May 5, 2009
Printable NEMS platform drives down cost of sensors
Today, microelectromechanical systems are an established technology in many product areas such as accelerometers, gyroscopes, pressure sensors and digital micromirror arrays. What's more, devices are becoming smaller with dimensions in the nanometre range and possess a range of useful physical properties, which is paving the way for new applications.
In a recent study, published in Nanotechnology, scientists in Sweden have investigated a totally new printable approach to manufacturing nanoelectromechanical systems (NEMS). The devices are based on nanometre-sized, high aspect ratio, tuneable grating structures (interdigitated pairs of walls). Because the structures are fixed along their length at the bottom, in contrast to free cantilevers, the device can be fabricated directly by nanoimprint lithography in a photoresist or a plastic material.
Following a metallization step, the structures are ready for use. Almost any kind of substrate could be used, even no substrate at all. Some of the functioning devices were printed directly into plastic foil. As shown in the image above, a DC voltage applied to the metal layer on top of the structures gives rise to an electrostatic force between the walls whereupon the upper parts of the fingers bend towards each other. Adding an AC voltage causes an oscillatory motion, which allows for frequency response measurements in which the resonance frequency is recorded. This property was also used in the main application: a gas sensor. Airborne molecules may be caught on the sensor surface and by adding their mass to the oscillating walls they reduce the resonance frequency. It's hard to believe, but the plastic structures oscillate at frequencies of a few hundred megahertz, which together with the light material makes the device's responsitivity exceptionally high (0.1 Hz/zeptogram).
The same technique may also be used for other applications such as optical and sub-wavelength gratings, accelerometers and radio frequency devices. The plastic NEMS show that micromechanics may follow the examples of both microelectronics and photonics by also moving into the world of polymers.
About the author
The work was performed at NEMS AB, a research start-up developing a technology platform for printable polymer MEMS, in co-operation with Lund University, Sweden. Dr Sara Ghatnekar Nilsson was CTO of NEMS AB, currently at TetraPak. Thomas Parker is the CEO, Dr Andrej Litwin and Prof. Lars Montelius are the founders and Ivan Karlsson and Anders Kvennefors are employees of NEMS. Dr Vilma Zela is a postdoc and Gang Luo and Mats Ärlelid are PhD students studying at the Lund University.