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Magnetic MEMS and Micropower Systems

Magnetic MEMS and Micropower Systems. David P. Arnold Assistant Professor Interdisciplinary Microsystems Group Department of Electrical and Computer Engineering University of Florida 229 Benton Hall PO Box 116200 Gainesville, FL 32611-6200 (352) 392-4931 phone (352) 392-1104 fax

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Magnetic MEMS and Micropower Systems

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  1. Magnetic MEMS and Micropower Systems David P. Arnold Assistant Professor Interdisciplinary Microsystems Group Department of Electrical and Computer Engineering University of Florida 229 Benton Hall PO Box 116200 Gainesville, FL 32611-6200 (352) 392-4931 phone (352) 392-1104 fax darnold@ufl.edu http://www.img.ufl.edu Magnetic MEMS & Micropower Systems April 27, 2006

  2. Overview • Microscale Magnetics • Advantages • Challenges • Applications • Magnetic MEMS Applications • Microactuators • Vibrational Energy Harvesting • Micromotors/Generators • Magnetic Self-Assembly Magnetic MEMS & Micropower Systems April 27, 2006

  3. Capacitive Microphone Ultrasonic Proximity Transducer/Sensor Electroosmotic Pump Packaged Piezoresistive Microphone 1mm Thermally Actuated Micromirror 3-Axis Capacitive Accelerometer MEMS Overview • Microelectromechanical Systems (MEMS) - integration of mechanical elements, sensors, actuators, and/or electronics on a common silicon substrate through microfabrication technologies Magnetic MEMS & Micropower Systems April 27, 2006

  4. Microscale Magnetics Magnetic MEMS & Micropower Systems April 27, 2006

  5. 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) Magnetic MEMS & Micropower Systems April 27, 2006

  6. Hard Magnet (“magnet”, “permanent magnet”) Electromagnet Soft Magnet (“back iron”) Types of “Magnets” Ferromagnetic Materials Magnetic MEMS & Micropower Systems April 27, 2006

  7. Cone Diaphragm Frame Magnetic Yoke Magnet Coil Cone Coil Flexible Diaphragm Magnet 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). Magnetic MEMS & Micropower Systems April 27, 2006

  8. 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 Magnetic MEMS & Micropower Systems April 27, 2006

  9. Magnetic Actuation • Magnet - Magnet • No transduction (only magnetic energy domain) • Uses: Bistable “latches”, Bonding, Constant mechanical force Magnetic MEMS & Micropower Systems April 27, 2006

  10. Magnet-Magnet Electrodynamic Electromagnet-Magnet Magnetic Scaling Laws k = scale reduction; ki = current density increase O. Cugat, J. Delamare, and G. Reyne, “Magnetic Micro-Actuators and Systems (MAGMAS),” IEEE Trans. Magn., vol. 39, no. 5, Nov. 2003. Magnetic MEMS & Micropower Systems April 27, 2006

  11. Processes Geometries Materials Microscale Magnetics • Challenges for Microscale Magnetic Systems • Process Limitations • PVD (Sputtering/Evaporation) • Electroplating • Spin-coating • Material Limitations • Material selection limited by deposition processes • No “advanced processing” capabilities (quenching, rolling, sintering, annealing, etc.) • Geometries • “Thick” magnetic films (10’s or 100’s of microns) • Three-dimensional solenoidal coils Magnetic MEMS & Micropower Systems April 27, 2006

  12. Coils • Multilevel Electroplating • Usually Cu or Au NiFe-core inductor [J. Y. Park, 1998]. Planar spiral coil Planar Cu windings 3D air core RF inductors [Y.-K. Yoon, 2003]. Magnetic MEMS & Micropower Systems April 27, 2006

  13. 60 μm Electroplated CoPt magnets, Zana et al., 2004-5 Electroplated NiFe core and Cu windings in a planar induction motor, Cros et al., 2004 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 CoNiP, Guan & Nelson., 2005 Magnetic MEMS & Micropower Systems April 27, 2006

  14. Magnetic Actuators Magnetic MEMS & Micropower Systems April 27, 2006

  15. Magnetic Valve • Electromagnet-Magnet actuation • Magnet-Magnet bistability • Surface-micromachined (multi-level electroplating) • Cu coil, NiFe superstructure, CoPt PM Permanent Magnet Ferromagnet Coil J. Sutanto, Ph.D. Dissertation, Georgia Tech, 2004 Magnetic MEMS & Micropower Systems April 27, 2006

  16. 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 Magnetic MEMS & Micropower Systems April 27, 2006

  17. 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) Coil Rigid Piston Permanent Micro Magnets Coil Substrate Magnetic MEMS & Micropower Systems April 27, 2006

  18. Microscale Power Systems Magnetic MEMS & Micropower Systems April 27, 2006

  19. 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 Vibrational Energy Harvesting Scheme Energy Storage Permanent Magnet Vibrating Body Coils Magnetic MEMS & Micropower Systems April 27, 2006

  20. 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. Magnetic MEMS & Micropower Systems April 27, 2006

  21. Vibrational Magnetic Generators • Published articles Magnetic MEMS & Micropower Systems April 27, 2006

  22. 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 Magnetic MEMS & Micropower Systems April 27, 2006

  23. 10 mm [M. A. Schmidt, 2002] Integrated Microengine • Integrated Gas-Turbine Engine and Electrical Generator • 10 - 100 W • High speed (~1 Mrpm) • High temp. (300 - 1400˚C) Magnetic MEMS & Micropower Systems April 27, 2006

  24. Tethered Rotor Stator Rotor Upper Wafer Lower Wafer Fusion-Bonded Stator (cutaway view) Silicon-Based Magnetic Induction Machine • Integration of magnetics in silicon • 2.5 mN-m motoring torque • 33 mN-m/cm3 torque density Magnetic MEMS & Micropower Systems April 27, 2006

  25. Rotor Stator Rotor Stator Magnet Poles 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) Magnetic MEMS & Micropower Systems April 27, 2006

  26. Magnetic Self-Assembly Magnetic MEMS & Micropower Systems April 27, 2006

  27. 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 Magnetic MEMS & Micropower Systems April 27, 2006

  28. Self-Assembly • Mixing Forces • Fluidic flow • Vibrational energy • Bonding forces • Gravity • Capillary • Electrostatic • Magnetic Magnetic MEMS & Micropower Systems April 27, 2006

  29. 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 Magnetic MEMS & Micropower Systems April 27, 2006

  30. Magnetic Self-Assembly • Bonding structures much smaller than the size of the component • “Lock and Key” pattern-matching mechanism • Asymmetric and diverse patterns Magnetic MEMS & Micropower Systems April 27, 2006

  31. Deposit seed layer Pattern photoresist 20X Plate magnets Etch mold and seed layer Dice wafer Substrate 200X Magnetic Self-Assembly • CoPt Hard Micromagnets • Micromolding and electrodeposition Magnetic MEMS & Micropower Systems April 27, 2006

  32. Out of plane measurement In plane measurement Magnetic Self-Assembly • Magnetic Measurements of Film Properties • Vibrating Sample Magnetometer (VSM) Magnetic MEMS & Micropower Systems April 27, 2006

  33. Magnetic Self-Assembly • Force projections for CoPt micromagnets Weight-force of a 5 mm x 5 mm x 0.5 mm chip Magnetic MEMS & Micropower Systems April 27, 2006

  34. 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 & Micropower Systems April 27, 2006

  35. Magnetic MEMS & Micropower Systems April 27, 2006

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