Thomas Adams, PhD
¿Quien soy y por
qué estoy aquí?
En el mundo hispano:
Tomás McDaniel Adams McDaniel
Soy profesor de ingeniería mecánica en
Rose-Hulman Institute of Technology
Mis estudiantes me llaman “Doctor Tom”.
Más cabello
Terre Haute, Indiana, USA
Private university with ~ 2000 students, mostly
undergraduate (pregrado)
Ciencias, ingeniería, y matemáticas
Introduction to MEMS
(micro-tecnología)
Movie of a motor
Motor and gear train movies from Sandia National Laboratory
Movie of a motor
Motor and gear train movies from Sandia National Laboratory
Still pictures of motor
Another view of the engine
A still picture of the motor…
with a spider mite on it!
Movie of a motor
Motor and gear train movies from Sandia National Laboratory
Movie of a motor
Motor and gear train movies from Sandia National Laboratory
Movie of a motor
Motor and gear train movies from Sandia National Laboratory
Course overview and objectives
Overview:
This course gives an introductory treatment of MEMS, also known as microsystems and
micro-technology (MST). Fabrication, device functionality, and modeling strategies are
explored.
Objectives (Objetivos):
Through the student work in the course program, the student will be able to:
 Identify the relative importance of different physical phenomena based on length
scale
 Identify and describe the most commonly used fabrication processes in making
MEMS devices
 For a simple MEMS device, identify the major required fabrication steps and put
them in the appropriate order (create a process flow)
 Use the principles of elastic theory in predicting the stress/strain state of MEMS
devices
Course overview and objectives
Objectives (Objetivos) continued:
Through the student work in the course program, the student will be able to:
 List a number of common MEMS transducers and explain their operating
principles
 Explain in detail the operating principles of a piezoresistive MEMS pressure
sensor, and predict the performance of such a device
 Give a well-formed argument considering a microtechnology-based solution
for a given problem
 Gain experience using English in spoken and written forms as a means of
expressing technical ideas
Topics
Specific topics
1. Introduction to MEMS: Scaling and basic fabrication
2. The Substrate
3. Additive Techniques
4. Creating Patterns – Lithography
5. Bulk Micromachining
6. Surface Micromachining
7. Process flow
8. Solid mechanics
9. Overview of MEMS operating principles
10. Modeling case study: piezoresistive sensors
References
Required
• Introductory MEMS: Fabrication and Applications by
Thomas Adams and Richard Layton, Springer
Disponible (¡gratis! ) en los bases de datos de PUCP:
http://biblioteca.pucp.edu.pe/colbasd.html
Suggested (sugerencias)
• Fundamentals of Microfabrication by Marc J. Madou, CRC Press.
• Microsystem Design by Stephen Senturia, Springer
• Foundations of MEMS by Chang Liu, Prentice Hall.
¿Cómo va a ser el curso?
Notas:
Problems/reading summaries
Midterm exam
Final Exam
Report
Attendance/participation
10%
30%
35%
15%
10%
100%
I will correct your English, but it will not affect
your grade. The reading summaries will be based
on effort.
No quiero que este curso sea una dictación sino un diálogo. Por eso creo que es
importante que nos charlemos en una manera relajada para entender mejor y practicar
nuestros idiomas. (Ustedes, inglés y yo, español.)
¿Cómo va a ser el curso?
Reading summaries:
Report:
• One each week on assigned reading
• Inlcude a brief summary of the major
points (¡No me den otro libro!)
• Describe the thing you feel you
understand the best (Algo que
entiendes bien)
• Describe the thing you feel you
understand the least (Algo que no
entiendes para nada)
Can be about any aspect of MEMS you would
like—a new or advanced fabrication technique
not covered in the book/lectures, a particular
MEMS device, a particular class of MEMS
technology, modeling strategies, etc.
Some examples:
•
•
•
•
•
•
•
Focused ion beam instruments
Micro fuel cell technology
Dyanamic systems modeling in MEMS
Advanced photolithography techniques
Digital microfluidics
MEMS gyroscopes
MEMS packaging
What are MEMS?
Acronym (acrónimo) for micro-electro-mechanical systems.
Micro: Small size. The basic unit of measure is the micrometer or micron (μm)
1 μm = 10-6 m
Electro: MEMS have electrical components (quizás)
Mechanical: MEMS have moving parts (quizás)
Systems: Refers to integration of components. (Funcionan juntos.)
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
MEMS accelerometer
MEMS accelerometers
are used widely to
deploy airbags. (Casi
todos los coches los
tienen.)
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
Movie of a motor
Can be used in reverse as an actuator. With alienating current (corriente alterna) it becomes
a motor. In MEMS this type of motor is called a comb drive.
Ink jet print heads
Ink dots are tiny (10-30
per mm) and so are the
nozzles that fire them.
Ink jet print heads
• Ink-filled chambers are
heated by tiny resistive
heating element
• By heating the liquid
ink a bubble is
generated
Ink jet print heads
• The vaporized part of the ink is
propelled towards the paper in a tiny
droplet
• Chambers are filled again by the ink
through microscopic channels
Micromirrors
Micromirrors are used as optical switches
and even computer displays
Micromirrors
An array of micromirrors
Micromirrors
Video of micromirror actuation from
Sandia National Labs
More examples
Labs-on-a-chip can
replace entire chemical
and biological analysis
laboratories.
More examples
There are many other
MEMS devices in
development…
More examples
…some more useful than
others.
Why go micro?
What are some reasons that you would want to
make micro-sized devices?
• Smaller devices require less
• Micro devices are inexpensive (?)
material to make. (Earth has
 Less material
limited resources.)
 Can be fabricated in batch
• Smaller devices require less energy
processes
to run.
• Redundancy can lead to increased
safety. (You can use an array of
sensors instead of just one.)
Más cabello
Why go micro?
What are some reasons that you would want to
make micro-sized devices?
• 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.
Examples of small scale effects
Hot arm actuator
A poly-silicon hot-arm actuator fabricated using surface micromachining
Examples of small scale effects
Hot arm actuator
+
V
-
I
A poly-silicon hot-arm actuator fabricated using surface micromachining
Examples of small scale effects
Electro-osmotic flow
entry port
separation
column
junction
+V-
Electricity can move fluids!
Scaling laws
Activity – Demo with key and key ring
key ring, but it
• Gravity (weight) pulls water down. Surface
tension holds water up. Which one wins? (¿Quien
gana?)
stays in the smaller
• Weight depends on volume/area/length
holes of the key
• Surface tension depends on volume/area/length
(llave). Why?
• Entonces, surface tension   ~
Water spills out of
weight
W
Scaling laws
Te toca a ti – La musaraña (shrew) es el animal más pequeño que
es de sangre caliente. Si no come constantemente, se muere. Usa
“scale analysis” para explicar.
Scaling laws
Te toca a ti – Use scale analysis to show that every animal on the
planet can jump approximately the same height. Es decir, que la
habilidad de saltar no cambia con la dimensión.
Scaling laws
Favorable scalings at the microscale
• Heat transfer (tranferencia del calor) is faster
• Frequency response is faster
• Electrostatic forces are more prominent (más
fuertes)
• Surface tension can move fluids
• And more
How are MEMS made?
• Many techniques borrowed from
integrated circuit (IC) fabrication
- Silicon wafers are commonly used
- Bulk micromachining
• Surface micromachining
• Other techniques
How are MEMS made?
Bulk micromachining example A diaphragm for a pressure sensor
Membrane is piezoresistive; i.e.,
the electrical resistance changes
with deformation.
Adapted from MEMS: A Practical Guide to Design, Analysis, and Applications, Ed. Jan G. Korvink and
Oliver Paul, Springer, 2006
Bulk micromachining
Bulk micromachining example A diaphragm for a pressure sensor
Mask
Unexposed
Silicon
resist
removed anisotropically
etched with KOH
Glass
plate
Grow
2
SiO2SiO
chemically
etched with HFl
Silicon wafer
Opaque
region
Spin on photoresist
Unexposed photoresist removed
by developer
Bulk micromachining
Depending on the
chemical/structure
combinations, etching can
be…
isotropic
or anisotropic
Anisotropic etches
001 silicon wafer
011 silicon wafer
Surface micromachining
The Si wafer functions like the
big green flat plate.
Some Jenga pieces are removed. The
ones that remain form the MEMS
structure.
+
= Surface micromachining
Surface micromachining
Surface micromachining example –
Creating a cantilever
Deposit aluminum (structural
layer—the Jenga pieces that remain)
Deposit polyimide (sacrificial layer—
the Jenga pieces that are removed)
Remove sacrificial
layer (release)
Etch part of
the layer.
Silicon wafer (Green
Lego® plate)
Micromachining
Complicated structures can be made by
combining these techniques and repeating
Micromachining
Everything has to be very clean!
(¡Ojala estén limpias todas cosas!)
Surface micromachining
Te toca a ti—Come up with the process steps needed to make the
cantilever in the last example. (Deposition, photolithography, etc.)
Side view
Top view
Hint: You will need two masks and two photolithography steps.