MEMS: Making Micro Machines

Transcription

1 MEMS: Making Micro Machines Knowledge Probe (Pre-test) Activities (3) Film Script Participant Guide

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3 Southwest Center for Microsystems Education (SCME) University of New Mexico MEMS: Making Micro Machines Learning Module Supports the film by Silicon Run Productions: This learning module contains the following activities: Knowledge Probe (Pre-quiz) Activity 1: Microfluidics Activity 2: Optical MEMS Activity 3: Sensors Final Assessment (Post-Quiz) The MEMS Film Script Target audiences: High School, Community College, University, Industry Technologists. Support for this work was provided by the National Science Foundation's Advanced Technological Education (ATE) Program through Grants #DUE Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and creators, and do not necessarily reflect the views of the National Science Foundation. Copyright by the Southwest Center for Microsystems Education and The Regents of the University of New Mexico Southwest Center for Microsystems Education (SCME) 800 Bradbury Drive SE, Suite 235 Albuquerque, NM Phone: Website: MEMS Film Website:

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5 Knowledge Probe (Pre-Quiz) Introduction This knowledge probe is part of the learning module based on the film MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. The purpose of this knowledge probe is to determine your knowledge of MEMS, MEMS applications, fabrication, packaging and design prior to viewing the film and completing the activities. You are not expected to know all of the answers to the questions. You may be asked to retake this assessment after viewing the film. There are twenty (20) questions. 1. MEMS is an acronym for a. Micro Energy Manufacturing Systems b. Microelectromechanical Systems c. Microelectronics Memory Systems d. Micro Electron Machines and Semiconductors e. Many Engineers Making Stuff 2. MEMS are tiny micromachines that can consist of several types of components. Which of the following types of components would you find in a MEMS? a. Mechanical b. Electrical c. Optical d. Fluidic e. All of the above could be found in MEMS 3. MEMS inertial sensors sense change in which of the following? a. Acceleration b. Pressure c. Rotation d. Color e. a and c 4. The MEMS device used to trigger airbag deployment is a(n) a. Pressure Sensor b. Actuator c. Gyroscope d. Accelerometer e. Light Meter Southwest Center for Microsystems Education (SCME) Page 3 of 6 MEMS_video_KP_PG_ Knowledge Probe

6 5. Which of the following components is used in a MEMS pressure sensor to sense changes in pressure, for example blood pressure or tire pressure? a. Proof mass b. Membrane c. Gyroscope d. Moveable mirror e. a and c 6. Digital Mirror Devices are used in which of the following applications? a. Digital projectors b. Medical imaging equipment c. Computer Monitors d. Data communication networks 7. MEMS incorporate microfluidic structures in which of the following applications? a. Inertial Sensors b. Digital Mirror Devices c. Inkjet print heads d. Blood Pressure Monitors e. b and c 8. In a thermal inkjet print head, which of the following pushes the ink from the micronozzle after the resistive heater is turned on? a. Convection Cycle b. Microdroplet c. Bubble d. Powder e. Pixel 9. What is the optical MEMS device that consists of an array of millions of micromirrors? a. Digital Mirror Device (DMD) b. Millions of Mirrors Device (MMD) c. Digital Pixel Device (DPD) d. Mirror Array (MA) e. None of the above 10. What type of MEMS components move other MEMS devices such as micromirrors? a. Pressure Sensors b. Actuators c. Gyroscopes d. Accelerometers e. Yokes Southwest Center for Microsystems Education (SCME) Page 4 of 6 MEMS_video_KP_PG_ Knowledge Probe

7 11. Which of the following MEMS fabrication process steps transfers a pattern into a light sensitive film on the wafer s surface? a. Etch b. Photolithography c. Chemical vapor deposition d. Sputtering e. Deep Reactive Ion Etch (DRIE) 12. Which of the following MEMS fabrication process steps is used to remove unwanted material from a thin film on the surface of the wafer or from within the wafer substrate? a. Etch b. Photolithography c. Chemical vapor deposition d. Sputtering 13. Much of the technology used to fabricate microelectronics (e.g., CMOS chips) can be applied to making MEMS devices. a. True b. False 14. In MEMS fabrication what is the layer called that provides spacing between two or more moving components by first being deposited and then later removed? a. Structural layer b. Conductive layer c. Sacrificial layer d. Masking layer e. Insulating layer 15. Which of the following fluidic properties allows a liquid to refill a microchannel without the use of valves or pumps? a. Stiction b. Torsion c. Energy transfer d. Capillary action e. Laminar flow 16. Which of the following is an advantage of the micronozzles in an inkjet print head being less than 100 microns? a. A higher viscosity of ink b. Greater print resolution (more pixels) c. Minimal turbulence in the flow of the ink d. Self-filling microchannels (no need for a mechanical pump) e. b and d Southwest Center for Microsystems Education (SCME) Page 5 of 6 MEMS_video_KP_PG_ Knowledge Probe

8 17. In the game Guitar Hero, accelerometers measure the movement of the guitar by measuring a change in which of the following electrical characteristics of the accelerometer? a. resistance b. inductance c. voltage d. capacitance e. electromagnetic 18. Which of the following personnel is NOT needed as a member of the design team for a new MEMS device? a. Mechanical engineer b. Electrical engineer c. Marketing personnel d. Systems engineer e. All of the above are needed as members of the design team 19. Before a MEMS device is sent to manufacturing, a model of the design must be constructed and tested to ensure that the design meets the customer requirements and specifications. a. True b. False c. Most of the time, but not always 20. Which of the following macro-sized devices is LEAST likely to be redesigned to micro size due to impracticality? a. A rotary motor b. Hydraulic pump c. A gear drive d. Stadium Lights e. A syringe Support for this work was provided by the National Science Foundation's Advanced Technological Education (ATE) Program. Southwest Center for Microsystems Education (SCME) Page 6 of 6 MEMS_video_KP_PG_ Knowledge Probe

9 Southwest Center for Microsystems Activity 1 - Microfluidics Participant Guide Description and Estimated Time to Complete This is the first of three activities for the film MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. This activity is designed to be completed with the first part of the film: Microfluidics. This activity consists of two parts: A crossword puzzle that tests your knowledge of the terminology and acronyms associated with MEMS applications and microfluidics, and Post-activity questions that ask you to demonstrate your understanding of microfluidics and microfluidics fabrication. Estimated Time to Complete Allow at least 30 minutes to complete this activity. Southwest Center for Microsystems Education (SCME) Page 1 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

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11 Introduction Microfluidics is a multidisciplinary field that deals with the behavior of fluids in the microliter and smaller volume range. As volume decreases, the ratio of surface area to volume increases. As a result, the surface properties of fluids become dominant as one deals with smaller and smaller volumes. Therefore, the interaction of the fluid with the walls of micro chamber and channel surfaces dominates fluid behavior. The surface area to volume ratio of a 100μm per side cube is 0.06cm -1 and that of a 10μm per side cube is 0.6cm -1, ten times larger! Therefore, a fluid will cool or heat much faster in a smaller chamber. This image is of an array of microfluidic channels and reservoirs created at the University of California, Berkeley. The width of the reservoirs are smaller than the diameter of a strain of hair (60 to 100 μm). Think about how small the microchannels are! [C. Ionescu-Zanetti, R. M. Shaw, J. Seo, Y. Jan, L. Y. Jan, and L. P. Lee (PNAS, 2005). Printed with permission by Luke Lee, Dept. of Bioengineering, UC- Berkeley) Southwest Center for Microsystems Education (SCME) Page 3 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

12 Fluid flow is enhanced as channels decrease in size due to surface tension effects, called capillary action. The microfluidics field includes the science of these behaviors as well as the technology used to incorporate and leverage the small-scale behavior of fluids. Microfluidic systems are found in many application areas such as biomedical, molecular biology, consumer products, filtration and purification systems, environmental testing and micropumps. The film MEMS: Making Micro Machines discusses the fabrication of a microfluidic device called a thermal inkjet printhead, also referred to as a bubblejet printhead. This printhead is a microfluidic device that uses the capillary effect of a fluid in a microchannel as well as the rapid heating of a fluid (due to high surface area to volume ratio) to produce a fast, high resolution printhead. A thermal inkjet printhead is a non-mechanical micropump, meaning it has no moving parts. In this pump, heat is applied locally to a microchamber filled with ink. Very quickly ( seconds) the ink evaporates forming a bubble. The bubble forces a tiny droplet of ink out through the micro nozzle and onto the paper. When the heat is removed, the bubble collapses bringing more ink into the chamber through capillary action. Surface tension prevents the ink from flowing out of the nozzle once the chamber is full. 1 Let's take a more detailed look at how this thermal inkjet printhead works. The process of pumping a droplet of ink from an inkjet printhead (micropump) is a multiple stage process. (Refer to the diagram and film as you follow this process.) 1. The microchannel fills with ink. Because the microchannel s dimensions are so small (approximately a micrometer in diameter) the liquid automatically fills the microchannel due to capillary action. Southwest Center for Microsystems Education (SCME) Page 4 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

13 2. An electrical voltage is applied to the heater (a resistive element). Current through the heater creates enough heat energy to evaporate the ink in less than seconds. 3. Evaporation of the ink forms a bubble. 4. As the bubble forms it forces the ink through the nozzle and out of the channel. 5. The ink is sprayed onto the paper below. 6. The voltage is removed, the heater turns off, and the bubble collapses. 7. The microchannel automatically refills due to capillary action. To make an inkjet printhead, "hundreds of these microscopic MEMS devices are typically fabricated in pairs of columns that surround an ink supply manifold." 2 Some of the newest printers produce droplets as small as 5 picoliters and can print up to 9 pages per minute in full color (14 pages in black and white). 3 The first part of the film MEMS: Making Micro Machines covers the fabrication of these inkjet printheads. Activity Objectives and Outcomes Activity Objectives Identify the related terms or acronyms associated with definitions related to MEMS, MEMS applications, microfluidics and microfluidics fabrication. Demonstrate your understanding of microfluidics and microfluidics fabrication by correctly answering the Post-Activity questions. Resources MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production "MEMS Applications". Southwest Center for Microsystems Education (SCME) "Photolithograpy". Southwest Center for Microsystems Education (SCME) "Deposition". Southwest Center for Microsystems Education (SCME) Documentation 1. Completed Crossword Puzzle 2. Questions and Answers to the Post-Activity Questions Southwest Center for Microsystems Education (SCME) Page 5 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

14 Activity 1: Microfluidics Crossword Puzzle Complete the crossword puzzle using the clues on the following page EclipseCrossword.com Southwest Center for Microsystems Education (SCME) Page 6 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

15 Across 1. MEMS used to stabilize the image of a camcorder or the effect of impact on a football helmet. 4. Acronym for Microelectromechanical Systems. 6. A quartz plate that contains a pattern and is used for the exposed step in photolithography. 8. In CMOS fabrication the metal layer is used as a(n). 9. In a thermal inkjet print head, the heater vaporizes ink to form a. 12. Acronym for the optical MEMS that consists of an array of millions of digital micromirrors. 13. The thermo component that is used as a heater in an inkjet printhead. 17. A micro- is a trench between two rows of nozzles in an inkjet printhead. 18. Acronym for chemical vapor deposition. 21. In a MEMS, the type of components that convert information to and from digital. 22. The fabrication process that removes select material from the surface layer. Process can be wet or dry. 23. In CMOS manufacturing the silicon dioxide layer can be used as a(n). Down 2. In an inkjet printhead, action is the property of microfluids that refills the microchannels. 3. Common term for equipment that moves objects such as wafers from one place to another or one stage of the process to another (pick and place). 4. The study of the behavior of small volume fluids. 5. Acronym for scanning electron microscope. 6. In MEMS, the type of component that moves something. 7. A fabrication process that deposits metal layers using a plasma and ion bombardment. 9. A micromachining process that etches into the substrate (bulk, surface or LIGA). 10. A soft evaporates solvents from the photoresist. 11. Micromachining process that etches layers of thin films (bulk, surface or LIGA). 14. The CVD process that deposits a silicon dioxide thin film using a vaporized liquid that contains silicate is called. 15. A MEMS device that moves clinical lab testing out of the laboratory and into the field. 16. A fabrication process that deposits a thin film on the wafer s surface. 17. Photolithography step that spins resist onto the wafer. 19. Photolithography process that removes the exposed resist. 20. A of ionized chlorine based gases and inert gases is used to etch metal. Southwest Center for Microsystems Education (SCME) Page 7 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

16 Post-Activity Questions 1. What is microfluidics? 2. Name three applications of microfluidics. 3. Briefly discuss two challenges that engineering might face in the design and fabrication of microfluidic devices. 4. Create a block diagram of the photolithography process showing the steps as presented in the MEMS film. 5. Sketch and describe how an inkjet microsystem works. Summary Microfluidics is a multidisciplinary field that deals with the behavior of fluids in the micro, nano and even picoliter scales. The behavior of fluids in these scales can differ from those of larger volumes. The design and fabrication of microfluidic devices must address these differences and create effective solutions. The manufacturing of an inkjet print head is an excellent example of how fluid behavior at these small scales is applied through microsystems fabrication technology in creating a highly effective consumer product. References "Micropumps Overview". Southwest Center for Microsystems Education MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. Canon Bubblejet S520. High speed, high quality printer for the office. Support for this work was provided by the National Science Foundation's Advanced Technological Education (ATE) Program. Southwest Center for Microsystems Education (SCME) Page 8 of 8 MEMS_video_AC1_PG_ Activity 1-Microfluidics

17 Activity 2 Optical MEMS Participant Guide Description and Estimated Time to Complete This is the second of three activities for the film MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. This activity is designed to be completed with the second part of the film: Optical MEMS. This activity consists of two parts: A crossword puzzle that tests your knowledge of the terminology and acronyms associated with MEMS applications, optical MEMS, and the packaging and testing of optical MEMS. Post-activity questions that ask you to demonstrate your understanding of optical MEMS and optical MEMS fabrication and testing processes. Estimated Time to Complete Allow at least 30 minutes to complete this activity.

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19 Introduction The objective for optical MEMS is to integrate optical, mechanical and electronic functions into one device. Optical MEMS usually consist of moveable micromirrors, lenses, diffraction elements for modulating light. Actuators for moving these elements, sensors and electronics for receiving, processing, and transmitting signals as well as providing the inputs for the actuators. MEMS micromirror arrays are often the key components used in spatial light modulators or SLM s. These devices are used in high definition display systems as well as optical switching networks. Optical micromirror arrays transmit optical information without going through the timely and costly signal conversion process of optical to electronic and back to optical. The micromirrors can act as switches that direct light from a fiber optic to another fiber optic or to a specific output port by moving up and down, left to right or swiveling to a desired position. This requires the individual mirrors to be actuated, supported on a movable mount or stage, and integrated into a digital network. The scanning electron microscope image to the right shows a popped-up micromirror. Notice the hinge allowing for the different angles needed to direct light in different directions. Also notice the track that assists in positioning the mirror at the correct angle. MEMS Pop-up mirror for optical applications [Image Courtesy of Sandia National Laboratories SUMMIT TM Technologies, Southwest Center for Microsystems Education (SCME) Page 3 of 8 MEMS_video_AC2_PG_ Activity 2 Optical MEMS

20 Applications of optical MEMS include the following: Projection displays (GLV's and DMD s) Tunable lasers and filters Spatial Light Modulators (SLMs) Variable optical attenuators Optical Spectrometers Bar code readers Maskless lithography Optical MEMS have already been quite successful in display technologies. This success is rapidly growing with the innovations of high definition (HD) displays. Texas Instrument's Digital Mirror Devices (DMD) have been used for several years in a variety of projection systems including film projection and digital cinema. The technology is called digital light processing or DLP TM, a trademark owned by Texas Instruments, Inc. A DMD is an array of micromirrors (see figure of DMD array below and left). Each micromirror (between 5um and 20um per side) is designed to tilt into (ON) or away from (OFF) a light source. The mirror tilts when a digital signal energizes an electrode beneath the mirror. The applied actuator voltage causes the mirror corner to be attracted to the actuator pad resulting in the tilt of the mirror. When the digital signal is removed, the mirror returns to the "home" position. In the ON position, the mirror reflects light towards the output lens. In the OFF position, the light is reflected away from the output optics to a light absorber within the projection system housing. One mirror can be turned OFF and ON over 30,000 times per second. There can be over 2 million mirrors in an array with less than 1 μm spacing between each mirror. The DLP 1080p technology delivers more than 2 million pixels for true 1920x1080p resolution. (1,2) The diagram below right illustrates how the DLP projection system works. The left set of images are scanning electron microscope images of the DMD mirrors and underlying hinge system. Levels of a DMD Array (left) and How a DLP system works (right). [Images Courtesy of Texas Instruments] Southwest Center for Microsystems Education (SCME) Page 4 of 8 MEMS_video_AC2_PG_ Activity 2 Optical MEMS

21 The illustration below breaks down a digital mirror of a DMD into three levels. It shows the mirror, support post, hinge, yoke and electrodes discussed in the film. The film MEMS: Making Micro Machines discusses the fabrication, packaging and testing of this DMD. You should recognize some of the components mentioned in the film (e.g., mirror, torsion hinge, yoke). To learn more about the operation of a digital light projector (DLP), visit Texas Instruments webpage How DLP Technology Works. [Images Courtesy of Texas Instruments] Activity Objectives and Outcomes Activity Objectives Identify terms or acronyms associated with definitions related to MEMS, optical MEMS, optical MEMS fabrication, packaging and testing. Demonstrate your understanding of digital MEMS and DLP fabrication, packaging and testing by correctly answering the Post-Activity questions. Resources MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. "MEMS Applications". Southwest Center for Microsystems Education (SCME) "Photolithography". Southwest Center for Microsystems Education (SCME) "Deposition". Southwest Center for Microsystems Education (SCME) Documentation 1. Completed Crossword Puzzle 2. Questions and Answers to the Post-Activity Questions Southwest Center for Microsystems Education (SCME) Page 5 of 8 MEMS_video_AC2_PG_ Activity 2 Optical MEMS

22 Activity 2: Optical MEMS Crossword Puzzle Complete the crossword puzzles using the clues on the following page EclipseCrossword.com Southwest Center for Microsystems Education (SCME) Page 6 of 8 MEMS_video_AC2_PG_ Activity 2 Optical MEMS

23 Across 2. MEMS components that move mirrors or other MEMS devices are called. 5. Three or more colored are contained in the color wheel of a DLP system to provide a colored output from the DMD array. 7. The acronym for digital light processing. 8. After fabrication a DMD goes through a series of tests, most of which are electrical. The final test is a test. 10. To electrically a DMD array, the mirrors are turned ON and OFF for 2 to 24 hours inside a burn-in furnace. 13. When a DMD mirror is not reflecting light it is said to be. 14. A strip is placed on DMD windows for the purpose of absorbing moisture. 17. To is to join two or more components together. 18. An anti- coating that enhances the transmission of light is applied to the protective windows in a DMD 22. The tendency for surface forces to cause small structures to stick. 24. In MEMS fabrication a layer provides spacing between two or more components by first being deposited then removed. 25. When a micromirror is reflecting light it is said to be. Down 1. The component of a DMD micromirror that supports the mirror's support post. 3. Small spring tips are constructed on the yoke of a DMD mirror to overcome, the tendency of a micromirror to stay ON with voltage removed. 4. The fabrication process used to remove the protective resist layer after the develop process step is called a plasma. 6. A microsystems device that integrates optical, mechanical and electrical. 7. The acronym for digital mirror device. 9. The material used to construct the post, hinge and yoke of a DMD micromirror. 11. In a DMD, one micromirror is one. 12. A is applied to the electrode of a micromirror to turn the mirror ON. 15. The thin film used as a sacrificial layer that provides spacing and protection for the micromirrors. 16. A(n) is used to harden epoxy. 17. A process uses UV light, heat and pressure to connect the windows of the DMD to the CMOS wafer. 19. In a DMD the hinge that is fabricated to overcome stiction is called the hinge. 20. The fabrication process that removes unwanted material from a layer. 21. Hundreds and even thousands of micromirrors on a chip is called a(n). 23. The fabricated channels that provide access to the CMOS circuitry. Southwest Center for Microsystems Education (SCME) Page 7 of 8 MEMS_video_AC2_PG_ Activity 2 Optical MEMS

24 Post-Activity Questions 1. What is the objective of optical MEMS? 2. For the transmission of data optical information, optical mirrors may be faster and cheaper because they eliminate the conversion process of. 3. Micromirrors need to move. What MEMS components are required to move micromirrors? 4. What company developed DMDs? 5. In your own words, briefly explain how a DMD works. 6. How is the resolution of DLP devices increased? 7. Once the DMD array is fabricated, how is it protected during shipping to the packaging location? 8. In the fabrication of a micromirror, photo resist is used as a sacrificial layer. What is the purpose of this sacrificial layer? 9. How is mirror movement tested? 10. The output of a DMD is black and white. How is this black and white image converted to color? Summary Optical MEMS integrate optical, mechanical and electronic functions into one device. Micromirror arrays are used for data transmission and for optical image production in DLP projection systems. There may be hundreds of thousands and even millions of mirrors in an array, fabricated on a single chip. Surface micromachining fabrication methods similar to those used in making computer chips are the primary fabrication technology used to make these devices. In the final tests, all of the mirrors must work in order for the chip to be used in a DLP device. This creates a special challenge in the fabrication and packaging of micromirror arrays. References 1 "How DLP sets work." Tracy V. Wilson and Ryan Johnson. HowStuffWorks. 2 "How DLP Technology Works". DLP Texas Instruments. 3 MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. Support for this work was provided by the National Science Foundation's Advanced Technological Education (ATE) Program. Southwest Center for Microsystems Education (SCME) Page 8 of 8 MEMS_video_AC2_PG_ Activity 2 Optical MEMS

25 Activity 3 MEMS Sensors Design Participant Guide Description and Estimated Time to Complete This is the third of three activities for the film MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production. This activity is designed to be completed with the third part of the film: Sensors (MEMS Design Process and Design Team). This activity consists of two parts: A crossword puzzle that tests your knowledge of the terminology and acronyms associated with MEMS sensors and the MEMS design process. Post-activity questions that ask you to demonstrate your understanding of MEMS sensors and the MEMS design process. Estimated Time to Complete Allow at least 30 minutes to complete this activity. Introduction Sensor components are critical in microelectromechanical systems (MEMS) and in MEMS applications. A MEMS sensor receives an input from the environment. It converts its input signal into a digital or analog electronic representation. For example, a type of MEMS chemical sensor monitors the change in mechanical stress on a microcantilever as a result of a chemical reaction occurring on a surface coating. The sensor responds to the change by producing an electrical output (change in resistance) that represents the amount of chemical reaction occurring on the microcantilever transducer surface. Two common types of MEMS sensors are pressure sensors (which sense changes in pressure) and inertial sensors (which sense movement, acceleration and inclination). MEMS sensors can be used in combinations with other sensors for multisensing applications. For example, a MEMS can be designed with sensors to measure the flow rate of a liquid sample and at the same time identify any contaminates within the sample.

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27 MEMS Pressure Sensors MEMS pressure sensors are designed to measure absolute or differential pressures. They typically use a flexible diaphragm as the sensing device as seen in the picture to the right. One side of the diaphragm is exposed to a sealed, reference pressure and the other side is open to an external pressure. The diaphragm moves with a change in the external pressure. This movement is measured as a change in resistance due to additional strain on the piezoresistive elements fabricated onto the diaphragm. MEMS pressure sensors are specified to work over a variety of ranges, depending on the design and specific application. There are MEMS pressure sensors that can measure pressures near 0 ATM or as high as 10 ATM or ~150 psi. MEMS Pressure Sensor [Courtesy of the MTTC, University of New Mexico] Applications of MEMS pressure sensors include the following areas: Automotive industry (e.g., measure tire pressure, fuel pressure, intake manifold pressure) Biomedical (e.g., measure blood pressure, intracranial pressures, pressure due to blockage in catheters and infusion pump systems) Environmental (e.g., measure barometric pressure, ocean pressures sensors, and pressures found within roads and bridges) Non-destructive testing (e.g., identify defects and cracks in materials) Southwest Center for Microsystems Education (SCME) Page 3 of 8 MEMS_video_AC3_PG_ Activity 3 MEMS Sensors Design

28 MEMS Inertial Sensors MEMS inertial sensors are designed to sense a change in an object's acceleration, vibration, orientation and inclination. MEMS inertial sensors include accelerometers and gyroscopes. Acceleration is defined as a change in velocity (speed and/or direction). In order to accelerate an object, a force must be applied to that object. If an object changes velocity (accelerates), the object, including any imbedded MEMS inertial sensor, will experience a force acting on it. Hence, inertial sensors are used to measure force related variables such as inclination, orientation, vibration, changes in speed, direction and impact forces. MEMS inertial sensors can be found in many applications including navigation devices, image stabilization systems for high-magnification video cameras, airbag deployment systems, the Apple iphone, pacemakers, and stabilization systems found in washing machines. MEMS inertial sensors are one of the fastest growing segments of the MEMS market. "Driven by accelerometer applications like the Apple iphone and the Nintendo Wii, and by the coming legislation requiring stability-control systems in all vehicles, these devices have moved out of industrial segments and into consumer ubiquity." ("MEMS-based inertial sensor is not your grandfather's gyroscope." Randy Torrence, Chipworks. Electronics, Design, Strategy News. December 2008.) Like pressure sensors, MEMS accelerometers are devices that can be used in a variety of sensing applications due to their simplicity and versatility. MEMS Accelerometer [Photo courtesy of Khalil Najafi, University of Michigan] The simplest MEMS accelerometer sensor consists of an inertial mass suspended by springs (see SEM image above). Forces affect this mass as a result in an acceleration (change in velocity speed and/or direction). The forces cause the mass to be deflected from its nominal position. As with the movement of the pressure sensor's diaphragm, the deflection of the mass is converted to an electrical signal as the sensor's output. ("MEMS Targeting Consumer Electronics". EE Times. Gina Roos. September 2002.) Southwest Center for Microsystems Education (SCME) Page 4 of 8 MEMS_video_AC3_PG_ Activity 3 MEMS Sensors Design

29 MEMS Gyroscopes Gyroscopes are used to either maintain orientation of a moving object, such as a spacecraft, or to monitor the orientation changes of an object. The classical gyroscope we are used to seeing consists of a spinning wheel or disk. The rotating object tends to maintain its axis in a fixed orientation. Think of a fast spinning top, the top axis tends to point in the same direction. Another example is that of a bicycle wheel if you spin a bicycle wheel very quickly, the axis tends to point in the same direction. Vibrating systems can also act as a gyroscope. An example is a tuning fork device set into motion. The tines of the fork will vibrate within a plane of motion. This is based on the physical principal that a vibrating object (proof mass) tends to keep vibrating or oscillating in the same plane. MEMS gyroscopic based sensors have been made using both methods, spinning and vibrating structures. With these types of structures, changes in yaw, pitch and roll can be measured. The third part of the film, MEMS: Making Micro Machines, shows you the process of designing MEMS sensors. There are many team members who work together and with the customer to achieve success of the project. Each team member contributes within the area of expertise but must also be multidisciplined enough to understand and communicate effectively with others in the team. The design process shown is typical of what is used in most MEMS design and fabrication organizations. As is obvious in this part of the film, having excellent communication skills is critical, this includes all aspects, listening, writing, reading and speaking. Activity Objectives and Outcomes Activity Objectives Identify the terms or acronyms associated with definitions related to MEMS, MEMS sensors, and MEMS design. Demonstrate your understanding of MEMS, MEMS sensors, and MEMS design by correctly answering the Post-Activity questions. Resources MEMS: Making Micro Machines, an overview of microelectromechanical systems, produced and directed by Ruth Carranza of Silicon Run Production "MEMS Applications". Southwest Center for Microsystems Education (SCME) "Sensors, Transducers, and Actuators." Southwest Center for Microsystems Education (SCME) Documentation 1. Completed Crossword Puzzle 2. Questions and Answers to the Post-Activity Questions Southwest Center for Microsystems Education (SCME) Page 5 of 8 MEMS_video_AC3_PG_ Activity 3 MEMS Sensors Design

30 Activity: MEMS Sensors Design Crossword Puzzle Complete the crossword puzzles using the clues on the following page EclipseCrossword.com Southwest Center for Microsystems Education (SCME) Page 6 of 8 MEMS_video_AC3_PG_ Activity 3 MEMS Sensors Design

31 Across 2. A change on the input of a sensor can create a change in capacitance which gets converted to. 5. The designer creates an architectural design and writes the specifications for the MEMS. 6. The design phase brings together the MEMS and the ASIC blocks to their performance and ensure results meet product specifications. 7. The ratio is the ratio of etch depth (or height) to its width. 8. The etch process that creates etch profiles with high aspect ratios. 9. A logical sequence of steps for solving a problem is called an. 13. Each block of a MEMS design has a mathematical representation that consists of lines of equations, or. 14. A MEMS consists of various engineers, marketing and sales personnel. 15. It is the responsibility of the Microsystems Group to divide or to partition the components of the system into specific. 16. In an inertial sensor, the space between the mass and electrode is measured as an electrical. 17. It is the responsibility of the mechanical design engineer to determine transducer limitations. 18. Deep Reactive or DRIE uses a process known as the Bosch Process to create deep, straight, etched walls. Down 1. The MEMS inertial sensor that measures rotational movement is called a. 3. A(n) measures linear movement along the x, y, and z axes. 4. MEMS accelerometers use an to sense mass movement and produce an electrical output representative of the movement. 6. The Application Specific Integrated Circuit designer is also called the designer. 9. is defined as a change in velocity (speed and/or direction). 10. MEMS sensors are designed to sense a change in an object's acceleration, vibration, orientation and inclination. 11. A virtual and sometimes physical is constructed to test predictions and different situations. 12. A or diaphragm is the moveable component in a MEMS pressure sensor. 16. Sensors are designed to monitor and detect at the input. 17. In a MEMS accelerometer, a proof moves when affected by an external force. Southwest Center for Microsystems Education (SCME) Page 7 of 8 MEMS_video_AC3_PG_ Activity 3 MEMS Sensors Design

32 Post-Activity Questions Based on what is in the film and the Introduction of this activity, answer the following questions: 1. What do MEMS inertial sensors sense? 2. What are two types of MEMS inertial sensors? 3. Name at least three applications of MEMS inertial sensors. 4. Name at least three applications of MEMS pressure sensors. 5. When designing a new MEMS, who determines the requirements (e.g., operating parameters, specifications)? 6. Why does it take a team of engineers (mechanical, electrical, systems, process and sometimes chemical, biochemical, etc.), marketing and sales experts to develop MEMS? 7. Virtual models and sometimes, macro-sized models, are constructed before a MEMS device is fabricated. What is the purpose of these models? 8. If you had to choose one of the roles highlighted in the film, which one would you choose? Which one is of most interest to you? Why? What sort of education do you think you would need to fill this role? What subjects should you focus on in school to acquire the necessary knowledge and skills? Summary One of the most common applications of MEMS is as sensors. MEMS pressure sensors and accelerometers were some of the first MEMS devices to make it to the market. These sensors are found in cars, planes, medical equipment, and gaming devices. No matter what the device, all MEMS must go through a rigid design process before being sent to manufacturing. The design process involves engineers from several areas, all of which play an important role in the final design. By the time a MEMS device is sent to manufacturing, it has been tested, tweaked and retested many, many times to ensure that it meets the customer's requirements and specifications. Support for this work was provided by the National Science Foundation's Advanced Technological Education (ATE) Program. Southwest Center for Microsystems Education (SCME) Page 8 of 8 MEMS_video_AC3_PG_ Activity 3 MEMS Sensors Design

33 MEMS: Making Micro Machines Script with Chapters (Scene Selections) Chapter 1 Introduction to MEMS 1. Mechanical ingenuity combined with micro or nano manufacturing methods has evolved into Microelectromechanical Systems known as MEMS, micro machines, or microsystems. 2. These tiny micro machines have both mechanical and electrical components that are either side-by-side within a single package, or integrated on a single chip. In their mechanical function they move masses, liquids and light, or sense vibration and pressure. In their electronic function they convert mechanical information to digital information and digital information to mechanical motion. 3. If microprocessors and microcontrollers are the brains of electronic products, then MEMS are the eyes, ears, nose, and physical extensions that provide information to that brain. 4. MEMS are all around us in our digitized world. In the thermal inkjet printhead, hundreds of microfluidic devices direct the flow of ink and eject thousands of tiny drops a second. In medicine, microfluidic pumps help people monitor insulin levels. Lab-on-a-chip provides tiny channels leading to mini labs used in chemical and biomedical research. 5. In Digital Light Processing, MEMS devices project the images seen at theaters. Inside this theater projector are DLP chips that contain millions of microscopic mirrors. Smaller DLP chips are also found in televisions and business projectors. 6. In cars MEMS pressure sensors monitor things like engine control to improve fuel efficiency. In camcorders, MEMS accelerometers stabilize the image. In football they monitor the effects of impact on a player s head. In gaming accelerometers allow us to be active players. They re also used in cell phones and GPS systems. The combination of MEMS gyroscopes and accelerometers are found in the segway and the space shuttle. 7. MEMS are an international enterprise. In today s global economy a MEMS device is often researched, designed, manufactured, and packaged by staff in different countries around the world. 8. While there are many types of MEMS devices three important catagories are microfluidics, optical MEMS, and sensors. Chapter 2 Inkjet Printheads FABRICATION (Thermal Inkjet Printhead) 9. To see how these devices are fabricated, let's begin at Hewlett Packard s facility where the inkjet printhead is manufactured 10. MEMS are fabricated in various ways depending on their application. With silicon based MEMS, there are two major types of micromachining. 11. Surface Micromachining uses semiconductor processes like deposition, photolithography, etch and ion implantation to create the MEMS structure. These processes are similar to making computer chips and use some of the same equipment. In Bulk Micromachining, the silicon wafer itself is bulk etched to create the MEMS device components within the wafer. Silicon Run Productions 1 3/10/09

34 MEMS: Making Micro Machines Script with Chapters (Scene Selections) 12. The thermal inkjet printhead contains hundreds of microscopic MEMS devices typically fabricated in pairs of columns that surround an ink supply manifold. 13. Each device has a nozzle, a chamber, a resistor and a slot that connects it to the ink channel. 14. When current is applied, the resistor heats to boiling temperatures. It vaporizes the first layer of ink into a gas bubble that acts like a piston to eject the ink through the nozzle. 15. With the current off, the collapsing bubble drops back onto the resistor surface. The ink flows in and refills the chamber. Capillary forces pin the ink back at the nozzle's surface preventing it from flowing out until the resistor fires again. 16. Inkjet printheads are integrated devices. Both the MEMS devices and the CMOS circuitry, which provides the electrical current, are fabricated at the same time. Beneath these rows are the transistors, which have already been built. In this video we'll take a close look at how the MEMS devices are created from bare crystalline silicon. 17. The materials used in the creation of an inkjet printhead must withstand high heat, high duty cycles, and liquid environments containing acidic and basic inks. Therefore these materials are selected for their electrical, mechanical, and chemical properties. Chapter 3 Building the Thermal Resistors 18. Before the resistors are built, insulation is needed to protect the wafer. In this chemical vapor deposition system TEOS, a vaporized liquid that contains silicate, is used to deposit a silicon dioxide layer at low temperatures. Temperatures higher than 400 degrees Celsius would alter the aluminum copper used for the integrated circuits on other parts of the wafer. 19. Inside the CVD chamber TEOS reacts with oxygen to form silicon dioxide on the bare silicon surface. This silicon dioxide layer insulates the silicon wafer from the firing resistor. 20. The wafers move on to a metal deposition system where a conductive layer that will provide leads to the resistor will be deposited. First the wafers are conditioned by undergoing a physical sputter with Argon to remove any oxides or trace conductors. Then the wafers move to the metal deposition chamber. Here sputtering is used to transfer metal from a target to a layer of an aluminum copper alloy on the wafer. 21. Photolithography is used to pattern the metal layer. As we see here, the exposure system is next to the coat, develop, and bake track system. As the wafer spins a positive photo resist spreads across the wafer. The final spin speed of the wafer determines the specific thickness of the resist. 22. A tiny solvent stream removes the resist bead that forms along the edge. This prevents particle contamination when a wafer touches the cassettes or other tooling. 23. From the back of the track system, we see the wafers move to a hot plate where they are baked to remove most of the solvent. 24. Wafers then move into the I-line stepper. Here, a light source of a specific wavelength filters through a mask and a lens to expose the wafer. The resist is positive. The areas exposed to light are changed Silicon Run Productions 2 3/10/09

35 MEMS: Making Micro Machines Script with Chapters (Scene Selections) chemically. The wafers move back to the track system. Here developer is puddled onto the wafer, and the exposed areas are rinsed away. 25. To insure quality, measuring feature size is important throughout the process. This SEM, or scanning electron microscope, is measuring the dimensions produced by the photo resist process. 26. The exposed metal will now be etched using plasma. In this chamber chlorine based and inert gases etch the aluminum copper alloy. This defines the resistor leads and removes the highly conductive aluminum copper layer from the area where the resistor material will be. While still under vacuum, the wafer moves to the ash chamber where the photo resist and etch residues are evaporated and pumped away. 27. The resistor metal in now deposited. After the wafer's surface is conditioned it goes to the sputter chamber where a thin layer of resistor metal is deposited. 28. Photolithography once again patterns the resistor metal layer. 29. In the plasma etch system the resistor metal layer is etched from unwanted regions. When current is eventually forced from two metal layers to one thin metal layer, it will create the heat that fires the resistors. A thin-film stack of three layers will now be deposited on the resistors to provide electrical, chemical and mechanical protection. 30. This system deposits the first two dielectric layers over the resistor. The first layer will provide electrical isolation between the ink and the firing resistor. In the same chamber, new gases deposit the second layer, which protects against the corrosive chemical attack from the ink. 31. The third protective layer is metallic so it can resist the mechanical forces of the collapsing bubble. The wafers go into a sputter etch chamber to prepare the surface and then into a sputter deposition chamber where a thin metal layer is deposited. Chapter 4 Building the Chamber Walls 32. Now that the resistors are protected, the chamber walls where the vapor bubble forms are built. The wafers are washed and prepped. A de-ionized water and ozone treatment removes any residual 33. The deposition of barrier material used for the chamber walls is similar to the photolithography process. As the wafer spins, a thick negative resist-like material is spiraled onto the wafer. In soft bake, the solvent is slowly driven out to "set" the barrier material and make it more uniform. 34. In this bake and expose system, the wafers go directly to the stepper where they are exposed. As a negative resist, the barrier material exposed to light forms a polymer and hardens. Because this resist is so thick, the exposure times are much longer than for standard photo resist. After exposure, the wafers move to the bake ovens. The areas exposed to light induce cross-linking and become a permanent part of the chamber. 35. The non-exposed areas are removed when developed. Instead of the usual puddle develop, spray develop is used here. Spraying droplets of developer provides a higher surface area that can attack the thick barrier material more easily. Silicon Run Productions 3 3/10/09

36 MEMS: Making Micro Machines Script with Chapters (Scene Selections) 36. A big open chamber now exists. We can see that small pillars have also been created from the barrier material. These pillars at the entrance to the chamber serve as a filter to block particles that might be in the ink from clogging the nozzle. 37. After develop, the wafers are placed in an oven, exposed to higher temperatures and allowed to cure. Thickness measurements are made after each layer is cured. 38. A thick photo resist resin, called a sacrificial wax, is spiraled onto the wafer and spun. The wax fills the cavity and covers the entire wafer. A soft bake sets the wax and a portion of it is removed to bring it flush with the chamber surface. The wax holds up the shape of the chamber as the building process continues. Chapter 5 Creating the Nozzles 39. In a dry process a layer of barrier material is pressed onto the wafers to create the nozzles. The nozzle material on this roll is sandwiched between two protective sheets of carrier films. The dry application will minimize the interaction between the nozzle layer and the sacrificial wax. Here, the bottom carrier film has been peeled away, and we see the nozzle material placed directly on the wafer. materials that might remain on the surface from previous steps. 40. After the dry film is applied, a blade cuts around the remaining films and a new layer is prepared for the next wafer. 41. The robot moves the wafer with the nozzle material and its carrier film to the next stage. 42. In a separate tool, the carrier film is removed. A strip of tape is rolled across the wafer and a pick-up roll lifts the carrier film off. 43. Photolithography is now used to create the nozzle orifice. The exposed areas become cross-linked and remain a permanent part of the printhead. When developed, the unexposed nozzle material and the sacrificial wax are removed. 44. The wafers undergo a final cure. 45. To create the channels the inks will flow through, a laser and etch process forms a trench between two rows of nozzles. Inside the laser system, the wafers are placed backside up. A pulsating laser scans the back of the wafer and defines the dimensions of the slot. Without breaking through the silicon, it then drills a deep narrow trench within the slot. 46. The final slot shape is created in a bulk etch process. In this anisotropic etch, chemicals such as KOH and TMAH etch the silicon crystal and remove the remaining thin silicon layer left after laser micromachining. 47. Wafers are automatically mounted onto a ring and tape. This holds the die in place as the wafer is sawed into individual units. 48. Following singulation, the wafers are rinsed and dried to remove any particulates. Silicon Run Productions 4 3/10/09