(This column, which originally appeared in Global SMT & Packaging magazine 6.1 (Jan 2006), is also available as a free PDF.)

As one reads the articles and literature on micro electromechanical systems or MEMS, as it is more commonly known, one might get the impression that it is a new technology.

In truth, however, MEMS technology is nearly 25 years old (some products have actually been on the market since the mid 1980s), and the technology is presently maturing at a very rapid rate. It is a vital and vibrant technology that is providing an array of new capabilities not otherwise possible.

The general intent of MEMS technology is, as its name implies, to integrate various mechanical devices, such as sensors and actuators of various types, with electronic circuits. This is accomplished most generally by using standard silicon wafers and by co-manufacturing the disparate technologies on the wafers. The electronics potion of the MEMS device is typically created using traditional integrated circuit process sequences, and the micro mechanical elements of the device are created using suitable processes that either selectively micro-machine selected areas of the silicon wafer, using etching processes familiar to semiconductor manufacturing, or add new structural layers. The result is a device that has integrated electrical/electronic and mechanical functions.

Promoters and proponents of MEMS technology see a very bright future being promised by this microscopic marriage of electrical/electronic circuits and mechanical function, both to solve a wide array of sensing, measurement and process challenges in the future and to create miniscule smart products with limits that are bounded only by the developers’ imagination and the fundamental physics of the processes used.

One of the early demonstrations of MEMS was performed at Sandia National Laboratories, where they fabricated a microscopic motor including gears from silicon, as can be seen in the accompanying figure. It was an impressive demonstration, but it also privately dismayed some in the MEMS community as it set in play, with some observers, a misunderstanding of the full potential of micro electromechanical systems technology. The clever and still important demonstration was pretty far removed from the first commercial applications, which were focused on more mundane pressure sensing applications in automotive and medical products.  Presently MEMS technology serves in a wide and expanding range of product applications, including sensors of many types, such as accelerometers, gyroscopes, rate sensors, vibration sensors, and medical devices, such as disposable blood pressure sensors. Other areas where MEMS have shown their ability include RF technology, where they are being used to create RF switches, tunable filters, microscopic antennas and phase shifters. 

There is also a subset of MEMS known by the acronym of MOEMs (micro optical electronic machines) These have proven useful in optical switching applications for some telecommunication products to handle light-based, high-bandwidth data traffic routing. Another highly visible application for MOEMS (no pun intended) is in display technology where optical MEMS technology, developed at Texas Instruments, is now commonly found in computer video projectors. 

One of the beauties of MEMS technologies is that they are highly cost effective. The simple fact that thousands of devices can be processed in parallel on a single silicon wafer is highly compelling, and that can be leveraged in the same manner as integrated circuits, to drive costs down--even to the point of allowing them to be used in disposable fashion in certain applications.

Packaging of MEMS devices shares some commonality with traditional IC packaging, but there are some significant differences. Various MEMS devices, for example, will require different packaging solutions depending on the operational requirements of the device in its application. In some cases, the devices may be ‘pre-packaged’ at wafer level to preserve the mechanical function in a vacuum or inert gas environment, and thus protect it from the environment. In other applications, access to the environment is a requirement, such as in analytical (e.g lab on chip) applications and applications requiring fluid sensing, control, and/or transport. 

In summary, MEMS technology is already here with a wide and increasing range of devices being created that allow the minuscule microsystems to sense, monitor and/or control an environment. MEMS sensors will increasingly be used to gather mechanical, optical, thermal, biological and chemical information, allowing that information to be further processed and responded to. The range of potential applications is likely to be huge as product designers become more familiar with this no-longer-emerging technology.

References:
1.    www.sandia.gov/mstc/technologies/micromachines/tech-info/overview/index.html
2.    www.darpa.mil/MTO/MEMS/
3.    www.amkor.com/enablingtechnologies/MEMs/index.cfm