Credit: USC/ISI

Using an electrochemical fabrication process (called EFAB), Adam Cohen and a team of engineers at the University of Southern California have made several multi-layered structures, such as the 12-layer nickel chain shown here that has six freely moving links. The chain is not much thicker than a sheet of paper, probably making it the world's thinnest. But for the engineers who created it, the most exciting thing about the chain is not its size, but the process used to build it.

The EFAB technique can produce arbitrary 3-D micro-devices in a simple, automated process. EFAB is inspired by the commercial process of ‘rapid prototyping’, which uses a stacking procedure to build a solid object from layers hundreds of micrometres thick. Devices made by rapid prototyping are usually plastic, whereas EFAB can create metal objects from layers that are 5-8 μm or less.

Each layer is made by depositing a ‘sacrificial’ material using a high-speed ‘instant masking’ technique, followed by a blanket deposit of metal. The layer is levelled, and the process repeats, following a computer-generated pattern. Chemically etching away the sacrificial material leaves behind the desired 3-D structure. Instant masking uses a prefabricated plate that deposits material much like a printing press, making the whole process quicker.

Traditional micro-fabrication requires customized processes, and expensive cleanrooms. Through mass production, EFAB promises to substantially lower the costs of producing many micro-scale devices.