Micro-Electro-Mechanical System, or MEMS, is a miniature device or machine that is made of both mechanical and electrical components, using techniques of microfabrication.
The term ‘MEMS’ is often used to describe both a category of micromechatronic systems and the process technology employed to manufacture them. Some MEMS do not have mechanical components, but since they convert certain mechanical signals into electrical or optical ones, they are classified as MEMS.
In Europe, MEMS are more commonly known as microsystems technology, and in Japan, it is referred to as micromachines.
Table of Contents
Size of MEMS
The physical dimensions of MEMS devices can range from 20 micrometers to one millimeter. They are made of components between 1 and 100 micrometers in size.
While individual components can be smaller than the width of a human hair, multiple modules arranged in arrays can occupy an area of more than a 10-centimeter square.
MEMS devices usually contain central data processing units (such as microprocessors) and tiny instruments that interact with surroundings (such as microsensors).
Types of MEMS
There are two forms of MEMS switch technology: ohmic and capacitive.
1. Ohmic MEMS switches are developed using electrostatic cantilevers. Since cantilevers deform over time, these switches can fail from contact wear or metal fatigue.
2. Capacitive switches are controlled by a moving plate or sensing element that alters the capacitance. By exploiting their resonant characteristics, they can be configured to outperform ohmic devices in specific frequency ranges.
How Are They Constructed?
While the interest in producing MEMS grew in the 1980s, it took nearly two decades to establish the design and manufacturing infrastructure required for their commercial development. One of the first few such devices produced were inkjet printheads and airbag controllers.
Using this technology, researchers were able to build a projector with micromirrors (which utilizes MEMS) in the late 1990s. Over time, microsensors became more popular: they were gradually integrated into different types of sensors, including sensors for radiation, magnetic fields, temperature, and pressure.
Today, MEMS are used in almost all smart devices, and they have become much more efficient (in terms of performance and energy consumption) than their larger counterparts. They are composed of parts such as microprocessors, microactuators, microsensors, and several data processing units.
The fabrication of MEMS involves the same techniques that are used to create integrated circuits and semiconductor devices. The basic techniques are
- Deposition: Thin layers (between 1 and 100 micrometers) of material are deposited on a special surface.
- Patterning: A pattern is transferred into a material using a process called lithography.
- Etching: The material is dissolved either in a chemical solution or using reactive ions to produce the required shapes.
- Die preparation: Once MEMS devices are prepared on a silicon wafer, individual dies are separated, and then wafer dicing is performed through a cooling liquid or a dry laser process.
Silicon is the most common material used to create MEMS. It is readily available, inexpensive, and has substantial advantages, especially in the field of microelectronics. For example, silicon suffers very little fatigue and almost no energy dissipation.
Some MEMS are made of metal through electroplating, evaporation, and sputtering processes. Metals that exhibit high degrees of reliability include gold, platinum, silver, tungsten, copper, titanium, and aluminum.
Polymers can also be used to manufacture MEMS devices, as they can be produced in large volumes, with various material characteristics.
How Are MEMS Different From NEMS?
NEMS (short for nano-electro-mechanical systems) are a class of devices featuring electrical and mechanical characteristics on the nanoscale. NEMS form the next logical miniaturization step from MEMS.
In simple terms, NEMS are similar to MEMS but smaller: they have critical structural elements at or below 100 nanometers (atomic or molecular scales).
While NEMS and MEMS are referred to as separate technologies, they are dependent on one another. For instance, a scanning tunneling-tip microscope, which detects atoms, is a MEMS device.
In MEMS technology, forces produced by fluid dynamics and ambient electromagnetism play an important role. Whereas in NEMS technology, surface-based sensing mechanisms and large quantum mechanical effects are also crucial.
Unlike MEMS, NEMS technology utilizes carbon-based materials, specifically diamond, carbon nanotubes, and graphene. Due to substantial advances in growth, manipulation, and knowledge of the electrical and mechanical properties of graphene, researchers are taking more interest in graphene for NEMS devices. These devices include pressure sensors, resonators, accelerometers, and more.
Examples and Applications
The accelerometer in a smartphone | YouTube
As MEMS become more efficient and less expensive to build, they are expected to play a crucial role in the IoT (Internet of Things) and home automation. The common commercial applications of MEMS are:
- Accelerometers in vehicles for various purposes, such as electronic stability control and airbag deployment
- Sensor-driven cooling and heating systems for building management systems
- The optical switch used for switching technology and alignment for data communications
- Disposable blood pressure sensors and vehicle pressure sensors made of silicon
- Electrostatic, electromagnetic, and piezoelectric microharvesters (used for energy harvesting)
- Small microphones, barometers, and gyroscopes to support smartphone applications
- Micronozzles used in inkjet printers to control the flow of ink.
Challenges in MEMS Fabrication and Reliability
Several factors impact the performance and widespread adoption of MEMS. The following are the key challenges in these areas:
Miniaturization Precision: Since MEMS devices operate at a microscopic scale, they require a high degree of precision in their fabrication. Achieving the desired level of miniaturization demands complex manufacturing processes that can manipulate materials at the microscale.
Fabrication Techniques: Two common techniques used in MEMS fabrication are bulk micromachining and surface micromachining, each with its own limitations. Bulk micromachining faces constraints related to material compatibility and scalability. On the other hand, surface micromachining has limitations in creating three-dimensional structures and tends to exhibit lower aspect ratios.
Material Compatibility: Materials used in MEMS fabrication must have specific electrical, mechanical, and thermal properties. Identifying the most suitable material meeting these criteria and seamlessly integrating it into manufacturing techniques remains an ongoing challenge.
Packaging Challenges: MEMS devices require encapsulation or packaging to shield them from environmental factors. Creating packaging solutions that reliably preserve device integrity while enabling functionality can be a tough task.
Cost Constraints: Attaining high precision and reliability often requires sophisticated manufacturing processes, which can be expensive. Striking a balance between performance and cost-effectiveness remains an ongoing challenge in MEMS fabrication.
An innovation base for microelectromechanical system (MEMS) sensors has been inaugurated in Shijiazhuang, capital city of N China’s Hebei, according to its developer. The innovation base serves to develop, design, package and test, and integrate MEMS sensors. pic.twitter.com/AtyxXoTxmZ
— China Science (@ChinaScience) January 8, 2024
Global Market
Many companies are working on MEMS projects. Smaller firms offer value in innovative solutions and handle the expense of customized fabrication with high sales margins. Larger firms mostly manufacture high-volume, inexpensive parts or packaged solutions for end markets, such as electronics, biomedical, and automobiles.
Generally, both small and large companies invest in research and development to build new MEMS technology.
The global MEMS market is projected to reach approximately $64.15 billion by 2032, compared to nearly $28.6 billion in 2022. North America is poised for the fastest growth in the forecast period.
Given the rising trend of connected lifestyles, the dominant segment is expected to be consumer electronics, accounting for over 40% of the global revenue share.
Market growth might face hindrances due to calibration and accuracy issues. However, fierce competition is expected to compel industry players to maintain low prices in the upcoming years.
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