6.777J/2.372J: The MEMSclass Introduction to MEMS and MEMS ... · Introduction to MEMS and MEMS Design Joel Voldman (with ideas from SDS) Massachusetts Institute of Technology. JV:

JV: 2.372J/6.777J Spring 2007, Lecture 1 - 1

Cite as: Joel Voldman, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

6.777J/2.372J: The MEMSclassIntroduction to MEMS and MEMS Design

Joel Voldman

(with ideas from SDS)

Massachusetts Institute of Technology



Outline

> Class odds and ends

> Intro to MEMS

> The challenge of MEMS Design

> Course outline

> Design projects

and then, Microfab Part I



Handouts

> General Information Handout• Lecturers: Carol Livermore, Joel Voldman• Text: Senturia’s Microsystem Design

» Beware: Errata on website

> Schedule

> Student Information Sheet• VERY IMPORTANT• Fill out and hand back at end of class



Handouts

> Lecture notes• Handed out at beginning of class• Extra copies available at Carol’s office

> Library Orientation NEXT FRIDAY FEBRUARY 16• Learn how to use online databases, journals, etc.• This will be VERY useful for Problem Set 2

… and for life!



Course overview

> Course is broken into two halves

> First half• MEMS design and modeling • Seven problem sets

» Differing lengths and complexity» Due on due date IN CLASS

> Second half• Case studies• Design projects

> Grading• 15% Problem sets

» Regrades on psets must be requested promptly • 35% Take-home design problem• 50% Final project



Course conduct and ethics> See policy on cooperation in General Info handout

> We encourage teamwork during the psets• Literature solutions are OK• Students must follow ethical guidelines

» All students must write up their own pset» List those you work with on problem set» Cite any literature solutions used

• Some behavior is patently unacceptable» Use of prior years’ homework solutions

> Cooperation is essential in final design project

> No cooperation is allowed on take-home design problem

> Any breaches will be dealt severely, with no warnings

> Please consult us before doing anything questionable

> web.mit.edu/academicintegrity/handbook/handbook.pdf



Course overview

> What makes this course challenging?

> Relevant physics in lots of fields must be grasped quickly

• We teach a great deal of material in ~2/3 semester

> Every student will learn new concepts

> Design projects• Complex open-ended design problems• Team dynamics

> All of you can learn MEMS design, and we will try to make it easier and fun!



Outline


> Intro to MEMS


> Course outline

> Design projects


Lucas NovasensorCite as: Joel Voldman, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

What are MEMS?

> Micro-Electro-Mechanical Systems

> Microsystems

> Microfabrication

> Microtechnology

> Nanotechnology

> Etc.

Image removed due to copyright restrictions.


JV: 2.372J/6.777J Spring 2007, Lecture 1 -

SandiaCite as: Joel Voldman, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

What are MEMS?

> Microfabrication is a manufacturing technology• A way to make stuff• Adapted from semiconductor industry

» With changes• Therefore, MANY standard design principles hold

> But has unique elements• New materials: SU-8, PDMS• New ways to shape them: DRIE• New material properties

» Bulk vs. thin film• Different physics regimes

» Si at small scales




What are MEMS?

> Definitions vary• Usually made via semiconductor batch fabrication• Usually small

» Some important dimension is <1 mm• Ideally, useful• Used to be actual electro-mechanical systems

» Sensors: Something moves and is sensed electricallyOR

» Actuators: An electrical signal moves something



What are MEMS?> Now, many “MEMS” have no

“E” or “M”• Static microfluidic structures• But often are multi-domain• Electro other domain is very

popular» e.g., Electro Thermal Fluidic

actuation» Microbubble

pumps

Liwei Lin (UCB)

Diffuser valveElectric connection

through holePumpingchamber

Nozzle valve

Liquid outletSilicon

Liquid inletAluminumheater

Pyrex glass

Dual bubble

(B)

50040030020010000

1

2

3

4

5

6

Vol

ume

flow

rate

(µl/m

in)

Pulse frequency (Hz)

Duty = 5%Duty = 10%Duty = 15%

Image by MIT OpenCourseWare.

Images by MIT OpenCourseWare.



MEMS: Starting points

> Some starting points:• 1961 first silicon pressure sensor (Kulite)

» Diffused Si piezoresistors mounted onto package to form diaphragm

» Dr. Kurtz (founder) is MIT graduate, of course• Mid 60’s: Westinghouse Resonant Gate Transistor

» H.C. Nathanson, et al., The Resonant Gate Transistor, IEEE Trans. Electron Devices, March 1967, 14(3), 117-133.

Figure 1 on page 119 in: Nathanson, H. C., W. E. Newell, R. A. Wickstrom,and J. R. Davis, Jr. "The Resonant Gate Transistor." IEEE TransacationsonElectron Devices 14, no. 3 (1967): 117-133. © 1967 IEEE.

Courtesy of IEEE Transactions on Electron Devices. Used with permission.


project


MEMS: Important early work

> Stanford Gas Chromatograph (1975)

• SC Terry, JH Jerman and JB Angell, IEEE Trans Electron Devices ED-26 (1979) 1880

• WAY ahead of it’s time

> 70’s to today: Ken Wise (Michigan) neural probes

> 70’s Inkjet printheads

> 70’s Start of TI DMD

Courtesy of Kensall D. Wise. Used with permission.

Figure 3 on page 1882 in: Terry, S. C., J. H. Jerman, and J. B.Angell. "A Gas Chromatographic Air Analyzer Fabricated on aSilicon Wafer." IEEE Transactions on Electron Devices 26,no. 12 (1979): 1880-1886. © 1979 IEEE.




> MEMS blossomed in the 80’s

> 1982 Kurt Petersen “Silicon as a mechanical material”

• Proc. IEEE, 70(5), 420-457, 1982.

> Mid-80’s BSAC folks (Howe, Mulleetc.) polysilicon surface micromachining

R. T. Howe and R. S. Muller, “Polycrystalline silicon micromechanical beams,” J. of the Electrochemical Society, 130, 1420-1423, (1983).

T. Lober, MIT


r,




> Electrostatic Micromotors• Introduced in 1988-1990• MIT and Berkeley

> Microchip capillary electrophoresis and lab-on-a-chip

• Introduced ~1990-1994• A. Manz, D.J. Harrison,

others

Harrison et al., Science 261:895, 1993

Fan et al., IEDM ’88, p 666.





Lucent micromirrorCite as: Joel Voldman, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

MEMS: Some current hot topics

> Optical MEMS • Switching of optical signals• Big boom in the late 90’s• Big bust in the early 00’s

Muller et al., Proc. IEEE, 8:1705, 1998.Fig. 1 on page 1706 in: Muller, R. S., and K. Y. Lau. "Surface-Micromachined Microoptical Elements and Systems." Proceedingsof the IEEE 86, no. 8 (August 1998): 1705-1720. © 1998 IEEE.



07. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

MEMS: Some current hot topics> RF MEMS

• Smaller, cheaper, better way to manipulate RF signals

• Reliability is issue, but getting there


Figure 15 on p. 64 in: Nguyen, C. T.-C."Micromechanical Filters for Miniaturized Low-power Communications." Proceedings of SPIE Int Soc Opt Eng 3673 (July 1999): 55-66.

Cite as: Joel Voldman, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 20

Image removed due to copyright restrictions.Figure 9 on p. 17 in: Nguyen, C. T.-C. "Vibrating RF MEMS Overview: Applications to Wireless Communications." Proceedings of SPIE Int Soc Opt Eng 5715 (Jan. 2005): 11-25.



MEMS: Some current hot topics> BioMEMS

• Shows promise for diagnostics

• Next era of quantitative biology

• No commercial winners yet Wise (UMich)

Mathies (UCB)Chen (UPenn)Voldman (MIT)

Courtesy of Joel Voldman. Used with permission.Courtesy of Richard A. Mathies.Used with permission.


Courtesy of Kensall D. Wise. Used with permission.



MEMS: Commercial success

> This isn’t just academic curiosity

> There are products you can actually buy• Pressure sensors in your car & in your body• Accelerometers EVERYWHERE• Gyroscopes• Ink-jet print heads• Texas Instruments’ micro-mirror array

Nintendo WiiMotorola Razr

HP





» Moderately precise & accurateCite as: Joel Voldman, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

MEMS: Commercial success

> The major successes have been pressure and inertial sensors

• Why?» Most mature: 40+ years» Huge initial market: automotive

al


Honeywell microswitch

Image removed due to copyright restrictions.Analog Devices pressure sensor.

» Recent access to huger commercial market

» Easy access to physical sign» Smaller than alternatives» Cheaper than alternatives

– In medical market, that means disposable

» Can be integrated with electronics

JV: 2.372/6.777 Spring 2007, Lecture 1 - 22

Outline


> Intro to MEMS


> Course outline

> Design projects



MEMS Design

> For our purposes, design means• Create a device or system• With quantitative performance parameters (e.g., sensitivity)• Subject to constraints

» Size, price, materials, physics» Some clearly defined … some not

> This is hard no matter what the device is



MEMS Design

> MEMS design is hard because• The manufacturing technology is actually quite imprecise

» 10% tolerance on in-plane dimensions is typical» Out-of-plane tolerances may be much better

… or much worse• Fabrication success is NOT a given AND is tied to the design• The material properties are unknown or poorly known• The physics are often “different”

» Not the traditional size scales• The system must be partitioned

» Which parts to integrate on-chip?• Packaging is non-trivial

» NOT like ICsAll these questions should be answered early on



Some solutions to this challenge

> Approach #1• Make something easy or not useful, etc.

> Approach #2• Do incorrect back-of-the-envelope design and then proceed

> Approach #3 (grad student favorite)• Create a large range of structures One of them will work, hopefully

> Approach #4 (the MEMS class way)• Predictive design of all you know to enable chance of 1st round

success• Determine necessary modeling strategies for a given problem

» From analytical to numerical» In THIS class we concentrate on analytical and tell you where it

fails• Be aware of what you don’t know, can’t control, and what your

assumptions are



MEMS Design

> Different levels of design• Analytical design

» Abstracted physics» ODEs, Scaling, Lumped-element models

• Numerical design» Intermediate approach between physical and analytical

design• Physical level:

» 3-D simulation of fundamental physics» PDEs, finite-element modeling, etc.

> Tradeoff between accuracy and effort/time

> Always limited by fundamental knowledge of properties or specifications



Outline


> Intro to MEMS


> Course outline

> Design projects



Course goal

> Course goal: Learn how to design any microfabricated device/system

> Learn how to• Understand the design process• Partition the system• Determine and model relevant physics• Evaluate different designs & fabrication technologies• Understand the linkage between fabrication and design



Course outline

• Not true of many other worlds• Example: diaphragm pressure sensor

» Would like to use Si because of piezoresistors

» Material choice sets fabrication technology: KOH

» Fabrication technology determines shapes and physical limits: diaphragm thickness

» This in turn affects performancedeflection ~ (thickness)-3

> Material properties also matter greatly• MEMS material properties are often poorly characterized

> First up: fabrication and material properties (4.5 lectures)

> MEMS fabrication is intimately coupled with design

Image removed due to copyright restrictions.Photograph of Motorola MPX200 x-ducer.



Course outline

> Fabrication lectures will focus on MEMS process development

• Unit processes• Order-of-operations• Front-end and back-end processing

> These themes will be broadcast throughout the term



Course outline

> Next we introduce the electrical and mechanical domains (2 lectures)

> This gives us something concrete to design

> Split class into two groups for Lectures 6 & 7

> Group 1: Basic Elasticity and Structures

> Group 2: Basic Electronics (Circuits, Devices, Opamps)

> Goal is to teach fundamentals at a slower pace without boring “experts”

> Rejoin at Lecture 8



Course outline

> Split sessions

> Which session should I attend?

> Go for material you are less familiar with• MEs go to Electronics• EEs go to Elasticity/Structures

> Notes for both lectures will be available to all

> What if you don’t know either subject?• We will hold makeup lectures of Elasticity/Structures• Please let us know ASAP if you need a makeup



Course outline

> Next we present an approach to design (3 lectures)• Lumped-element modeling• Different energy domains all use common language

» Electrical, Magnetic, Structural, Fluidic, Thermal• Therefore, when you encounter a new domain, you can

quickly attach it to existing knowledge• Enables quick design• But has limits…



Course outline

> Then we explore additional energy domains (6 lectures)

• Structures, Thermal, Fluids & Transport• What physics are relevant?

» Not all of fluids, just low-Reynolds-number flows• How do we extract lumped-element or analytical models?

» What is the “resistance” of a microfluidic channel?



Course outline

> Systems issues (4 lectures)• Noise, feedback, packaging, design tradeoffs

> Partitioning• A major theme of the course• Can’t design device with process• Also can’t design device without package• Should you put any electronics on-chip?• Can you design MEMS to make read-out easier?• What are the trade-offs between different choices



Course outline

> Finally, case studies• Integrate everything we have up to now to learn about design

process of actual devices• Analog Devices accelerometer• TI micro-mirror• BioMEMS such as integrated PCR devices



Outline


> Intro to MEMS


> Course outline

> Take-home and team design projects



Design projects

> Design is the heart of this course

> We will have short design problems on the psets

> In March, we will have a take-home graded design problem

• Multifaceted: fabrication, electromechanical analytical design• Students will prove their design to staff

> In April, team design projects start



Design projects

> Projects, projects, projects• Teams of 4-6 people• Chosen by US, with input from you• Only students taking class for CREDIT can participate• All teams have a mentor

> Paper design of a MEMS-based device• Quantitative system-level specifications• Analytical design, finite-element modeling, fabrication,

packaging, electronics, calibration, etc.• Final project grade 50% due to team, 50% due to individual

> Lectures will focus on case studies

> Almost no more homeworks



Design projects

> Project timeline• Short description March 9• Your preferences March 23• Teams assigned April 4• Preliminary report

» Is team functioning and has it started?• Intermediate report

» Is team functioning and is it going to finish?• Final presentations and report

» ~30-min presentation in front of judges» 20-pg manuscript-quality report» Significant prize to winning team



Design projects

> Use to illustrate course approach

> A piezoresistive sensor for biomolecular recognition (2003)

• The goal of this project is to create cantilever-based device that detects stress induced by molecular binding.

• Two cantilevers (operated differentially) will be created out ofSi with integrated poly-Si piezoresistors.

• The packaged device will be used in a hand-held point-of-care diagnostic monitor and so must be robust, small, and connected to a circuit that gives an output proportional to the logarithm of the concentration ratio.

> Show slides from presentation to illustrate design process

Images removed due copyright restrictions.Student final presentation: Gerhardt, Antimony L., Saif A. Kahn, Adam D. Rosenthal,Nicaulas A. Sabourin, and Keng-Hoong Wee. "A Piezoresistive Molecular Binding Detector."


CL: 6.777J/2.372J Spring 2007, Lecture 1 - 1

Cite as: Carol Livermore, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Microfabrication for MEMS: Part I

Carol Livermore

Massachusetts Institute of Technology

* With thanks to Steve Senturia, from whose lecture notes some of these materials are adapted.



Outline

> A way to think about process design

> Surface and bulk micromachining concepts

> Next class: substrates, lithography and patterning, and thin films

> Class #3: etching, wafer bonding (including bulk micromachining), surface micromachining and process integration

> Class #4: in class process design exercise

> Class #5: fabrication for the life sciences and material properties



Learning to “speak” fab

> There are huge lists of things that you can and can’t do in microfab (vocabulary)

> There are limits on how you can combine steps together to form a process (grammar)

> An experienced microfabricator knows most of these capabilities and limits from long experience (fluency)

> A beginning microfabricator must struggle to master details and rules

> Our goal: teach enough vocabulary and grammar to get you started (today starts with grammar)

> Only practice will make you fluent!



The promise and the pain

> Microfabrication can produce a near infinite array of structures

> But making your particular structure can be very difficult!

> You’d think it would be easy…• Functional requirements dictate materials and geometry

> … but it’s not! Fabrication processes are not ideal.• Materials property variability• Geometric variability

> Early phase design must seek a self-consistent solution to the question of “what will I make and how will I make it?”

> But for that, we must be familiar with our tools and how they work



Crayon Engineering

> At the early stages of MEMS design, conceptual process design rather than highly detailed process design is required

> It is necessary to obey• The laws of physics• Constraints on temperatures• Constraints on chemical compatibility• Design rules on geometry

> But we can draw our processes with crayons• Hence the phrase “crayon engineering”

> As we approach the final design, we need CAD tools


Integrated circuits outCite as: Carol Livermore, course materials for 6.777J / 2.372J Design and Fabrication of Microelectromechanical Devices, Spring 2007. MIT OpenCourseWare (http://ocw.mit.edu/), Massachusetts Institute of Technology. Downloaded on [DD Month YYYY].

Making integrated circuits

1. The Front End (creating transistors, etc.):

Hot processes: growing defect-free oxides, diffusing dopants to create transistorsClean processes: Junk will diffuse in, too, if you let it

2. The Back End (wiring up the system):

Cooler processes:depositing metal inter-connects, separating layers with less perfect insulatorsNot-so-clean processes:Dirt is still bad, but you can wash it off

Wafers in



Things to remember about IC fab

> A LOT of effort has gone into designing IC processes so that they achieve the desired result and don’t violate the laws of physics

> Why these processes are hard to design and improve:• What if the circuit would be better if it included feature A, but

making feature A requires a back end step followed by a front end step?

• Typical solutions: omit feature A or create a back end version of the front end step

• An unacceptable solution: just go from the back end process into the front end tool. This will contaminate the fab line and may melt your back end features in the process.

> Bottom line: IC processing is always done the same way, with a few variants



Things to remember about MEMS fab

> You are subject to many of the same restrictions as the IC designers…

• Laws of physics• Restrictions imposed by vendors: you can’t do x because it would

contaminate my tools from the point of view of my other customers

> … but you have additional challenges and advantages• Often there is no baseline process to work from (though the

literature can often give you a good start)• There is no guarantee that conventional processes and tools can

produce your part• The MEMS tool kit is significantly broader than the IC tool kit (so

there’s more available, but it’s up to you to figure out how to turn the raw material into a functional process)



The MEMS tool kit

The Front End (with some front end-compatible

MEMS additions)

The Back End (with some back end-compatible

MEMS additions)

Everything else:

Soft lithography (polymers, stamping, microcontact printing…)ElectroplatingElectron beam lithographySpin-cast materials (e.g. spin-on glass)PiezoelectricsMagnetic materialsAnodic bonding of glass to silicon



An important caveat

> MEMS processes also basically flow from the front end to the back end

> The lines between front end and back end processes are not set in stone – they depend on your tolerance for risk/contamination.

• How clean is clean?• How hot is hot?

> We will present unit processes according to whether they are roughly front end, back end, or “everything else” processes, but it is up to you, the process designer, to consider the actual temperatures, contamination, and materials compatibilities that are involved. What is clean for my application may not be cleanenough for yours.



Implementation of rules is lab-specific (MTL example)

Complete chart is at http://www-mtl.mit.edu/services/fabrication/ptc_matrix.html

Chart removed due to copyright restrictions.



Outline

> A way to think about process design

> Surface and bulk micromachining concepts

> Next class: substrates, lithography and patterning, and thin films

> Class #3: etching, wafer bonding (including bulk micromachining), surface micromachining and process integration

> Class #4: in class process design exercise

> Class #5: fabrication for the life sciences and material properties



Fundamentals of Surface MicromachiningSurface Micromachining> A technique for fabricating micromechanical devices by

selectively depositing and etching thin films on the surface of a substrate

> Structural layers are the thin films that form the final structure

> Sacrificial layers are thin films that support a MEMS structure during fabrication, until it is released (that is, until the sacrificial layer is etched away)

Important techniques for surface micromachining> Lithography and patterning> Wet and dry etching> Deposit thin films by CVD, PECVD, thermal oxidation,

evaporation, etc.

Sandia: surface micromachined gear chain


Courtesy of Sandia National Laboratori es, SUMMiT™ Technologies, www.mems.sandia.gov


http://www.mems.sandia.gov/



Texas Instruments Digital Mirror Display

> One MEMS example: inside the projector

http://www.dlp.com/

Images removed due to copyright restrictions.

Figures 48 and 50 in Hornbeck, Larry J. "From Cathode Rays to Digital Micromirrors: A History of Electronic Projection DisplayTechnology." Texas Instruments Technical Journal 15, no. 3 (July-September 1998): 7-46.

http://www.dlp.com/



Berkeley: surface micromachined microphotonics

Figure 5 on page 316 in: Friedberger, A., and R. S. Muller. "Improved Surface-micromachined Hingesfor Fold-out Structures." Journal of Microelectromechanical Systems 7, no. 3 (1998): 315-319. © 1998 IEEE.



Fundamentals of Bulk Micromachining

Bulk Micromachining

> Selectively etch bulk substrate to create microelectronic or micromechanical structures

> Remaining material forms the device structure> Moving structures, trenches, and membranes possible

Important Techniques for Bulk Micromachining

> Lithography and patterning> Wet and dry etching

• Etch rate and profiles are important• Selectivity and masking materials, too!

> Wafer bonding• A process for permanently attaching two wafers together



MEMS energy harvester

Designed for microWatts.

Figure 5 on page 67 in: Meninger, S., J. O. Mur-Miranda, R. Amirtharajah,A. Chandrakasan, and J. H. Lang. "Vibration-to-electric Energy Conversion."IEEE Transactions on Very Large Scale Integration (VLSI) Systems 9, no. 1(2001): 64-76. © 2001 IEEE.

Mur-Miranda, Jose Oscar. "Electrostatic Vibration-to-ElectricEnergy Conversion." Doctoral diss., Massachusetts Instituteof Technology, 2004, p. 88.



MIT: bulk micromachined microengine

Image removed due to copyright restrictions.3-D cutaway of a micromachined microengine. Photograph by Jonathan Protz.



NIST: bulk micromachined micro-heater

PolysiliconPolysilicon micromicro--heater suspended heater suspended above silicon substrateabove silicon substrate

Figure 1 on page 57 in: Parameswaran, M., A. M. Robinson, D. L. Blackburn, M.Gaitan, and J. Geist. "Micromachined Thermal Radiation Emitter from a CommercialCMOS Process." IEEE Electron Device Letters 12, no. 2 (Feb. 1991): 57-59. © 1991 IEEE.



Preview: Unit Processes and Integration> Next class we will start to fill in the details of the front end, back

end, and everything else with a set of unit process steps out ofwhich processes can be built (vocabulary)

• Oxidation• Implantation and Diffusion• Lithography• Selective Etching• … etc.

> But always remember to consider compatibility of the steps in the overall, integrated process sequence (grammar) – this is critical to the success of the MEMS device

> Also remember that theoretical compatibility isn’t enough! The process sequence must be available at your facility or your vendor’s facility in order for you to use it!

Documents

6.777J/2.372J: The MEMSclass Introduction to MEMS and MEMS ... · Introduction to MEMS and MEMS Design Joel Voldman (with ideas from SDS) Massachusetts Institute of Technology. JV: