This article explores the basic characteristics and common applications of a technology that has been incorporated into a wide variety of high-performance electronic devices.
I always appreciate a name that is truly informative and in this regard the term “microelectromechanical systems” (MEMS) does not disappoint, it is as concise a definition as a name.
So what does MEMS mean?
MEMS refers to technology that allows mechanical structures to be miniaturized and fully integrated with electrical circuits, resulting in a single physical device that actually looks more like a system, where “system” indicates that mechanical components and electrical components are working together to implement the desired functionality. Therefore, it is a micro (that is, very small) electrical and mechanical system.
Mechanical to electrical to (micro) mechanical
Mechanical components and systems are generally considered less technologically advanced than comparable solutions based primarily on electrical phenomena, but this does not mean that the mechanical approach is universally inferior. The mechanical relay, for example, is much older than transistor-based devices that provide similar functionality, but mechanical relays are still widely used.
However, typical mechanical devices will always have the disadvantage of being hopelessly bulky compared to electronic components found in integrated circuits. The space limitations of a given application may make electrical components favored or required, even where a mechanical implementation would have resulted in a simpler or higher performance design.
MEMS technology represents a conceptually simple solution to this dilemma: if we modify mechanical devices so that they are not only very small but also fully compatible with IC manufacturing processes, we can, to some extent, have the best of both. . worlds “.
This is a physical gear and chain. This machinery moves and works as you would expect a gear and chain to move and work. However, the links in the chain are about 50. µm long, that is, less than the diameter of a human hair. Image courtesy of Sandia National Laboratories.
What does a MEMS do?
In the previous section, I said that MEMS technology is a conceptually straightforward solution As you might expect, coming up with the idea of ​​a microscopic mechanical device is much easier than building it.
We use the verb “machined” to describe the work of turning a piece of metal into a mechanical component like a gear or pulley. In the MEMS world, the equivalent term is “micromachine”. The tiny mechanical structures in a MEMS device are made by physically modifying the silicon (or other substrate material) using specialized techniques about which I know almost nothing. These silicon mechanical structures are then combined with silicon integrated circuits, and the resulting electromechanical system is packaged and sold as a single device.
As explained in an article on MEMS published by Loughborough University in England, MEMS devices use micromachined structures, sensors and actuators. Sensors allow a MEMS to detect thermal, mechanical, magnetic, electromagnetic, or chemical changes that can be converted by electronic circuitry into usable data, and actuators create physical changes rather than simply measuring them.
Examples of MEMS devices
Let’s look at an example of the functionality and internal structure of a MEMS device.
Micromachined cantilever switch beams. Image courtesy of Analog devices.
This graphic conveys the physical structure of micro-machined cantilever switch beams. There are four switching beams and each has five contacts (using multiple contacts is a technique to reduce resistance in the state). The switching beams are driven by an applied voltage.
Image courtesy of Analog devices.
Here we see the MEMS switch (on the right) and associated controller circuits (on the left), interconnected and housed in a QFN package. The controller circuitry allows a typical digital device, such as a microcontroller, to effectively control the switch as it does everything necessary to generate a high voltage drive signal that promotes effective and reliable switch operation.
MEMS Applications: When Are MEMS Devices Used?
MEMS technology can be incorporated into a wide variety of electronic components. The companies that make these components would presumably claim that a MEMS implementation is superior to what was used before the MEMS version was available. It would be difficult to verify a sufficient number of these claims to justify a general statement along the lines of “MEMS devices perform significantly better than non-MEMS devices.” However, my general impression is that, in many situations, MEMS is an important step forward. And if performance or ease of deployment is a priority in your design, you’d look at MEMS devices first.
In the context of electrical engineering, MEMS technology has been incorporated into four product categories:
- Audio
- Sensors
- Switches
- Oscillators
There may be some less common products that do not fit into one of these categories; If you are aware of something I missed, feel free to let us know in the comments.
Audio
In the audio domain, we have MEMS microphones and MEMS speakers. The basic characteristics of a MEMS microphone are conveyed in the following diagram.
Sensors
Sensors are the dominant application of MEMS techniques; There are MEMS gyros, inclinometers, accelerometers, flow sensors, gas sensors, pressure sensors, and magnetic field sensors.
Switches
Electrically controlled switches are, in my opinion, a particularly interesting application of MEMS technology. The ADGM1004, which I wrote about in this article, is easy to control, operates at signal frequencies from 0 Hz to greater than 10 GHz, has less than 1 nA of leakage current in the off state, and provides a pick-up life. of at least one billion cycles.
The combination of a micromachined resonator with drive circuits and holding circuits results in a MEMS oscillator. If you want to research a real MEMS component, you can check out a news article from 2017 where I talked about SiTime’s SiT2024B MEMS Oscillator.
Diagram courtesy of SiTime.
Oscillators
I don’t have a lot of experience with MEMS oscillators, but I think they could be an excellent choice in demanding applications; In the aforementioned SiT2024B article, I note that based on information from SiTime, a MEMS oscillator can greatly outperform quartz-based oscillators.
conclusion
Many electronic devices incorporate MEMS technology, and you are likely to come across a MEMS component sooner or later, if not every time you design a board. I hope this article has provided a good overview of what MEMS is and how it is used in electronic design.
