Profs explore use of MEMS

By Daniel Holevoet

Contributing Reporter

Cellular phones squeeze a microphone, transmitter and battery pack into a small package for convenience, but some problems must have small solutions as a necessity rather than a luxury.

Professors in Yale’s Engineering and Physics Departments are tackling these problems by developing microelectromechanical systems, or MEMS, to perform tasks where larger devices will not suffice. MEMS are traditional electronic circuits like those found inside a computer, but with added sensors and mechanical components that allow the system to respond intelligently to its environment. And, because they are produced in a manner similar to other circuits, they may be produced at low cost, according to the MEMS and Nanotechnology Clearinghouse.

While they are on the cutting edge of science, there are already a number of MEMS available in public products. One of the most notable areas in which MEMS play a role is automobile sensors and controllers. Pressure sensors in automobile engines, developed during the 1970s, were one of the first MEMS applications. Presently, accelerometers detect when to deploy airbags or when a car is being stolen, and condition sensors detect impurities in fuel and oil.

Yale professors are exploring future applications of MEMS technology in their labs.

“Practical applications are the first thing we consider before we even start a research project,” electrical engineering professor Hur Koser said. “Microdevices are cool, but eventually the driving force for success is the market demand or the need for a new, innovative solution, and not the coolness factor.”

Koser is currently researching ways to gather data on cellular behavior. In particular, one of his projects involves using MEMS to deliver and trace single molecules as they travel through the body — potentially aiding in the discovery of cures for Alzheimer’s, Parkinson’s and multiple sclerosis.

On a slightly larger scale are systems that painlessly monitor glucose levels in diabetic patients and warn the individual if he or she needs medication. Systems to actually the deliver medication, Koser said, are in the experimental stage at this point.

Yale produces all its own bio-MEMS devices, and a new lab at the Center for Microelectronic Materials and Structures will provide additional testing facilities.

According to Koser and his colleague Ainissa Ramirez, a professor of mechanical engineering, the greatest problem in constructing MEMS devices is how material and physical properties change on an extremely small scale.

“Materials act differently when they are the thickness of your hair,” Ramirez said. “Lots of phenomena that we ignore on our scale are forces to reckon with on the scale of MEMS. We are learning about some of the fundamental mechanisms of these materials. This knowledge will allow us to predict materials’ properties and enable MEMS engineers to make educated decisions.”

Ramirez is working on new biocompatible materials called shape memory alloys composed of nickel titanium, which return to their previous shape when heated. She said this property is desirable for micropumps, micromanipulators and heart valves.

“We aim to make robust materials, so that reliable devices can be made,” Ramirez said. “Our strength is materials. My collaborators are strong in device fabrication. Together we aim to make reliable devices.”

Koser said MEMS will play a highly significant role in the future — existing markets will get larger, and new markets in biotechnology and biomedical engineering will open up.

“The interface gap between the nano world and the macro world will be filled by MEMS devices,” he said.

Scanning electron micrograph of a MEMS structure used as an injector 
nozzle for a micropower source. The high aspect silicon nozzle was 
fabricated at the Cornell NNIN facility. (Credit: Frank Li, advisor 
Prof. 
Mark Reed).”
Courtesy MarkReed
Scanning electron micrograph of a MEMS structure used as an injector nozzle for a micropower source. The high aspect silicon nozzle was fabricated at the Cornell NNIN facility. (Credit: Frank Li, advisor Prof. Mark Reed).”

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