CHAPTER 1 IntroductionA little historyFIGURE 1. A semiconductor triode (the first transistor). Note that the symbol for the bipolar tr...FIGURE 2. The Intel Pentium. 3.3 million transistors, 133 MHz, 0.35 micron lithography, 4 layer ...FIGURE 3. Moore ’s Law: The number of transistors per chip doubles every 18 months. Semiconducto...FIGURE 4. ADXL50 accelerometer. The first surface micromachined product.ADXL50TI DMDFIGURE 5. TI Digital Mirror Device. Each chip contains hundreds of thousands of mirror cells. Ea...FIGURE 6. The Resonant Gate Transistor, the first surface micromachined device.FIGURE 7. Roger Howe’s resonant vapor sensor.FIGURE 8. First Hinge.FIGURE 9. Intel Pentium microprocessor.What are MEMS?What MEMS is notMEMS DesignThe IC Design CycleThe (traditional) MEMS Design CycleFIGURE 10. Traditional MEMS design cycle.FIGURE 11. The IC design cycle.Foundries and the New MEMS Design CycleFIGURE 12. The MOSIS foundry model.FIGURE 13. Sandia micromirror driven by a gear train with a combination lock.FIGURE 14. Closeup of Sandia gears and 24 bit locking mechanism.CAD for MEMSSUGAR available on the weblayout tools available on the web?lots of matlab exercisesno FEAReferencesProblems1. How many lasers do you have in your home? (CDs, pointers, ...)2. How many motors do you have in your car?3. How many sensors do you have in your home? How many have a minimum size necessary for their pe...4. On the web, find examples of MEMS companies that sell: pressure sensors, accelerometers, mirro...5.Introduction to MEMS Design 9CHAPTER 1 IntroductionWe are entering a golden age of MEMS. Tremendous progress has been made in the last decade on materials and processes at the micron to millimeter scale. We now have a solid understanding of most of the energy domains and interactions at this scale, and CAD support is emerging which is capable of predictive modeling. In short, if you can dream it up, and it doesn’t violate the laws of physics, we can probably build it!Physics in the MEMS world is fundamentally just the same as the physics of mac-roscopic systems, but all of the coefficients are funny. Frictional forces, for exam-ple, are tremendously important, and as a result most designs utilize flexures instead of bearings. Electrostatic forces dominate over magnetic forces, so most MEMS motors use electrostatics. Thermal systems can have time constants in the microsecond range, so it is possible to make very fast shape memory actuators. Air starts to look like molasses. Gravity is not important. Mechanical time constants are in the microsecond to millisecond range. Surface effects dominate: surface ten-sion and Van del Wahls forces can destroy structures.For many years the conventional wisdom in the field was that things were changing too rapidly for a text book to have any longevity or relevance. Over the last five years, however, it has become clear that there are core concepts that any student of the field should know. While things are still changing rapidly, the fundamental principles remain the same. If you want to view paradise, Simply look around and view it. Anything you want to, do it. You can change the world, There’s nothing to it. Willie WonkaIntroduction10 Introduction to MEMS DesignI’ve been trying to build micro robots since 1990. As a graduate student at UC Ber-keley in the late 1980s, I started off with a very process-centric view of MEMS. The field at that time was dominated by people inventing new processes to make new devices, or to make the same devices in a better way. The only players in MEMS were those research labs (mostly academic) fortunate enough to have their own clean rooms for semiconductor fabrication. Lots of people published papers on processes and devices, very few published papers on applications, and almost no one published anything on systems. I was inspired by the title of the early conferences in the field: the Micro Robots and Micro Tele-operators Workshop. My goal for my PhD was to make a micro robot, but I ended up developing and demonstrating a process that might be useful in mak-ing micro robots. The robots themselves elude me to this day.Leaving Berkeley I went to UCLA, which at the time had a beautiful brand new clean room, with almost no equipment in it. Faced with the choice between pouring my soul into developing a new clean room for a few years or switching research directions, I opted for the new direction, which turned out to be MEMS design. Shortly after I arrived at UCLA as an assistant professor, Karen Markus and her colleagues at MCNC created a new MEMS fabrication service called MUMPS, the Multi-User MEMS Process Service. MUMPS provided low-cost access to MEMS fabrication to those who didn’t have their own clean room.Given the opportunity to think about the design of MEMS, and without the oppor-tunity to make contributions in the development of new MEMS processes, a new breed of MEMS researcher was born, the designer. From the traditional process-centric MEMS perspective, the new designers had the curse of working in a single process without any control over design parameters. This curse, however, turned out to be a blessing.In this text I present a design-centric (rather than process-centric) view of this excit-ing technology. I hope that you enjoy it as much as I do.A little historyIn 1947, Bardeen and Brattain published a paper describing the “semiconductor tri-ode”, which we now call a transistor. In 19xx, Gordon Moore predicted that the number of transistors which could fit on a silicon chip would double every 18 months. This remarkable prediction has held true for decades, and has becomeIntroduction to MEMS Design 11A little historyknown as Moore’s Law. This law predicts chips with nearly 10 billion transistors in 2010.The semiconductor industry has perfected the art of miniaturizing construction. Like Bardeen and Brattain’s first transistor, the modern transistor is a three dimen-sional sculpture combining many different materials in precise alignment. In the late 1980s it became apparent that these were just the characteristics needed to make micro mechanical devices as well. A new field was born: Micro ElectroMe-chanical Systems.The first major milestone in the evolution of silicon from electronics to electrome-chanics was the discovery of piezoresistivity in silicon in 1954. This led fairly quickly to the first silicon strain gauges sold commercially in 1958,
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