Key Technology Where Does MEMS Sensor Technology Come from, Where is it Headed?

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MEMS sensors are built into every smartphone but can also play a significant role in industrial technology. They have greatly expanded our ability to detect certain mechanical parameters and respond to them very quickly. But what exactly is the technology behind the acronym MEMS, and what currently untapped possibilities do they offer for professional applications?

MEMS sensors make it easy to change the screen orientation of a smartphone simply by rotating it. Hardly anyone is unfamiliar with this feature, as it is used daily. On the other hand, few people know how this mechanism works and the diverse applications MEMS technology offers beyond this.

Indispensable for Digitalization

Especially in industrial applications, MEMS technology can make a significant contribution to the digital transformation of the economy through data-driven manufacturing. To generate high added value, production systems must process as many, sometimes very diverse, types of data as possible in a value-adding manner. Sensors and transducers serve as information sources.

They provide the higher-level systems with information about physical parameters and plant conditions as a basis for decision-making in control and regulation, as well as plant operation and maintenance. In this way, MEMS sensors can help prevent machine downtime and quality issues while increasing sustainability through improved manufacturing and energy efficiency.

Sensor Technology With Growing Importance

Detecting and measuring physical parameters often requires converting the measured variable into an electrical signal. In the past, this frequently required very complex precision mechanical arrangements. These were often large and expensive, making their integration into compact mechatronic units challenging.

Especially in mechanical and plant engineering, the integration of additional sensors was met with skepticism, as every added complexity was considered a potential cause of failure. Furthermore, the processing power of control electronics was limited. These restrictions, however, are now a thing of the past.

Not only in mechanical and plant engineering but in general, it has become evident that increasing the efficiency and effectiveness of devices, machines, and systems is only possible with a broader data base.

Revolution Through Micro-Electromechanics

The widespread use of sensors—particularly for three-dimensional measurements required in applications such as mechanical engineering, robotics, or aerospace—is made possible through their miniaturization. Here, MEMS technology plays a leading role. MEMS sensors are extremely small. They can be manufactured alongside electronics for preprocessing the collected data and offered in an extremely compact form.

But what exactly is MEMS? The English abbreviation "MEMS" stands for Microelectromechanical Systems, meaning very small mechatronic systems. They emerged as a result of a technological shift. When classical precision engineering reached the limits of physical feasibility about 40 years ago, the well-established manufacturing processes of the semiconductor industry were utilized to produce extremely small and yet quite complex mechanical structures.

That was the birth of microsystem technology, which integrates electronic, mechanical, and optical components into the smallest spaces. It has made practically invisible hearing aids possible with extremely small microphones and speakers and brought forth tiny actuators used, for instance, to create pumps or motors for medical purposes that can be integrated into blood vessels. MEMS technology is also a significant branch of microsystem technology.

Monolithic Manufacturing—MEMS from A Single Mold

MEMS sensors are manufactured like semiconductor chips using etching processes on silicon wafers. As with semiconductors, the process is repeated multiple times with different masks to create 3D structures. By successively removing material, structures containing movable parts can be created.

The special feature is that these parts are no longer manufactured individually and then assembled as was traditionally done. Instead, they are created as a whole from a single block. This not only allows them to be significantly smaller but also eliminates the need for creating connections or simplifies and enhances precision through the subtractive process (removing everything that is not part of the sensor or a supporting auxiliary structure).

Reliable Conclusions

The basic principle is the same for all MEMS sensors. They measure the effect of the measured variable on the position or movement of their fixed and movable parts relative to each other. For this purpose, these parts are shaped during the manufacturing process so that their surfaces form a capacitor. Since this is very small due to the microscopic dimensions, these surfaces are often arranged in multiples. This can basically be imagined as two interlocking combs forming the electrodes.

With the distance between the electrodes changing, its capacitance is altered. This can be measured, and deviations from the normal value provide information about the relative position of the parts to each other. Through inertia, this enables conclusions to be drawn about the acceleration to which this arrangement is subjected.

Due to the material properties of the silicon crystals used and the applied exposure and etching processes, fluctuations and external influences play a minor role. This allows for the production of sensors that deliver consistently high measurement quality over very long periods and enable reliable conclusions about the mechanical measurement variables.

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Resounding Success

The functioning structures in MEMS sensors can be designed to be highly sensitive for measurements. Nevertheless, MEMS sensors are available in extremely robust, industrial-grade designs. Since many of them have no freely moving parts or joints in between, they are also resistant to vibrations and temperature fluctuations.

MEMS sensors are now very widespread and found in many applications. MEMS technology is primarily used in accelerometers and gyroscopes, but also in flow, pressure, inclination, and temperature sensors, as well as sensors for gas composition or air quality. It is not always obvious that MEMS sensors are involved. They can be a deeply integrated part of more complex electronic modules or products, as well as of industrial measurement transmitters.

Universal Applicability

The enduring success of MEMS sensors is due to their extremely small dimensions. Additionally, MEMS technology offers the possibility of combining sensors for various measurements into complete micromechatronic subsystems on a single chip. Their compact size, low cost, and processability into highly robust devices enable the measurement of numerous parameters in locations where the use of conventional sensors was previously not practical.

In most cases, MEMS technology is not specifically highlighted, as its use has already become standard in many areas. MEMS sensors play an important role not only in automotive engineering but also in medical technology. There, they are used in wearable and implantable medical devices, such as pacemakers, for the continuous monitoring of vital functions like heart rate or blood sugar levels.

In applications such as mining or the process engineering production of chemicals or pharmaceuticals, MEMS sensors enable real-time monitoring of process-critical and safety-relevant parameters, such as gas concentrations or pressure conditions. This allows for simultaneous optimization of production processes, product quality, and occupational safety.

In mechanical engineering, the simultaneous use of MEMS sensors at numerous points within the same devices, machines, or systems can greatly enhance system efficiency by simultaneously determining the position, path, or relative positions of movable machine parts. For example, software can significantly improve responsiveness to unexpected events, better maintain the quality of the produced product, and ensure functional safety.

Here to Stay

At the same time, the measurements collected by MEMS sensors provide the ability to infer the effects of wear or inadequate maintenance from factors such as high-frequency vibrations. Such information enables preventive inspections and interventions by maintenance personnel, as well as adjustments to processing parameters to prevent damage or downtime.

The development of MEMS sensors is far from complete. In addition to further miniaturization, reducing energy consumption, and increasing robustness, the focus is on deeper integration into IIoT networks. For instance, in the future, wireless MEMS sensors with Bluetooth Low Energy or 5G integration will enable energy-efficient, flexible networking of machines for continuous condition monitoring with remarkable density.

The direct integration of MEMS sensors into edge devices with artificial intelligence (AI) not only enables more efficient data processing through preprocessing of sensor signals directly at the point of capture. This not only reduces the costs and uncertainties of data transmission to the cloud for AI analysis but also allows for automatic adjustment of production parameters to subtle changes, raising the efficiency and quality of production processes to an unprecedented level.

MEMS sensors can make cars, machines, and systems much more sensitive and sustainably change the way we move and produce things. They are here to stay.

Christian Reinwald, Head of Product Management & Marketing, Reichelt Elektronik GmbH & Co. KG