Sandia LabNews

World's smallest microchain drive fabricated at Sandia

Except that each link and pivot could rest comfortably atop a human hair, a microchain that closely resembles a bicycle chain has been fabricated at Sandia.

(The distance between chain link centers is 50 microns. The diameter of a human hair is approximately 70 microns.)

Because a single microchain can rotate many drive shafts, the device could make it unnecessary to place many tiny microelectromechanical systems (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," says Sandia technician Ed Vernon (2614), 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, says 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 work stations — for example, sewing machines — before the dawn of the age of electricity.

Chain systems, unlike stroke systems, do not require back-and-forth movements but instead allow for both continuous and intermittent drive translation.

Ed fabricated a microchain rather than a microbelt because though 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, on the other hand, 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 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.