Microelectromechanical systems (MEMS) consist of extremely tiny mechanical elements, often integrated together with electronic circuitry.

How small exactly? The photo above shows a silicon motor together with a strand of human hair. MEMS systems are measured in micrometers (microns), that is, millionths of a meter. The diameter of human hair is about 100 microns.

MEMS devices are made in a similar fashion to computer microchips. The advantage of this manufacturing process is not simply that small structures can be achieved but also that thousands or even millions of system elements can be fabricated simultaneously. This allows systems to be both highly complex and extremely low-cost.

Thus, just as electronics and computing have become commonplace, systems to sense and control our physical environment are also becoming possible to deploy pervasively. This is seen to have the potential for revolutionary impact on future society.

Of what use are such tiny machines? Here is a broad sampling of applications:

• The gizmo that senses when to deploy your airbag
• Video projection via a million individually steerable mirrors
• Micro-optical systems for fiber-optic communications
• Super-fast electrophoresis systems for DNA separation
• Micro-robots
• Micro-tweezers
• Neural probes

The recent big boom in MEMS came with the advent of surface micromachining technology. IC semiconductor processing is much like baking a tort, built up layer by layer. The key to surface micromachining was the introduction of the sacrificial layer, a material (let's say, like the cream in a tort) which keeps other layers separated as the structure is being built up but is dissolved in the very last step to free up the other layers. To learn more, try the following links:

• Sandia Labs Movie Gallery of MEMS Devices
• Sandia Labs MEMS Technologies overview
• Danny Banks' Microengineering Overviews
• Chronos MUMPs Design Rules (see Process Overview)