ksjp, 7/01 MEMS Design & Fab Overview Quick look at some common MEMS actuators Piezoelectric Thermal Magnetic Next: Electrostatic actuators Actuators and mechanism Beams

ksjp, 7/01 MEMS Design & Fab MEMS Actuation Options Piezoelectric Thermal Magnetic Electrostatic Dynamics Beam bending Damping

ksjp, 7/01 MEMS Design & Fab Ferroelectrics (piezoelectrics) Huge energy densities Good efficiency Huge force, small displacement Major fabrications challenges Continuously promising technology

ksjp, 7/01 MEMS Design & Fab Piezoelectric effect Polyvinylidene flouride (PVDF) Zinc oxide - ZnO Lead zirconate titanate – PZT PMNPT L A d - piezoelectric coefficient rank 2 tensor: e.g. d 11, d 31 V

ksjp, 7/01 MEMS Design & Fab Piezoelectric products Quartz resonators (single crystal) E.g. crystal oscillators ~10Million/day, $0.10 each, vacuum packaged L A V

ksjp, 7/01 MEMS Design & Fab Bimorph for STM and AFM ZnO Aluminum electrodes After Akamine, Stanford, ~90

ksjp, 7/01 MEMS Design & Fab Piezoelectric 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, 7/01 MEMS Design & Fab Thermal Expansion.  =  T is the thermal expansion strain (  L/L)  =  is the thermal expansion stress F = A  is the thermal expansion force  silicon ~ 2.3x10 -6 /K A L

ksjp, 7/01 MEMS Design & Fab Thermal 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, 7/01 MEMS Design & Fab Plot by: R. Conant, UCB. Thermal expansion: The heatuator

ksjp, 7/01 MEMS Design & Fab Thermal Actuators Current input pad Actuator translates in this direction Cold arm Hot arm Current output pad Uses thermal expansion for actuation Very effective and high force output per unit area Cascaded thermal actuators for high force

ksjp, 7/01 MEMS Design & Fab Thermal actuators in CMOS Shen, Allegretto, Hu, Robinson, U. Alberta Joule heating of beams leads to differential thermal expansion, changing the angle of the mirror

ksjp, 7/01 MEMS Design & Fab Bubble actuators (thermal and other) Lin, Pisano, UCB, ~92? HP switch Papavasiliu, Pisano, UCB - electrolysis

ksjp, 7/01 MEMS Design & Fab Thermal 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 dominate

ksjp, 7/01 MEMS Design & Fab Magnetic actuators Lorentz force Internal current in an external (fixed) magnetic field Dipole actuators Internal magnetic material in an external (varying) field

ksjp, 7/01 MEMS Design & Fab Magnetic Actuation (external field) Silicon substrate NiFe electroplated on polysilicon External magnetic field Fabrication: NiFe electroplating Switching external field Packaging

ksjp, 7/01 MEMS Design & Fab Magnetic Parallel Assembly Solid-State Sensor and Actuator Workshop Hilton Head 1998 Figure 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 H ext 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 H ext is increased. Parallel assembly of Hinged Microstructures Using Magnetic Actuation Yong Yi and Chang Liu Microelectronics Laboratory University of Illinois at Urbana-Champaign Urbana, IL 61801

ksjp, 7/01 MEMS Design & Fab Parallel assembly Solid-State Sensor and Actuator Workshop Hilton Head 1998 Parallel assembly of Hinged Microstructures Using Magnetic Actuation Yong Yi and Chang Liu Microelectronics Laboratory University of Illinois at Urbana-Champaign Urbana, IL Figure 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 H ext = H 1; (c) full 3-D assembly is achieved at H ext = H 2 (H 2 > H 1 ). 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, 7/01 MEMS Design & Fab Magnetic actuators – Onix switch? Magnetic actuation, electrostatic hold

ksjp, 7/01 MEMS Design & Fab Magnetic actuators in CMOS Resonant Magnetometer B. Eyre, Pister, Judy Lorentz force excitation Piezoresistive detection

ksjp, 7/01 MEMS Design & Fab LIGA: synchrotron lithography, electroplated metal Micro Electro Mechanical Systems Jan., 1998 Heidelberg, Germany Closed Loop Controlled, Large Throw, Magnetic Linear Microactuator with 1000  m Structural Height H. Guckel, K. Fischer, and E. Stiers U. Wisconsin

ksjp, 7/01 MEMS Design & Fab Magnetic Actuation in LIGA Micro Electro Mechanical Systems Jan., 1998 Heidelberg, Germany U. Wisconsin

ksjp, 7/01 MEMS Design & Fab Magnetic Actuation in LIGA Micro Electro Mechanical Systems Jan., 1998 Heidelberg, Germany U. Wisconsin

ksjp, 7/01 MEMS Design & Fab Maxell (Hitachi) RF ID Chip

ksjp, 7/01 MEMS Design & Fab Magnetic actuator summary High current, low voltage (contrast w/ electrostatics) Typically low efficiency Potentially large forces and large displacements Some process integration issues