Micro-electromechanical systems or MEMS are tiny integrated devices that combine mechanical and electrical components. Traditional manufacturing techniques such as milling, turning, and molding become impractical at small scales so MEMS devices are fabricated using the same batch processing techniques used to fabricate integrated circuits. These devices can range in size from a few microns to several millimeters.

Because MEMS devices are a hybrid of mechanical and electronic mechanisms, they’re generally fabricated using a combination of traditional integrated circuit technologies and more sophisticated methods that manipulate both silicon and other substrates in a manner that exploit their mechanical properties.

In bulk micromachining, the substrate is removed in a manner similar to traditional integrated circuit techniques.

Surface micromachining, by comparison, is a predominantly additive in nature and is used to create more complex MEMS-based machinery. Material is deposited on the surface of the substrate in layers of thin films.

High-aspect-ratio micromachining differs dramatically from the other two techniques in that it’s reminiscent of traditional casting.

The accelerometers used in automotive airbag sensors were one of the first commercial devices using MEMS technology. In widespread use today, they measure the rapid deceleration of a vehicle upon hitting an object by sensing a change in voltage. Based on the rate of this voltage change, the on-die circuity subsequently sends a signal to trigger the airbag’s explosive charge.