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Thomas Adams, PhD
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”.
Terre Haute, Indiana, USA
Private university with ~ 2000 students, mostly undergraduate (pregrado)
Ciencias, ingeniería, y matemáticas
Introduction to MEMS(micro-tecnología)
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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
A still picture of the motor…
with a spider mite on it!
Another view of the engine
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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
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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 fabrication2. The Substrate3. Additive Techniques 4. Creating Patterns – Lithography5. Bulk Micromachining 6. Surface Micromachining7. Process flow8. Solid mechanics 9. Overview of MEMS operating principles10. Modeling case study: piezoresistive sensors
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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 10%Midterm exam 30%Final Exam 35%Report 15%Attendance/participation 10%
100%
No quiero que este curso sea una dictación sino un diálogo. Por eso creo que esimportante que nos charlemos en una manera relajada para entender mejor y practicarnuestros idiomas. (Ustedes, inglés y yo, español.)
I will correct your English, but it will not affect your grade. The reading summaries will be based on effort.
¿Cómo va a ser el curso?
Report:
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
Reading summaries:
• 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 youunderstand the least (Algo que no entiendes para nada)
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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. (Casitodos los coches los tienen.)
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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.
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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
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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.
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More examples
There are many other MEMS devices in development…
More examples
…some more useful than others.
Why go micro?
• Smaller devices require less material to make. (Earth has limited resources.)
• Smaller devices require less energy to run.
• Redundancy can lead to increased safety. (You can use an array of sensors instead of just one.)
• Micro devices are inexpensive (?) Less material Can be fabricated in batch
processes
What are some reasons that you would want to make micro-sized devices?
Más cabello
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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?
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
A poly-silicon hot-arm actuator fabricated using surface micromachining
I
+V-
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Examples of small scale effects
Electro-osmotic flow
Electricity can move fluids!
junction
separationcolumn
entry port
+ V -
Scaling laws
Water spills out of
key ring, but it
stays in the smaller
holes of the key
(llave). Why?
Activity – Demo with key and key ring
• Gravity (weight) pulls water down. Surface tension holds water up. Which one wins? (¿Quiengana?)
• Weight depends on volume/area/length
• Surface tension depends on volume/area/length
• Entonces,
Scaling laws
Te toca a ti – La musaraña (shrew) es el animal más pequeño quees de sangre caliente. Si no come constantemente, se muere. Usa“scale analysis” para explicar.
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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
• 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
Favorable scalings at the microscale
How are MEMS made?
• Many techniques borrowed from
integrated circuit (IC) fabrication
- Silicon wafers are commonly used
- Bulk micromachining
• Surface micromachining
• Other techniques
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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 andOliver Paul, Springer, 2006
Membrane is piezoresistive; i.e., the electrical resistance changes with deformation.
Bulk micromachining
Bulk micromachining example -A diaphragm for a pressure sensor
Silicon wafer
Grow SiO2
Spin on photoresistGlass plate
Opaque region
Unexposed photoresist removed by developer
SiO2 chemically etched with HFl
Unexposed resist
removedSilicon
anisotropicallyetched with KOH
Mask
Bulk micromachining
Depending on the chemical/structure combinations, etching can be…
isotropic or anisotropic
001 silicon wafer 011 silicon wafer
Anisotropic etches
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Surface micromachining
= Surface micromachining
+
The Si wafer functions like thebig green flat plate.
Some Jenga pieces are removed. The ones that remain form the MEMS
structure.
Surface micromachining
Surface micromachining example –Creating a cantilever
Silicon wafer (Green Lego® plate)
Deposit aluminum (structural layer—the Jenga pieces that remain)
Remove sacrificial layer (release)
Deposit polyimide (sacrificial layer—the Jenga pieces that are removed)
Etch part of the layer.
Micromachining
Complicated structures can be made by combining these techniques and repeating
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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.
