Slide 1a.1 Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc,...

Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug.-Sep., 2003. G. K. Ananthasuresh Slide 1a.1

Lecture 1aRole of Structures and Mechanisms in MEMS A general overview of structural aspects of MEMS .


Contents

• Structures, Mechanisms, and MEMS• Early MEMS devices• Kinematic pairs and mechanisms in

MEMS: excitement vs. practicality• Deformable structures in MEMS• Example 1: tilting micro-mirrors• Example 2: micromanipulation


Structures and Mechanisms• Structures support and transmit loads.• Mechanisms transfer/transform motion AND

support and transmit loads.• Another view: both transfer and transform

energy (load*motion)• There is no need to limit this energy to

mechanical energy.Microelectromechanical Systems (MEMS)

• Most MEMS are sensors and actuators, i.e., they are transducers.

• Transducers are energy transformers and transmitters.

If we limit MEMS to mechanical energy domain or if we expand the scope of energy in structures/mechanisms to other domains, the role of structures and mechanisms in MEMS is easily apparent.

Willis


Accepted size range for MEMS

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Precision machiningNano-machining

Micro-machiningMacro-machining


MEMS devices in 1970’s and early 80’s

Roylance L.M., Angell J.B. “A batch fabricated silicon accelerometer” IEEE Trans. on Electron Devices 26, 1911-1917 (1979)

Schroeder C.M. "Accurate silicon spacer chips for an optical fiber cable connector" Bell. Syst. Tech. J. 57, 91-97 (1977)

Petersen K.E. "Micromechanical light modulator array fabricated on silicon" Appl. Phys. Lett. 31, 521-523 (1977)

Bassous E., Taub H.H., Kuhn L. “Ink jet printing nozzle arrays etched in silicon” Appl. Phys. Lett. 31, 135 (1977)

Terry S.C., Jerman J.H., Angell J.B. “A gas chromatograph air analyzer fabricated on a silicon wafer” IEEE Trans on Electron Devices 26, 1880-1886 (1979)

Ink-jet printer head

Petersen K.E. “Silicon torsional scanning mirror” IBM J. Res. Dev. 24, 631-637 (1980)

Micro mirrors for steering light

Accelerometer

Optical fiber connector

Microfluidic device


MEMS devices in 1970’s and early 80’s

Stemme G. “A monolithic gas flow sensor with polyimide as thermal insulator” IEEE Trans. on Electron Devices TED-33, 1470-1464 (1986)

Kimura K. “Microheater and microbolometer using microbridge of SiO2 film on silicon” Elect. Lett. 17, 80-82 (1981)

Najafi K., Wise K.D., Mochizuki T. “A high-yield IC-compatible multichannel recording array” IEEE Trans on Electron Devices 32, 1206-1211 (1985)

Ko W.-H., Hynecek J., Boettcher S.F. “Development of a miniature pressure transducer for biomedical applications” IEEE Trans. on Electron Devices T-ED26, 896-1905 (1979)

Clark S.K., Wise K.D. “Pressure sensitivity in anisotropically etched thin diaphragm pressure sensors” IEEE Trans. on Electron Devices TED-26, 1887-1896 (1979)

Pressure sensors

Other types of sensors

Gustafsson K., Hök B. “Fiberoptic switching and multiplexing with a micromechanical scanning mirror” Proc. 4th Int. Conf. on Solid-State Sensors and Actuators, Tokyo, June 3-5, P 212 (1987)

Optical switching and multiplexing


What is common to all those early MEMS devices?

• A beam or a diaphragm• A bulk-micromachined silicon, glass,

etc.• Electrical and electronic components for

sensing a signal

Micro-electro-mechanical systems (MEMS)


A MEMS accelerometer made in 1979

Roylance L.M., Angell J.B. “A batch fabricated silicon accelerometer” IEEE Trans. on Electron Devices 26, 1911-1917 (1979)

Bulk micro machiningPiezoresistor-based sensing


Bulk micromachining

(100) silicon

(110) silicon

(111) plane

(111)

With agitation

Without agitation

Isotropic etching

Anisotropic etching

Slantedsurfaces


Kinematic joint-based motion in MEMS

• The excitement began only after a rotary motor, revolute (pin) joints, and prismatic (sliding) joints were demonstrated.– At U. C. Berkeley, MIT, and Bell Labs– The reason for the excitement was batch-

fabrication of “assembled” micro-mechanisms without assembly.

– Crucial development: sacrificial layer process using polysilicon as the structural layer.


M. Mehregany, K.J. Gabriel, and W.S.N. Trimmer, "Fabrication of Integrated Polysilicon Mechanisms," IEEE Trans. Electron Devices, vol. ED-35, no. 6, pp. 719-723, June 1988.

M. Mehregany, S.F. Bart, L.S. Tavrow, J.H. Lang, S.D. Senturia, and M.F. Schlecht, "A Study of Three Microfabricated Variable-Capacitance Motors," Sensors and Actuators, vol. A21–A23, pp. 173-179, 1990.

L.S. Fan, Y.C. Tai, R.S. Muller, "Integrated Movable Micromechanical Structures for Sensors and Actuators," IEEE Trans. on Electron Devices, Vol. ED-35, No. 6, pp. 724-730, June 1988.

Y.C. Tai and R.S. Muller, "IC-processed Electrostatic Synchronous Motor," Sensors and Actuators, Vol. 20, No. 1&2, pp. 49-56, Nov. 15, 1989.

M. Mehregany, K.J. Gabriel, and W.S.N. Trimmer, "Micro Gears and Turbines Etched from Silicon," Sensors and Actuators, vol. 12, pp. 341-348, Nov./Dec. 1987

Early MEMS with kinematic joints

Gears

Revolute joints and linkages

Micro rotary motors


Electrostatic micro rotary motor

MUMPs process (MCNC)

Sacrificial layer process to make a revolute joint

Ravi Jain, undergraduate at Penn.


Sandia’s micro mechanisms

Courtesy of Sandia laboratories, Albuquerque, New Mexico


Sandia’s in-plane revolute joint

Substrate

Pin

Rotor


Floating in-plane revolute joints using only two structural layers

Floating Pin Joints Fabricated From Two Layers of Polysilicon at the Micro Level (Deanne Clements, Larry L. Howell, Nathan Masters, and Brent L. Weight) at Brigham Young University.


Pister’s out-of-plane revolute joint

A surface micromachined hinge(Kris Pister, Berkeley)


Floating revolute joint

Masklayout


Why aren’t kinematic joints not well suited for MEMS?

• More difficult to fabricate• Friction and wear

– Main cause for structural failure

• Clearance in microfabricated kinematic joints is huge– Less accurate than deformable structures

• Some assembly may be required– Cannot be justified economically

• Not always amenable for different types of actuation

• Stiction– Surfaces in close proximity tend to stick together


Example 1: tilting micro-mirrors:single-axis

(Source: www.howstuffworks.com)


Agere (Lucent)’s two-axis mirrorsRaised above using Pister-type revolute jointsSurpentine “torsional” springs-- to get large angles of rotation


Steerable vertical mirrors

Khiem Ng,Central High School, Philadelphia2002

A surpentine torsional spring


Example 2: Micro-manipulation of biological cells

Laser tweezers and scissors operating on a cell (Berns, 1998)

Cell injection using micro pipettes (Nelson, 2000)


Polysilicon microgrippers

C. J. Kim, A. Pisano, and R. S. Muller, Silicon-processes overhanging microgripper, JMEMS, Vol. 1, No. 1, 1992, pp. 31-36.


Minimally invasive capture of cells using a micro cage

C. J. Kim, UCLABi-metal cantilevers curled due to residual stress.Opened with actuating the bottom membrane


Actuation in liquid environments is difficult

CCD camera view of the micro device with a micro object

Micro probe(top view)

Markers

Sponge

Beam width = 375 m In-plane

hydraulic/pneumatic actuation using a vertical membrane.

Manipulation using compliant mechanisms


Main points

• Kinematic joints in MEMS are cool but have limited (or no) practical use.

• Simple deformable structures have been used wisely by MEMS researchers.– Two examples to illustrate this point

follow…


Electrostatic comb-drive actuator– a clever structural design

anchorShuttlemass

Folded-beam suspension Movingcombs

Fixedcombs

Misaligned parallel-plate capacitor


Cancer detection using a cantilever

A. Majumdar, Berkeley

The presence of the virus makes the cantilevers bend.

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