Overview Quick look at some common MEMS actuators

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

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

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

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

Piezoelectric products V A L • E. g. crystal oscillators • ~10 Million/day, $0. 10 each, vacuum packaged MEMS Design & Fab ksjp, 7/01 • Quartz resonators (single crystal)

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

Piezoelectric Actuator Summary • High voltage, low current • ~100 V/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 MEMS Design & Fab ksjp, 7/01 • “Continuously promising”

Thermal Expansion L e = g DT is thermal expansion strain (d. L/L) s= E e is thermal expansion stress F = A s is thermal expansion force A. MEMS Design & Fab ksjp, 7/01 gsilicon ~ 2. 3 x 10 -6/K

Thermal actuator worksheet • Assume that you have a silicon beam that is 100 microns long, and 1 um square. You heat it by 100 K. How much force do you get if you constrain it? How much elongation if you allow it to expand? TCE for silicon is 2. 3 x 10^-6/K. MEMS Design & Fab ksjp, 7/01 Area= e= g DT = s= E e = F=As= d. L= e L=

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

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

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

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

Thermal actuator summary • • • displacement Typically very inefficient Time constants ~1 ms Substantial conduction through air Minimal convection in sub-millimeter designs Radiation losses important above ~300 C Instant heating, slow cooling • Except when radiative losses dominate MEMS Design & Fab ksjp, 7/01 • Easy process integration! • Large forces, small displacements • Need lever mechanisms to trade off force for

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

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

Magnetic Parallel Assembly Parallel assembly of Hinged Microstructures Using Magnetic Actuation 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 Hext is increased. Solid-State Sensor and Actuator Workshop Hilton Head 1998 Figure 2. (a) SEM micrograph of a Type II structure. (b) Schematic cross-sectional view of the structure at rest; (c) schematic crosssectional view of the structure when Hext is increased. MEMS Design & Fab ksjp, 7/01 Yong Yi and Chang Liu Microelectronics Laboratory University of Illinois at Urbana-Champaign Urbana, IL 61801

Parallel assembly of Hinged Microstructures Using Magnetic Actuation Yong Yi and Chang Liu Microelectronics Laboratory University of Illinois at Urbana-Champaign Urbana, IL 61801 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 Hext = H 1; (c) full 3 -D assembly is achieved at Hext = H 2 (H 2 > H 1 ). Solid-State Sensor and Actuator Workshop Hilton Head 1998 MEMS Design & Fab ksjp, 7/01 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.

Magnetic actuators – Onix switch? MEMS Design & Fab ksjp, 7/01 • Magnetic actuation, electrostatic hold

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

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

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

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

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

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