Lecture 1 a Role of Structures and Mechanisms

Lecture 1 a Role of Structures and Mechanisms in MEMS A general overview of structural aspects of MEMS. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 1

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 Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 2

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 Willis scope of energy in structures/mechanisms to other domains, the role of structures and mechanisms in MEMS is easily apparent. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 3

Accepted size range for MEMS Nano-machining Micro-machining Precision machining Plain old machines Humans Animals Plamts Planes, trains, and automobiles 10 m 100 mm Packaged ICs Packaged MEMS Lab-on-a-chip 1 mm Optical fibers 10 um MEMS Smallest microelectronic features 0. 1 um Nanostructures Virus Molecules DNA Atoms 1 nm Microsystems Meso Macrosystems 1 um 100 um 10 mm 1 m Bacteria Biological cells Dust particles Dia. of human hair Nanotechnology 10 nm Macro-machining Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 4

MEMS devices in 1970’s and early 80’s Ink-jet printer head Bassous E. , Taub H. H. , Kuhn L. “Ink jet printing nozzle arrays etched in silicon” Appl. Phys. Lett. 31, 135 (1977) Micro mirrors for steering light Petersen K. E. "Micromechanical light modulator array fabricated on silicon" Appl. Phys. Lett. 31, 521 -523 (1977) Petersen K. E. “Silicon torsional scanning mirror” IBM J. Res. Dev. 24, 631 -637 (1980) Accelerometer Roylance L. M. , Angell J. B. “A batch fabricated silicon accelerometer” IEEE Trans. on Electron Devices 26, 1911 -1917 (1979) Optical fiber connector Schroeder C. M. "Accurate silicon spacer chips for an optical fiber cable connector" Bell. Syst. Tech. J. 57, 91 -97 (1977) Microfluidic device 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) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 5

MEMS devices in 1970’s and early 80’s Pressure sensors 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) Ko W. -H. , Hynecek J. , Boettcher S. F. “Development of a miniature pressure transducer for biomedical applications” IEEE Trans. on Electron Devices T-ED 26, 896 -1905 (1979) Other types of sensors Kimura K. “Microheater and microbolometer using microbridge of Si. O 2 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) Stemme G. “A monolithic gas flow sensor with polyimide as thermal insulator” IEEE Trans. on Electron Devices TED-33, 1470 -1464 (1986) Optical switching and multiplexing Gustafsson K. , Hök B. “Fiberoptic switching and multiplexing with a micromechanical scanning mirror” Proc. 4 th Int. Conf. on Solid-State Sensors and Actuators, Tokyo, June 3 -5, P 212 (1987) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 6

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) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 7

A MEMS accelerometer made in 1979 Bulk micro machining Piezoresistorbased sensing Roylance L. M. , Angell J. B. “A batch fabricated silicon accelerometer” IEEE Trans. on Electron Devices 26, 1911 -1917 (1979) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 8

Bulk micromachining Isotropic etching With agitation Without agitation Anisotropic etching (111) plane (100) silicon Slanted surfaces (111) (110) silicon Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 9

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 batchfabrication of “assembled” micro-mechanisms without assembly. – Crucial development: sacrificial layer process using polysilicon as the structural layer. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 10

Early MEMS with kinematic joints Gears 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 Revolute joints and linkages 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. 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. Micro rotary motors 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, 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. A 21–A 23, pp. 173 -179, 1990. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 11

Electrostatic micro rotary motor Sacrificial layer process to make a revolute joint MUMPs process (MCNC) Ravi Jain, undergraduate at Penn. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 12

Sandia’s micro mechanisms Courtesy of Sandia laboratories, Albuquerque, New Mexico Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 13

Sandia’s in-plane revolute joint Pin Rotor Substrate Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 14

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. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 15

Pister’s out-of-plane revolute joint A surface micromachined hinge (Kris Pister, Berkeley) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 16

Floating revolute joint Mask layout Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 17

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 Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 18

Example 1: tilting micro-mirrors: single-axis (Source: www. howstuffworks. com) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 19

Agere (Lucent)’s two-axis mirrors Raised above using Pister-type revolute joints Surpentine “torsional” springs -- to get large angles of rotation Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 20

Steerable vertical mirrors A surpentine torsional spring Khiem Ng, Central High School, Philadelphia 2002 Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 21

Example 2: Micro-manipulation of biological cells Laser tweezers and scissors operating on a cell (Berns, 1998) Cell injection using micro pipettes (Nelson, 2000) Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 22

Polysilicon microgrippers C. J. Kim, A. Pisano, and R. S. Muller, Silicon-processes overhanging microgripper, JMEMS, Vol. 1, No. 1, 1992, pp. 31 -36. Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 23

Minimally invasive capture of cells using a micro cage C. J. Kim, UCLA Bi-metal cantilevers curled due to residual stress. Opened with actuating the bottom membrane Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 24

Actuation in liquid environments is difficult Beam width = 375 m Micro probe (top view) Markers In-plane hydraulic/pneumatic actuation using a vertical membrane. Sponge CCD camera view of the micro device with a micro object Manipulation using compliant mechanisms Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 25

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… Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 26

Electrostatic comb-drive actuator– a clever structural design Folded-beam suspension Moving combs Shuttle mass Misaligned parallel-plate capacitor anchor Fixed combs Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 27

Cancer detection using a cantilever The presence of the virus makes the cantilevers bend. A. Majumdar, Berkeley Stiff Structures, Compliant Mechanisms, and MEMS: A short course offered at IISc, Bangalore, India. Aug. -Sep. , 2003. G. K. Ananthasuresh Slide 1 a. 28