MEMS' World - History and main applications

This page introduces examples of commercial MEMS applications (and how many are application fields) that have reached the market and are really available at this time, meaning that are used in real life! For example, MEMS actuators featuring electrostatic actuation that are used all around the world will be introduced here! This page shows that MEMS don't exist only in laboratory but everywhere around you!
MEMS devices have started when microelectronics people realize that polysilicon, one of the most used material at the beginning of microelectronics, has very good mechanical properties. Since then, these properties have been largely used and now MEMS use a lot of different materials to achieve an increasing number of applications

History of MEMS

Commercial MEMS Applications

You probably ignore it, but there are already MEMS around you. In your car, maybe in your television, and in your mobile phone!
I can't reference here all of the currently available applications, but I will talk about the most common and the most spectacular ones.

Summary

Inertial sensors

Inertial sensors are mechanics sensors aiming at measuring accelerations, in the mechanics science definition. An acceleration is a changing in the speed, could it be translational and/or rotational.

There are two categories of inertial sensors: accelerometers, and gyroscopes. The first ones measure varation of translational speed, and the last ones measure variation of rotational speed.

Microaccelerometers were the first MEMS device to flood the market.
The microaccelerometers are already used in daily life! They are parts of the tiny systems that try to take care of us while we ignore them. To realize it, you should remember microaccelerometers measure variation of translational speed. So acceleration, deceleration, even very high deceleration, like... shock! The sensor that detects a shock and launch the airbag is a microaccelerometer combined with a electronic circuit able to decide wether or not the shock was an accident or just your car passing a pothole.

Photo of a complete microaccelerometer chip Photo of a microaccelerometer device
Photos of a microaccelerometer, ADXL series, produced by Analog Device.
Copyright Analog Devices, Inc. All rights reserved.

On these photos, you can see a microaccelerometer device and the chip including associated electronics, made by Analog Device. This is a two axis microaccelerometer: this means it is able to measure accelerations in two directions at a time (in the directions of the plane).

There are a lot of other applications, like navigation, microaccelerometers can help in increasing precision, because GPS does hardly better than several meters, integrating accelerations and direction changing can help in calculating a position. In industrial device monitoring, an accelerometer can detect any changing in the vibration emitted by the device and preempts a breakdown.
There are more and more to say about microaccelerometers, they are still the spearhead of MEMS industry.

Microgyroscopes are newer in the market compared to microaccelerometers. Some devices have appeared on the market for navigation applications. The key point in these devices is sensitivity, and it has been the subject of research and development for several years before devices become interesting for real-life applications.

RF switches

RF switches have been under development for many years, but the commercial applications just begin to appear. The reason is the difficulty to combine high efficiency, reproducibility and reliability.
RF switches will be prefered to full-electronic switches on applications where security, integration capabilities, power consumption and other parameters are critical.

Animation of a R.F. microswitch
Schematics of a R.F. electromechanical microswitch in action

Optical multiplexers

Texas Instruments's DMD

Micromirrors have also been studied for a long time before a device become commercially available. Texas Instruments has developped a micromirrors' matrix for video display: the Digital Micromirror Device. It is now the base of high quality video projector, and you can find televisions carrying the DLP letters, meaning they embed Texas Instrument's DMD technology.

Microscopic photos of the DMD
Photos of Texas Instrument's DMD
Copyright Texas Instruments, Inc. All right reserved

DLP, standing for Digital Light Processor, is made of a large matrix of micromirrors (DMD), each mirror corresponding to a pixel. These mirrors can change their orientation angle thanks to an electrostatic actuation. So, if you send incident light on the matrix, the mirrors reflect a quantity of light to the screen depending on their orientation, so orientation angle controls the luminance for each pixel.

Schematics of single chip projection system
Schematics of a projection system with a single DMD chip
Copyright Texas Instrument, Inc. All right reserved

There are several kind of systems using DLP devices. Some of them use 3 DMD, one for each color. One of them uses a single DMD device, with a color filter system. Since micromirror actuation is very fast compared to the persistence of light on the screen, it is possible during an image cycle to switch between each of the filters so that the mirrors send successively a dose of each color for the same pixel without possibility for human eyes to see the sequence.

The advantages of DLP based system compared to existing ones, like plasma, LCD, or electronic beams are high resolution, and the best power ratio between light source and displayed light. Microtechnology also allows a very high productivity, reducing the cost of the devices as the market's demand grows.

Micromirrors devices have just reached the consumer market, and they are a promising technology that should eventually find a place in most of the display devices, like mobile phone screens, etc.

Note: Analog Devices, ADXL, Texas Instruments, DLP, DMD are registered trademarks. Photos on these pages have been taken from other websites with the authorizations of their owner. Don't ask me if you can reuse them, ask them!