A team from the Research Lab of Electronics were trying to build an electrical circuit by printing a pattern onto a thin silver film. They expected their plastic stamp to pull away the silver it made contact with, leaving an electrode that could control an organic light-emitting diode. Instead, the stamp pulled away the entire silver film.
“The first couple of times we did this, we were like ‘Ah! Bummer, man.’ And then a light bulb went off and we said, ‘Well but we’ve just made the word’s first printed MEMS,” said Vladimir BuloviÄ‡, professor of electrical engineering.
The MIT researchers started with a sheet of grooved rubbery plastic coated with electrically conductive indium tin oxide and used a transfer pad to press a film of metal against the plastic. Between the pad and metal film there is a layer of organic molecules that weaken the metal’s adhesion to the pad and if pulled away fast enough, the metal remains stuck to the plastic.
Corinne Packard, a postdoctoral researcher in the lab liked it to cellotape on a piece of paper: “if you peel it off slowly, you can delaminate the tape very easily. But if you peel fast you’ll rip the paper.”
The plastic can be made to behave like an actuator – the moving part in MEMS – by applying a voltage between the indium tin oxide coating and the film, which causes it to bend downwards into the groove. By varying the voltage the sheet can be made to vibrate and act like the diaphragm of a speaker. The practical applications of the material are still being uncovered.