MEMS sensors are installed in every smartphone, but can also play an important role in industrial technology. It has greatly expanded our capacity for recording certain mechanical measured variables and responding to them very quickly. But: What technology lies behind the acronym MEMS, and what currently untapped opportunities does its use offer in professional applications?
MEMS sensors allow the image orientation to be easily changed by rotating your smartphone. The majority of people use this feature on a daily basis and therefore would be familiar with this simple example. However, few people know how this mechanism works and the wide range of uses MEMS technology offers.
Essential for digitalisation
Particularly in industrial applications, MEMS technology can make a significant contribution to the digital transformation of the economy through data-driven production. For production systems to generate high added value, they must process as much data as possible, sometimes highly diverse data, in a way that adds value. Sensors and sensing elements are used as sources of information.
They provide the higher-level systems with information about physical parameters and plant statuses, serving as a basis for decision making for control and regulation, as well as plant operation and maintenance. MEMS sensors can thus help to avoid machine downtimes and quality issues and improve sustainability by increasing production and energy efficiency.
Increasingly important sensor technology
Detecting and measuring physical parameters usually requires converting the variable to be measured into an electrical signal. In the past, this often required very complex precision engineering setups. These were often large and cost-intensive, making them difficult to integrate into compact mechatronic units.
Particularly in mechanical and plant engineering, the integration of more sensors was met with scepticism, as every additional source of complexity was considered a potential cause of failure. In addition, the processing power of the control electronics was limited. But these restrictions are now a thing of the past.
Not only in mechanical and plant engineering, but also in general, it has become widely accepted that increases in the efficiency and effectiveness of devices, machines and systems are only possible on the basis of a broader database.
Micro-electromechanics leads the revolution
The widespread use of sensor technology—particularly three-dimensional measurements, which are required in applications such as mechanical engineering and robotics or in aerospace—is made possible by its miniaturisation. MEMS technology plays a central role here. MEMS sensors are extremely small. They can be produced together with electronics for the preliminary processing of the collected data and offered in an extremely compact form.
But what actually is MEMS? MEMS stands for micro-electromechanical systems, i.e. very small mechatronic systems. They arose out of a technological shift. When traditional precision engineering reached the limits of what was physically possible around 40 years ago, the manufacturing processes of the semiconductor industry, which were already well established at the time, were used to produce extremely small yet rather complex mechanical structures.
This 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 has produced tiny actuators that have been used, for example, to create pumps or motors for medical purposes that can be integrated into blood vessels. MEMS technology is also an important branch of microsystems technology.
Monolithic production — MEMS from a single block
MEMS sensors are manufactured from silicon wafers using etching processes, similar to semiconductor chips. In both cases, the process is repeated several times with different masks to achieve 3D structures. In this way, structures can be created that contain moving parts by successively removing material.
What’s so special about that: These parts are not manufactured individually and then assembled in a conventional manner. Rather, they are formed in their entirety from a single block. As a result, they can be significantly smaller. The creation of connections is also eliminated or made easier and more accurate by the subtractive process (the removal of 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 moving parts relative to each other. To achieve this, they are shaped during the manufacturing process so that their surfaces form a capacitor with each other. Since this is very small in view of the microscopic dimensions, these surfaces are often arranged in multiples. In principle, you can imagine this as two combs inserted into each other forming the electrodes.
The distance between the electrodes changes the capacitance of the electrodes. This can be measured, and its deviation from the normal value indicates the relative position of the parts in relation to each other. The inertia of the mass makes it possible to draw conclusions about the acceleration to which this arrangement is exposed.
Due to the material properties of the silicon crystals used and the exposure and etching processes applied, fluctuations and external influences play merely a minor role. In this way, sensors can be manufactured that provide consistently high measurement quality over very long periods of time and allow reliable conclusions to be drawn about the mechanical measured variables.
Resounding success
The active structures in MEMS sensors can be designed to be highly sensitive in terms of measurement technology. However, MEMS sensors are available in extremely robust, industrial-grade designs. As many of them have no freely moving parts or joints between them, they are also insensitive to vibrations and temperature fluctuations.
MEMS sensors are now very widespread and can be found in numerous applications. MEMS technology is used primarily in acceleration sensors and gyroscopes, but also for 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 responsible. They can be a deeply integrated component of more complex electronic modules or products, but also of industrial measuring transmitters.
Universal applicability
The MEMS sensors owe their long-term success to their extremely small dimensions. In addition, the MEMS technology enables sensors for various measured values to be combined into entire micro-mechatronic subsystems on a single chip. Their small footprint, low cost and suitability for application in very robust devices enable the measurement of numerous variables in locations where the use of conventional sensors was previously impractical.
In most cases, there is no specific reference to MEMS technology, as its use is already a matter of course in many fields. MEMS sensors play an important role not only in automotive engineering, but also in medical technology. They are used in portable and implantable medical devices, e.g. pacemakers, for continuous monitoring of vital functions such as heart rate or blood sugar levels.
In applications such as mining or the process-based manufacturing of chemicals or pharmaceuticals, MEMS sensors enable real-time monitoring of process-critical and safety-relevant variables, such as gas concentrations or pressure conditions. This enables simultaneous optimisation of production processes and product quality as well as occupational safety.
In mechanical engineering, the simultaneous use of MEMS sensors at numerous points in the same devices, machines or plants can significantly improve plant efficiency by simultaneously determining the position, path or relative position of moving machine parts. For example, software can be used to significantly improve their response to unexpected events and to better ensure the quality of the manufactured product and functional safety.
Here to stay
Measured variables collected by MEMS sensors also make it possible to draw conclusions about high-frequency vibrations to the effects of wear and tear or inadequate maintenance, for example. Such information enables preventive checks and interventions by maintenance personnel and the adaptation of processing parameters to prevent damage or downtimes.
The development of MEMS sensors is far from being exhausted. In addition to further miniaturisation, reducing energy consumption and increasing robustness, the focus is on deeper integration into IIoT networks. For example, wireless MEMS sensors with Bluetooth Low Energy or 5G integration will enable energy-efficient, flexible networking of machines for continuous, high-density condition monitoring.
The direct integration of MEMS sensor technology into edge devices with artificial intelligence (AI) enables more efficient data processing by pre-processing the sensor signals directly at the point of acquisition. This not only saves the costs and uncertainties of data transfer to the cloud for AI analyses. By automatically adapting the production parameters to subtle changes, the efficiency and quality of the production processes can also be increased to an unprecedented level.
Bilder: reichelt elektronik
