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Parylene: Protecting MEMS in the Military

Posted by Sean Horn

Monday, December 23, 2013 1:47

@ 1:47 PM

Offering sensitivity and performance in a compact package, microelectromechanical systems (MEMS) have become increasingly prevalent in U.S. military applications over the last few decades and are enabling significant technological advances. As with all things military, however, robust protection of these sensitive electronics is imperative in order to ensure that they can withstand the harsh conditions often found on the battlefield. Conformal coatings such as Parylene can help MEMS-based military technologies withstand conditions such as extreme temperatures, humidity, dust/dirt, chemicals, and rugged terrain.

Because of the exciting advancements it allows, MEMS technology is the subject of a great deal of military R&D. MEMs sensors typically outperform those that are made on the “macro” scale, which makes them not only more efficient, but cheaper to manufacture in bulk as well. Cheaper and more efficient are certainly attractive options that the military looks for when developing or adapting new technology such as MEMS for weapons platforms, communications systems, or sensor suites designed for multiple uses.

With the onslaught of improvised explosive devices (IEDs) being implemented on the battlefield over the last decade, researchers have been tasked with designing new portable ‘bomb sniffing’ devices, for example, that are able to pinpoint hidden explosives buried under different substrates such as dirt, concrete, and asphalt. Scientists have even succeeded in developing a MEMS-based device that allows soldiers to detect explosive compounds as well as volatile organic compounds and chemicals based on gas chromatography (GC) and surface acoustic wave (SAW) detectors. Developed by scientists from Sandia National Labs, the mini-PDID (Pulsed-Discharge Ionization Detector), for instance, has shown that it is capable of not only detecting explosive compounds, but also detecting human odors, bacteria, pesticides, and carbon dioxide/monoxide gas as well as a host of other organic compounds.

The military is also interested in radiofrequency (RF) MEMS microtechnology for use in satellite and wireless communications, which theoretically could have data transfer speeds in excess of 100 GHz when coupled with laser optics. Soldiers on the ground will greatly benefit from RF MEMS technology, which is incredibly important in combat where real-time information is crucial. Current communications devices are used to transmit classified voice communications only and are widely known to be limited when it comes to interoperability; however, RF MEMS are not restricted to that limitation and, in fact, can provide much more in terms of functionality.

Boston MicroMachines has developed a working prototype radio, known as SCOUT (Secure Communicating Optical Ultra-small Transponder) that was originally designed to provide soldiers with an accurate IFF (Identification- Friend or Foe) system to prevent fratricide; however, they soon found that the device was capable of handling that task and delivering line-of-sight communications in much the same fashion as current military radios. The SCOUT transponder, however, has greater range and increased communications speed than that of conventional radios and is both smaller and lighter in weight as well. The key to that transponder is a modulated retroreflector, which is a MEMS-based deformable mirror that modulates light along with an optical device that sends that light back to the point of origin.

With more MEMS and nanotechnology being implemented into such novel new devices, developers often turn to conformal coatings, such as Parylene, to protect their microelectronics’ delicate moving parts, ensure reliability, and allow long life. The coating acts as a force field of sorts against such hazards as moisture, chemicals, dust, and temperature extremes without impeding movement or function. The coating is also often used in conjunction with hardened and rubberized outer casings to compensate for impacts, such as being dropped, that render the device inoperable.

In addition to protection of these critical components, Parylene conformal coating offers the benefit of offering performance in a thin film. In turn, the coating adds negligible weight and stress to the substrate—a critical feature for MEMS, in particular.

Suffice it to say, without the protection of Parylene or other conformal coatings, MEMS-based technology for military applications could be limited in scope, job function, or feasibility. Instead, Parylene helps to enable the realization of innovative, useful, MEMS-based military technologies that help keep us safe.

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