At Georgia Tech, more than 20 research teams focus on MEMS-related research and development.
MEMS, or microelectromechanical systems, are devices that operate on a very small size scale, on the order of microns (millionths of a meter).
Supporting them is the Institute for Electronics and Nanotechnology (IEN), one of Georgia Tech’s nine Interdisciplinary Research Institutes. IEN’s extensive shared-user facilities, including advanced labs and cleanrooms, are used by as many as 200 Georgia Tech faculty, graduate students, and postdoctoral researchers who work on MEMS and other microsystems.
“More and more, our electronic systems must be aware of and even interact with their environment, and MEMS-based devices do that very well. They are the ear that detects sound and movement, the nose and tongue that detect toxic chemicals or smoke,” said Oliver Brand, a professor in Georgia Tech’s School of Electrical and Computer Engineering and executive director of IEN. “MEMS is like a sandbox of technologies and processes that lets us miniaturize sensors, and even put several sensing technologies onto a single chip, at low cost. It can enable many innovative applications, and it can also make conventional devices — like smoke or movement detectors — smaller, smarter, and more effective.”
Creating innovative sensors is highly interdisciplinary, Brand noted, requiring the joint efforts of electrical engineers, mechanical engineers, chemists, and biochemists — who are, in turn, supported by materials, packaging, and circuit-design experts. In addition, MEMS development is often expensive, demanding advanced facilities with device fabrication and characterization tools.
IEN enables Georgia Tech researchers to address these challenges, Brand said. Its cleanrooms and associated labs, open to Georgia Tech and non-Georgia Tech researchers, make state-of-the-art fabrication and characterization equipment widely available. As a result, most MEMS prototypes under development at Georgia Tech can be built right on campus.
Many of these micron-size devices utilize even smaller elements — nanotubes and nanowires — that aren’t much larger than a single molecule. These tiny nanoscale parts help microsystems detect what they’re looking for. The presence of moving nanoscale elements has given rise to the term nano-electromechanical systems (NEMS), but most researchers just use the term MEMS.
A wide variety of MEMS-related and microsystems projects are underway at Georgia Tech. The following are a few samples of current MEMS research led by Woodruff School professors.
FLASHLIGHT INSIDE BLOOD VESSELS
Looking inside human coronary arteries can be facilitated by both the power and tiny profile of MEMS technology. Levent Degertekin, a professor in the George W. Woodruff School of Mechanical Engineering, is developing minute systems that can be mounted on a catheter used to find blockages in arteries.
Currently, physicians guide a catheter through the body’s arterial system by viewing it from outside using X-ray technology or magnetic resonance imaging (MRI), which are two-dimensional projections and provide limited resolution. Moreover, current catheters are equipped with 2-D ultrasound technology that doesn’t offer a frontal view.
“Think of the current systems of moving the catheter as being like the GPS-based map in your car — it’s useful but it’s flat, and you can’t see that herd of sheep directly ahead of you,” Degertekin said. “The view from inside using today’s intravascular ultrasound doesn’t provide much help. It’s more like looking out a side window.”
Degertekin’s approach equips the catheter tip with a tiny MEMS device that uses 3-D ultrasound capable of showing what’s directly ahead in the artery. The work is sponsored by the National Institutes of Health.
He also wants to make these ultrasound systems compatible with MRI techniques instead of X-ray imaging. High-resolution 3-D MRI technology would give doctors a better outside view of the moving catheter, and avoid radiation-exposure issues.
“It’s a futuristic and challenging design. We’re basically jumping at least two steps ahead of current technology,” he said. “Combining 3-D ultrasound with MRI is challenging because the techniques can interfere with each other.”
Degertekin and his team are developing MEMS technology that produces 3-D ultrasound capabilities using thousands of tiny ceramic capacitors resembling drumheads. These tiny ultrasound elements, 30 microns wide, move up and down in response to acoustic signals. The drumheads are currently integrated with processing electronics on a single 1.4-millimeter silicon chip, and the researchers are working to reduce them to sub-millimeter size for some applications.
To support this tiny array, the team has also pioneered technology that reduces the number of cable connections to the catheter. This approach helps minimize catheter size.
EARLY WARNING OF CROP DISEASES
Identifying volatile organic compounds (VOCs) associated with crop disease can help farmers take quick action against pathogens. GTRI’s Jie Xu is working with Professor Peter Hesketh of the Georgia Tech School of Mechanical Engineering to develop another microsystem-based sensor platform, a portable gas chromatograph (GC) that detects VOCs in the air in real time.
The aim is to provide an early diagnostic capability that would let farmers take corrective action far sooner than traditional approaches that rely on visual inspection.
The researchers have fabricated a miniature GC that utilizes tiny separation columns micro-machined onto a silicon wafer. Combined with other sensors, it could seek a variety of fungus, mold, or other crop infections marked by the release of VOCs.
“We’re working toward a handheld GC that’s about cellphone size,” Hesketh said. “It would be a fraction of the size of traditional GCs, which use separation columns that are as long as 30 meters.”
Additional potential uses include mobile stations that track atmospheric pollution or those that monitor VOC emissions at locations associated with petroleum products, like oil refineries or power plants.
FINDING CONTAMINATION
Detecting microorganism contamination is another important element of Hesketh’s research. With funding from the U.S. Department of Agriculture, he’s working with a University of Georgia team on an improved method for detecting food contamination involving bacteria and viruses found in various sources.
The collaborators are developing a technique that uses magnetic beads to capture and extract microorganisms from a sample. The tiny beads are coated with an antibody that attracts the target organism.
The researchers place the sample and beads in a device that’s basically a compact disc etched with tiny microfluidic channels. The disc, rotating at extremely high speeds, is designed to mix the beads thoroughly with the sample, helping ensure that all the existing organisms are found.
To sense the extracted organisms, the researchers are designing a system that would use micro-cantilevers coated to attract the target bacteria. The cantilevers could employ tiny piezoelectric-resistive strain gauges capable of generating an electrical response when they make contact with the mass of even a single bacterium.
Written by: Rick Robinson
See full MEMS article on Research Horizons.
