A microchain that closely resembles a bicycle chain has been fabricated at the US Department of Energy’s Sandia National Laboratories. The distance between chain link centres is 50 microns.
Because a single microchain could rotate many drive shafts, the device would make it unnecessary to place multiple tiny microelectromechanical (MEMS) motors in close proximity. Usually, a separate driver powers each MEMS device. ‘All those drives take up a lot of real estate on chips,’ said Sandia technician Ed Vernon, who has received a patent for the silicon microchain.
The microchain also makes it possible to drive a MEMS device from a motor situated at a distance, again saving considerable space on the MEMS-bearing chip.
The microchain, said Ed, could be used to power microcamera shutters, as larger chains currently do in the macroworld. It could also be used in mechanical timing and decoding.
The 50-link silicon microchain is designed to transmit power somewhat like the drive belt in a 19th-century sewing factory. There, a central engine shaft powered by steam turned drive belts to power distant workstations such as sewing machines. Chain systems, unlike stroke systems, do not require back-and-forth movements but instead allow for both continuous and intermittent drive translation.
Vernon fabricated a microchain rather than a microbelt because although silicon belts are tough and flexible, they are spring-like and produce too much torque on gears not aligned in a straight line.
Each chain link is capable of plus-or-minus 52 degrees rotation with respect to the preceding link, without creating pressure on the support structure. The wide angle means MEMS designers can be relatively unconstrained in positioning multiple devices.
The longest span unsupported by gears or bracing is 500 microns. A microchain tensioner is needed to accommodate longer spans.
The multilevel surface-micromachined silicon device was constructed with the aid of Sandia’s patented Summit IV and Summit V technology, which enables construction of complicated MEMS devices.