Think Big, Build Small 
Students Design Nano Manipulators

How to manipulate anything from the size of a soda can on down to a nanotube-a cylindrical-shaped graphite tube, no bigger than a few molecules-using the same device, was the challenge undertaken by an MIT mechanical engineering grad student and his professor.

The student, Gordon Anderson, was working on his master's in mechanical engineering when his professor, Martin Culpepper suggested the idea to him. Culpepper felt that with applications for miniscule devices in the Micro-Electro-Mechanical Systems (MEMS) and nanotechnology fields increasing dramatically, an inexpensive, commercially feasible device that could manipulate very small things with six degrees of freedom would be a sure winner.

Martin Culpepper, an MIT professor of mechanical engineering, views the HexFlex design developed by one of his students.

That he was right was manifested recently when the resulting HexFlex concept, developed by Anderson under Culpepper's tutelage, won a 2003 R&D 100 Award. These awards honor the most technologically significant processes and products developed during the year, as determined by the editors of R&D Magazine.

The HexFlex Nanomanipulator derives its name from the fact that it has six-axis capability (hex) and is a compliant (flex) structure. It is intended to be used in manufacturing processes that require moving parts with nanometer resolution, as is the case with many fiber optics components.

Though nanomanipulators are currently on the market, they are "the size of a bread box and cost more than a new SUV," says Culpepper. The HexFlex Nanomanipulator mounts on a stage about half the size of a dinner plate, stands some four-inches tall by six-inches in diameter, and can move things around by several millimeters, as well as in increments of nanometers. Additionally, while the HexFlex can move in six degrees of freedom, it has
only one moving part and, according to Culpepper, "it could be manufactured for about $3,000."

Even Smaller
While Anderson was working on his device, another of Culpepper's grad students, Shih-Chi Chen, started developing an even smaller nanomanipulating device. The motivation for this second machine, dubbed the Micro-HexFlex, or MiHX, was to create a machine that could be embedded directly into miniscule devices,
 such as fiber-optic components containing numerous smaller devices that need to be kept in alignment over the life of the component. "Because we are limited by the fact that there is only so much room in the component to do alignment you can't put the larger HexFlex in there, so we needed a smaller device," explains Culpepper.

He also sees the Micro HexFlex as having the potential of enabling current large devices to be shrunk down to MEMS size. Atomic force microscopes, for example, "are now about the size of a TV," says Culpepper. "If you want to have a smaller microscope that is a couple of millimeters by a couple of millimeters, you need something inside to move things around." The MiHX could be just what the microscope needs.

It took Shih-Chi two years to develop and build just such a device, but the work paid off earlier this year when he completed the first MiHX prototype. Measuring all of a millimeter by a millimeter-less than a pencil eraser-the device is now undergoing testing. As with its larger sibling, the MiHX is designed to operate in six degrees of motion with only one moving part.

While the original HexFlex is created using conventional manufacturing processes, the MEMS-sized device was produced in a clean room using etching techniques similar to those used in semiconductor-manufacturing. "The moving part is a stacked structure consisting of two layers of silicon and one layer of silicon dioxide in between," said Shih-Chi.

Though "people have been working for a long time to build MEMS devices that you can integrate into a part, and have built three axis devices…As far as we know, nobody has built a device that can move in six degrees of freedom. Our device would be the first," says Culpepper. Such capability is important, he notes, to "be precise at the nanometer level."

Two views of the Micro-HexFlex, which is small enough to be embedded into MEMS devices to provide internal adjustments over their lifetimes.

The Actuators
Thermal actuators are used to manipulate the MiHX. An electric current is run to the actuators, which, when heated, push on the manipulator structure causing it to move. The full-sized HexFlex utilizes magnet coil actuators. Magnets are placed inside a coil, which when energized moves the magnets. They, in-turn, pull and push on the structure they are attached to.

Anderson, who built the original HexFlex has since received his master's degree in ME, and returned to his native South Africa. Shih-Chi, who developed the Micro HexFlex as his master's project, and is now working towards a doctorate in ME at MIT, says he found it to be "an exciting, and very interesting project."

One of the things he liked about it was that it was small in makeup as well as size. As a result, he was involved in every aspect of creating the device. Unlike "big projects, in which you learn teamwork, in a small project you learn everything," said Shih-Chi. He contrasted this to a friend of his "who worked on the Mars rovers. For two years he only worked on the wheels. I got to do everything," he said.