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ILP Institute Insider

February 28, 2013

Micromachines with Big Impact

Transforming electronics by thinking (very) small.

Alice McCarthy

Within MIT’s Microsystems Technology Lab (MTL) small is big and powerful. Though this concept is not unusual for a laboratory dedicated among other things to building electronics circuitry and systems, the sheer number of MTL-associated researchers dedicating themselves to the endeavor is. Under the MTL umbrella, between 400-500 resident PhD scientists, visiting scholars, industry partners, and graduate students are sorting out new ways of building and designing extremely small micro- and nanosystems for an expansive range of applications related to device fabrication, integrated circuits and systems, photonics, MEMS, and molecular and nanotechnologies

Hanqing Li
Research Scientist
MIT Microsystems Technology Labs

One of these MTL researchers, Hanqing Li, PhD, has been at the MTL micro/nano fabrication facility since 1998 after earning his PhD at the University of Nebraska and working at the National Institute of Standards and Technology.

MEMS Foundation

The unifying theme of Li’s work is the fabrication of microelectromechanical systems (MEMS) devices, or essentially very small machines or miniaturized mechanical and electro-mechanical elements assembled via microfabrication. Some of the best known applications of MEMS devices are automobile airbag sensors, inkjet printer heads, pressure sensors and motion sensors. You can also find MEMS sensors in cell phones, microphones, and controllers for games. “MEMS technology is everywhere,” Li says. “You can find it in practically every area of people’s lives including medical and chemical applications, biological devices, in aerospace, and in petroleum and energy.”

MEMS microfabrication—or micromachining—evoloved from semiconductor chip fabrication technology. But instead of building electronic devices the end goal of MEMS microfabrication is to build small machines and small sensors. MEMS technology is based on photolithography (which involves the transfer of high resolution photosensitive patterns to a substrate) and batch fabrication (which translates into building multiple devices in one wafer at one time). The end result is lower costs and increased precision.

“At MIT, we have all the tools, knowledge base and expertise to make these micro and nanoscale devices and also to design them in collaboration with our partners,” Li adds who is applying his own expertise toward three key MEMS projects.

Satellite microthruster

Today, dozens of nanosatellites—small satellites on the order of about 3-5 pounds—are orbiting Earth. But they lack a propulsion system to change orientation or orbit. To make them more efficient and ultimately to purposefully deactivate them after their useful lifetimes, Li and colleagues are engineering microthrusters thanks to funding from NASA. Powered by an ion electrospray system (IEPS), these microthrusters can directly power nanosatellites to a desired location.

The thruster is a small device covered with a generous array of microtips made of porous materials. “We fill the porous materials with ionic liquid and apply voltage of a couple of thousand volts across the tips,” explains Li. As a result, ions are pulled out of solution generating thrust in the opposite direction. With these tips located across the satellite, one can activate the thrusters directing the satellite to any desired location.

Microvacuum pump

Funded by a grant from the Defense Advanced Research Projects Agency (DARPA), Li is developing a microvacuum pump about 1-2 cm in size for use with portable mass spectroscopy machines or for any system requiring a diminutive pump. One of its other potential uses lies in inclusion in drug delivery devices.

Photonics device
The third project Li is pursuing is development of a communications photonics device layer for 3D computer chips. “It is a communication device stacked up between CPU and memory,” describes Li. “People are trying to stack up the chips instead of putting them side by side like current technology,” he adds.

Precisely because MEMS technology is an enabling technology it has already found its way into an expansive menu of uses. However, some applications are very small and each requires its own process flow. That presents a new set of challenges unlike semiconductors where all of the transistor building blocks are essentially the same for all the devices. This is where Li sees MIT’s strengths as an engineering powerhouse in the field of MEMS and other microsystem technologies are invaluable. “To shortcut the limitations of MEMS in terms of smaller applications and unique process flows, combining our expertise is essential to improve the chances of getting any device to market,” he says. “At MIT, we build up a team with design expertise, fabrication and testing people, and state-of-the-art fabrication facilities that allow us to solve a wide range of issues for our different customers and collaborators. That way I believe we can increase efficiency and generate the devices more quickly with lower cost.”