Maria Montero

Introduction to MEMS (Microelectromechanical Systems)

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.