OverviewMEMS Actuation OptionsFerroelectrics (piezoelectrics)Piezoelectric effectPiezoelectric productsBimorph for STM and AFMPiezoelectric Actuator SummaryThermal ExpansionThermal actuator worksheetThermal expansion: The heatuatorThermal ActuatorsThermal actuators in CMOSBubble actuators (thermal and other)Thermal actuator summaryMagnetic actuatorsMagnetic Actuation (external field)Magnetic Parallel AssemblyParallel assemblyMagnetic actuators – Onix switch?Magnetic actuators in CMOSLIGA: synchrotron lithography, electroplated metalMagnetic Actuation in LIGASlide 23Maxell (Hitachi) RF ID ChipMagnetic actuator summaryksjp, 7/01MEMS Design & FabOverview•Quick look at some common MEMS actuators•Piezoelectric•Thermal•Magnetic•Next:•Electrostatic actuators•Actuators and mechanism•Beamsksjp, 7/01MEMS Design & FabMEMS Actuation Options•Piezoelectric•Thermal•Magnetic•Electrostatic•Dynamics•Beam bending•Dampingksjp, 7/01MEMS Design & FabFerroelectrics (piezoelectrics)•Huge energy densities•Good efficiency•Huge force, small displacement•Major fabrications challenges•Continuously promising technologyksjp, 7/01MEMS Design & FabPiezoelectric effect•Polyvinylidene flouride (PVDF)•Zinc oxide - ZnO•Lead zirconate titanate – PZT•PMNPTV d L0AFLAd - piezoelectric coefficient rank 2 tensor: e.g. d11, d31Vksjp, 7/01MEMS Design & FabPiezoelectric products•Quartz resonators (single crystal)•E.g. crystal oscillators•~10Million/day, $0.10 each, vacuum packagedLAVksjp, 7/01MEMS Design & FabBimorph for STM and AFMZnOAluminum electrodesAfter Akamine, Stanford, ~90ksjp, 7/01MEMS Design & FabPiezoelectric Actuator Summary•High voltage, low current•~100V/um•No static current (excellent insulator)•Highest energy density of any MEMS actuator but•Large force, small displacement•Typically very difficult to integrate with other materials/devices•“Continuously promising”ksjp, 7/01MEMS Design & FabThermal Expansion. = T is the thermal expansion strain (L/L)= is the thermal expansion stressF = A is the thermal expansion forcesilicon ~ 2.3x10-6/KALksjp, 7/01MEMS Design & FabThermal actuator worksheet•Assume that you have a silicon beam that is 100 microns long, and 1um square. You heat it by 100K. How much force do you get if you constrain it? How much elongation if you allow it to expand? TCE for silicon is 2.3x10^-6/K .Area== T == =F = A =L= L=ksjp, 7/01MEMS Design & FabPlot by: R. Conant, UCB.Thermal expansion: The heatuatorksjp, 7/01MEMS Design & FabThermal ActuatorsCurrent input padActuator translatesin this directionCold armHot arm Current output padUses thermal expansion for actuationVery effective and high force output per unit areaCascaded thermal actuators for high forceksjp, 7/01MEMS Design & FabThermal actuators in CMOSShen, Allegretto, Hu, Robinson, U. AlbertaJoule heating of beams leads to differential thermal expansion, changing the angle of the mirrorksjp, 7/01MEMS Design & FabBubble actuators (thermal and other)•Lin, Pisano, UCB, ~92?•HP switch•Papavasiliu, Pisano, UCB - electrolysisksjp, 7/01MEMS Design & FabThermal actuator summary•Easy process integration!•Large forces, small displacements•Need lever mechanisms to trade off force for displacement•Typically very inefficient•Time constants ~1ms•Substantial conduction through air•Minimal convection in sub-millimeter designs•Radiation losses important above ~300C•Instant heating, slow cooling•Except when radiative losses dominateksjp, 7/01MEMS Design & FabMagnetic actuators•Lorentz force•Internal current in an external (fixed) magnetic field•Dipole actuators•Internal magnetic material in an external (varying) fieldksjp, 7/01MEMS Design & FabMagnetic Actuation (external field)Silicon substrateNiFe electroplatedon polysiliconExternal magneticfield•Fabrication: NiFe electroplating•Switching external field•Packagingksjp, 7/01MEMS Design & FabMagnetic Parallel AssemblySolid-State Sensor and Actuator WorkshopHilton Head 1998Figure 1. (a) An SEM micrograph of a Type I structure. The flap is allowed to rotate about the Y- axis. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the flap as Hext is increased.Figure 2. (a) SEM micrograph of a Type II structure. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the structure when Hext is increased.Parallel assembly of Hinged Microstructures Using Magnetic ActuationYong Yi and Chang LiuMicroelectronics LaboratoryUniversity of Illinois at Urbana-ChampaignUrbana, IL 61801ksjp, 7/01MEMS Design & FabParallel assemblySolid-State Sensor and Actuator WorkshopHilton Head 1998Parallel assembly of Hinged Microstructures Using Magnetic ActuationYong Yi and Chang LiuMicroelectronics LaboratoryUniversity of Illinois at Urbana-ChampaignUrbana, IL 61801Figure 8. Schematic of the assembly process for the flap 3-D devices. (a) Both flaps in the resting position; (b) primary flap raised to 90º at Hext = H1; (c) full 3-D assembly is achieved at Hext = H2 (H2 > H1 ).Figure 9. An SEM micrograph of a 3-D device using three Type I flaps. The sequence of actuation is not critical to the assembly of this device.ksjp, 7/01MEMS Design & FabMagnetic actuators – Onix switch?•Magnetic actuation, electrostatic holdksjp, 7/01MEMS Design & FabMagnetic actuators in CMOSResonant MagnetometerB. Eyre, Pister, JudyLorentz force excitationPiezoresistive detectionksjp, 7/01MEMS Design & FabLIGA: synchrotron lithography, electroplated metalMicro Electro Mechanical SystemsJan., 1998 Heidelberg, GermanyClosed Loop Controlled, Large Throw, Magnetic Linear Microactuator with 1000 m Structural HeightH. Guckel, K. Fischer, and E. StiersU. Wisconsinksjp, 7/01MEMS Design & FabMagnetic Actuation in LIGAMicro Electro Mechanical SystemsJan., 1998 Heidelberg, GermanyU. Wisconsinksjp, 7/01MEMS Design & FabMagnetic Actuation in LIGAMicro Electro Mechanical SystemsJan., 1998 Heidelberg, GermanyU. Wisconsinksjp, 7/01MEMS Design & FabMaxell (Hitachi) RF ID Chipksjp, 7/01MEMS Design & FabMagnetic actuator summary•High current, low voltage (contrast w/ electrostatics)•Typically low efficiency•Potentially large forces and large displacements•Some process integration
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