Researchers at the Massachusetts Institute of Technology (MIT) have invented a way to make microelectromechanical systems (MEMs) by stamping metal on to a plastic film. Traditionally, manufacturers built MEMs using photolithography, a process that deposits different layers of material on a semiconductor wafer substrate and then chemically etches away portions to form functional patterns. Wafers are a maximum of 12-in. across, so arranging them into large arrays requires bonding them to another surface.
The stamping technique significantly reduces the cost of manufacturing MEMs. The method could also make it feasible, for instance, to produce large sheets of sensors for covering airplane wings to gauge their structural integrity, or to make large digital displays that could be rolled up when not in use. Because the technique produces flexible MEMS, it is also feasible to build sensors with irregular shapes. Additionally, because the stamping process eliminates the harsh chemicals and high temperatures traditionally associated with MEMs production, the devices might employ a wider range of materials.
Instead of using wafers, the researchers use a grooved sheet of a rubbery plastic coated with the electrically conductive indium tin oxide. They then use what they call a “transfer pad” to press a thin film of metal against the grooved plastic. Between the metal film and the pad is a layer of organic molecules that weakens the metal’s adhesion to the pad. Pulling the pad away quickly causes the metal to remain stuck to the plastic.
The stuck metal film spans the grooves in the plastic like a bridge across a series of ravines. Applying a voltage to the film makes it bend into the grooves of the plastic. The film thus acts as a moveable actuator in different ways. For example, varying the voltage makes the film vibrate, like the diaphragm of a loudspeaker. Selectively bending different parts of the film makes them reflect light in different ways. Radically bending the film turns a smooth surface into a rough one. And applying pressure to the film generates an electric signal. In theory, the metal film should be capable of registering the pressure of sound waves.
MIT, Research Lab of Electronics, web.mit.edu