Explore how tiny tech shapes our world:
Dive into the fascinating world of MEMS with an expert,
Dr. Aaron Partridge of SiTime!
to measure acceleration with extreme precision in microgravity environments. Source & Image Credit: NASA
What’s Inside This Issue?
- Concepts and Terminology: Discover concepts and terminology introduced in the featured article.
- Featured Article: Join us as we explore the mind-blowing world of MEMS with Dr. Partridge and discover how these tiny technologies are revolutionizing our lives.
- About the Interviewee: Discover how Dr. Partridge’s journey from basement builder to industry pioneer ignited a passion for engineering’s potential to impact the world.
- Hands-On Activities: Engage in a fun activity to discover your phone’s motion magic.
- MEMS for Environmental Equity and Sustainability: Discover how these microscopic machines can help create a cleaner, greener, and fairer world for everyone.
- Glossary: Recap key concepts and terminology from the featured article.
Concepts and Terminology
- MEMS stands for Micro-Electro-Mechanical Systems. You’ll see it written many different ways, often without the capital letters and hyphens, blended together as ‘microelectromechanical systems.’ Just ‘MEMS’ is easier! Imagine building tiny machines, with parts smaller than the width of a human hair, that can do both mechanical and electrical things. That’s basically what MEMS are! These tiny wonders are used in everything from your smartphone to your car.
- Mechanical functions are abilities to do things that may involve forces and movement. In our every-day world, think of a bike chain moving the gears, or a door handle opening a door. In this tiny MEMS world, mechanical functions could be as simple as a swinging mass on a spring or as complex as a tiny pump moving liquid.
- Electrical functions are all about electricity. Imagine turning on a light switch. That’s an electrical function. In tiny MEMS tech, electrical functions might involve sending electrical signals to control something, like turning on a tiny motor, or receiving a signal, like measuring very small amounts of light.
- A capacitor is an electronic component that stores electrical energy in an electric field. Unlike batteries, capacitors can charge and discharge very quickly, making them ideal for applications requiring short bursts of power.
- An accelerometer is a device that measures changes in motion, specifically, changes in the speed or direction. It’s one kind of motion sensor.
Featured Article
Dr. Paul Dennig Sr. & Dr. Sik Lee Dennig, Writers
With Insights from Dr. Aaron Partridge of SiTime
Imagine this: You’re about to snap a selfie with your best friend. You hold up your phone, smile, and click. In that split second, several tiny, nearly invisible machines called MEMS (Micro-Electro-Mechanical Systems) are hard at work.
These tiny marvels aren’t limited to smartphones. They’re also behind your gaming world. Ever wondered how you can move your favorite video game characters so smoothly and realistically? Well, there are tiny MEMS devices inside gaming controllers, too, making sure every move you make feels real!
We’re excited to dive deep into this fascinating world of MEMS with you. To help us unravel their mysteries, we interviewed Dr. Aaron Partridge, a leading expert in the field. Get ready to be amazed as we discover what these minuscule marvels are and how they are shaping our future.
MEMS (Micro-Electro-Mechanical Systems) are called “Systems” because they gather many unique activities together in one unit. Electro implies something electrical is happening, meaning (i) an electric current is flowing or (ii) a voltage is present somewhere. Mechanical means (i) a mechanical force or (ii) a motion is happening. Put the two activities together, and you can create new functions that blend both mechanical movement and electronic sensing actions.
An example is combining a swinging pendulum with a capacitor to create a new device, like a motion-sensing accelerometer. These accelerometers are incredibly tiny, precise, inexpensive, and reliable, and are used in cars, game consoles, and cell phones. Later, we’ll do a hands-on activity with a related device called a gyroscope to give you a taste of how they work.
These tiny devices, which you can often only see with a magnifying glass, and their internal parts with a microscope, started in the 1960s and 1970s, evolving from the same technology used to make computer chips. Professor James Angell and his students at Stanford University were among the first to work on these “micro-machines.” A MEMS device is often constructed by modifying only the top part of a silicon wafer, and those modifications extend down only the thickness of paper or a human hair. An ordinary sheet of paper is about 100 micrometers thick, and a human hair is around 50-100 micrometers in diameter.
MEMS devices often bring new capabilities into our lives by replacing what used to be big, bulky, or heavy equipment. If you haven’t heard much about them yet, it may be because today they are small and thin and fit inside other products so you don’t see them, where they work behind the scenes. They provide all sorts of vital functions, like sensing how your phone is rotated (landscape or portrait?), or how fast a car is decelerating (did an accident just happen? should the car deploy the airbags?). Now you know that MEMS’ utility ranges from adding convenience to saving lives. That versatility makes peering inside MEMS so interesting!
Let’s take a closer look under the hood of a MEMS accelerometer and discover how it works! When acceleration occurs, the mechanical parts of a MEMS device start to move. These moving parts are crucial because they form a key component of an electrical element known as a capacitor. As the capacitor plates move, they cause a change in voltage, which is easily detected by an electronic circuit. This allows motion to be effortlessly converted into an electrical signal! The electronics on the MEMS chip, or a nearby one, then translate this signal into a language that a computer can understand.
Now, let’s explore how these parts move inside the device. Below are 3D computer drawings of a MEMS accelerometer. In the first image, you’ll notice most of the chip, especially around the edges and even beneath the surface, which remains stationary. At the center, there’s a section called the “inertial mass” that’s free to move. The large red arrow indicates the only direction this inertial mass can slide—back and forth. On either end of the mass are spring elements shaped like long, closed rectangles. These springs serve two purposes: they anchor the mass to the base to keep it in place, and they help recentralize it after movement. The springs aren’t so rigid that they prevent the mass from swinging, but they do restore it to its original position once the motion has been detected, ensuring the accelerometer is ready for the next use.
Source & Image Credit: Rudolf Herstek’s “How it works – MEMS Accelerometer”
Notice the fins carved into the silicon labeled “electrode”—these always stay still. Then, there are fins attached to the mass that move along with it, like the one outlined in red. This red-outlined fin is actually one plate of a capacitor, an essential electrical component. As the MEMS chip experiences different accelerations, this fin moves in sync with the inertial mass.
If you suddenly bump the accelerometer in the direction of the big red arrow, the inertial mass will oscillate back and forth before gradually coming to rest. During this motion, the MEMS chip is busy converting the movement into electrical signals, which are available to use outside that chip.
Now let’s zoom in to the red outline in the image.
at rest.
Here, the MEMS chip starts moving down and to the left,
temporarily leaving the mass and the mass’s fins behind because of inertia,
so the gap (d) increases.
Here’s what happens if the MEMS chip suddenly stops while moving as described earlier. The inertial mass wants to keep going (thanks to inertia), and all its fins move along with it. This motion reduces the gap (d). An electronic circuit can easily detect changes in this gap because the voltage across the capacitors—formed between the moving and stationary fins—changes precisely with it. A decrease in voltage indicates motion in one direction, while an increase indicates motion in the opposite direction. This is how the mechanical motion inside the tiny MEMS chip is transformed into a signal that a computer can read.
Today, MEMS technology is used in a wide range of applications beyond consumer products, including sensors for NASA’s wind tunnel testing to study airflow around aircraft.
The magic of MEMS comes from their tiny size and amazing abilities. Imagine super-small robots that are so tiny you need a magnifying glass or microscope to see them well. These miniature machines combine microscopic mechanical parts, sensors, and electronics to detect changes in pressure, temperature, and even chemicals. They convert these changes into electrical signals that other devices can use to react or make decisions.
MEMS microphones are a good example of this technology. These tiny devices detect changes in air pressure to accurately capture sound, making them essential components in smartphones, laptops, and various other electronic devices. Below is an image of Vesper’s tiny but highly sensitive MEMS microphone.
Vesper’s miniature 0.5-millimeter square MEMS diaphragm (top) is connected via tiny wires to an application-specific integrated circuit (ASIC, bottom). An integrated circuit is a tiny computer chip that contains many electronic components.
Image Credit: Vesper
Source: RadioLocman: Industry’s Most Sensitive MEMS Mic
Silicon, a common element found in sand, is the foundation for MEMS technology. Dr. Partridge explains, “The element silicon is one of the most abundant elements on the Earth’s crust and is a fantastic material, and we use it as the basis to make MEMS. For starters, silicon is a Goldilocks material for electronics: an energy property called its bandgap is just right, compared to its neighbors, carbon and germanium, in the same periodic table column. Silicon can be refined from sand or quartz and made very pure, and then we can tailor the electrical properties for what we need by adding back very small amounts of special impurities. We call that process ‘doping.’”
Silicon is also a Goldilocks mechanical material: it’s stable, strong, hard, and stiff; and it can be polished smooth. Plus, because it’s very well understood, small things can be made precisely from it. For example, the silicon’s atoms near its surface can be chemically reacted with oxygen to form a uniform protective layer that’s strongly attached. However, where needed, that oxide can be removed in precise shapes. All of silicon’s exceptional properties make it the ideal material for widespread use in MEMS.
Image Credit: Enricoros at English Wikipedia, Public domain, via Wikimedia Commons
Silicon wafers are thin, round slices of highly pure silicon used as a foundation for the production of MEMS and other devices.
Image Credit: NASA
In addition, Dr. Partridge notes, “There are now MEMS that are based on different operating principles: chemical, electro-chemical, optical, electro-optical, mechanical-optical, and so on, in addition to electro-mechanical operation. But what they all have in common is there’s some mechanical aspect and that mechanical aspect is usually made of silicon. Other materials may be used, too, including metals and plastics, and may also be made on a microscopic scale.”
Creating MEMS is like building tiny, high-tech masterpieces. It all goes down in a super clean room called a “fab.” Think of it as a special place for makers. They use mind-blowing techniques like photolithography – that’s where light turns a silicon wafer into a blueprint for tiny parts. Next comes etching, basically sculpting with chemicals to shape these super small structures in MEMS parts. Then, to add the finishing touches, they layer on materials more accurately than the best pro cake decorator. The coolest part? They can crank out millions of these tiny wonders, all super precise, perfect, and affordable. The end result? A world of gadgets that are smarter, faster, and way cooler than you ever imagined!
Interestingly, the etching process used for MEMS has a long history. Over 500 years ago, artists used a similar technique to create detailed prints by scratching grooves into metal sheets, then etching those grooves deeper to carry ink. Today, we use a modern version of this technique in MEMS to precisely remove material where it’s not needed, showing how old methods can inspire new technologies. Both versions allow replicas to be made.
“The Artist’s Mother with Her Hand on Her Chest” (1631)
Image Credit: Park West Gallery
(less than 1/32”)
Image Credit: Geek Mom Projects
Most MEMS are tiny sensors that help us interact with the world and provide essential data to our devices. Dr. Partridge highlights some cool examples:
Keeping Time, Perfectly: Imagine a tiny bell vibrating millions of times per second. That’s the heart of a MEMS oscillator, a minuscule device delivering incredibly precise timekeeping with remarkably low energy consumption. Dr. Partridge was a pioneer in this MEMS-based technology, revolutionizing the timing industry two decades ago. These lightning-fast, microscopic “bells” now help drive the internal workings of countless devices, from the smartphones in our pockets to the satellites orbiting our planet.
The Smallest Timing Device by SiTime (2013)
Image Credit: SiTime
Inkjet Printers: In inkjet printers, MEMS printheads actually do the spraying, controlling the ink from tiny nozzles, precisely placing ink droplets on paper. This ensures your prints are sharp and vibrant by carefully controlling where each drop lands.
Cross-sectional diagram of a single print nozzle in an inkjet cartridge
Image Credit: DP3
Smartphone Image Stabilization: These MEMS contain tiny sensors called accelerometers and gyroscopes. Accelerometers measure how your phone moves in different directions, while gyroscopes track its rotation. By using MEMS, these sensors can quickly adjust for shaking or tilting, helping to keep your photos and videos sharp and clear. Other MEMS help detect when you’re holding your phone close to your face.
This zoomed-in image shows a human hair next to a piece of an acceleration-sensing MEMS chip. The hair helps you see how incredibly small the chip’s parts are. When the chip is shaken, some of those parts move a little and help the chip sense the motion.
Image Credit: PR Newswire
Healthcare: MEMS are reshaping healthcare. Their tiny sensors can detect subtle changes in your body, allowing for earlier diagnoses. Imagine a wearable device, a silent sentinel on your wrist, monitoring your heart rate and blood pressure 24/7. Or a tiny implant, a microscopic guardian within your body, detecting the earliest signs of cancer.
MEMS technology also enables surgical precision. Surgeons can use MEMS-based tools to perform minimally-invasive procedures. This reduces patient trauma and speeds up recovery time. Furthermore, MEMS can deliver medicine directly to the enemy, minimizing collateral damage to healthy cells.
One groundbreaking example is lab-on-a-chip. These miniature medical laboratories can perform a multitude of tests, from blood analysis to DNA sequencing, in a fraction of the time. Imagine a device that can diagnose a disease in minutes, right at the point of care. MEMS technology makes this possible by shrinking down essential lab components into a tiny package. It’s like having a powerful medical lab in the palm of your hand.
The needles connect to tiny, hair-width channels inside the device.
Image Credit: National Institute of Standards and Technology, Public domain, via Wikimedia Commons
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For high school students interested in technology or engineering, Dr. Partridge advises diving right into hands-on projects. He encourages students to experiment with building things they’re passionate about. “If you’re curious about constructing something complex, like an AI robot, you should go ahead and try,” he said. When you build your robot, you can include MEMS sensors – accelerometers and gyroscopes – to help it navigate. You might need to reach out to local universities or libraries for guidance and resources. Libraries can be great places to research and gather information. Also, some professors are willing to help. Even if your initial building attempts don’t succeed, you’ll gain valuable experience and knowledge from the process.
In the field of MEMS technology, Dr. Partridge highlights the importance of specialized knowledge. Today’s work in MEMS requires expertise in areas such as biology, chemistry, and physics. The technology has advanced from its early days of sharing a fab with microelectronics folks. Back then, pushing fab tools to their limits and fixing them was a learning experience. Now, many processes are refined and carried out using specialized tools to make MEMS. However, the most exciting breakthroughs often come from innovative applications and exploring new possibilities.
A great place to start learning how MEMS work is to take, at a minimum, introductory physics in high school for your physical science requirement. There, you’ll learn more about the difference between electrical and mechanical functions, and more.
About the Interviewee
Dr. Aaron Partridge, a Stanford-educated electrical engineer, transformed his childhood fascination with electronics into a groundbreaking career in MEMS technology. His pioneering work at SiTime has revolutionized timekeeping across industries by developing minuscule silicon resonators, or tiny “bells,” that provide the precise timing essential for modern electronics. Beyond technological advancements, Dr. Partridge is a passionate advocate for sustainability, believing engineers hold the key to addressing global challenges. His commitment is embodied in the development of energy-efficient MEMS devices, contributing to a greener future. From a basement tinkerer to a leading innovator, Dr. Partridge’s journey exemplifies the power of curiosity, perseverance, and a deep-rooted passion for engineering.
Hands-on Activities
We mentioned that MEMS devices are used inside your cell phone to help with steadying the camera focus. Did you also know that MEMS are often there as the microphone and to generally detect the phone’s orientation and movement? They can even sense when your face is near to turn off the screen, so you don’t accidentally press buttons!
For this hands-on activity, we’ll focus on your phone’s abilities to sense changes in rotation and acceleration. There’s a fun and free app, with one version available for Apple™ phones and another for Android™ phones. It lets you safely check the operation of the MEMS motion sensors inside your phone.
With this app, you can instantly plot and see the outputs of your phone’s built-in MEMS sensors, like accelerometers and gyroscopes. In this activity, you’ll try rotating your phone and look for what your gyros see.
To get started, install Physics Toolbox Accelerometer™ if you have an Android™ phone; install Physics Toolbox Sensor Suite™ if you have an iPhone.
Next, we need to explain how those apps relate to your phone. Here’s a simple diagram that shows your phone as a gray flat box. On it, we see what your app means by the terms x-, y-, and z-axis. Now practice tipping your phone about only one axis at a time, pausing a little while between each try.
x, y, and z axes on your phone
If you’re using an Android™ phone, open the app, and you’ll immediately see data being recorded. Tap the pause button (two parallel bars) on the top right. This stops the data recording on the chart, giving you time to plan your next move. Tap the three horizontal bars in the upper left to see your options, then select “Gyroscope” to follow our example. The rewind icon will clear the screen and start recording again. Notice the colors of x, y, and z readouts in the upper left region.
Physics Toolbox Accelerometer™ on an Android™ phone
On the other hand, if you’re using an Apple™ phone, you’ll see this home screen below. It shows many options. Select the one called “Gyroscope.”
Physics Toolbox Sensor Suite™ on an iPhone™ phone
On the iPhone, here are the gyro traces, following the same steps of rocking the phone as we did before (rock the x-axis, pause, rock the y-axis, pause, and rock the z-axis):
When we rocked our phone only on the x-axis, that motion resulted in the red traces in the images shown above. You’ll see similar behavior when we restrict our motions to the y-axis (green traces) and z-axis (blue traces). All three sensors are very sensitive and are always active, meaning that our rocking motions were not purely one-dimensional, even when we try hard to keep the other two axes still.
Want to save a picture of your phone screen? On an Android™ phone, quickly pressing volume-down + power. On an Apple™ phone, find your version here. Then, send the picture to yourself to use later in a presentation or report.
Did you know that today’s MEMS gyroscopes are so sensitive that they can detect the rotation of the Earth?
MEMS for Environmental Equity and Sustainability
Revolutionizing Healthcare Accessibility:
Imagine getting hurt and needing to see what’s happening inside your body. Traditionally, this meant heading to a large hospital for an ultrasound or X-ray, which could be costly and time-consuming. But MEMS are changing that!
Dr. Partridge highlights a MEMS device, Capacitive Micromachined Ultrasound Transducers (CMUTs), which are tiny sensors that can produce detailed images of what’s inside your body, similar to traditional ultrasounds. They can even be miniaturized and integrated with smartphones, making them incredibly convenient.
Because CMUTs are so small and affordable, they can be used in areas with few doctors, like remote villages. This means more people can access the healthcare they need, no matter where they live. It’s like giving everyone a fair chance at staying healthy!
Butterfly iQ™, an ultrasound device, is approved for use in the U.S., with a wired connection to an iPhone™. Inside the top end of the hourglass-shaped probe on the left is a CMUT MEMS device. With this system, probe and phone, doctors can look inside ears, veins and arteries, the womb, heart and lungs, and more. They are said to have similar diagnostic accuracy as traditional cart-based models.
Image Credit: CCS Insight
Enhancing Air Quality Monitoring:
Ever wondered what’s lurking in the air you breathe? MEMS sensors can sniff out nasty pollutants in the air. Because they’re small and inexpensive, they can be placed almost anywhere! As a result, you could have a whole network of these sensors giving you real-time updates on the air quality. With this info, your community can figure out where the pollution is coming from and how to clean it up. It’s like having a secret weapon against bad air days!
The Mercury News
Improving Water Quality and Management:
Imagine your school’s water supply suddenly had harmful chemicals or bacteria in it. Or maybe you’re worried about the health of your local river. MEMS can act like water detectives, sniffing out harmful contaminants like lead, chlorine, or even pesticides in your water. Think of them as microscopic lifeguards for your water. Again, because they are cheap and easy to use, you could have a whole army of them guarding your water supply! With so many eyes on the water, we can catch problems before they get out of hand. Plus, they can help scientists learn more about water quality and keep our planet healthy.
A variety of land-based factors contribute to water contamination
Image Credit: NOAA Center of Excellence for Great Lakes and Human Health.
Glossary
| Definition |
|---|
An accelerometer is a device that measures changes in motion, specifically, changes in the speed or direction. It’s one kind of motion sensor. |
A bandgap is like a tiny energy barrier. Imagine a hill. You need a certain amount of energy to get over the top. In electronics, a bandgap is the amount of energy needed to make electrons jump from one energy level to another. It’s important because it helps control how electricity flows. When electrons have enough energy, they flow. |
A capacitor is an electronic component that stores electrical energy in an electric field. Unlike batteries, capacitors can charge and discharge very quickly, making them ideal for applications requiring short bursts of power. |
Electrical functions are all about electricity. Imagine turning on a light switch. That’s an electrical function. In tiny tech, electrical functions might involve sending electrical signals to control something, like saying when to turn on a motor. Alternatively, signals can be received, like measuring small amounts of light. |
Electronics involves the use of electric currents and voltages to sense and control devices, circuits, and systems. Think of your phone or TV. |
Fabrication is the process of creating something, like building a model car or a robot. It involves cutting, shaping, and joining materials together. MEMS are built inside of a fabrication facility, called a ‘fab,’ for short. |
A gyroscope has historically been a spinning wheel that helps things stay balanced. It’s like the spinning top that keeps from falling over. MEMS folks have cleverly re-invented it, so it doesn’t need spinning parts. |
Mechanical functions are abilities to do things that may involve forces and movement. In our every-day world, think of a bike chain moving the gears, or a door handle opening a door. In this tiny MEMS world, mechanical functions could be as simple as a swinging mass on a spring or as complex as a tiny pump moving liquid. |
MEMS stands for Micro-Electro-Mechanical Systems. Imagine building tiny machines, with parts smaller than the width of a human hair, that can do both mechanical and electrical things. That’s basically what MEMS are! These tiny wonders are used in everything from your smartphone to your car. |
An oscillator is something that moves back and forth repeatedly, like a swing. In electronics, it creates electrical signals that go up and down. |
Silicon is the second-most-common element on Earth’s surface, after oxygen. We typically start with sand and make it into super-pure crystals. Slices of silicon are the backbone of the electronics world. Almost every computer chip and MEMS device is made from silicon. It’s like the LEGO brick of the tech world! |
Ultrasound uses high-pitched sound waves to create images of things inside your body. It’s like a super-powerful echo listener. |
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