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 1 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 2 MEMS Overview Microelectromechanical Systems (MEMS) - integration of mechanical elements, sensors, actuators, and/or electronics on a common silicon substrate through microfabrication technologies Ultrasonic Proximity Transducer/Sensor Capacitive Microphone Electroosmotic Pump Packaged Piezoresistive Microphone 3-Axis Capacitive Accelerometer 1mm Thermally Actuated Micromirror Magnetic MEMS & Micropower Systems April 27, 2006 3 Microscale Magnetics Magnetic MEMS & Micropower Systems April 27, 2006 4 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 5 Types of “Magnets” Hard Magnet (“magnet”, “permanent magnet”) Ferromagnetic Materials Electromagnet Soft Magnet (“back iron”) Magnetic MEMS & Micropower Systems April 27, 2006 6 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). i 2 F Bli S N 1 F Cone Cone Diaphragm Coil Frame Flexible Diaphragm Magnet Magnet Magnetic MEMS & Micropower Systems Magnetic Yoke Coil April 27, 2006 7 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 2 F 2 μ0 Ag Magnetic MEMS & Micropower Systems April 27, 2006 8 Magnetic Actuation B. Magnet - Magnet - No transduction (only magnetic energy domain) Uses: Bistable “latches”, Bonding, Constant mechanical force F μ0( H M )dV V Magnetic MEMS & Micropower Systems April 27, 2006 9 Magnetic Scaling Laws MagnetMagnet k = scale reduction; ki = current density increase Electrodynamic 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 ElectromagnetMagnet April 27, 2006 10 Microscale Magnetics Challenges for Microscale Magnetic Systems Processe s 1. Process Limitations PVD (Sputtering/Evaporation) Electroplating Spin-coating Geometries Materials 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 Magnetic MEMS & Micropower Systems April 27, 2006 11 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 12 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 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 MEMS & Micropower Systems April 27, 2006 13 Magnetic Actuators Magnetic MEMS & Micropower Systems April 27, 2006 14 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 15 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 16 Electrodynamic Actuator Proposed Electrodynamic Actuator Extend concept of Cheng, et al., but use multiple micromagnets “Swiss roll” spiral coil design Coil Rigid Piston Permanent Micro Magnets Coil Applications: Microspeaker Flow-control actuator (synthetic jet) Substrate Magnetic MEMS & Micropower Systems April 27, 2006 17 Microscale Power Systems Magnetic MEMS & Micropower Systems April 27, 2006 18 Vibrational Energy Harvesters Electrodynamic and magnetic transducers for harvesting “waste” (μWmW scale) power from oscillating or vibrating systems Examples: self-powered sensors, hybrid power sources dΦ V N dt Vibrational Energy Harvesting Scheme Permanent Magnet Energy Storage Vibrating Body Coils Magnetic MEMS & Micropower Systems April 27, 2006 19 Vibrational Magnetic Generators Theoretical Performance Estimates P mY02ωn2 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 20 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 43 mm3 3.0 mW/cm3 7.4 kHz 240 μm Magnetic MEMS & Micropower Systems April 27, 2006 21 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 22 Integrated Microengine Integrated Gas-Turbine Engine and Electrical Generator 10 - 100 W High speed (~1 Mrpm) High temp. (300 - 1400˚C) 10 mm [M. A. Schmidt, 2002] Magnetic MEMS & Micropower Systems April 27, 2006 23 Silicon-Based Magnetic Induction Machine Integration of magnetics in silicon 2.5 mN-m motoring torque 33 mN-m/cm3 torque density Tethered Rotor Stator Upper Wafer 250 mm 10 mm 20 mm Lower Wafer Fusion-Bonded Stator (cutaway view) Rotor Magnetic MEMS & Micropower Systems April 27, 2006 24 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) Rotor Stator Magnet Poles Rotor Stator Magnetic MEMS & Micropower Systems April 27, 2006 25 Magnetic Self-Assembly Magnetic MEMS & Micropower Systems April 27, 2006 26 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 27 Self-Assembly Mixing Forces Fluidic flow Vibrational energy Bonding forces Gravity Capillary Electrostatic Magnetic Magnetic MEMS & Micropower Systems April 27, 2006 28 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 29 Magnetic Self-Assembly Part B (Flip Chip) Array of Magnetic South Poles Part C (Capacitor) Solder Bumps Array of Magnetic North Poles Part A (Circuit Board) 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 30 Magnetic Self-Assembly CoPt Hard Micromagnets Micromolding and electrodeposition Deposit seed layer Substrate Pattern photoresist 20X Plate magnets Etch mold and seed layer Dice wafer 200X Magnetic MEMS & Micropower Systems April 27, 2006 31 Magnetic Self-Assembly Magnetic Measurements of Film Properties Vibrating Sample Magnetometer (VSM) Out of plane measurement In plane measurement Magnetic MEMS & Micropower Systems April 27, 2006 32 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 33 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 34 Magnetic MEMS & Micropower Systems April 27, 2006 35