Key Technology Where Does MEMS Sensor Technology Come From, and 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 measure certain mechanical parameters and react to them very quickly. But what technology actually lies behind the acronym MEMS, and what currently untapped possibilities arise in professional applications through their use?

MEMS sensors make it possible to easily change the screen orientation of a smartphone by tilting it. There’s hardly anyone who doesn’t use this function daily and is therefore unfamiliar with this simple example. On the other hand, few know how this mechanism works and the diverse applications that 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 ensure production systems generate high value, they must process as many, sometimes very diverse, data as possible in a value-adding way. Sensors and measuring transducers serve as sources of information.

They provide the systems above them with information about physical parameters and plant conditions as a basis for decision-making in control, regulation, plant operation, and maintenance. In this way, MEMS sensors can help prevent machine downtime and quality problems, as well as increase sustainability by improving manufacturing and energy efficiency.

Sensor Technology With Growing Importance

Detecting and measuring physical parameters usually require converting the quantity to be measured into an electrical signal. In the past, this often required very complex precision engineering arrangements. These were frequently large and expensive, making them unsuitable for integration into compact mechatronic units.

Especially in mechanical and plant engineering, the integration of more sensors met with skepticism, as each additional complexity factor was seen as a potential source of failure. Moreover, the processing power of the control electronics was limited. These limitations are now a thing of the past.

Not only in mechanical and plant engineering but more generally, it has become clear that improvements in the efficiency and effectiveness of devices, machines, and systems are only possible based on a broader data foundation.

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 together with electronics for preprocessing the collected data and offered in a highly 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 possibilities around 40 years ago, the well-established manufacturing processes of the semiconductor industry were utilized to produce extremely small yet quite complex mechanical structures.

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

Monolithic Manufacturing—MEMS from A Single Mold

MEMS sensors are manufactured like semiconductor chips using etching processes from silicon wafers. In both cases, the process is repeated multiple times with different masks to achieve 3D structures. In this way, structures containing movable parts can be created through successive material removal.

The special aspect of this: These parts are no longer manufactured individually and then assembled, as was traditionally the case. 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 connections, or simplifies and improves them 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, these parts are shaped during the manufacturing process so that their surfaces form a capacitor. Since the capacitance is very small due to the microscopic dimensions, these surfaces are often arranged in multiples. This can essentially be imagined as two interlocking combs forming the electrodes.

The capacitance changes with the distance between the electrodes. This can be measured, and its deviation from the normal value allows conclusions about the relative position of the parts to each other. Through mass inertia, this enables, for example, determining 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 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 active 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 movable parts or joints in between, they are also resistant to vibrations and temperature fluctuations.

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

Universal Applicability

MEMS sensors owe their lasting success to their extremely small dimensions. In addition, MEMS technology offers the possibility to combine sensors for various measurements into entire micro-mechatronic subsystems on a single chip. Their minimal space requirements, low costs, and ability to be processed into highly robust devices allow for the measurement of numerous variables in locations where the use of conventional sensors was previously impractical.

In most cases, MEMS technology is not specifically highlighted, as its use is already taken for granted in many fields. 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 continuous monitoring of vital functions like heart rate or blood sugar levels.

In applications such as mining or process engineering for the 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 simultaneous optimization of production processes, product quality, and occupational safety.

In mechanical engineering, the simultaneous use of MEMS sensors at numerous points on the same devices, machines, or systems can significantly improve plant efficiency by simultaneously determining the position, path, or relative positions of moving machine parts. For instance, software can significantly enhance their responsiveness to unexpected events, better maintain the quality of the manufactured product, and improve 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 insufficient maintenance from high-frequency vibrations, for example. Such information enables preventive inspections and interventions by maintenance personnel and the adjustment of 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 exceptional density.

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

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