a glimpse of mems - penn engineeringmeam550/fall2001/notes2001/meam550intro.pdf · a glimpse of...

G.K. Ananthasuresh, U. of Pennsylvania, Sep. 2001

Mechanical Engineering and Applied MechanicsUniversity of Pennsylvania

A glimpse of MEMS

G. K. AnanthasureshSeptember 17, 2001

Presented to MEAM 550 (Fall 2001) students


What’s in a name?

� Micro-Electro-Mechanical Systems (MEMS)Widely used in Americas.

� MicroSystems Technology (MST)Popular in Europe.

� MicromachinesUsed in Japan.

� MicroscienceSome people prefer to call it this way as they begin to explore scientific aspects of MEMS.


Outline

� What are they?� How small are they?� How are they useful?� How do they work?� What are they made of?� How are they made?� How do you design them?� What are the modeling and design issues

and challenges for us?


A MEMS design question

What does this mean?

1. MEMS field is somewhat mature because people are asking routine questions about how to design them.

2. There must be something different about designing them.

3. There is a need to learn the basics of the field and be familiar with the jargon of the field.

And so we begin…


What are they?

� MEMS are systems that integrate…� sensing� actuation� computation� control� communication� power They are…

smallermore functionalfasterless power-consuming

and cheaper!

G.K. Ananthasuresh, U

. of Pennsylvania, Sep. 2001

How

small are they?

0A1 nm

0.1 um10 um

1 mm

100 mm

10 m

10 nm1 um

100 um10 m

m1 m

Atoms

MoleculesDNA

NanostructuresVirus

Smallest micro-electronic features

Nanotechnology

Microsystem

sM

esoM

acrosystems

BacteriaBiological cellsDust particles

Dia. of human hair

MEMS Optical fibers

Packaged ICsPackaged MEMSLab-on-a-chip

Plain old machinesHumansAnimalsPlamtsPlanes, trains, and automobiles

Precision machining

Nano-m

achiningM

icro-machining

Macro-m

achining


Why are they small?

“Micro” size is almost incidental.

� They are small because of the technologies used to make them.

� And it is economical to make them small –when made in large volumes just like microelectronics.

� Of course, there are some MEMS devices that would not work if they are any bigger.


A bit of history…

� “There is plenty of room at the bottom”- A 1959 lecture by Richard Feynman

� Pioneered by Professor James Angell at Stanford University, researchers at Westinghouse in late 1960’s into 1970’s

� “Infinitesimal Machinery”- A 1983 lecture by Richard Feynman

� Formal identity (“MEMS”) to the field came in late1980’s


What (more) are they?

Solid state transducers MEMSEarly on…

And later…

Integrated systems

sensorsactuators

• are batch fabricated• are economical• have more functionality• involve physical, chemical, biochemical phenomena at small scales• act upon macro scale too

Take leverage of the enormously successful VLSI technology


How are they useful

� Pressure sensors� Accelerometers� Ink-jet printer heads� Projection display with micro mirror array� Portable clinical analyzers� etc.

Movable solids and fluids at microscale made possiblelots and lots of sensors and actuators.

Commercial successes


More applications

� Inertial measurement devices� Accelerometers, gyroscopes

� Mass data storage� Opto-mechanical devices

� Projection displays, photonics, optics-on-a-chip

� Flow control� Bio-chemical lab-on-a-chip� Communication hardware

� Mechanical filters, RF-switches and relays

� Chemical microreactors� Power MEMS

� Micro engines, generators


A slide from DARPA-MTO website


A slide from DARPA web siteUCLA

MEMS creating large effects – an example


A slide from DARPA-MTO web site

Towards lab-on-a-chip

Bio-flips


A slide from DARPA-MTO web site

Impact on the health-care


Outline

� What are they?� How small are they?� How are they useful

� How do they work?

Pressure sensor

V

Capacitive sensing Piezoresistive sensing


How do they work?

V

Accelerometer

Side view

Top view


How do they work?

torsional beam

actuating electrode 1

Tiltablemirror

torsional beam

actuating electrode 2

TI’s digital light processor


What lies beneathTI’s digital light processor (DLP) and deformable mirror display (DMD)

Ant’s leg on the DMD array

Anatomy of DLP/DMD


How do they work

Ink-jet printer head

“drive” air bubble

ejectedink dropletWeight: ng

paper

resistive heater

orifice

�Electronics are integrated to trigger the drive bubble


How do they work?

A mechanical relay

V

Dielectric

Signal input

Signal output


How do they work?

A normally closed fluidic valve

FlowGlass

Trapped fluid Glass

Silicon

(Redwood Microsystems)


How do they work?

V

A diaphragm pump

Diaphragm

Passive inlet valve Passive outlet valve


Outline

� What are they?� How small are they?� How are they useful� How do they work?

� What are they made of?� How are they made?


What are they made of?

Phase 1: Old materials and old processesSilicon, its oxide, nitride, and some metalsIC-chip processing technology

LithographyThin film deposition (e.g., chemical vapor deposition – CVD)EtchingDoping

Phase 2: Old materials and new processesSilicon, its oxide, nitride, glass, polysilicon, and some metalsIC-chip processing techniques enhanced as “micromachining” techniquesSacrificial layer process

Deep reactive ion etchingLIGA HexilDissolved wafer process

Etc.Wafer bonding


What are they made of (contd.)

Phase 3: New materials and old processesPolymersMore metalsCeramicsSilicon carbidePiezoelectric filmsFerroelectric filmsShape-memory materials, etc.

Phase 4: New materials and new processesProcesses unconventional to the microelectronic fieldProcesses that re-define the size of MEMS – micro to meso or nanoDeposition and etching for the new materials

e.g., PDMSGeorge Whitesides at Harvard


How are they made?

� Surface micromachining� Deposition of thin films (mainly polysilicon)� Etching using masks� Layered construction

� Bulk-micromachining� Carving features into “bulk” wafers by etching

� Wafer bonding� Patterning individual wafers� Wafer-to-wafer bonding

� LIGA� HEXIL


Micromachining is not precision machining!

Precision machining � Relative tolerance (feature to part size) is better than 10-4.

For micromachinig, it is 10-2 to 10-3.Roughly what we have for building houses.

With micromachining,

You can make it small, but not precisely.(at least not yet. Wait for nanotechnology…)


Surface micromachining

Silicon wafer

Deposit or grow silicon dioxide

Pattern the oxide using a maskDeposit polysilicon

Pattern polysilicon

Sacrifice oxide layer by dissolving

The sacrificial layer process to make released structures (Berkeley)


Types of etching

(100) silicon

(110) silicon

(111) plane

(111)

With agitation

Without agitation

Isotropic etching

Anisotropic etching

Slantedsurfaces


Bulk micromachining

Silicon wafer

Etch using a mask

Boron doping using a mask

Dissolve undoped silicon

Boron doped dissolved wafer process (Michigan)

Flip and bond to a glass

Glass


Wafer bonding

Etch a cavity in a wafer

Thin down / polish and etch

Bond another wafer

Released cantilever using MIT’s wafer bonding process


Making an electrostatic micromotorusing surface micromachining

Cronos MUMPs (formerly MCNC MUMPs)

Stator poles

Rotor

Top view

Side view

After sacrificing oxide layers…


Making a micromotor

Deposit poly0 Etch poly0 Deposit oxide1

Dimples in oxide1 Etch oxide1 Deposit poly1


Making a micromotor (contd.)

Etch poly1 Deposit oxide2

Cross-section up to this point…



Making the micromotor (contd.)

Etch oxide2 Deposit poly2 Etch poly2

Deposit and etch metal

Cross-section before sacrificing oxide layersCronos MUMPs (formerly MCNC MUMPs)


Finished micromotor


Micromotor after “release”



How much should we know about u-fab?

www.seas.upenn.edu/~meam550


Visualize device from a verbal description of the process

Being able to draw the process flow diagrams from a description.

Shallow pits were etched into n-type substrates, and p-type deflection electrodes were diffused in the above pits, followed by fusion bonding of a second wafer above the first. The top wafer was then ground and polished down to a thickness of 6 um. A passivation layer was then formed on the top wafer and sensing piezoesistors were formed using ion implantation, after which contact holes for metallization to connect to he diffused deflection electrodes were etched. Bond pads and interconnect metallization were then deposited and patterned, followed by etching of the diaphragm from the back of the wafer. Finally, two slots were etched next to the beam to release it over the buried cavity. (Petersen et al., 1991)

See http://www.seas.upenn.edu:8080/~meam550/solution2.html


Visualize the process steps from a device cross section

Visualizing a process from a cross-section.

How was this made?See http://www.seas.upenn.edu:8080/~meam550/solution2.html


MEMS Foundries

Cronos MUMPs (formerly MCNC’s MUMPs)Now, owned and operated by Uniphase.

You don’t have to make them if you don’t want to or can’t.


Making elements of mechanisms

A surface micromachined hinge(Kris Pister, Berkeley)

Substrate hinge


Floating hinges

Masklayout


Electrostatic comb drive

anchorShuttlemass

Folded-beam suspension Movingcombs

Fixedcombs

Misaligned comb capacitors align creating actuation.


Sandia’s micro mechanical lock

Pin in a maze


Close-up of Sandia’s micro lock


Merry go-around for mites

See Sandia’s web site for animation


Sandia’s SUMMiT process revolute joint

Substrate

Pin

Rotor


Deep etching

Deep RIE (reactive ion etching) to get vertical sidewalls over large depths of several hundred microns.

E.g., SCREAM (Cornell) bulk-micromachining


SCREAM process

Deposit and pattern mask oxide

Deep RIE silicon etch

Deposit sidewall oxide

Etch bottom sidewall oxide

Second deep RIE silicon etch

Isotropic silicon etch

Noel MacDonald, Cornell university


Packaging!

Packaging is a big problem with MEMS. Sometimes, it may be better not integrate sensor/actuator and electronics.

Signal redistributionMechanical supportPower distributionThermal managementFluidic fittingsEtc.

Packaging � access to and protection from the external macro world

Ball and wire bondingFlip-chipSandia’s processResearch continues…

Packaging serves…

Some techniques


Outline

� What are they?� How small are they?� How are they useful� How do they work?� What are they made of?� How are they made?

� How do you design them?� What are the modeling and design issues

and challenges for us?


Modeling and design of MEMS –What is different?

Integration of sensor, actuator, mechanism, processor, power, and communication makes system level tasks challenging

-- common representation for multiple energy domains

Device level too has multiple energy domains-- macromodels

Component level-- coupled energy domain equations

Mask level-- geometric modeling


Modeling and design of MEMS

System

Device

Component(physical)

Artwork of masksand process

Each level involves designThere is “analysis” (forward) problem and “synthesis” (inverse) problem.

Representing as block diagrams of multi-domain subsystems

Reduced order “macro models” of the components

Multiple, coupled energy behavioral simulations

Defining mask geometry for the process steps


The future of MEMS?

The proverb:

Forecasting is difficult, especially the future.(from Chinese fortune cookies)

In any case, MEMS will impact the following industries:

AutomotiveAerospaceBiomedical/bio-techHealth-careTelecommunicationInformation technology


Further reading

�Principles of microfabrication – Marc Madou

�Micromachined transducers: A source book – Greg Kovacs

�Microsystem Design – Steve Senturia

�MEMS: Advanced materials and fabrication methods – National Research Council (NRC)

committee report, 1997

�An Introduction to Microelectromechanical Systems Engineering – N. Maluf

�Microsensors – J. W. Gardner

�Sensor Technology and Devices – L. Ristic

�Transducers, Sensors, and Detectors – R. G. Seippel

�Microactuators: Electrical, Magnetic, Thermal, Optical, Mechanical, Chemical, and Smart

Structures – M. Tabib-Azar

�Nano- and Microelectromechanical Systems: Fundamentals of Nano- and

Microengineering – S. E. Lyshevski

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