Introduction to mems

mems

1. Introduction to MEMS IV B.Tech EIE, VIII Semester GST, GITAM University, Hyderabad.

2. S.No Topics to be Covered Lectures UNIT – 1 – INTRODUCTION 1 History of MEMS, Overview of MEMS Processes, Properties of Silicon, A Sample MEMS Process. 1,2 2 Definitions and Terminology, A sample Process, Lithography and Etching. 3 3 Micromachining: Subtractive Processes (Wet and Dry etching), 4,5 4 Additive Processes (Evaporation, Sputtering, Epitaxial growth) 6,7 5 Fundamental Devices and Processes: Basic mechanics and electrostatics for MEMS, parallel plate actuators, pull-in point, comb drives. 8,9 6 Electrostatic actuators; MEMS foundries 10,11 7 Cronos MUMPs (multi user MEMS process) 12 UNIT – 2 – MUMPs (Multi User MEMS Process) 8 JDS Uniphase MUMPs processing sequence and design rules. 13,14 9 Design rules; applications; 15,16 10 Micro hinges 17 11 Deployment actuators. 18 12 CMOS MEMS: CMOS foundry processes, 19 13 integrated IC/MEMS, 20 14 MEMS postprocessing, applications. 21,22 UNIT –3 – Thermal Transducers 15 Bimorphs, “ heatuators ”, cilia arrays. 23,24,25 16 MicroOptoElectroMechanical Systems (MOEMS): Micro Scanners, Digital Mirror Display, Retinal Scanning Display. 26,27 17 Grating light valve, 28 18 Coroner cube retroreflector , optical switches, other micro-optical devices 29-30 19 Piezoresistivity ; Scanning Probe Microscopy: scanning tunneling microscope (STM), 31,32 20 Atomic force microscope (AFM)(3 Hrs) 33 UNIT – 4 – Wireless MEMS 21 Mechanical and electrical resonators 34 22 Q-factor, switches, filters 35-36 23 Power for MEMS: thin film batteries, micro fuel cells, energy fields, MEMS 37-38 24 Packaging and Assembly: microassembly: serial and parallel, deterministic and stochastic; microgrippers: HexSil process; packaging techniques 39-40 UNIT-5- The future of MEMS 25 Biomems – neural implants, gene chips, diagnostic chips; 41 29 MEMS in space; mechanical computers; 42 30 Invisible and ubiquitous computing 43 31 Revision 44-45 Total No. of Classes 45

3. Text Books: 1. Fundamentals of Microfabrication : The Science of Miniaturization, Second Edition ISBN: 0849308267, CRC Press, 1997 by Marc J Madou 2. MEMS a Practical Guide of Design, Analysis, and Applications Korvink , Jan, Paul, Oliver 2006. 3. Mechanics of Microelectromechanical Systems Lobontiu , Nicolae , Garcia, Ephrahim 2004. 4. MEMS & Microsystems TMGH 2002 by Tai-ran Hsu 5. Microsensors , MEMS & Smart Devices John Wiley 2002 by JW Gardner & VK Varadan

4. UNIT – 1 – INTRODUCTION History of MEMS, Overview of MEMS Processes, Properties of Silicon, A Sample MEMS Process. Definitions and Terminology, A sample Process, Lithography and Etching. Micromachining: Subtractive Processes (Wet and Dry etching), Additive Processes (Evaporation, Sputtering, Epitaxial growth) Fundamental Devices and Processes: Basic mechanics and electrostatics for MEMS, parallel plate actuators, pull-in point, comb drives. Electrostatic actuators; MEMS foundriesm,Cronos MUMPs (multi user MEMS process)

5. MEMS

6. What are MEMS? Acronym for m icro- e lectro- m echanical s ystems. M icro : Small size. The basic unit of measure is the micrometer or micron ( μ m) 1 μ m = 10 -6 m E lectro : MEMS have electrical components M echanical : MEMS have moving parts S ystems : Refers to integration of components .

7. A brief history of MEMS 1750s first electrostatic motors (Benjamin Franklin, Andrew Gordon) 1824 Silicon discovered (Berzelius) 1927 Field effect transistor patented ( Lilienfield ) 1947 invention of the transistor (made from germanium) 1954 Smith, C.S., " Piezoresistive effect in Germanium and Silicon, Physical Review, 1958 silicon strain gauges commercially available 1961 first silicon pressure sensor demonstrated ( Kulite ) 1967 Invention of surface micromachining ( Nathanson , Resonant Gate Transistor) 1970 first silicon accelerometer demonstrated ( Kulite ) 1977 first capacitive pressure sensor (Stanford) 1980 Petersen, K.E., "Silicon Torsional Scanning Mirror", IBM J. R&D, v24, p631, 1980. 1982 disposable blood pressure transducer (Foxboro/ICT, Honeywell, $40) 1982 active on-chip signal conditioning 1984? First polysilicon MEMS device (Howe, Muller ) 1988 Rotary electrostatic side drive motors (Fan, Tai, Muller) 1989 Lateral comb drive (Tang, Nguyen, Howe) 1991 polysilicon hinge ( Pister , Judy, Burgett , Fearing) 1992 Grating light modulator ( Solgaard , Sandejas , Bloom) 1992 MCNC starts MUMPS 1993 first surface micromachined accelerometer sold (Analog Devices, ADXL50) 1994 XeF2 used for MEMS

8. History

9. Early Semiconductor Fabrication J. Bardeen, W.H. Brattain, “ The first transistor, a semiconductor triode ”, Phys. Rev., 74, 230 (1948).

10. Intel 133 MHz Pentium Processor 3.3 million transistors 0.35 micron lithography 4 layer metalization First silicon: May 1995

11. Example - Inertial MEMS Mechanical component Signal Processing Integrated electronics Silicon substrate Integrated mechanical and electrical components Smart microsensor systems

12. Scales and Dimensions - MEMS 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1 10 -0 10 -1 Human hair ( f 80-100 m m) Silicon die (5 x 5 mm) MEMS Pollen

13. Examples of MEMS You can find MEMS in Automobiles (Air bag sensors) Computer printers (Ink jet print heads) Cell phones (RF devices) Lab-on-a-chip (Microfluidics) Optical devices ( Micromirrors ) Lots of other things

14. MEMS accelerometer MEMS accelerometers are used widely to deploy airbags .

15. MEMS accelerometer Most accelerometers use electrical capacitance to sense acceleration. Se llama “comb structure ( estructura de peine ) Adapted from Microsystem Design by Stephen Senturia , Springer

16. Ink jet print heads Ink dots are tiny (10-30 per mm) and so are the nozzles that fire them.

17. Micromirrors Micromirrors are used as optical switches and even computer displays

18. Why go micro? Micro devices are minimally invasive and can be treated as disposable. (Especially good for chemical and medical applications .) Many physical phenomena are favored at small scales . What are some reasons that you would want to make micro-sized devices?

19. How are MEMS made ? Many techniques borrowed from integrated circuit (IC) fabrication Silicon wafers are commonly used Bulk micromachining Surface micromachining Other techniques

20. How are MEMS made ? Bulk micromachining example - A diaphragm for a pressure sensor Adapted from MEMS : A Practical Guide to Design , Analysis, and Applications , Ed. Jan G. Korvink and Oliver Paul, Springer, 2006 Membrane is piezoresistive ; i.e., the electrical resistance changes with deformation.

21. Bulk micromachining Bulk micromachining example - A diaphragm for a pressure sensor Silicon wafer Grow SiO 2 Spin on photoresist Glass plate Opaque region Unexposed photoresist removed by developer SiO 2 chemically etched with HFl Unexposed resist removed Silicon anisotropically etched with KOH Mask

22. Surface micromachining Surface micromachining example – Creating a cantilever Silicon wafer Deposit aluminum Remove sacrificial layer ( release ) Deposit polyimide Etch part of the layer .

23. Surface Micromachining Mechanical structures formed on the surface of a substrate. Formed from materials deposited on the substrate. Most common method of surface micromachining is known as Sacrificial Layer Technology. Additive process growing / depositing layers of materials, patterning and selectively removing them Substrate Structure

24. Surface Micromachining Silicon Silicon Nitride Silicon Dioxide Dry etch Poly Si Dry etch Wet etch Example on silicon:

25. Micromachining Complicated structures can be made by combining these techniques and repeating

26. Micromachining Everything has to be very clean ! http://www.memsnet.org/news/

27. Fabrication IC Fabrication Deposition Lithography Removal Bulk micromachining Crystal planes Anisotropic etching Deep Reactive Ion Etching Surface micromachining Sacrificial etching Molding Bonding

28. Process Flow Integrated Circuits and MEMS identical Process comlexity /yield related to # trips through central loop Deposition Lithography Etch Wafers Chips

29. Materials Metals Al, Au, Cu, W, Ni, TiNi, NiFe, Insulators SiO 2 - thermally grown or vapor deposited (CVD) Si 3 N 4 - CVD Polymers The King of Semiconductors: Silicon stronger than steel, lighter than aluminum single crystal or polycrystalline 10nm to 10mm

30. Applications Pressure sensors Automotive, Medical, Industrial, … Accelerometers Automotive, Medical, Industrial Gyros Automotive Displays TI DMD, SLM GLV Fiber optics Switches, attenuators, alignment RF components Relays, filters, tunable passive elements Biomedicine Drug delivery, DNA sequencing, chemical analysis