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MEMS stands for Micro Electro-Mechanical Systems, referring to functional machine systems with components measured in micrometers. MEMS is often viewed as a stepping stone between conventional macroscale machinery and futuristic nanomachinery. MEMS-precursors have been around for a while in the form of microelectronics, but these systems are purely electronic, incapable of processing or outputting anything but a series of electrical impulses. However, modern MEMS-fabrication techniques are largely based upon the same technology used to manufacture integrated circuits, that is, film-deposition techniques which employ photolithography.
Largely considered an enabling technology rather than an end in itself, the fabrication of MEMS is seen by engineers and technologists as another welcome advance in our ability to synthesize a wider range of physical structures designed to perform useful tasks. Most often mentioned in conjunction with MEMS is the idea of a "lab-on-a-chip," a device that processes tiny samples of a chemical and returns useful results. This could prove quite revolutionary in the area of medical diagnosis, where lab analysis results in added costs for medical coverage, delays in diagnosis and inconvenient paperwork.
MEMS are fabricated in one of two ways: either through surface micromachining, in which successive layers of material are deposited on a surface and then etched to shape, or through bulk micromachining, where the substrate itself is etched to produce a final product. Surface micromachining is most common because it builds on the advances of integrated circuits. Unique to MEMS, deposition techniques sometimes leave behind "sacrificial layers," layers of material meant to be dissolved and washed away at the end of the fabrication process, leaving a remaining structure. This process allows a MEMS device to have complex structure in 3 dimensions. Various microscale gears, pumps, sensors, pipes, and actuators have been fabricated and some of them are already integrated into everyday commercial products.
Examples of modern-day MEMS use include inkjet printers, accelerometers in automobiles, pressure sensors, high-precision optics, microfluidics, monitoring of individual neurons, control systems, and microscopy. There is currently no such thing as a productive microscale machine system on the order of productive macroscale assembly lines, but it seems that the invention of such a device is only a matter of time. The prospect of manufacturing with MEMS is exciting because arrays of such systems working in tangent could be substantially more productive than macroscale systems occupying the same volume and consuming the same amount of energy. One prominent limitation, however, would be that macroscale products built by microscale machine systems would need to be composed primarily of prefabricated microscale building blocks.