Micro-electro-mechanical system (MEMS)

The MEMS technology (acronym of Micro Electro Mechanical Systems) is a manufacturing technology of microelectronic devices that, combining the principles of electronic technology based on silicon with micromachining, allows the creation of “intelligent” devices with high integration between electronic circuits and optomechanics devices, on the same chip. It merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology.

The remarkable advantages of this technology are lower energy absorption, lower weight, and very small dimensions, better performance, lower cost, and more excellent reliability and performance.

The fabrication of MEMS evolved from the process technology in semiconductor device fabrication, i.e., the basic techniques are deposition of material layers, patterning by photolithography and etching to produce the required shapes.[1] Materials for MEMS manufacturing are silicon, polymers, metals, and ceramics.

The functioning of a MEMS can be described considering an integrated circuit as the “brain” of the system that makes it possible to monitor the surrounding environment through the other devices (“senses” and “arms”) present on the same chip. In this way the system collects information by measuring mechanical, thermal, biological, optical and magnetic phenomena; electronics process the information derived from the sensors and reacts by enabling the actuators to respond by means of movements, positioning, filtration, pressure, etc. or even rechecking, using the same sensors, the changes that occurred in the time interval in the surrounding environment.

There is, therefore, a system capable of acquiring information from the environment by transducing the physical quantities into electrical impulses, processing this information using appropriate logic and, finally, responding with specific actions.

Applications of MEMS technology

MEMS technology is adopted in the most varied application areas, many of which can be divided into the following categories.

Sensors and actuators

  • MEMS pressure sensors are used in the military, aerospace, automotive and biomedical sectors.
  • The accelerometers and gyroscopes are mainly used in airbag systems for cars, smartphones, drones, and even in the games console industry.
  • MEMS magnetic field sensor (magnetometer) may also be incorporated in such devices to provide directional heading.
  • Speed sensors were introduced in the 1990s and are used both in the automotive industry (stability control systems, tire pressure sensors, GPS receivers) and in consumer electronics products (cameras stability control, GPS receivers for mobile phones).
  • MEMS are also used in Inertial navigation systems (INSs) of modern cars, airplanes, submarines and other vehicles to detect yaw, pitch, and roll; for example, the autopilot of an airplane.
  • Weight and force sensors are used for the construction of measurement and control devices.
  • Actuators are used to generate movement or force capable of moving other MEMS components. They can be divided into electrostatic and thermal type actuators.
  • Micro-fluid MEMS devices are designed to operate with fluids at a microscopic level. Typical applications of this type of MEMS are valves, pumps, injectors (used for example for the realization of inkjet printers).
  • Bio-MEMS are similar to micro-fluid MEMS, with the difference that they are designed to work with biological fluids, typically blood. Bio-MEMS are mainly used in the biomedical and health sectors.

Uses in radio frequency

They are mainly used in mobile phones, cordless phones, and GPS receivers. They present remarkable properties in terms of extremely reduced dimensions, wide bandwidth, low cost, and a very high signal-to-noise ratio, fundamental in all radio frequency applications. This type of MEMS is spreading rapidly and is replacing the traditional solutions realized in solid-state technology.

Optics and optoelectronics

MEMS optical devices are used to guide, amplify or attenuate, and reflect an optical signal of a specific wavelength. They are mainly used in the production of optical switches and optical modules for fiber optic transmission systems.

In conventional optical switches and systems for the cross-connection of DWDM channels, it is necessary to modify and control the optical path of the light. This is achieved through the use of micromirrors made with MEMS technology; used also to create other sophisticated optoelectronic devices.

For example switches for laser signals, sensors for telescopes, deforming lenses, projectors, and advanced displays, but also inertial sensors, precision accelerometers, retinal scanners, digital shutters, interferometers, sensors for sophisticated measurements.

References

  1. R. Ghodssi; P. Lin (2011). MEMS Materials and Processes Handbook. Berlin: Springer. ISBN 978-0-387-47316-1.
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