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.