone

MagneticYoke

Frame


Magnetic Transduction

2. Magnetic: motor action produced by the tendency for magnetic moments to align and/or close a magnetic air gap (e.g., solenoid).

A. Electromagnet - Magnet

gAμF

0

2

2


Magnetic Actuation

B. Magnet - Magnet- No transduction (only magnetic energy domain)

- Uses: Bistable “latches”, Bonding, Constant mechanical force

dVMHμF V

0 )(


Magnetic Scaling Laws

O. Cugat, J. Delamare, and G. Reyne, “Magnetic Micro-Actuators and Systems (MAGMAS),” IEEE Trans. Magn., vol. 39, no. 5, Nov. 2003.

k = scale reduction; ki = current density increaseElectromagnet-

MagnetElectrodynamic

Magnet-Magnet


Microscale Magnetics

Challenges for Microscale Magnetic Systems

1. Process Limitations PVD (Sputtering/Evaporation) Electroplating Spin-coating

2. Material Limitations Material selection limited by deposition processes No “advanced processing” capabilities (quenching, rolling,

sintering, annealing, etc.)

3. Geometries “Thick” magnetic films (10’s or 100’s of microns) Three-dimensional solenoidal coils

Processes

Materials Geometries


Coils

Multilevel Electroplating Usually Cu or Au

NiFe-core inductor [J. Y. Park, 1998].

3D air core RF inductors [Y.-K. Yoon, 2003].

Planar spiral coil

Planar Cu windings


Magnetic Thick-Films

Electrodeposited Magnetic “Thick” Films 10’s or 100’s of μm thick Soft Magnets: NiFe, NiFeMo, CoFe, etc. Hard Magnets: CoNiP, CoPt, FePt

Electroplated NiFe core and Cu windings in a planar induction motor, Cros et al., 2004

Electroplated CoPt magnets, Zana et al., 2004-5

60 μm

Electroplated CoNiP, Guan & Nelson., 2005


Magnetic Actuators


Magnetic Valve

Electromagnet-Magnet actuation Magnet-Magnet bistability Surface-micromachined (multi-level electroplating)

Cu coil, NiFe superstructure, CoPt PM

J. Sutanto, Ph.D. Dissertation, Georgia Tech, 2004

Coil

FerromagnetPermanent

Magnet


Electrodynamic Speaker

Electrodynamic actuation using fringing fields Bulk-micromachined

Silicon nitride membrane Electroplated copper coil NdFeB permanent magnet (bulk)

M.-C. Cheng, et al., “A Novel Micromachined Electromagnetic Loudspeaker for Hearing Aid,” Proceedings of Eurosensors XV, Munich, Germany, Jun 10-14, 2001


Electrodynamic Actuator

Proposed Electrodynamic Actuator Extend concept of

Cheng, et al., but use multiple micromagnets

“Swiss roll” spiral coil design

Applications: Microspeaker Flow-control actuator

(synthetic jet)

Permanent Micro

Magnets

Coil

Coil Rigid Piston

Substrate


Microscale Power Systems


Vibrational Energy Harvesters

Electrodynamic and magnetic transducers for harvesting “waste” (μW-mW scale) power from oscillating or vibrating systems

Examples: self-powered sensors, hybrid power sources

Vibrating Body

Vibrational Energy Harvesting Scheme Permanent

Magnet

Coils

Energy Storage

dt

dNV

Φ


Vibrational Magnetic Generators

Theoretical Performance Estimates

Human Powered: μW/cm3 range (1-10 Hz) Vibrating Structure: mW/cm3 range (0.1-1 kHz)

P. D. Mitcheson, et al., “Architectures for Vibration-Driven Micropower Generators”, Journal of MEMS, vol. 13, no. 3, June 2004.

220 nωmYP


Vibrational Magnetic Generators

Published articles

Output Power

Resonant Freq.

Vibration Amplitude

Size Power Density

Yates, et al., 1995-96

0.3 μW 4400 Hz 0.5 μm 4.4 mm3 70 μW /cm3

Anantha, 1998 400 μW

Li et al., 2000 40 μW 80 Hz 200 μm 1 cm3 40 μW /cm3

El-hami, 2001 530 μW 320 Hz 25 μm 240 mm3 2.2 mW/cm3

P. Glynne-Jones, et al. 2004

157 μW 3.15 cm3 50 μW/cm3

Kulkarni, et al., 2006 (*theoretical)

128 μW 7.4 kHz 240 μm 43 mm3 3.0 mW/cm3


Microengine Concept

Turbine Engine Electrical Generator

Hydrocarbon Fuel

- >3,000 W·hr/kg (25 % efficiency)- Compact (few cm3)- Refuelable

12,000-14,000 W·hr/kg


Integrated Microengine

[M. A. Schmidt, 2002]

10 mm

Integrated Gas-Turbine Engine and Electrical Generator

10 - 100 W High speed (~1 Mrpm) High temp. (300 - 1400˚C)


Silicon-Based Magnetic Induction Machine

Integration of magnetics in silicon 2.5 N-m motoring torque 33 N-m/cm3 torque density

Fusion-BondedStator (cutaway view)

UpperWafer

LowerWafer

Tethered Rotor

Stator

250 m 10 mm

20 m

250 m 10 mm

20 m

Rotor


High-Speed Permanent-Magnet Generator

Hybrid microfabrication and assembly 300,000 rpm 8 W DC power delivered >40 W/cm3 power density (10-20x larger

than macroscale)

StatorRotor

Rotor Magnet Poles

Stator


Magnetic Self-Assembly


Assembly of Small Components

Conventional Assembly of Small Components Device subcomponents fabricated separately Assembled together in serial fashion Robotic pick and place

Issues with Conventional Approach Manufacturing bottleneck Manipulation of small parts

Alignment and positioning tolerances “Sticking” problem


Self-Assembly

Mixing Forces Fluidic flow Vibrational energy

Bonding forces Gravity Capillary Electrostatic Magnetic


Magnetically Directed Self-Assembly

Objective To enable 3-D structures to be formed in parallel from a

heterogeneous mixture of parts of arbitrary size and shape

Magnetics offers Bi-directional forces between components Attractive or repulsive forces between

components Controllable force and range (magnet

geometry, materials, and magnetization direction)

Favorable scaling to micro- and nanoscale Functionality in either wet or dry environments Low-cost, batch-integrability



Bonding structures much smaller than the size of the component “Lock and Key” pattern-matching mechanism Asymmetric and diverse patterns

Part A (Circuit Board)

Part B (Flip Chip) Part C (Capacitor)

Solder Bumps

Array of Magnetic

South Poles

Array of Magnetic

North Poles

Part A (Circuit Board)

Part B (Flip Chip)Part B (Flip Chip) Part C (Capacitor)Part C (Capacitor)

Solder Bumps

Array of Magnetic

South Poles

Array of Magnetic

North Poles



CoPt Hard Micromagnets Micromolding and electrodeposition

200X

20X

Deposit seed layer

Pattern photoresist

Plate magnets

Etch mold and seed layer

Substrate

Dice wafer



Magnetic Measurements of Film Properties Vibrating Sample Magnetometer (VSM)

Out of plane measurement

In plane measurement



Force projections for CoPt micromagnets

Weight-force of a 5 mm x 5 mm x

0.5 mm chip


Summary

Magnetic Microdevices are rich in: Materials Development Design Fabrication Characterization

Many opportunities for advancements in micromagnetics: Actuators Power Generators Self-Assembly Others: Sensor technologies

Integrated power inductors for power converters

Magnetic MEMS and Micropower Systems

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