This is a presentation I gave about MEMS processing at Tyndall in 2008. It goes over the various fabrication possibilities at Tyndall. I personally like slide 3 and 4 trying to hook the history of watch making in with MEMS fabrication. This drive to go smaller and smaller with watch making can also be seen in electronics. Coincidentally, the first MEMS device was a time-keeping pendulum.

1. Tyndall National Institute
MEMS Fabrication at
Tyndall
NAP Open Day Presentations
Wednesday 7th May 2008
– Jaap Verheggen
www.tyndall.ie
Introduction
Contents
• Introduction
– A history of small
mechanical things
– How MEMS came about
• MEMS fabrication • MEMS is a big word
– Micro ‘Electro’ Mechanical systems
– Photolithography
• Or Microsystems Technology or
– Etching Micromechatronics or
– Deposition Micromachines
– Growing – Small Movable Parts
– Embossing, Bonding – Applications in: bio, opto, RF,
thermal, radio, electro, etc…
– Either Sensor, process or actuator
MEMS fabrication: the process of making small movable
MEMS fabrication: the process of making small movable
things by transferring a mask to the surface of the device
things by transferring a mask to the surface of the device
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2. History of Small Mechanical Things
The watch
1480 - P.Henlein creates a
springloaded pocketwatch
1659 - C.Huygens invents the
Remontoire, more accurate
1709 - Jewel bearings are used
1844 - A.LeCoultre invents the
millionometre, Micrometer.
1957 - Battery driven watch
1960 – First electronic watch
(transistor pulser) Quartz resonator
1962 - First quarz-based watch Transistor pulser
1972 - First LCD watch Ruby
Watchmakers lathe, Old-style ‘micro’fabrication equipment
achieves accuracy of Drill, lathe, milling, cutting
‘10 μm’
by sharp edge, laser, plasma, discharge,
water, sand, etc.
Limited to ~25 μm accuracy
Not a parallel method, takes a long time to
make (this is not MEMS)
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History of MEMS devices
1987 – The term MEMS ‘invented’ at a
transducers conference
• 1991 – AD commercialize MEMS
accelerometer
• 1993 – Raytheon Commercialize RF MEMS
Switch
• 1993 – TI commercialize DMD (research
started in 1977)
Today, application of MEMS are in
automotive, gyroscopes, mobile com,
microphones, displays, bio medical, etc.
Back in history
• 1977 – First inkjet nozzle
• 1972 – First Pressure sensor
• 1967 – Resonant gate transistor
– Transistor with a micro-pendulum
for oscillation
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3. Photolithography based machining
New-style micro-fabrication, MEMS fab
• To make small movable things by
transferring a mask to the surface of
the device
• Photolithography
– Photoresist is light sensitive,
when exposed it will either
harden or break down
– The design on the mask is
transferred to the photoresist
– For positive resist, exposed parts
become soluble and are washed
away
– Leaves a soft mask on the wafer 30 µm
EV420 Photolithography
for further processing
www.tyndall.ie
Etching
MEMS fabrication
Etching • Photolithography
• (Deep) Reactive ion etching, a • Etching
chemically reactive plasma • Deposition
etches the surface • Growing
• Chemical vapor etching, a • Embossing
chemical gas that reacts on the
surface is pumped in the
chamber
• Chemical wet etching, The
wafer is placed in a chemical 30 µm
bath
• Examples:
– NAP 87, Stokes Inst, crash
test cantilevers
– NAP 124, Waterford IT,
Preparation of molecular
imprinted polymer beads
– DRIE etch, high aspect ratio
etch, geometry dependent
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4. Etching
Crash test cantilevers, NAP 87, Stokes Inst.
– KOH wet etch from the back
– Deposit etch, Aluminum, polyimide
– Deep reactive Ion Etch from the top
– Wet etch of polyimide and aluminum to release
the device
– Shock test, acceleration as function of time to
obtain material properties of silicon
Si Wafer, 525 µm 100 µm
= Silicon Oxide, 50nm = Polyimide, Sacrificial 10µm
= Alumium, Sacrificial, 6µm
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Deposition
Deposition MEMS fabrication
• Sputtering, argon atoms in a • Photolithography
plasma are accelerated towards a • Etching
solid target, this bombardment • Deposition
ejects target atoms that deposit • Growing
on the wafer
• Embossing
• Spin casting, an uncured resin is
poured on a spinning wafer to
form a thin layer, solidified
afterwards
• Evaporation, deposition by
condensation
• Chemical vapour deposition,
volatile gasses pumped in the
chamber react on the surface
• Examples:
– NAP 35, CIT Ultrasonic
membranes
– Humidity sensors, CTVR
– Wafer level Packaging of
MEMS
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5. Deposition
Multi-MEMS process
• Multi-Project Wafer (MPW)
– 3 by 3 mm dies
• MEMS and Zero-Level packaging
• Use of 17 mask layers, +120 fabrication
steps
– Sputtered Aluminium as structural
material
– CVD Silicon oxide as passivation
– Spin on and cured polyimide as
sacrificial layer
• 8 projects involved
Capacitor
plates
Moisture-sensitive
polyimide
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Growing
MEMS fabrication
Growing
• Photolithography
• Electroplating, a metal is plated onto
the surface in a photoresist mould to • Etching
form a structure • Deposition
• Oxidizing, in a oxide rich environment, • Growing
a layer of silicon oxide is created on • Embossing
the surface, this also consumes some
silicon
Examples:
• For Nap 103, TCD, 25 µm copper pillars
were electroplated.
– The pillars are connected to 30 µm
electrodes
– A channel is created over the
pillars for electrohydrodynamic
flow
• For Nap 112, CIT, 2 µm thick, 100 µm
diameter discs were grown on Si.
– Optical signal could be coupled in
the disc by use of an elongated
glass fiber, the light would
resonate in the disc.
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6. Bonding, Embossing
MEMS fabrication
Embossing • Photolithography
• Hot-emboss, a thermoplastic • Etching
polymer is heated above its glass • Deposition
transition temperature and forced • Growing
against a mould • Embossing
• PDMS can be poured on a mould, it
hardens when baked
Bonding
• Si to glass bonding, field assisted
• Fusion bonding of Si to Si, high
temperature
• Adhesive bonding: adhesive is spun
on and activated, other wafer is
placed on top
Si channel wafer
Glass wafer with electrodes, drilled through holes NAP 103, TCD
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Summary
• Fabrication at Tyndall
• Silicon Fabrication
• Compound semiconductor
fabrication
• MEMS fabrication
• All there to make small things
Irish (ROI + NI)
Researcher • Many variations
Fabrication
Design, Modeling
Theory, Idea
Device Integration
Measurement
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7. know more & more & more…
– Thanks for your attention
For more information, visit www.Tyndall.ie,
www.Tyndall.ie/research/MEMS and www.Tyndall.ie/NAP
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